feat: implement WYSIWYG markdown editor

Add full-stack markdown editor with Go backend and React frontend. Backend: - Cobra CLI with --data-dir, --port, --host flags - REST API for markdown file CRUD operations - File storage with flat directory structure - logrus logging for all operations - Static file serving for frontend - Comprehensive tests for CRUD and static assets Frontend: - React + TypeScript + Vite + Tailwind CSS - Live markdown preview with marked (GFM) - File management: list, create, open, save, delete - Theme system: Dark/Light/System with persistence - Responsive design (320px to 1920px) - Component tests for Editor, Preview, Sidebar Build: - Makefile for build, test, and run automation - Single command testing (make test) Closes SPEC.md requirements
2026-02-06 10:01:09 -05:00
parent 6b66cee21d
commit 773b9db4b2
44 changed files with 7692 additions and 0 deletions
--- a/41
+++ b/41
@@ -0,0 +1,41 @@
+.PHONY: all build test clean backend frontend run dev
+
+all: build
+
+build: frontend-build backend-build
+
+backend-build:
+	cd backend && go build -o ../bin/markdown-editor-backend
+
+frontend-build:
+	cd frontend && npm run build
+	@mkdir -p backend/static
+	@cp -r frontend/dist/* backend/static/
+	@ln -sf backend/static static
+
+test: backend-test frontend-test
+
+backend-test:
+	cd backend && go test ./... -v
+
+frontend-test:
+	cd frontend && npm test
+
+dev:
+	@echo "Starting development servers..."
+	@echo "Backend will run on http://127.0.0.1:8080"
+	@make -j2 dev-backend dev-frontend
+
+dev-backend:
+	cd backend && go run main.go --data-dir=./data
+
+dev-frontend:
+	cd frontend && npm run dev
+
+run: build
+	./bin/markdown-editor-backend --data-dir=./data
+
+clean:
+	rm -rf bin/
+	rm -rf backend/static/
+	rm -rf frontend/dist/
--- a/README.md
+++ b/README.md
@@ -0,0 +1,121 @@
+# WYSIWYG Markdown Editor
+
+A full-stack markdown editor with live preview, built with Go backend and React/TypeScript frontend.
+
+## Features
+
+- **Live Preview**: Real-time GFM markdown rendering as you type
+- **File Management**: Create, open, edit, save, and delete markdown files
+- **Three Themes**: Light, Dark, and System (auto-detect) with theme persistence
+- **Responsive Design**: Works on mobile (320px) and desktop (1920px)
+- **CRUD API**: RESTful API for file operations
+
+## Tech Stack
+
+- **Backend**: Go with Cobra CLI, logrus logging, standard HTTP server
+- **Frontend**: React, TypeScript, Tailwind CSS, Vite, marked (GFM parser)
+- **Storage**: Local filesystem (flat structure)
+
+## Quick Start
+
+### Prerequisites
+
+- Go 1.21+
+- Node.js 20+
+- Nix (optional, for development environment)
+
+### Development
+
+1. Enter the development environment (with Nix):
+   ```bash
+   nix develop
+   ```
+
+2. Start the backend:
+   ```bash
+   make dev-backend
+   # or: cd backend && go run main.go
+   ```
+
+3. Start the frontend (in another terminal):
+   ```bash
+   make dev-frontend
+   # or: cd frontend && npm run dev
+   ```
+
+4. Open http://localhost:5173 (frontend dev server) or http://127.0.0.1:8080 (backend)
+
+### Build & Run
+
+```bash
+# Build everything (frontend + backend)
+make build
+
+# Run the built application
+make run
+# or: ./bin/markdown-editor-backend
+
+# Run tests
+make test
+```
+
+### CLI Options
+
+```
+./bin/markdown-editor-backend --help
+
+Flags:
+  --data-dir string   Storage path for markdown files (default "./data")
+  --host string       Bind address (default "127.0.0.1")
+  --port int          Server port (default 8080)
+```
+
+## API Endpoints
+
+| Method | Endpoint | Description |
+|--------|----------|-------------|
+| GET | `/api/health` | Health check |
+| GET | `/api/files` | List all files |
+| POST | `/api/files` | Create new file |
+| GET | `/api/files/{name}` | Get file content |
+| PUT | `/api/files/{name}` | Update file |
+| DELETE | `/api/files/{name}` | Delete file |
+
+## Project Structure
+
+```
+.
+├── backend/
+│   ├── main.go              # CLI entry point
+│   ├── server/              # HTTP server
+│   ├── handlers/            # API handlers
+│   ├── storage/             # File storage
+│   └── static/              # Frontend build output
+├── frontend/
+│   ├── src/
+│   │   ├── components/      # React components
+│   │   ├── api/             # API client
+│   │   └── types.ts         # TypeScript types
+│   └── dist/                # Build output
+├── data/                    # Markdown files storage
+├── bin/                     # Compiled binaries
+├── Makefile                 # Build automation
+└── flake.nix                # Nix development environment
+```
+
+## Testing
+
+```bash
+# Run all tests
+make test
+
+# Backend tests only
+make backend-test
+
+# Frontend tests only
+make frontend-test
+```
+
+## License
+
+MIT
--- a/backend/go.mod
+++ b/backend/go.mod
@@ -0,0 +1,11 @@
+module markdown-editor-backend
+
+go 1.25.5
+
+require (
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/sirupsen/logrus v1.9.4 // indirect
+	github.com/spf13/cobra v1.10.2 // indirect
+	github.com/spf13/pflag v1.0.9 // indirect
+	golang.org/x/sys v0.13.0 // indirect
+)
--- a/backend/go.sum
+++ b/backend/go.sum
@@ -0,0 +1,14 @@
+github.com/cpuguy83/go-md2man/v2 v2.0.6/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=
+github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2s0bqwp9tc8=
+github.com/inconshreveable/mousetrap v1.1.0/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
+github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
+github.com/sirupsen/logrus v1.9.4 h1:TsZE7l11zFCLZnZ+teH4Umoq5BhEIfIzfRDZ1Uzql2w=
+github.com/sirupsen/logrus v1.9.4/go.mod h1:ftWc9WdOfJ0a92nsE2jF5u5ZwH8Bv2zdeOC42RjbV2g=
+github.com/spf13/cobra v1.10.2 h1:DMTTonx5m65Ic0GOoRY2c16WCbHxOOw6xxezuLaBpcU=
+github.com/spf13/cobra v1.10.2/go.mod h1:7C1pvHqHw5A4vrJfjNwvOdzYu0Gml16OCs2GRiTUUS4=
+github.com/spf13/pflag v1.0.9 h1:9exaQaMOCwffKiiiYk6/BndUBv+iRViNW+4lEMi0PvY=
+github.com/spf13/pflag v1.0.9/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
+golang.org/x/sys v0.13.0 h1:Af8nKPmuFypiUBjVoU9V20FiaFXOcuZI21p0ycVYYGE=
+golang.org/x/sys v0.13.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
--- a/backend/handlers/handlers.go
+++ b/backend/handlers/handlers.go
@@ -0,0 +1,176 @@
+package handlers
+
+import (
+	"encoding/json"
+	"net/http"
+	"strings"
+
+	"github.com/sirupsen/logrus"
+	"markdown-editor-backend/storage"
+)
+
+// Handler contains HTTP handlers for the API
+type Handler struct {
+	storage *storage.Storage
+	log     *logrus.Logger
+}
+
+// New creates a new Handler instance
+func New(storage *storage.Storage, log *logrus.Logger) *Handler {
+	return &Handler{
+		storage: storage,
+		log:     log,
+	}
+}
+
+// FileRequest represents a request body for file operations
+type FileRequest struct {
+	Name    string `json:"name"`
+	Content string `json:"content"`
+}
+
+// FileResponse represents a file response
+type FileResponse struct {
+	Name    string `json:"name"`
+	Content string `json:"content,omitempty"`
+}
+
+// ErrorResponse represents an error response
+type ErrorResponse struct {
+	Error string `json:"error"`
+}
+
+// FilesHandler handles list and create operations
+func (h *Handler) FilesHandler(w http.ResponseWriter, r *http.Request) {
+	switch r.Method {
+	case http.MethodGet:
+		h.listFiles(w, r)
+	case http.MethodPost:
+		h.createFile(w, r)
+	default:
+		h.sendError(w, http.StatusMethodNotAllowed, "method not allowed")
+	}
+}
+
+// FileHandler handles get, update, and delete operations for a specific file
+func (h *Handler) FileHandler(w http.ResponseWriter, r *http.Request) {
+	// Extract filename from URL path
+	path := strings.TrimPrefix(r.URL.Path, "/api/files/")
+	if path == "" {
+		h.sendError(w, http.StatusBadRequest, "filename required")
+		return
+	}
+
+	name := strings.TrimSuffix(path, ".md")
+
+	switch r.Method {
+	case http.MethodGet:
+		h.getFile(w, r, name)
+	case http.MethodPut:
+		h.updateFile(w, r, name)
+	case http.MethodDelete:
+		h.deleteFile(w, r, name)
+	default:
+		h.sendError(w, http.StatusMethodNotAllowed, "method not allowed")
+	}
+}
+
+func (h *Handler) listFiles(w http.ResponseWriter, r *http.Request) {
+	h.log.Debug("Handling list files request")
+
+	files, err := h.storage.List()
+	if err != nil {
+		h.log.WithError(err).Error("Failed to list files")
+		h.sendError(w, http.StatusInternalServerError, "failed to list files")
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(files)
+}
+
+func (h *Handler) createFile(w http.ResponseWriter, r *http.Request) {
+	h.log.Debug("Handling create file request")
+
+	var req FileRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		h.log.WithError(err).Warn("Invalid request body")
+		h.sendError(w, http.StatusBadRequest, "invalid request body")
+		return
+	}
+
+	if req.Name == "" {
+		h.sendError(w, http.StatusBadRequest, "name is required")
+		return
+	}
+
+	if err := h.storage.Save(req.Name, req.Content); err != nil {
+		h.log.WithError(err).Error("Failed to create file")
+		h.sendError(w, http.StatusInternalServerError, "failed to create file")
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(http.StatusCreated)
+	json.NewEncoder(w).Encode(FileResponse{Name: req.Name, Content: req.Content})
+}
+
+func (h *Handler) getFile(w http.ResponseWriter, r *http.Request, name string) {
+	h.log.WithField("name", name).Debug("Handling get file request")
+
+	content, err := h.storage.Get(name)
+	if err != nil {
+		if err.Error() == "file not found" {
+			h.sendError(w, http.StatusNotFound, "file not found")
+			return
+		}
+		h.log.WithError(err).Error("Failed to get file")
+		h.sendError(w, http.StatusInternalServerError, "failed to get file")
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(FileResponse{Name: name, Content: content})
+}
+
+func (h *Handler) updateFile(w http.ResponseWriter, r *http.Request, name string) {
+	h.log.WithField("name", name).Debug("Handling update file request")
+
+	var req FileRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		h.log.WithError(err).Warn("Invalid request body")
+		h.sendError(w, http.StatusBadRequest, "invalid request body")
+		return
+	}
+
+	if err := h.storage.Save(name, req.Content); err != nil {
+		h.log.WithError(err).Error("Failed to update file")
+		h.sendError(w, http.StatusInternalServerError, "failed to update file")
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(FileResponse{Name: name, Content: req.Content})
+}
+
+func (h *Handler) deleteFile(w http.ResponseWriter, r *http.Request, name string) {
+	h.log.WithField("name", name).Debug("Handling delete file request")
+
+	if err := h.storage.Delete(name); err != nil {
+		if err.Error() == "file not found" {
+			h.sendError(w, http.StatusNotFound, "file not found")
+			return
+		}
+		h.log.WithError(err).Error("Failed to delete file")
+		h.sendError(w, http.StatusInternalServerError, "failed to delete file")
+		return
+	}
+
+	w.WriteHeader(http.StatusNoContent)
+}
+
+func (h *Handler) sendError(w http.ResponseWriter, status int, message string) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	json.NewEncoder(w).Encode(ErrorResponse{Error: message})
+}
--- a/backend/main.go
+++ b/backend/main.go
@@ -0,0 +1,53 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/sirupsen/logrus"
+	"github.com/spf13/cobra"
+	"markdown-editor-backend/server"
+)
+
+var (
+	dataDir string
+	port    int
+	host    string
+	log     = logrus.New()
+)
+
+var rootCmd = &cobra.Command{
+	Use:   "markdown-editor-backend",
+	Short: "WYSIWYG Markdown Editor Backend",
+	Long:  `A Go backend server for the WYSIWYG Markdown Editor with CRUD operations for markdown files.`,
+	Run: func(cmd *cobra.Command, args []string) {
+		log.SetFormatter(&logrus.TextFormatter{
+			FullTimestamp: true,
+		})
+		log.SetLevel(logrus.InfoLevel)
+
+		log.WithFields(logrus.Fields{
+			"dataDir": dataDir,
+			"host":    host,
+			"port":    port,
+		}).Info("Starting server")
+
+		srv := server.New(dataDir, host, port, log)
+		if err := srv.Start(); err != nil {
+			log.WithError(err).Fatal("Server failed to start")
+		}
+	},
+}
+
+func init() {
+	rootCmd.Flags().StringVar(&dataDir, "data-dir", "./data", "Storage path for markdown files")
+	rootCmd.Flags().IntVar(&port, "port", 8080, "Server port")
+	rootCmd.Flags().StringVar(&host, "host", "127.0.0.1", "Bind address")
+}
+
+func main() {
+	if err := rootCmd.Execute(); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}
--- a/backend/server/server.go
+++ b/backend/server/server.go
@@ -0,0 +1,172 @@
+package server
+
+import (
+	"encoding/json"
+	"fmt"
+	"net"
+	"net/http"
+
+	"github.com/sirupsen/logrus"
+	"markdown-editor-backend/handlers"
+	"markdown-editor-backend/storage"
+)
+
+// Server represents the HTTP server
+type Server struct {
+	dataDir    string
+	host       string
+	port       int
+	log        *logrus.Logger
+	storage    *storage.Storage
+	handler    *handlers.Handler
+	staticPath string
+	listener   net.Listener
+}
+
+// New creates a new Server instance
+func New(dataDir, host string, port int, log *logrus.Logger) *Server {
+	store := storage.New(dataDir, log)
+	handler := handlers.New(store, log)
+	return &Server{
+		dataDir:    dataDir,
+		host:       host,
+		port:       port,
+		log:        log,
+		storage:    store,
+		handler:    handler,
+		staticPath: "./static",
+	}
+}
+
+// SetStaticPath sets the path for static files (used for embedding frontend)
+func (s *Server) SetStaticPath(path string) {
+	s.staticPath = path
+}
+
+// Start initializes storage and starts the HTTP server
+func (s *Server) Start() error {
+	if err := s.storage.Init(); err != nil {
+		return err
+	}
+
+	mux := http.NewServeMux()
+
+	// API routes
+	mux.HandleFunc("/api/files", s.handler.FilesHandler)
+	mux.HandleFunc("/api/files/", s.handler.FileHandler)
+
+	// Health check
+	mux.HandleFunc("/api/health", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(map[string]string{"status": "ok"})
+	})
+
+	// Static file serving - serve frontend build
+	fs := http.FileServer(http.Dir(s.staticPath))
+	mux.Handle("/", fs)
+
+	// CORS middleware
+	handler := s.corsMiddleware(mux)
+
+	addr := fmt.Sprintf("%s:%d", s.host, s.port)
+	s.log.WithField("address", addr).Info("Server starting")
+
+	listener, err := net.Listen("tcp", addr)
+	if err != nil {
+		return err
+	}
+	s.listener = listener
+
+	return http.Serve(listener, handler)
+}
+
+// StartAsync starts the server asynchronously and returns the actual address
+func (s *Server) StartAsync() (string, error) {
+	if err := s.storage.Init(); err != nil {
+		return "", err
+	}
+
+	mux := http.NewServeMux()
+
+	// API routes
+	mux.HandleFunc("/api/files", s.handler.FilesHandler)
+	mux.HandleFunc("/api/files/", s.handler.FileHandler)
+
+	// Health check
+	mux.HandleFunc("/api/health", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(map[string]string{"status": "ok"})
+	})
+
+	// Static file serving - serve frontend build
+	fs := http.FileServer(http.Dir(s.staticPath))
+	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		if len(r.URL.Path) >= 4 && r.URL.Path[:4] == "/api" {
+			return
+		}
+		fs.ServeHTTP(w, r)
+	})
+
+	// CORS middleware
+	handler := s.corsMiddleware(mux)
+
+	addr := fmt.Sprintf("%s:%d", s.host, s.port)
+	if s.port == 0 {
+		addr = fmt.Sprintf("%s:0", s.host)
+	}
+
+	listener, err := net.Listen("tcp", addr)
+	if err != nil {
+		return "", err
+	}
+	s.listener = listener
+
+	actualAddr := listener.Addr().String()
+	s.log.WithField("address", actualAddr).Info("Server starting")
+
+	go http.Serve(listener, handler)
+
+	return actualAddr, nil
+}
+
+// Stop stops the server
+func (s *Server) Stop() error {
+	if s.listener != nil {
+		return s.listener.Close()
+	}
+	return nil
+}
+
+// corsMiddleware adds CORS headers for frontend development
+func (s *Server) corsMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+		w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS")
+		w.Header().Set("Access-Control-Allow-Headers", "Content-Type")
+
+		if r.Method == "OPTIONS" {
+			w.WriteHeader(http.StatusOK)
+			return
+		}
+
+		next.ServeHTTP(w, r)
+	})
+}
+
+// GetStorage returns the storage instance (for testing)
+func (s *Server) GetStorage() *storage.Storage {
+	return s.storage
+}
+
+// GetStaticPath returns the static files path (for testing)
+func (s *Server) GetStaticPath() string {
+	return s.staticPath
+}
+
+// GetAddr returns the server address (for testing)
+func (s *Server) GetAddr() string {
+	if s.listener != nil {
+		return s.listener.Addr().String()
+	}
+	return fmt.Sprintf("%s:%d", s.host, s.port)
+}
--- a/backend/server/server_test.go
+++ b/backend/server/server_test.go
@@ -0,0 +1,255 @@
+package server_test
+
+import (
+	"bytes"
+	"encoding/json"
+	"io"
+	"net/http"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/sirupsen/logrus"
+	"markdown-editor-backend/server"
+)
+
+func TestServerCRUD(t *testing.T) {
+	// Create temp directory for test data
+	tempDir, err := os.MkdirTemp("", "markdown-test-*")
+	if err != nil {
+		t.Fatalf("Failed to create temp dir: %v", err)
+	}
+	defer os.RemoveAll(tempDir)
+
+	// Create static directory
+	staticDir := filepath.Join(tempDir, "static")
+	if err := os.MkdirAll(staticDir, 0755); err != nil {
+		t.Fatalf("Failed to create static dir: %v", err)
+	}
+	if err := os.WriteFile(filepath.Join(staticDir, "index.html"), []byte("<html></html>"), 0644); err != nil {
+		t.Fatalf("Failed to create index.html: %v", err)
+	}
+
+	// Create logger
+	log := logrus.New()
+	log.SetLevel(logrus.WarnLevel)
+
+	// Create server with dynamic port
+	srv := server.New(tempDir, "127.0.0.1", 0, log)
+	srv.SetStaticPath(staticDir)
+
+	// Start server asynchronously
+	addr, err := srv.StartAsync()
+	if err != nil {
+		t.Fatalf("Failed to start server: %v", err)
+	}
+	defer srv.Stop()
+
+	// Wait for server to be ready
+	time.Sleep(100 * time.Millisecond)
+
+	baseURL := "http://" + addr
+	client := &http.Client{Timeout: 5 * time.Second}
+
+	// Test health endpoint
+	t.Run("HealthCheck", func(t *testing.T) {
+		resp, err := client.Get(baseURL + "/api/health")
+		if err != nil {
+			t.Fatalf("Health check failed: %v", err)
+		}
+		defer resp.Body.Close()
+
+		if resp.StatusCode != http.StatusOK {
+			t.Errorf("Expected status 200, got %d", resp.StatusCode)
+		}
+
+		var result map[string]string
+		if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
+			t.Fatalf("Failed to decode response: %v", err)
+		}
+
+		if result["status"] != "ok" {
+			t.Errorf("Expected status 'ok', got '%s'", result["status"])
+		}
+	})
+
+	// Test Create
+	t.Run("CreateFile", func(t *testing.T) {
+		body := map[string]string{
+			"name":    "test-file",
+			"content": "# Hello World\n\nThis is a test file.",
+		}
+		jsonBody, _ := json.Marshal(body)
+
+		resp, err := client.Post(baseURL+"/api/files", "application/json", bytes.NewBuffer(jsonBody))
+		if err != nil {
+			t.Fatalf("Create file failed: %v", err)
+		}
+		defer resp.Body.Close()
+
+		if resp.StatusCode != http.StatusCreated {
+			t.Errorf("Expected status 201, got %d", resp.StatusCode)
+		}
+
+		var result map[string]string
+		if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
+			t.Fatalf("Failed to decode response: %v", err)
+		}
+
+		if result["name"] != "test-file" {
+			t.Errorf("Expected name 'test-file', got '%s'", result["name"])
+		}
+	})
+
+	// Test List
+	t.Run("ListFiles", func(t *testing.T) {
+		resp, err := client.Get(baseURL + "/api/files")
+		if err != nil {
+			t.Fatalf("List files failed: %v", err)
+		}
+		defer resp.Body.Close()
+
+		if resp.StatusCode != http.StatusOK {
+			t.Errorf("Expected status 200, got %d", resp.StatusCode)
+		}
+
+		var result []string
+		if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
+			t.Fatalf("Failed to decode response: %v", err)
+		}
+
+		found := false
+		for _, name := range result {
+			if name == "test-file" {
+				found = true
+				break
+			}
+		}
+
+		if !found {
+			t.Errorf("Expected 'test-file' in list, got %v", result)
+		}
+	})
+
+	// Test Get
+	t.Run("GetFile", func(t *testing.T) {
+		resp, err := client.Get(baseURL + "/api/files/test-file")
+		if err != nil {
+			t.Fatalf("Get file failed: %v", err)
+		}
+		defer resp.Body.Close()
+
+		if resp.StatusCode != http.StatusOK {
+			t.Errorf("Expected status 200, got %d", resp.StatusCode)
+		}
+
+		var result map[string]string
+		if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
+			t.Fatalf("Failed to decode response: %v", err)
+		}
+
+		if result["name"] != "test-file" {
+			t.Errorf("Expected name 'test-file', got '%s'", result["name"])
+		}
+
+		if result["content"] != "# Hello World\n\nThis is a test file." {
+			t.Errorf("Expected specific content, got '%s'", result["content"])
+		}
+	})
+
+	// Test Update
+	t.Run("UpdateFile", func(t *testing.T) {
+		body := map[string]string{
+			"content": "# Updated Content\n\nThis file has been updated.",
+		}
+		jsonBody, _ := json.Marshal(body)
+
+		req, _ := http.NewRequest(http.MethodPut, baseURL+"/api/files/test-file", bytes.NewBuffer(jsonBody))
+		req.Header.Set("Content-Type", "application/json")
+
+		resp, err := client.Do(req)
+		if err != nil {
+			t.Fatalf("Update file failed: %v", err)
+		}
+		defer resp.Body.Close()
+
+		if resp.StatusCode != http.StatusOK {
+			t.Errorf("Expected status 200, got %d", resp.StatusCode)
+		}
+
+		// Verify the update
+		resp2, _ := client.Get(baseURL + "/api/files/test-file")
+		defer resp2.Body.Close()
+
+		var result map[string]string
+		json.NewDecoder(resp2.Body).Decode(&result)
+
+		if result["content"] != "# Updated Content\n\nThis file has been updated." {
+			t.Errorf("Expected updated content, got '%s'", result["content"])
+		}
+	})
+
+	// Test Delete
+	t.Run("DeleteFile", func(t *testing.T) {
+		req, _ := http.NewRequest(http.MethodDelete, baseURL+"/api/files/test-file", nil)
+
+		resp, err := client.Do(req)
+		if err != nil {
+			t.Fatalf("Delete file failed: %v", err)
+		}
+		defer resp.Body.Close()
+
+		if resp.StatusCode != http.StatusNoContent {
+			t.Errorf("Expected status 204, got %d", resp.StatusCode)
+		}
+
+		// Verify deletion
+		resp2, _ := client.Get(baseURL + "/api/files/test-file")
+		defer resp2.Body.Close()
+
+		if resp2.StatusCode != http.StatusNotFound {
+			t.Errorf("Expected status 404 for deleted file, got %d", resp2.StatusCode)
+		}
+	})
+
+	// Test 404
+	t.Run("GetNonExistentFile", func(t *testing.T) {
+		resp, err := client.Get(baseURL + "/api/files/nonexistent")
+		if err != nil {
+			t.Fatalf("Request failed: %v", err)
+		}
+		defer resp.Body.Close()
+
+		if resp.StatusCode != http.StatusNotFound {
+			t.Errorf("Expected status 404, got %d", resp.StatusCode)
+		}
+
+		var result map[string]string
+		if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
+			t.Fatalf("Failed to decode response: %v", err)
+		}
+
+		if result["error"] != "file not found" {
+			t.Errorf("Expected error 'file not found', got '%s'", result["error"])
+		}
+	})
+
+	// Test static file serving
+	t.Run("StaticFiles", func(t *testing.T) {
+		resp, err := client.Get(baseURL + "/")
+		if err != nil {
+			t.Fatalf("Get static file failed: %v", err)
+		}
+		defer resp.Body.Close()
+
+		if resp.StatusCode != http.StatusOK {
+			t.Errorf("Expected status 200, got %d", resp.StatusCode)
+		}
+
+		body, _ := io.ReadAll(resp.Body)
+		if string(body) != "<html></html>" {
+			t.Errorf("Expected '<html></html>', got '%s'", string(body))
+		}
+	})
+}
--- a/backend/static/assets/index-BRD_q2gl.js
+++ b/backend/static/assets/index-BRD_q2gl.js
--- a/backend/static/assets/index-CevFFMbj.css
+++ b/backend/static/assets/index-CevFFMbj.css
--- a/backend/static/index.html
+++ b/backend/static/index.html
@@ -0,0 +1,14 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <link rel="icon" type="image/svg+xml" href="/vite.svg" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>Markdown Editor</title>
+    <script type="module" crossorigin src="/assets/index-BRD_q2gl.js"></script>
+    <link rel="stylesheet" crossorigin href="/assets/index-CevFFMbj.css">
+  </head>
+  <body>
+    <div id="root"></div>
+  </body>
+</html>
--- a/backend/static/vite.svg
+++ b/backend/static/vite.svg
@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" aria-hidden="true" role="img" class="iconify iconify--logos" width="31.88" height="32" preserveAspectRatio="xMidYMid meet" viewBox="0 0 256 257"><defs><linearGradient id="IconifyId1813088fe1fbc01fb466" x1="-.828%" x2="57.636%" y1="7.652%" y2="78.411%"><stop offset="0%" stop-color="#41D1FF"></stop><stop offset="100%" stop-color="#BD34FE"></stop></linearGradient><linearGradient id="IconifyId1813088fe1fbc01fb467" x1="43.376%" x2="50.316%" y1="2.242%" y2="89.03%"><stop offset="0%" stop-color="#FFEA83"></stop><stop offset="8.333%" stop-color="#FFDD35"></stop><stop offset="100%" stop-color="#FFA800"></stop></linearGradient></defs><path fill="url(#IconifyId1813088fe1fbc01fb466)" d="M255.153 37.938L134.897 252.976c-2.483 4.44-8.862 4.466-11.382.048L.875 37.958c-2.746-4.814 1.371-10.646 6.827-9.67l120.385 21.517a6.537 6.537 0 0 0 2.322-.004l117.867-21.483c5.438-.991 9.574 4.796 6.877 9.62Z"></path><path fill="url(#IconifyId1813088fe1fbc01fb467)" d="M185.432.063L96.44 17.501a3.268 3.268 0 0 0-2.634 3.014l-5.474 92.456a3.268 3.268 0 0 0 3.997 3.378l24.777-5.718c2.318-.535 4.413 1.507 3.936 3.838l-7.361 36.047c-.495 2.426 1.782 4.5 4.151 3.78l15.304-4.649c2.372-.72 4.652 1.36 4.15 3.788l-11.698 56.621c-.732 3.542 3.979 5.473 5.943 2.437l1.313-2.028l72.516-144.72c1.215-2.423-.88-5.186-3.54-4.672l-25.505 4.922c-2.396.462-4.435-1.77-3.759-4.114l16.646-57.705c.677-2.35-1.37-4.583-3.769-4.113Z"></path></svg>
--- a/backend/storage/storage.go
+++ b/backend/storage/storage.go
@@ -0,0 +1,150 @@
+package storage
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+
+	"github.com/sirupsen/logrus"
+)
+
+// Storage handles file operations for markdown files
+type Storage struct {
+	dataDir string
+	mu      sync.RWMutex
+	log     *logrus.Logger
+}
+
+// New creates a new Storage instance
+func New(dataDir string, log *logrus.Logger) *Storage {
+	return &Storage{
+		dataDir: dataDir,
+		log:     log,
+	}
+}
+
+// Init ensures the data directory exists
+func (s *Storage) Init() error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	s.log.WithField("dataDir", s.dataDir).Info("Initializing storage")
+
+	if err := os.MkdirAll(s.dataDir, 0755); err != nil {
+		s.log.WithError(err).Error("Failed to create data directory")
+		return fmt.Errorf("failed to create data directory: %w", err)
+	}
+	return nil
+}
+
+// List returns all markdown files in the data directory
+func (s *Storage) List() ([]string, error) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	s.log.Debug("Listing all files")
+
+	entries, err := os.ReadDir(s.dataDir)
+	if err != nil {
+		s.log.WithError(err).Error("Failed to read data directory")
+		return nil, fmt.Errorf("failed to read data directory: %w", err)
+	}
+
+	var files []string
+	for _, entry := range entries {
+		if !entry.IsDir() && strings.HasSuffix(entry.Name(), ".md") {
+			files = append(files, strings.TrimSuffix(entry.Name(), ".md"))
+		}
+	}
+
+	s.log.WithField("count", len(files)).Debug("Listed files")
+	return files, nil
+}
+
+// Get reads a markdown file by name
+func (s *Storage) Get(name string) (string, error) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	s.log.WithField("name", name).Debug("Getting file")
+
+	if !isValidFilename(name) {
+		s.log.WithField("name", name).Warn("Invalid filename")
+		return "", fmt.Errorf("invalid filename")
+	}
+
+	path := filepath.Join(s.dataDir, name+".md")
+	content, err := os.ReadFile(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			s.log.WithField("name", name).Warn("File not found")
+			return "", fmt.Errorf("file not found")
+		}
+		s.log.WithError(err).WithField("name", name).Error("Failed to read file")
+		return "", fmt.Errorf("failed to read file: %w", err)
+	}
+
+	return string(content), nil
+}
+
+// Save writes content to a markdown file
+func (s *Storage) Save(name, content string) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	s.log.WithField("name", name).Debug("Saving file")
+
+	if !isValidFilename(name) {
+		s.log.WithField("name", name).Warn("Invalid filename")
+		return fmt.Errorf("invalid filename")
+	}
+
+	path := filepath.Join(s.dataDir, name+".md")
+	if err := os.WriteFile(path, []byte(content), 0644); err != nil {
+		s.log.WithError(err).WithField("name", name).Error("Failed to write file")
+		return fmt.Errorf("failed to write file: %w", err)
+	}
+
+	s.log.WithField("name", name).Info("File saved")
+	return nil
+}
+
+// Delete removes a markdown file
+func (s *Storage) Delete(name string) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	s.log.WithField("name", name).Debug("Deleting file")
+
+	if !isValidFilename(name) {
+		s.log.WithField("name", name).Warn("Invalid filename")
+		return fmt.Errorf("invalid filename")
+	}
+
+	path := filepath.Join(s.dataDir, name+".md")
+	if err := os.Remove(path); err != nil {
+		if os.IsNotExist(err) {
+			s.log.WithField("name", name).Warn("File not found for deletion")
+			return fmt.Errorf("file not found")
+		}
+		s.log.WithError(err).WithField("name", name).Error("Failed to delete file")
+		return fmt.Errorf("failed to delete file: %w", err)
+	}
+
+	s.log.WithField("name", name).Info("File deleted")
+	return nil
+}
+
+// isValidFilename checks if a filename is safe to use
+func isValidFilename(name string) bool {
+	if name == "" {
+		return false
+	}
+	// Prevent path traversal
+	if strings.Contains(name, "/") || strings.Contains(name, "\\") || strings.Contains(name, "..") {
+		return false
+	}
+	return true
+}
--- a/bin/markdown-editor-backend
+++ b/bin/markdown-editor-backend
--- a/frontend/.gitignore
+++ b/frontend/.gitignore
@@ -0,0 +1,24 @@
+# Logs
+logs
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+pnpm-debug.log*
+lerna-debug.log*
+
+node_modules
+dist
+dist-ssr
+*.local
+
+# Editor directories and files
+.vscode/*
+!.vscode/extensions.json
+.idea
+.DS_Store
+*.suo
+*.ntvs*
+*.njsproj
+*.sln
+*.sw?
--- a/frontend/README.md
+++ b/frontend/README.md
@@ -0,0 +1,73 @@
+# React + TypeScript + Vite
+
+This template provides a minimal setup to get React working in Vite with HMR and some ESLint rules.
+
+Currently, two official plugins are available:
+
+- [@vitejs/plugin-react](https://github.com/vitejs/vite-plugin-react/blob/main/packages/plugin-react) uses [Babel](https://babeljs.io/) (or [oxc](https://oxc.rs) when used in [rolldown-vite](https://vite.dev/guide/rolldown)) for Fast Refresh
+- [@vitejs/plugin-react-swc](https://github.com/vitejs/vite-plugin-react/blob/main/packages/plugin-react-swc) uses [SWC](https://swc.rs/) for Fast Refresh
+
+## React Compiler
+
+The React Compiler is not enabled on this template because of its impact on dev & build performances. To add it, see [this documentation](https://react.dev/learn/react-compiler/installation).
+
+## Expanding the ESLint configuration
+
+If you are developing a production application, we recommend updating the configuration to enable type-aware lint rules:
+
+```js
+export default defineConfig([
+  globalIgnores(['dist']),
+  {
+    files: ['**/*.{ts,tsx}'],
+    extends: [
+      // Other configs...
+
+      // Remove tseslint.configs.recommended and replace with this
+      tseslint.configs.recommendedTypeChecked,
+      // Alternatively, use this for stricter rules
+      tseslint.configs.strictTypeChecked,
+      // Optionally, add this for stylistic rules
+      tseslint.configs.stylisticTypeChecked,
+
+      // Other configs...
+    ],
+    languageOptions: {
+      parserOptions: {
+        project: ['./tsconfig.node.json', './tsconfig.app.json'],
+        tsconfigRootDir: import.meta.dirname,
+      },
+      // other options...
+    },
+  },
+])
+```
+
+You can also install [eslint-plugin-react-x](https://github.com/Rel1cx/eslint-react/tree/main/packages/plugins/eslint-plugin-react-x) and [eslint-plugin-react-dom](https://github.com/Rel1cx/eslint-react/tree/main/packages/plugins/eslint-plugin-react-dom) for React-specific lint rules:
+
+```js
+// eslint.config.js
+import reactX from 'eslint-plugin-react-x'
+import reactDom from 'eslint-plugin-react-dom'
+
+export default defineConfig([
+  globalIgnores(['dist']),
+  {
+    files: ['**/*.{ts,tsx}'],
+    extends: [
+      // Other configs...
+      // Enable lint rules for React
+      reactX.configs['recommended-typescript'],
+      // Enable lint rules for React DOM
+      reactDom.configs.recommended,
+    ],
+    languageOptions: {
+      parserOptions: {
+        project: ['./tsconfig.node.json', './tsconfig.app.json'],
+        tsconfigRootDir: import.meta.dirname,
+      },
+      // other options...
+    },
+  },
+])
+```
--- a/frontend/eslint.config.js
+++ b/frontend/eslint.config.js
@@ -0,0 +1,23 @@
+import js from '@eslint/js'
+import globals from 'globals'
+import reactHooks from 'eslint-plugin-react-hooks'
+import reactRefresh from 'eslint-plugin-react-refresh'
+import tseslint from 'typescript-eslint'
+import { defineConfig, globalIgnores } from 'eslint/config'
+
+export default defineConfig([
+  globalIgnores(['dist']),
+  {
+    files: ['**/*.{ts,tsx}'],
+    extends: [
+      js.configs.recommended,
+      tseslint.configs.recommended,
+      reactHooks.configs.flat.recommended,
+      reactRefresh.configs.vite,
+    ],
+    languageOptions: {
+      ecmaVersion: 2020,
+      globals: globals.browser,
+    },
+  },
+])
--- a/frontend/index.html
+++ b/frontend/index.html
@@ -0,0 +1,13 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <link rel="icon" type="image/svg+xml" href="/vite.svg" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>Markdown Editor</title>
+  </head>
+  <body>
+    <div id="root"></div>
+    <script type="module" src="/src/main.tsx"></script>
+  </body>
+</html>
--- a/frontend/package-lock.json
+++ b/frontend/package-lock.json
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -0,0 +1,43 @@
+{
+  "name": "frontend",
+  "private": true,
+  "version": "0.0.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "tsc -b && vite build",
+    "lint": "eslint .",
+    "preview": "vite preview",
+    "test": "vitest run",
+    "test:watch": "vitest"
+  },
+  "dependencies": {
+    "@types/marked": "^5.0.2",
+    "lucide-react": "^0.563.0",
+    "marked": "^17.0.1",
+    "react": "^19.2.0",
+    "react-dom": "^19.2.0"
+  },
+  "devDependencies": {
+    "@eslint/js": "^9.39.1",
+    "@testing-library/jest-dom": "^6.9.1",
+    "@testing-library/react": "^16.3.2",
+    "@testing-library/user-event": "^14.6.1",
+    "@types/node": "^24.10.1",
+    "@types/react": "^19.2.5",
+    "@types/react-dom": "^19.2.3",
+    "@vitejs/plugin-react": "^5.1.1",
+    "autoprefixer": "^10.4.24",
+    "eslint": "^9.39.1",
+    "eslint-plugin-react-hooks": "^7.0.1",
+    "eslint-plugin-react-refresh": "^0.4.24",
+    "globals": "^16.5.0",
+    "jsdom": "^28.0.0",
+    "postcss": "^8.5.6",
+    "tailwindcss": "^3.4.19",
+    "typescript": "~5.9.3",
+    "typescript-eslint": "^8.46.4",
+    "vite": "^7.2.4",
+    "vitest": "^4.0.18"
+  }
+}
--- a/frontend/postcss.config.cjs
+++ b/frontend/postcss.config.cjs
@@ -0,0 +1,6 @@
+module.exports = {
+  plugins: {
+    tailwindcss: {},
+    autoprefixer: {},
+  },
+}
--- a/frontend/public/vite.svg
+++ b/frontend/public/vite.svg
@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" aria-hidden="true" role="img" class="iconify iconify--logos" width="31.88" height="32" preserveAspectRatio="xMidYMid meet" viewBox="0 0 256 257"><defs><linearGradient id="IconifyId1813088fe1fbc01fb466" x1="-.828%" x2="57.636%" y1="7.652%" y2="78.411%"><stop offset="0%" stop-color="#41D1FF"></stop><stop offset="100%" stop-color="#BD34FE"></stop></linearGradient><linearGradient id="IconifyId1813088fe1fbc01fb467" x1="43.376%" x2="50.316%" y1="2.242%" y2="89.03%"><stop offset="0%" stop-color="#FFEA83"></stop><stop offset="8.333%" stop-color="#FFDD35"></stop><stop offset="100%" stop-color="#FFA800"></stop></linearGradient></defs><path fill="url(#IconifyId1813088fe1fbc01fb466)" d="M255.153 37.938L134.897 252.976c-2.483 4.44-8.862 4.466-11.382.048L.875 37.958c-2.746-4.814 1.371-10.646 6.827-9.67l120.385 21.517a6.537 6.537 0 0 0 2.322-.004l117.867-21.483c5.438-.991 9.574 4.796 6.877 9.62Z"></path><path fill="url(#IconifyId1813088fe1fbc01fb467)" d="M185.432.063L96.44 17.501a3.268 3.268 0 0 0-2.634 3.014l-5.474 92.456a3.268 3.268 0 0 0 3.997 3.378l24.777-5.718c2.318-.535 4.413 1.507 3.936 3.838l-7.361 36.047c-.495 2.426 1.782 4.5 4.151 3.78l15.304-4.649c2.372-.72 4.652 1.36 4.15 3.788l-11.698 56.621c-.732 3.542 3.979 5.473 5.943 2.437l1.313-2.028l72.516-144.72c1.215-2.423-.88-5.186-3.54-4.672l-25.505 4.922c-2.396.462-4.435-1.77-3.759-4.114l16.646-57.705c.677-2.35-1.37-4.583-3.769-4.113Z"></path></svg>
--- a/frontend/src/App.css
+++ b/frontend/src/App.css
@@ -0,0 +1,42 @@
+#root {
+  max-width: 1280px;
+  margin: 0 auto;
+  padding: 2rem;
+  text-align: center;
+}
+
+.logo {
+  height: 6em;
+  padding: 1.5em;
+  will-change: filter;
+  transition: filter 300ms;
+}
+.logo:hover {
+  filter: drop-shadow(0 0 2em #646cffaa);
+}
+.logo.react:hover {
+  filter: drop-shadow(0 0 2em #61dafbaa);
+}
+
+@keyframes logo-spin {
+  from {
+    transform: rotate(0deg);
+  }
+  to {
+    transform: rotate(360deg);
+  }
+}
+
+@media (prefers-reduced-motion: no-preference) {
+  a:nth-of-type(2) .logo {
+    animation: logo-spin infinite 20s linear;
+  }
+}
+
+.card {
+  padding: 2em;
+}
+
+.read-the-docs {
+  color: #888;
+}
--- a/frontend/src/App.tsx
+++ b/frontend/src/App.tsx
@@ -0,0 +1,183 @@
+import { useState, useEffect, useCallback } from 'react'
+import { Sidebar } from './components/Sidebar'
+import { Editor } from './components/Editor'
+import { Preview } from './components/Preview'
+import { Header } from './components/Header'
+import type { Theme, FileItem } from './types'
+import { api } from './api'
+
+function App() {
+  const [theme, setTheme] = useState<Theme>('system')
+  const [files, setFiles] = useState<FileItem[]>([])
+  const [currentFile, setCurrentFile] = useState<FileItem | null>(null)
+  const [content, setContent] = useState('')
+  const [isSidebarOpen, setIsSidebarOpen] = useState(true)
+  const [isPreviewOpen, setIsPreviewOpen] = useState(true)
+  const [isLoading, setIsLoading] = useState(false)
+  const [error, setError] = useState<string | null>(null)
+
+  // Initialize theme
+  useEffect(() => {
+    const savedTheme = localStorage.getItem('theme') as Theme
+    if (savedTheme) {
+      setTheme(savedTheme)
+    }
+  }, [])
+
+  // Apply theme
+  useEffect(() => {
+    const root = window.document.documentElement
+    root.classList.remove('light', 'dark')
+
+    if (theme === 'system') {
+      const systemTheme = window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light'
+      root.classList.add(systemTheme)
+    } else {
+      root.classList.add(theme)
+    }
+
+    localStorage.setItem('theme', theme)
+  }, [theme])
+
+  // Load files on mount
+  useEffect(() => {
+    loadFiles()
+  }, [])
+
+  const loadFiles = async () => {
+    try {
+      setIsLoading(true)
+      setError(null)
+      const fileNames = await api.listFiles()
+      const fileItems: FileItem[] = fileNames.map(name => ({
+        id: name,
+        name,
+        content: '',
+      }))
+      setFiles(fileItems)
+    } catch (err) {
+      setError('Failed to load files')
+      console.error(err)
+    } finally {
+      setIsLoading(false)
+    }
+  }
+
+  const handleCreateFile = async (name: string) => {
+    try {
+      setError(null)
+      await api.createFile(name, '')
+      const newFile: FileItem = { id: name, name, content: '' }
+      setFiles([newFile, ...files])
+      setCurrentFile(newFile)
+      setContent('')
+    } catch (err) {
+      setError('Failed to create file')
+      console.error(err)
+    }
+  }
+
+  const handleOpenFile = async (file: FileItem) => {
+    try {
+      setError(null)
+      setIsLoading(true)
+      const fileData = await api.getFile(file.name)
+      const updatedFile = { ...file, content: fileData.content }
+      setCurrentFile(updatedFile)
+      setContent(fileData.content)
+    } catch (err) {
+      setError('Failed to open file')
+      console.error(err)
+    } finally {
+      setIsLoading(false)
+    }
+  }
+
+  const handleSaveFile = async () => {
+    if (!currentFile) return
+    try {
+      setError(null)
+      await api.updateFile(currentFile.name, content)
+      const updatedFiles = files.map(f =>
+        f.id === currentFile.id ? { ...f, content } : f
+      )
+      setFiles(updatedFiles)
+      setCurrentFile({ ...currentFile, content })
+    } catch (err) {
+      setError('Failed to save file')
+      console.error(err)
+    }
+  }
+
+  const handleDeleteFile = async (file: FileItem) => {
+    try {
+      setError(null)
+      await api.deleteFile(file.name)
+      setFiles(files.filter(f => f.id !== file.id))
+      if (currentFile?.id === file.id) {
+        setCurrentFile(null)
+        setContent('')
+      }
+    } catch (err) {
+      setError('Failed to delete file')
+      console.error(err)
+    }
+  }
+
+  const handleContentChange = useCallback((newContent: string) => {
+    setContent(newContent)
+  }, [])
+
+  return (
+    <div className="min-h-screen bg-white dark:bg-gray-900 text-gray-900 dark:text-gray-100 transition-colors duration-200">
+      <Header
+        theme={theme}
+        onThemeChange={setTheme}
+        currentFile={currentFile}
+        onSave={handleSaveFile}
+        onToggleSidebar={() => setIsSidebarOpen(!isSidebarOpen)}
+        onTogglePreview={() => setIsPreviewOpen(!isPreviewOpen)}
+        isSidebarOpen={isSidebarOpen}
+        isPreviewOpen={isPreviewOpen}
+      />
+
+      {error && (
+        <div className="bg-red-100 dark:bg-red-900 text-red-800 dark:text-red-200 px-4 py-2 text-sm">
+          {error}
+        </div>
+      )}
+
+      <div className="flex h-[calc(100vh-64px)]">
+        {isSidebarOpen && (
+          <Sidebar
+            files={files}
+            currentFile={currentFile}
+            onCreateFile={handleCreateFile}
+            onOpenFile={handleOpenFile}
+            onDeleteFile={handleDeleteFile}
+            isLoading={isLoading}
+          />
+        )}
+
+        <div className="flex-1 flex">
+          <div className={`flex-1 ${isPreviewOpen ? 'w-1/2' : 'w-full'}`}>
+            <Editor
+              content={content}
+              onChange={handleContentChange}
+              placeholder={currentFile ? "Start typing..." : "Select or create a file to start editing"}
+              disabled={!currentFile}
+            />
+          </div>
+
+          {isPreviewOpen && (
+            <div className="flex-1 w-1/2 border-l border-gray-200 dark:border-gray-700">
+              <Preview content={content} />
+            </div>
+          )}
+        </div>
+      </div>
+    </div>
+  )
+}
+
+export default App
--- a/frontend/src/api/index.ts
+++ b/frontend/src/api/index.ts
@@ -0,0 +1,51 @@
+import type { FileResponse } from '../types'
+
+const API_BASE = '/api'
+
+async function handleResponse<T>(response: Response): Promise<T> {
+  if (!response.ok) {
+    const error = await response.json().catch(() => ({ error: 'Unknown error' }))
+    throw new Error(error.error || `HTTP ${response.status}`)
+  }
+  if (response.status === 204) {
+    return null as T
+  }
+  return response.json()
+}
+
+export const api = {
+  async listFiles(): Promise<string[]> {
+    const response = await fetch(`${API_BASE}/files`)
+    return handleResponse<string[]>(response)
+  },
+
+  async getFile(name: string): Promise<FileResponse> {
+    const response = await fetch(`${API_BASE}/files/${encodeURIComponent(name)}`)
+    return handleResponse<FileResponse>(response)
+  },
+
+  async createFile(name: string, content: string): Promise<FileResponse> {
+    const response = await fetch(`${API_BASE}/files`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ name, content }),
+    })
+    return handleResponse<FileResponse>(response)
+  },
+
+  async updateFile(name: string, content: string): Promise<FileResponse> {
+    const response = await fetch(`${API_BASE}/files/${encodeURIComponent(name)}`, {
+      method: 'PUT',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ content }),
+    })
+    return handleResponse<FileResponse>(response)
+  },
+
+  async deleteFile(name: string): Promise<void> {
+    const response = await fetch(`${API_BASE}/files/${encodeURIComponent(name)}`, {
+      method: 'DELETE',
+    })
+    return handleResponse<void>(response)
+  },
+}
--- a/frontend/src/assets/react.svg
+++ b/frontend/src/assets/react.svg
@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" aria-hidden="true" role="img" class="iconify iconify--logos" width="35.93" height="32" preserveAspectRatio="xMidYMid meet" viewBox="0 0 256 228"><path fill="#00D8FF" d="M210.483 73.824a171.49 171.49 0 0 0-8.24-2.597c.465-1.9.893-3.777 1.273-5.621c6.238-30.281 2.16-54.676-11.769-62.708c-13.355-7.7-35.196.329-57.254 19.526a171.23 171.23 0 0 0-6.375 5.848a155.866 155.866 0 0 0-4.241-3.917C100.759 3.829 77.587-4.822 63.673 3.233C50.33 10.957 46.379 33.89 51.995 62.588a170.974 170.974 0 0 0 1.892 8.48c-3.28.932-6.445 1.924-9.474 2.98C17.309 83.498 0 98.307 0 113.668c0 15.865 18.582 31.778 46.812 41.427a145.52 145.52 0 0 0 6.921 2.165a167.467 167.467 0 0 0-2.01 9.138c-5.354 28.2-1.173 50.591 12.134 58.266c13.744 7.926 36.812-.22 59.273-19.855a145.567 145.567 0 0 0 5.342-4.923a168.064 168.064 0 0 0 6.92 6.314c21.758 18.722 43.246 26.282 56.54 18.586c13.731-7.949 18.194-32.003 12.4-61.268a145.016 145.016 0 0 0-1.535-6.842c1.62-.48 3.21-.974 4.76-1.488c29.348-9.723 48.443-25.443 48.443-41.52c0-15.417-17.868-30.326-45.517-39.844Zm-6.365 70.984c-1.4.463-2.836.91-4.3 1.345c-3.24-10.257-7.612-21.163-12.963-32.432c5.106-11 9.31-21.767 12.459-31.957c2.619.758 5.16 1.557 7.61 2.4c23.69 8.156 38.14 20.213 38.14 29.504c0 9.896-15.606 22.743-40.946 31.14Zm-10.514 20.834c2.562 12.94 2.927 24.64 1.23 33.787c-1.524 8.219-4.59 13.698-8.382 15.893c-8.067 4.67-25.32-1.4-43.927-17.412a156.726 156.726 0 0 1-6.437-5.87c7.214-7.889 14.423-17.06 21.459-27.246c12.376-1.098 24.068-2.894 34.671-5.345a134.17 134.17 0 0 1 1.386 6.193ZM87.276 214.515c-7.882 2.783-14.16 2.863-17.955.675c-8.075-4.657-11.432-22.636-6.853-46.752a156.923 156.923 0 0 1 1.869-8.499c10.486 2.32 22.093 3.988 34.498 4.994c7.084 9.967 14.501 19.128 21.976 27.15a134.668 134.668 0 0 1-4.877 4.492c-9.933 8.682-19.886 14.842-28.658 17.94ZM50.35 144.747c-12.483-4.267-22.792-9.812-29.858-15.863c-6.35-5.437-9.555-10.836-9.555-15.216c0-9.322 13.897-21.212 37.076-29.293c2.813-.98 5.757-1.905 8.812-2.773c3.204 10.42 7.406 21.315 12.477 32.332c-5.137 11.18-9.399 22.249-12.634 32.792a134.718 134.718 0 0 1-6.318-1.979Zm12.378-84.26c-4.811-24.587-1.616-43.134 6.425-47.789c8.564-4.958 27.502 2.111 47.463 19.835a144.318 144.318 0 0 1 3.841 3.545c-7.438 7.987-14.787 17.08-21.808 26.988c-12.04 1.116-23.565 2.908-34.161 5.309a160.342 160.342 0 0 1-1.76-7.887Zm110.427 27.268a347.8 347.8 0 0 0-7.785-12.803c8.168 1.033 15.994 2.404 23.343 4.08c-2.206 7.072-4.956 14.465-8.193 22.045a381.151 381.151 0 0 0-7.365-13.322Zm-45.032-43.861c5.044 5.465 10.096 11.566 15.065 18.186a322.04 322.04 0 0 0-30.257-.006c4.974-6.559 10.069-12.652 15.192-18.18ZM82.802 87.83a323.167 323.167 0 0 0-7.227 13.238c-3.184-7.553-5.909-14.98-8.134-22.152c7.304-1.634 15.093-2.97 23.209-3.984a321.524 321.524 0 0 0-7.848 12.897Zm8.081 65.352c-8.385-.936-16.291-2.203-23.593-3.793c2.26-7.3 5.045-14.885 8.298-22.6a321.187 321.187 0 0 0 7.257 13.246c2.594 4.48 5.28 8.868 8.038 13.147Zm37.542 31.03c-5.184-5.592-10.354-11.779-15.403-18.433c4.902.192 9.899.29 14.978.29c5.218 0 10.376-.117 15.453-.343c-4.985 6.774-10.018 12.97-15.028 18.486Zm52.198-57.817c3.422 7.8 6.306 15.345 8.596 22.52c-7.422 1.694-15.436 3.058-23.88 4.071a382.417 382.417 0 0 0 7.859-13.026a347.403 347.403 0 0 0 7.425-13.565Zm-16.898 8.101a358.557 358.557 0 0 1-12.281 19.815a329.4 329.4 0 0 1-23.444.823c-7.967 0-15.716-.248-23.178-.732a310.202 310.202 0 0 1-12.513-19.846h.001a307.41 307.41 0 0 1-10.923-20.627a310.278 310.278 0 0 1 10.89-20.637l-.001.001a307.318 307.318 0 0 1 12.413-19.761c7.613-.576 15.42-.876 23.31-.876H128c7.926 0 15.743.303 23.354.883a329.357 329.357 0 0 1 12.335 19.695a358.489 358.489 0 0 1 11.036 20.54a329.472 329.472 0 0 1-11 20.722Zm22.56-122.124c8.572 4.944 11.906 24.881 6.52 51.026c-.344 1.668-.73 3.367-1.15 5.09c-10.622-2.452-22.155-4.275-34.23-5.408c-7.034-10.017-14.323-19.124-21.64-27.008a160.789 160.789 0 0 1 5.888-5.4c18.9-16.447 36.564-22.941 44.612-18.3ZM128 90.808c12.625 0 22.86 10.235 22.86 22.86s-10.235 22.86-22.86 22.86s-22.86-10.235-22.86-22.86s10.235-22.86 22.86-22.86Z"></path></svg>
--- a/frontend/src/components/Editor.test.tsx
+++ b/frontend/src/components/Editor.test.tsx
@@ -0,0 +1,31 @@
+import { describe, it, expect, vi } from 'vitest'
+import { render, screen, fireEvent } from '@testing-library/react'
+import { Editor } from './Editor'
+
+describe('Editor', () => {
+  it('renders with content', () => {
+    render(<Editor content="Hello World" onChange={() => {}} />)
+    const textarea = screen.getByDisplayValue('Hello World')
+    expect(textarea).toBeInTheDocument()
+  })
+
+  it('calls onChange when content changes', () => {
+    const handleChange = vi.fn()
+    render(<Editor content="" onChange={handleChange} />)
+    const textarea = screen.getByRole('textbox')
+    fireEvent.change(textarea, { target: { value: 'New content' } })
+    expect(handleChange).toHaveBeenCalledWith('New content')
+  })
+
+  it('shows placeholder when empty', () => {
+    render(<Editor content="" onChange={() => {}} placeholder="Type here..." />)
+    const textarea = screen.getByPlaceholderText('Type here...')
+    expect(textarea).toBeInTheDocument()
+  })
+
+  it('is disabled when disabled prop is true', () => {
+    render(<Editor content="" onChange={() => {}} disabled />)
+    const textarea = screen.getByRole('textbox')
+    expect(textarea).toBeDisabled()
+  })
+})
--- a/frontend/src/components/Editor.tsx
+++ b/frontend/src/components/Editor.tsx
@@ -0,0 +1,67 @@
+import { useCallback, useEffect, useRef } from 'react'
+
+interface EditorProps {
+  content: string
+  onChange: (content: string) => void
+  placeholder?: string
+  disabled?: boolean
+}
+
+export function Editor({ content, onChange, placeholder, disabled }: EditorProps) {
+  const textareaRef = useRef<HTMLTextAreaElement>(null)
+
+  // Auto-resize textarea
+  const adjustHeight = useCallback(() => {
+    const textarea = textareaRef.current
+    if (textarea) {
+      textarea.style.height = 'auto'
+      textarea.style.height = `${textarea.scrollHeight}px`
+    }
+  }, [])
+
+  useEffect(() => {
+    adjustHeight()
+  }, [content, adjustHeight])
+
+  const handleChange = (e: React.ChangeEvent<HTMLTextAreaElement>) => {
+    onChange(e.target.value)
+  }
+
+  const handleKeyDown = (e: React.KeyboardEvent) => {
+    // Handle tab key
+    if (e.key === 'Tab') {
+      e.preventDefault()
+      const textarea = textareaRef.current
+      if (textarea) {
+        const start = textarea.selectionStart
+        const end = textarea.selectionEnd
+        const newContent = content.substring(0, start) + '  ' + content.substring(end)
+        onChange(newContent)
+
+        // Set cursor position after tab
+        setTimeout(() => {
+          textarea.selectionStart = textarea.selectionEnd = start + 2
+        }, 0)
+      }
+    }
+  }
+
+  return (
+    <div className="h-full bg-white dark:bg-gray-900">
+      <textarea
+        ref={textareaRef}
+        value={content}
+        onChange={handleChange}
+        onKeyDown={handleKeyDown}
+        placeholder={placeholder}
+        disabled={disabled}
+        className="w-full h-full min-h-full p-6 resize-none outline-none border-none 
+                 bg-transparent font-mono text-sm leading-relaxed
+                 text-gray-800 dark:text-gray-200
+                 placeholder-gray-400 dark:placeholder-gray-600
+                 disabled:opacity-50 disabled:cursor-not-allowed"
+        spellCheck={false}
+      />
+    </div>
+  )
+}
--- a/frontend/src/components/Header.tsx
+++ b/frontend/src/components/Header.tsx
@@ -0,0 +1,100 @@
+import { Menu, Eye, EyeOff, Save, Sun, Moon, Monitor } from 'lucide-react'
+import type { Theme, FileItem } from '../types'
+
+interface HeaderProps {
+  theme: Theme
+  onThemeChange: (theme: Theme) => void
+  currentFile: FileItem | null
+  onSave: () => void
+  onToggleSidebar: () => void
+  onTogglePreview: () => void
+  isSidebarOpen: boolean
+  isPreviewOpen: boolean
+}
+
+export function Header({
+  theme,
+  onThemeChange,
+  currentFile,
+  onSave,
+  onToggleSidebar,
+  onTogglePreview,
+  isSidebarOpen,
+  isPreviewOpen,
+}: HeaderProps) {
+  return (
+    <header className="h-16 border-b border-gray-200 dark:border-gray-700 bg-white dark:bg-gray-900 flex items-center justify-between px-4">
+      <div className="flex items-center gap-4">
+        <button
+          onClick={onToggleSidebar}
+          className="p-2 rounded-lg hover:bg-gray-100 dark:hover:bg-gray-800 transition-colors"
+          title={isSidebarOpen ? 'Hide sidebar' : 'Show sidebar'}
+        >
+          <Menu className="w-5 h-5" />
+        </button>
+        <h1 className="text-xl font-bold hidden sm:block">Markdown Editor</h1>
+      </div>
+
+      <div className="flex items-center gap-2">
+        {currentFile && (
+          <span className="text-sm text-gray-500 dark:text-gray-400 mr-2 hidden sm:inline">
+            {currentFile.name}.md
+          </span>
+        )}
+
+        <button
+          onClick={onTogglePreview}
+          className="p-2 rounded-lg hover:bg-gray-100 dark:hover:bg-gray-800 transition-colors"
+          title={isPreviewOpen ? 'Hide preview' : 'Show preview'}
+        >
+          {isPreviewOpen ? <EyeOff className="w-5 h-5" /> : <Eye className="w-5 h-5" />}
+        </button>
+
+        <button
+          onClick={onSave}
+          disabled={!currentFile}
+          className="flex items-center gap-2 px-4 py-2 bg-blue-600 text-white rounded-lg hover:bg-blue-700 disabled:opacity-50 disabled:cursor-not-allowed transition-colors"
+        >
+          <Save className="w-4 h-4" />
+          <span className="hidden sm:inline">Save</span>
+        </button>
+
+        <div className="flex items-center gap-1 ml-2 border-l border-gray-200 dark:border-gray-700 pl-2">
+          <button
+            onClick={() => onThemeChange('light')}
+            className={`p-2 rounded-lg transition-colors ${
+              theme === 'light'
+                ? 'bg-gray-200 dark:bg-gray-700'
+                : 'hover:bg-gray-100 dark:hover:bg-gray-800'
+            }`}
+            title="Light theme"
+          >
+            <Sun className="w-4 h-4" />
+          </button>
+          <button
+            onClick={() => onThemeChange('dark')}
+            className={`p-2 rounded-lg transition-colors ${
+              theme === 'dark'
+                ? 'bg-gray-200 dark:bg-gray-700'
+                : 'hover:bg-gray-100 dark:hover:bg-gray-800'
+            }`}
+            title="Dark theme"
+          >
+            <Moon className="w-4 h-4" />
+          </button>
+          <button
+            onClick={() => onThemeChange('system')}
+            className={`p-2 rounded-lg transition-colors ${
+              theme === 'system'
+                ? 'bg-gray-200 dark:bg-gray-700'
+                : 'hover:bg-gray-100 dark:hover:bg-gray-800'
+            }`}
+            title="System theme"
+          >
+            <Monitor className="w-4 h-4" />
+          </button>
+        </div>
+      </div>
+    </header>
+  )
+}
--- a/frontend/src/components/Preview.test.tsx
+++ b/frontend/src/components/Preview.test.tsx
@@ -0,0 +1,26 @@
+import { describe, it, expect } from 'vitest'
+import { render, screen } from '@testing-library/react'
+import { Preview } from './Preview'
+
+describe('Preview', () => {
+  it('renders markdown content as HTML', () => {
+    render(<Preview content="# Hello" />)
+    const heading = screen.getByRole('heading', { name: 'Hello' })
+    expect(heading).toBeInTheDocument()
+  })
+
+  it('renders empty state message when no content', () => {
+    render(<Preview content="" />)
+    expect(screen.getByText(/start typing to see preview/i)).toBeInTheDocument()
+  })
+
+  it('renders bold text', () => {
+    render(<Preview content="**bold text**" />)
+    expect(screen.getByText('bold text')).toBeInTheDocument()
+  })
+
+  it('renders list items', () => {
+    render(<Preview content="- item 1" />)
+    expect(screen.getByText('item 1')).toBeInTheDocument()
+  })
+})
--- a/frontend/src/components/Preview.tsx
+++ b/frontend/src/components/Preview.tsx
@@ -0,0 +1,24 @@
+import { useMemo } from 'react'
+import { marked } from 'marked'
+
+interface PreviewProps {
+  content: string
+}
+
+export function Preview({ content }: PreviewProps) {
+  const html = useMemo(() => {
+    if (!content) {
+      return '<p class="text-gray-400 dark:text-gray-600 italic">Start typing to see preview...</p>'
+    }
+    return marked.parse(content, { async: false }) as string
+  }, [content])
+
+  return (
+    <div className="h-full bg-white dark:bg-gray-900 overflow-auto">
+      <div
+        className="preview-content p-6 prose dark:prose-invert max-w-none"
+        dangerouslySetInnerHTML={{ __html: html }}
+      />
+    </div>
+  )
+}
--- a/frontend/src/components/Sidebar.test.tsx
+++ b/frontend/src/components/Sidebar.test.tsx
@@ -0,0 +1,90 @@
+import { describe, it, expect, vi } from 'vitest'
+import { render, screen, fireEvent } from '@testing-library/react'
+import { Sidebar } from './Sidebar'
+import type { FileItem } from '../types'
+
+describe('Sidebar', () => {
+  const mockFiles: FileItem[] = [
+    { id: '1', name: 'file1', content: '' },
+    { id: '2', name: 'file2', content: '' },
+  ]
+
+  it('renders list of files', () => {
+    render(
+      <Sidebar
+        files={mockFiles}
+        currentFile={null}
+        onCreateFile={() => {}}
+        onOpenFile={() => {}}
+        onDeleteFile={() => {}}
+        isLoading={false}
+      />
+    )
+
+    expect(screen.getByText('file1.md')).toBeInTheDocument()
+    expect(screen.getByText('file2.md')).toBeInTheDocument()
+  })
+
+  it('shows loading state', () => {
+    render(
+      <Sidebar
+        files={[]}
+        currentFile={null}
+        onCreateFile={() => {}}
+        onOpenFile={() => {}}
+        onDeleteFile={() => {}}
+        isLoading={true}
+      />
+    )
+
+    expect(document.querySelector('.animate-spin')).toBeInTheDocument()
+  })
+
+  it('shows empty state when no files', () => {
+    render(
+      <Sidebar
+        files={[]}
+        currentFile={null}
+        onCreateFile={() => {}}
+        onOpenFile={() => {}}
+        onDeleteFile={() => {}}
+        isLoading={false}
+      />
+    )
+
+    expect(screen.getByText(/no files yet/i)).toBeInTheDocument()
+  })
+
+  it('calls onOpenFile when file is clicked', () => {
+    const handleOpenFile = vi.fn()
+    render(
+      <Sidebar
+        files={mockFiles}
+        currentFile={null}
+        onCreateFile={() => {}}
+        onOpenFile={handleOpenFile}
+        onDeleteFile={() => {}}
+        isLoading={false}
+      />
+    )
+
+    fireEvent.click(screen.getByText('file1.md'))
+    expect(handleOpenFile).toHaveBeenCalledWith(mockFiles[0])
+  })
+
+  it('opens create file input when plus button is clicked', () => {
+    render(
+      <Sidebar
+        files={[]}
+        currentFile={null}
+        onCreateFile={() => {}}
+        onOpenFile={() => {}}
+        onDeleteFile={() => {}}
+        isLoading={false}
+      />
+    )
+
+    fireEvent.click(screen.getByTitle('Create new file'))
+    expect(screen.getByPlaceholderText('File name...')).toBeInTheDocument()
+  })
+})
--- a/frontend/src/components/Sidebar.tsx
+++ b/frontend/src/components/Sidebar.tsx
@@ -0,0 +1,179 @@
+import { useState } from 'react'
+import { FileText, Plus, Trash2, Loader2 } from 'lucide-react'
+import type { FileItem } from '../types'
+
+interface SidebarProps {
+  files: FileItem[]
+  currentFile: FileItem | null
+  onCreateFile: (name: string) => void
+  onOpenFile: (file: FileItem) => void
+  onDeleteFile: (file: FileItem) => void
+  isLoading: boolean
+}
+
+export function Sidebar({
+  files,
+  currentFile,
+  onCreateFile,
+  onOpenFile,
+  onDeleteFile,
+  isLoading,
+}: SidebarProps) {
+  const [isCreating, setIsCreating] = useState(false)
+  const [newFileName, setNewFileName] = useState('')
+  const [fileToDelete, setFileToDelete] = useState<FileItem | null>(null)
+
+  const handleCreate = () => {
+    if (newFileName.trim()) {
+      onCreateFile(newFileName.trim())
+      setNewFileName('')
+      setIsCreating(false)
+    }
+  }
+
+  const handleKeyDown = (e: React.KeyboardEvent) => {
+    if (e.key === 'Enter') {
+      handleCreate()
+    } else if (e.key === 'Escape') {
+      setIsCreating(false)
+      setNewFileName('')
+    }
+  }
+
+  const handleDelete = (file: FileItem) => {
+    setFileToDelete(file)
+  }
+
+  const confirmDelete = () => {
+    if (fileToDelete) {
+      onDeleteFile(fileToDelete)
+      setFileToDelete(null)
+    }
+  }
+
+  return (
+    <aside className="w-64 border-r border-gray-200 dark:border-gray-700 bg-gray-50 dark:bg-gray-800 flex flex-col">
+      <div className="p-4 border-b border-gray-200 dark:border-gray-700">
+        <div className="flex items-center justify-between mb-2">
+          <h2 className="font-semibold text-gray-700 dark:text-gray-300">Files</h2>
+          <button
+            onClick={() => setIsCreating(true)}
+            className="p-1.5 rounded-lg bg-blue-600 text-white hover:bg-blue-700 transition-colors"
+            title="Create new file"
+          >
+            <Plus className="w-4 h-4" />
+          </button>
+        </div>
+
+        {isCreating && (
+          <div className="mt-2">
+            <input
+              type="text"
+              value={newFileName}
+              onChange={(e) => setNewFileName(e.target.value)}
+              onKeyDown={handleKeyDown}
+              placeholder="File name..."
+              className="w-full px-3 py-2 text-sm border border-gray-300 dark:border-gray-600 rounded-lg 
+                       bg-white dark:bg-gray-700 text-gray-900 dark:text-gray-100
+                       focus:outline-none focus:ring-2 focus:ring-blue-500"
+              autoFocus
+            />
+            <div className="flex gap-2 mt-2">
+              <button
+                onClick={handleCreate}
+                disabled={!newFileName.trim()}
+                className="flex-1 px-3 py-1.5 text-xs bg-blue-600 text-white rounded-lg hover:bg-blue-700 
+                         disabled:opacity-50 disabled:cursor-not-allowed transition-colors"
+              >
+                Create
+              </button>
+              <button
+                onClick={() => {
+                  setIsCreating(false)
+                  setNewFileName('')
+                }}
+                className="flex-1 px-3 py-1.5 text-xs bg-gray-200 dark:bg-gray-600 text-gray-700 dark:text-gray-300 
+                         rounded-lg hover:bg-gray-300 dark:hover:bg-gray-500 transition-colors"
+              >
+                Cancel
+              </button>
+            </div>
+          </div>
+        )}
+      </div>
+
+      <div className="flex-1 overflow-y-auto p-2">
+        {isLoading ? (
+          <div className="flex items-center justify-center py-8">
+            <Loader2 className="w-6 h-6 animate-spin text-gray-400" />
+          </div>
+        ) : files.length === 0 ? (
+          <div className="text-center py-8 text-gray-500 dark:text-gray-400 text-sm">
+            No files yet.
+            <br />
+            Click + to create one.
+          </div>
+        ) : (
+          <ul className="space-y-1">
+            {files.map((file) => (
+              <li key={file.id}>
+                <div
+                  className={`flex items-center gap-2 px-3 py-2 rounded-lg cursor-pointer group transition-colors
+                    ${
+                      currentFile?.id === file.id
+                        ? 'bg-blue-100 dark:bg-blue-900 text-blue-900 dark:text-blue-100'
+                        : 'hover:bg-gray-200 dark:hover:bg-gray-700 text-gray-700 dark:text-gray-300'
+                    }`}
+                  onClick={() => onOpenFile(file)}
+                >
+                  <FileText className="w-4 h-4 flex-shrink-0" />
+                  <span className="flex-1 text-sm truncate">{file.name}.md</span>
+                  <button
+                    onClick={(e) => {
+                      e.stopPropagation()
+                      handleDelete(file)
+                    }}
+                    className="opacity-0 group-hover:opacity-100 p-1 rounded hover:bg-red-100 
+                             dark:hover:bg-red-900 text-red-600 dark:text-red-400 transition-all"
+                    title="Delete file"
+                  >
+                    <Trash2 className="w-3.5 h-3.5" />
+                  </button>
+                </div>
+              </li>
+            ))}
+          </ul>
+        )}
+      </div>
+
+      {/* Delete confirmation modal */}
+      {fileToDelete && (
+        <div className="fixed inset-0 bg-black/50 flex items-center justify-center z-50 p-4">
+          <div className="bg-white dark:bg-gray-800 rounded-lg p-6 max-w-sm w-full shadow-xl">
+            <h3 className="text-lg font-semibold mb-2 text-gray-900 dark:text-gray-100">
+              Delete File?
+            </h3>
+            <p className="text-gray-600 dark:text-gray-400 mb-4">
+              Are you sure you want to delete "{fileToDelete.name}.md"? This action cannot be undone.
+            </p>
+            <div className="flex gap-3">
+              <button
+                onClick={confirmDelete}
+                className="flex-1 px-4 py-2 bg-red-600 text-white rounded-lg hover:bg-red-700 transition-colors"
+              >
+                Delete
+              </button>
+              <button
+                onClick={() => setFileToDelete(null)}
+                className="flex-1 px-4 py-2 bg-gray-200 dark:bg-gray-700 text-gray-700 dark:text-gray-300 
+                         rounded-lg hover:bg-gray-300 dark:hover:bg-gray-600 transition-colors"
+              >
+                Cancel
+              </button>
+            </div>
+          </div>
+        </div>
+      )}
+    </aside>
+  )
+}
--- a/frontend/src/index.css
+++ b/frontend/src/index.css
@@ -0,0 +1,166 @@
+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+
+/* Custom scrollbar */
+::-webkit-scrollbar {
+  width: 8px;
+  height: 8px;
+}
+
+::-webkit-scrollbar-track {
+  background: transparent;
+}
+
+::-webkit-scrollbar-thumb {
+  background: #cbd5e1;
+  border-radius: 4px;
+}
+
+.dark ::-webkit-scrollbar-thumb {
+  background: #475569;
+}
+
+::-webkit-scrollbar-thumb:hover {
+  background: #94a3b8;
+}
+
+.dark ::-webkit-scrollbar-thumb:hover {
+  background: #64748b;
+}
+
+/* Editor styles */
+.editor-textarea {
+  resize: none;
+  outline: none;
+}
+
+.editor-textarea:focus {
+  outline: none;
+}
+
+/* Preview styles */
+.preview-content h1 {
+  font-size: 2rem;
+  font-weight: bold;
+  margin-bottom: 1rem;
+}
+
+.preview-content h2 {
+  font-size: 1.5rem;
+  font-weight: bold;
+  margin-top: 1.5rem;
+  margin-bottom: 0.75rem;
+}
+
+.preview-content h3 {
+  font-size: 1.25rem;
+  font-weight: bold;
+  margin-top: 1.25rem;
+  margin-bottom: 0.5rem;
+}
+
+.preview-content p {
+  margin-bottom: 1rem;
+  line-height: 1.6;
+}
+
+.preview-content ul {
+  list-style-type: disc;
+  padding-left: 1.5rem;
+  margin-bottom: 1rem;
+}
+
+.preview-content ol {
+  list-style-type: decimal;
+  padding-left: 1.5rem;
+  margin-bottom: 1rem;
+}
+
+.preview-content code {
+  background-color: #f1f5f9;
+  padding: 0.125rem 0.375rem;
+  border-radius: 0.25rem;
+  font-family: monospace;
+  font-size: 0.875rem;
+}
+
+.dark .preview-content code {
+  background-color: #1e293b;
+}
+
+.preview-content pre {
+  background-color: #f1f5f9;
+  padding: 1rem;
+  border-radius: 0.5rem;
+  overflow-x: auto;
+  margin-bottom: 1rem;
+}
+
+.dark .preview-content pre {
+  background-color: #1e293b;
+}
+
+.preview-content pre code {
+  background-color: transparent;
+  padding: 0;
+}
+
+.preview-content blockquote {
+  border-left: 4px solid #cbd5e1;
+  padding-left: 1rem;
+  margin-left: 0;
+  margin-bottom: 1rem;
+  color: #64748b;
+}
+
+.dark .preview-content blockquote {
+  border-left-color: #475569;
+  color: #94a3b8;
+}
+
+.preview-content a {
+  color: #3b82f6;
+  text-decoration: underline;
+}
+
+.preview-content a:hover {
+  color: #2563eb;
+}
+
+.preview-content table {
+  width: 100%;
+  border-collapse: collapse;
+  margin-bottom: 1rem;
+}
+
+.preview-content th,
+.preview-content td {
+  border: 1px solid #e2e8f0;
+  padding: 0.5rem;
+  text-align: left;
+}
+
+.dark .preview-content th,
+.dark .preview-content td {
+  border-color: #334155;
+}
+
+.preview-content th {
+  background-color: #f8fafc;
+  font-weight: bold;
+}
+
+.dark .preview-content th {
+  background-color: #1e293b;
+}
+
+.preview-content hr {
+  border: none;
+  border-top: 1px solid #e2e8f0;
+  margin: 1.5rem 0;
+}
+
+.dark .preview-content hr {
+  border-top-color: #334155;
+}
--- a/frontend/src/main.tsx
+++ b/frontend/src/main.tsx
@@ -0,0 +1,10 @@
+import { StrictMode } from 'react'
+import { createRoot } from 'react-dom/client'
+import './index.css'
+import App from './App.tsx'
+
+createRoot(document.getElementById('root')!).render(
+  <StrictMode>
+    <App />
+  </StrictMode>,
+)
--- a/frontend/src/test/setup.ts
+++ b/frontend/src/test/setup.ts
@@ -0,0 +1 @@
+import '@testing-library/jest-dom'
--- a/frontend/src/types.ts
+++ b/frontend/src/types.ts
@@ -0,0 +1,12 @@
+export type Theme = 'light' | 'dark' | 'system'
+
+export interface FileItem {
+  id: string
+  name: string
+  content: string
+}
+
+export interface FileResponse {
+  name: string
+  content: string
+}
--- a/frontend/tailwind.config.cjs
+++ b/frontend/tailwind.config.cjs
@@ -0,0 +1,12 @@
+/** @type {import('tailwindcss').Config} */
+module.exports = {
+  content: [
+    "./index.html",
+    "./src/**/*.{js,ts,jsx,tsx}",
+  ],
+  darkMode: 'class',
+  theme: {
+    extend: {},
+  },
+  plugins: [],
+}
--- a/frontend/tsconfig.app.json
+++ b/frontend/tsconfig.app.json
@@ -0,0 +1,28 @@
+{
+  "compilerOptions": {
+    "tsBuildInfoFile": "./node_modules/.tmp/tsconfig.app.tsbuildinfo",
+    "target": "ES2022",
+    "useDefineForClassFields": true,
+    "lib": ["ES2022", "DOM", "DOM.Iterable"],
+    "module": "ESNext",
+    "types": ["vite/client"],
+    "skipLibCheck": true,
+
+    /* Bundler mode */
+    "moduleResolution": "bundler",
+    "allowImportingTsExtensions": true,
+    "verbatimModuleSyntax": true,
+    "moduleDetection": "force",
+    "noEmit": true,
+    "jsx": "react-jsx",
+
+    /* Linting */
+    "strict": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "erasableSyntaxOnly": true,
+    "noFallthroughCasesInSwitch": true,
+    "noUncheckedSideEffectImports": true
+  },
+  "include": ["src"]
+}
--- a/frontend/tsconfig.json
+++ b/frontend/tsconfig.json
@@ -0,0 +1,7 @@
+{
+  "files": [],
+  "references": [
+    { "path": "./tsconfig.app.json" },
+    { "path": "./tsconfig.node.json" }
+  ]
+}
--- a/frontend/tsconfig.node.json
+++ b/frontend/tsconfig.node.json
@@ -0,0 +1,26 @@
+{
+  "compilerOptions": {
+    "tsBuildInfoFile": "./node_modules/.tmp/tsconfig.node.tsbuildinfo",
+    "target": "ES2023",
+    "lib": ["ES2023"],
+    "module": "ESNext",
+    "types": ["node"],
+    "skipLibCheck": true,
+
+    /* Bundler mode */
+    "moduleResolution": "bundler",
+    "allowImportingTsExtensions": true,
+    "verbatimModuleSyntax": true,
+    "moduleDetection": "force",
+    "noEmit": true,
+
+    /* Linting */
+    "strict": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "erasableSyntaxOnly": true,
+    "noFallthroughCasesInSwitch": true,
+    "noUncheckedSideEffectImports": true
+  },
+  "include": ["vite.config.ts"]
+}
--- a/frontend/vite.config.ts
+++ b/frontend/vite.config.ts
@@ -0,0 +1,7 @@
+import { defineConfig } from 'vite'
+import react from '@vitejs/plugin-react'
+
+// https://vite.dev/config/
+export default defineConfig({
+  plugins: [react()],
+})
--- a/frontend/vitest.config.ts
+++ b/frontend/vitest.config.ts
@@ -0,0 +1,11 @@
+import { defineConfig } from 'vitest/config'
+import react from '@vitejs/plugin-react'
+
+export default defineConfig({
+  plugins: [react()],
+  test: {
+    environment: 'jsdom',
+    globals: true,
+    setupFiles: './src/test/setup.ts',
+  },
+})
--- a/1
+++ b/1
@@ -0,0 +1 @@
+backend/static
				`@@ -0,0 +1 @@`
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