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/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 @@
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--- 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',
+  },
+})
				`@@ -0,0 +1 @@`
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