# WYSIWYG Markdown Editor - Specification

## Overview

Build a WYSIWYG markdown editor with save functionality consisting of a Go backend and vanilla JavaScript frontend with Tailwind CSS.  
Beyond the listed features, no authentication, user accounts, collaborative editing, or version history are required.

## Backend (Go)

### Requirements

- Use Go with standard HTTP server
- Use Cobra library for CLI argument parsing
- Implement CRUD operations for markdown files:
  - Create: Add new markdown files
  - Read: Retrieve/View markdown files
  - Update: Edit existing markdown files
  - Delete: Remove markdown files
- Store markdown files on disk in a specified directory
- The server must handle concurrent requests safely; the last successful write wins
- Markdown file names are case-sensitive and must end in `.md`. Illegal characters for the current OS must be rejected with 400 Bad Request
- Directory structure under `--data-dir` is flat: every `.md` file is a sibling; sub-directories are ignored

### CLI Options

The application must support the following CLI flags:

- `--data-dir`: Path to the directory where markdown files will be stored (default: `./data`)
- `--port`: Port number to run the HTTP server on (default: `8080`)
- `--host`: Host address to bind to (default: `127.0.0.1`)  
  Cobra must generate help text for `--help` and `-h` that includes defaults.

### API Implementation

- Design and implement appropriate REST endpoints for CRUD operations
- Handle error responses appropriately
- Validate inputs appropriately
- Any operation that fails must return an HTTP 4xx/5xx code and a JSON body containing at least an `error` string

## Frontend (Vanilla JavaScript + Tailwind CSS)

### Requirements

- Vanilla JavaScript (no frameworks)
- Tailwind CSS for styling
- Single-page application interface
- No build step except running the Tailwind CLI once to generate the CSS file; runtime must work in a current Chrome/Edge/Firefox without polyfills

### Features

#### Markdown Editor

- Split-view or toggleable view with:
  - Edit pane: Textarea for markdown input
  - Preview pane: Rendered markdown preview
- Real-time preview updates
- Render markdown with GitHub-Flavored-Markdown (GFM) semantics

#### Theme Support

Three theme modes:

- **Dark**: Dark color scheme
- **Light**: Light color scheme
- **System**: Follows system preference

Theme switching requirements:

- Auto-detect system preference on load (prefers-color-scheme)
- Manual theme switcher with three options: Dark, Light, System
- Persist theme preference in localStorage under the key `wysiwyg-theme`
- Update theme immediately when changed
- Respect system theme changes when in "System" mode

#### File Management UI

- List all markdown files
- Create new files
- Open existing files for editing
- Save changes
- Delete files

#### Responsive Design

- Works on desktop and mobile
- Responsive layout using Tailwind classes

## Development Environment

The repository root contains a `flake.nix` locked to `github:NixOS/nixpkgs/nixos-25.11`.  
`nix develop` has already been executed; the resulting shell provides:

- go, gopls, golangci-lint
- tailwindcss
- gnumake

You must not modify the flake or add packages outside this environment.

## General Requirements

- No database - use file system
- Minimal dependencies
- Clean, maintainable code
- Proper error handling

## Testing & Observability

- Provide at least one automated test (unit, integration, or end-to-end) that can be run with a single command (`go test`, `make test`, etc.).
- The test must demonstrate that a markdown file can be created, read, updated, and deleted through the REST endpoints.
- On start-up the server must log its bound address in the format `listening on <host>:<port>` so evaluators can script against it.

## Evaluation Checklist

Evaluation will check:  
(1) CLI starts with defaults,  
(2) CRUD round-trip,  
(3) theme switch & persistence,  
(4) responsive layout on 320 px and 1920 px,