// Stateful: Depends on server session (not RESTful)
app.post('/login', (req, res) => {
  req.session.userId = 42; // Server State Saving
  res.send('logged in');
});

app.get('/profile', (req, res) => {
  const userId = req.session.userId; // Depends on the server status
  res.json({ id: userId, name: 'Alice' });
});

// Stateless：Include authentication information with every request（RESTful）
app.get('/profile', (req, res) => {
  const userId = verifyToken(req.headers.authorization);
  res.json({ id: userId, name: 'Alice' });
});

// POST: Creates a new resource on every call (Non-idempotent)
// 1st POST /tasks → Create id=1
// 2nd POST /tasks → Create id=2
app.post('/tasks', (req, res) => {
  const task = { id: nextId++, ...req.body };
  tasks.push(task);
  res.status(201).json(task);
});

// PUT: Replaces the same resource on every call (Idempotent)
// 1st PUT /tasks/1 → Replace id=1
// 2nd PUT /tasks/1 → Replace id=1 (The results are the same)
app.put('/tasks/:id', (req, res) => {
  const idx = tasks.findIndex(t => t.id === parseInt(req.params.id));
  if (idx === -1) return res.status(404).json({ error: 'Not found' });
  tasks[idx] = { id: parseInt(req.params.id), ...req.body };
  res.json(tasks[idx]);
});

// PATCH：Modify only the fields provided
app.patch('/tasks/:id', (req, res) => {
  const task = tasks.find(t => t.id === parseInt(req.params.id));
  if (!task) return res.status(404).json({ error: 'Not found' });
  Object.assign(task, req.body);
  res.json(task);
});

// Request：Modify only status Field
// PATCH /tasks/1  {"status": "done"}
// Raw Data：{"id":1,"title":"Learn REST","status":"pending"}
// Results：{"id":1,"title":"Learn REST","status":"done"}

# Mission Resources
GET    /tasks              # Get the task list
POST   /tasks              # Create a New Task
GET    /tasks/42           # Get a Single Task
PUT    /tasks/42           # Full Update Task
PATCH  /tasks/42           # Partial Update Task
DELETE /tasks/42           # Delete Task

# Comments on the Assignment（Nested Resources）
GET    /tasks/42/comments           # Get a Task42List of comments
POST   /tasks/42/comments           # For the mission42Add a comment
GET    /tasks/42/comments/7         # Get a Task42Comments on7
DELETE /tasks/42/comments/7         # Delete Comment7

# Filtering and Pagination
GET    /tasks?status=done&page=2&limit=20
GET    /tasks?sort=-created_at      # Sort by creation date in reverse chronological order

app.get('/tasks', (req, res) => {
  let result = [...tasks];

  // Filter
  if (req.query.status) {
    result = result.filter(t => t.status === req.query.status);
  }

  // Sort
  if (req.query.sort) {
    const field = req.query.sort.startsWith('-')
      ? req.query.sort.slice(1)
      : req.query.sort;
    const order = req.query.sort.startsWith('-') ? -1 : 1;
    result.sort((a, b) => (a[field] > b[field] ? order : -order));
  }

  // Pagination
  const page = parseInt(req.query.page) || 1;
  const limit = parseInt(req.query.limit) || 20;
  const start = (page - 1) * limit;
  result = result.slice(start, start + limit);

  res.json({
    data: result,
    page,
    limit,
    total: tasks.length
  });
});

// Create a Resource → 201 + Location
app.post('/tasks', (req, res) => {
  const task = { id: nextId++, ...req.body };
  tasks.push(task);
  res.status(201)
     .location(`/tasks/${task.id}`)
     .json(task);
});

// Delete Resource → 204（Non-responsive body）
app.delete('/tasks/:id', (req, res) => {
  const idx = tasks.findIndex(t => t.id === parseInt(req.params.id));
  if (idx === -1) return res.status(404).json({ error: 'Not found' });
  tasks.splice(idx, 1);
  res.status(204).end();
});

// Verification Failed → 400 + Error Details
app.post('/tasks', (req, res) => {
  if (!req.body.title) {
    return res.status(400).json({
      error: 'Validation failed',
      details: [{ field: 'title', message: 'Title is required' }]
    });
  }
  // ...
});

app.get('/tasks', (req, res) => {
  const page = parseInt(req.query.page) || 1;
  const limit = parseInt(req.query.limit) || 20;
  const start = (page - 1) * limit;
  const data = tasks.slice(start, start + limit);

  res.json({
    data,
    pagination: {
      page,
      limit,
      total: tasks.length,
      totalPages: Math.ceil(tasks.length / limit)
    }
  });
});

// Response Example
{
  "data": [
    {
      "id": "1",
      "title": "Learn REST",
      "status": "pending",
      "createdAt": "2025-07-03T10:30:00Z"
    }
  ],
  "pagination": {
    "page": 1,
    "limit": 20,
    "total": 1,
    "totalPages": 1
  }
}

// Unified Error Handling Middleware
app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(err.status || 500).json({
    error: err.message || 'Internal Server Error',
    details: err.details || [],
    requestId: req.id,
    timestamp: new Date().toISOString()
  });
});

// Custom Error Classes
class ApiError extends Error {
  constructor(status, message, details = []) {
    super(message);
    this.status = status;
    this.details = details;
  }
}

// Usage
app.get('/tasks/:id', (req, res, next) => {
  const task = tasks.find(t => t.id === parseInt(req.params.id));
  if (!task) {
    return next(new ApiError(404, 'Task not found', [
      { field: 'id', message: `No task with id ${req.params.id}` }
    ]));
  }
  res.json(task);
});

// Examples of Error Responses
{
  "error": "Task not found",
  "details": [
    { "field": "id", "message": "No task with id 999" }
  ],
  "requestId": "req-a1b2c3",
  "timestamp": "2025-07-03T10:30:00Z"
}

// Routing Structure
// /api/v1/tasks → v1 Logic
// /api/v2/tasks → v2 Logic

const express = require('express');
const app = express();

// v1 Routing
const v1Router = express.Router();
v1Router.get('/tasks', (req, res) => {
  res.json({ data: tasks, version: 'v1' }); // v1 Return Format
});

// v2 Routing（Response Format Upgrade）
const v2Router = express.Router();
v2Router.get('/tasks', (req, res) => {
  res.json({                        // v2 Return Format（Includes pagination）
    data: tasks,
    pagination: { page: 1, total: tasks.length }
  });
});

app.use('/api/v1', v1Router);
app.use('/api/v2', v2Router);

// Response Header Version
app.use('/api/v2', (req, res, next) => {
  res.setHeader('X-API-Version', '2.0');
  next();
});

app.get('/tasks/:id', (req, res) => {
  const task = tasks.find(t => t.id === parseInt(req.params.id));
  if (!task) return res.status(404).json({ error: 'Not found' });

  res.json({
    ...task,
    _links: {
      self: { href: `/tasks/${task.id}`, method: 'GET' },
      update: { href: `/tasks/${task.id}`, method: 'PUT' },
      delete: { href: `/tasks/${task.id}`, method: 'DELETE' },
      assign: { href: `/tasks/${task.id}/assignee`, method: 'POST' },
      comments: { href: `/tasks/${task.id}/comments`, method: 'GET' }
    }
  });
});

// Response
{
  "id": "1",
  "title": "Learn REST",
  "status": "pending",
  "createdAt": "2025-07-03T10:30:00Z",
  "_links": {
    "self": { "href": "/tasks/1", "method": "GET" },
    "update": { "href": "/tasks/1", "method": "PUT" },
    "delete": { "href": "/tasks/1", "method": "DELETE" },
    "assign": { "href": "/tasks/1/assignee", "method": "POST" },
    "comments": { "href": "/tasks/1/comments", "method": "GET" }
  }
}

const express = require('express');
const app = express();
app.use(express.json());

let tasks = [
  { id: 1, title: 'Design database schema', status: 'done', priority: 'high', createdAt: '2025-07-01T08:00:00Z' },
  { id: 2, title: 'Implement REST API', status: 'in-progress', priority: 'high', createdAt: '2025-07-02T09:00:00Z' }
];
let nextId = 3;

// GET /api/v1/tasks — Get the task list
app.get('/api/v1/tasks', (req, res) => {
  const { status, priority, page = 1, limit = 20 } = req.query;
  let result = [...tasks];
  if (status) result = result.filter(t => t.status === status);
  if (priority) result = result.filter(t => t.priority === priority);

  const start = (page - 1) * limit;
  const data = result.slice(start, start + Number(limit));

  res.json({
    data,
    pagination: {
      page: Number(page),
      limit: Number(limit),
      total: result.length,
      totalPages: Math.ceil(result.length / Number(limit))
    }
  });
});

// GET /api/v1/tasks/:id — Get a Single Task
app.get('/api/v1/tasks/:id', (req, res) => {
  const task = tasks.find(t => t.id === parseInt(req.params.id));
  if (!task) {
    return res.status(404).json({
      error: 'Task not found',
      details: [{ field: 'id', message: `No task with id ${req.params.id}` }],
      timestamp: new Date().toISOString()
    });
  }
  res.json({
    data: task,
    _links: {
      self: { href: `/api/v1/tasks/${task.id}` },
      update: { href: `/api/v1/tasks/${task.id}`, method: 'PUT' },
      delete: { href: `/api/v1/tasks/${task.id}`, method: 'DELETE' },
      comments: { href: `/api/v1/tasks/${task.id}/comments` }
    }
  });
});

// POST /api/v1/tasks — Create a Task
app.post('/api/v1/tasks', (req, res) => {
  const { title, priority } = req.body;
  if (!title) {
    return res.status(400).json({
      error: 'Validation failed',
      details: [{ field: 'title', message: 'Title is required' }],
      timestamp: new Date().toISOString()
    });
  }
  const task = {
    id: nextId++,
    title,
    status: 'pending',
    priority: priority || 'medium',
    createdAt: new Date().toISOString()
  };
  tasks.push(task);
  res.status(201).location(`/api/v1/tasks/${task.id}`).json({ data: task });
});

// PUT /api/v1/tasks/:id — Full Update
app.put('/api/v1/tasks/:id', (req, res) => {
  const idx = tasks.findIndex(t => t.id === parseInt(req.params.id));
  if (idx === -1) {
    return res.status(404).json({
      error: 'Task not found',
      details: [{ field: 'id', message: `No task with id ${req.params.id}` }],
      timestamp: new Date().toISOString()
    });
  }
  const { title, status, priority } = req.body;
  if (!title || !status) {
    return res.status(400).json({
      error: 'Validation failed',
      details: [
        ...(!title ? [{ field: 'title', message: 'Title is required' }] : []),
        ...(!status ? [{ field: 'status', message: 'Status is required' }] : [])
      ],
      timestamp: new Date().toISOString()
    });
  }
  tasks[idx] = { id: tasks[idx].id, title, status, priority: priority || 'medium', createdAt: tasks[idx].createdAt };
  res.json({ data: tasks[idx] });
});

// PATCH /api/v1/tasks/:id — Partial Update
app.patch('/api/v1/tasks/:id', (req, res) => {
  const task = tasks.find(t => t.id === parseInt(req.params.id));
  if (!task) {
    return res.status(404).json({
      error: 'Task not found',
      details: [{ field: 'id', message: `No task with id ${req.params.id}` }],
      timestamp: new Date().toISOString()
    });
  }
  Object.assign(task, req.body);
  res.json({ data: task });
});

// DELETE /api/v1/tasks/:id — Delete Task
app.delete('/api/v1/tasks/:id', (req, res) => {
  const idx = tasks.findIndex(t => t.id === parseInt(req.params.id));
  if (idx === -1) {
    return res.status(404).json({
      error: 'Task not found',
      details: [{ field: 'id', message: `No task with id ${req.params.id}` }],
      timestamp: new Date().toISOString()
    });
  }
  tasks.splice(idx, 1);
  res.status(204).end();
});

app.listen(3000, () => console.log('Task API running on port 3000'));

# Create a Task
curl -X POST http://localhost:3000/api/v1/tasks \
  -H "Content-Type: application/json" \
  -d '{"title":"Write documentation","priority":"high"}'

# Get the task list（Filter + Pagination）
curl http://localhost:3000/api/v1/tasks?status=pending&page=1&limit=10

# Partial Update
curl -X PATCH http://localhost:3000/api/v1/tasks/1 \
  -H "Content-Type: application/json" \
  -d '{"status":"done"}'

# Delete Task
curl -X DELETE http://localhost:3000/api/v1/tasks/2

// POST Created successfully → 201
Status: 201 Created
Location: /api/v1/tasks/3
{ "data": { "id": 3, "title": "Write documentation", "status": "pending", "priority": "high", "createdAt": "2025-07-03T10:30:00Z" } }

// PATCH Update successful → 200
{ "data": { "id": 1, "title": "Design database schema", "status": "done", "priority": "high", "createdAt": "2025-07-01T08:00:00Z" } }

// DELETE Success → 204
Status: 204 No Content
(empty body)

// 404 Error
{ "error": "Task not found", "details": [{ "field": "id", "message": "No task with id 999" }], "timestamp": "2025-07-03T10:30:00Z" }

// 400 Validation Error
{ "error": "Validation failed", "details": [{ "field": "title", "message": "Title is required" }], "timestamp": "2025-07-03T10:30:00Z" }