index.js

const express = require('express');
const app = express();
const cors = require('cors');
const bodyParser = require('body-parser');
const crypto = require('crypto'); // Built-in Node.js module for generating IDs

app.use(cors());
app.use(bodyParser.urlencoded({ extended: false }));
app.use(express.static('public'));

app.get('/', (req, res) => {
  res.sendFile(__dirname + '/views/index.html');
});

// In-memory "database"
let users = [];
let exercises = [];

// Helper function to generate a unique ID
const generateId = () => crypto.randomBytes(12).toString('hex');

// 1. POST to /api/users to create a new user.
app.post('/api/users', (req, res) => {
  const username = req.body.username;
  if (!username) {
    return res.status(400).json({ error: 'Username is required' });
  }

  const newUser = {
    username: username,
    _id: generateId()
  };

  users.push(newUser);
  res.json(newUser);
});

// 2. GET to /api/users to get a list of all users.
app.get('/api/users', (req, res) => {
  res.json(users);
});

// 3. POST to /api/users/:_id/exercises to add an exercise.
app.post('/api/users/:_id/exercises', (req, res) => {
  const userId = req.params._id;
  const { description, duration, date } = req.body;

  // Find the user by their ID
  const user = users.find(u => u._id === userId);
  if (!user) {
    return res.status(404).json({ error: 'User not found' });
  }

  // Validate required fields
  if (!description || !duration) {
    return res.status(400).json({ error: 'Description and duration are required' });
  }

  // Create the exercise object
  const exerciseDate = date ? new Date(date) : new Date();

  const newExercise = {
    userId: user._id,
    username: user.username,
    description: description,
    duration: parseInt(duration),
    date: exerciseDate
  };

  exercises.push(newExercise);

  // Return the user object with the exercise fields added
  res.json({
    _id: user._id,
    username: user.username,
    date: newExercise.date.toDateString(),
    duration: newExercise.duration,
    description: newExercise.description
  });
});

// 4. GET to /api/users/:_id/logs to retrieve a user's exercise log.
app.get('/api/users/:_id/logs', (req, res) => {
  const userId = req.params._id;
  const { from, to, limit } = req.query;

  const user = users.find(u => u._id === userId);
  if (!user) {
    return res.status(404).json({ error: 'User not found' });
  }

  // Get all exercises for this user
  let userExercises = exercises.filter(ex => ex.userId === userId);

  // Apply filters if they exist
  if (from) {
    const fromDate = new Date(from);
    userExercises = userExercises.filter(ex => ex.date >= fromDate);
  }
  if (to) {
    const toDate = new Date(to);
    userExercises = userExercises.filter(ex => ex.date <= toDate);
  }
  if (limit) {
    userExercises = userExercises.slice(0, parseInt(limit));
  }
  
  // Format the log array as required
  const log = userExercises.map(ex => ({
    description: ex.description,
    duration: ex.duration,
    date: ex.date.toDateString()
  }));

  // Construct the final response object
  res.json({
    _id: user._id,
    username: user.username,
    count: log.length,
    log: log
  });
});


const listener = app.listen(process.env.PORT || 3000, () => {
  console.log('Your app is listening on port ' + listener.address().port);
});