const express = require('express');
const router = express.Router();
const { pool } = require('../db');

/**
 * Validate the request body for bill create/update operations.
 *
 * Checks that all required fields are present and within acceptable ranges.
 * Amount is optional when `variable_amount` is true (defaults to 0 on save).
 *
 * @param {object} body - Request body.
 * @param {string}        body.name              - Bill name (non-empty).
 * @param {number|string} [body.amount]           - Bill amount; required when variable_amount is falsy.
 * @param {number|string} body.due_day            - Day of month (1–31).
 * @param {number|string} body.assigned_paycheck  - Which paycheck: 1 or 2.
 * @param {boolean}       [body.variable_amount]  - Whether the bill amount varies each month.
 * @returns {string|null} Validation error message, or null when valid.
 */
function validateBillFields(body) {
  const { name, amount, due_day, assigned_paycheck, variable_amount } = body;
  if (!name || name.toString().trim() === '') {
    return 'name is required';
  }
  // Amount is optional for variable bills (defaults to 0)
  if (!variable_amount && (amount === undefined || amount === null || amount === '')) {
    return 'amount is required';
  }
  if (amount !== undefined && amount !== null && amount !== '' && isNaN(Number(amount))) {
    return 'amount must be a number';
  }
  if (due_day === undefined || due_day === null || due_day === '') {
    return 'due_day is required';
  }
  const dueDayInt = parseInt(due_day, 10);
  if (isNaN(dueDayInt) || dueDayInt < 1 || dueDayInt > 31) {
    return 'due_day must be an integer between 1 and 31';
  }
  if (assigned_paycheck === undefined || assigned_paycheck === null || assigned_paycheck === '') {
    return 'assigned_paycheck is required';
  }
  const pc = parseInt(assigned_paycheck, 10);
  if (pc !== 1 && pc !== 2) {
    return 'assigned_paycheck must be 1 or 2';
  }
  return null;
}

// GET /api/bills — list all bills
router.get('/bills', async (req, res) => {
  try {
    const result = await pool.query(
      'SELECT * FROM bills ORDER BY assigned_paycheck, name'
    );
    res.json(result.rows);
  } catch (err) {
    console.error('GET /api/bills error:', err);
    res.status(500).json({ error: 'Failed to fetch bills' });
  }
});

// POST /api/bills — create a bill
router.post('/bills', async (req, res) => {
  const validationError = validateBillFields(req.body);
  if (validationError) {
    return res.status(400).json({ error: validationError });
  }

  const {
    name,
    amount,
    due_day,
    assigned_paycheck,
    category = 'General',
    active = true,
    variable_amount = false,
  } = req.body;

  try {
    const result = await pool.query(
      `INSERT INTO bills (name, amount, due_day, assigned_paycheck, category, active, variable_amount)
       VALUES ($1, $2, $3, $4, $5, $6, $7)
       RETURNING *`,
      [
        name.toString().trim(),
        Number(amount) || 0,
        parseInt(due_day, 10),
        parseInt(assigned_paycheck, 10),
        category || 'General',
        active !== undefined ? active : true,
        Boolean(variable_amount),
      ]
    );
    res.status(201).json(result.rows[0]);
  } catch (err) {
    console.error('POST /api/bills error:', err);
    res.status(500).json({ error: 'Failed to create bill' });
  }
});

// GET /api/bills/:id — get single bill
router.get('/bills/:id', async (req, res) => {
  try {
    const result = await pool.query('SELECT * FROM bills WHERE id = $1', [req.params.id]);
    if (result.rows.length === 0) {
      return res.status(404).json({ error: 'Bill not found' });
    }
    res.json(result.rows[0]);
  } catch (err) {
    console.error('GET /api/bills/:id error:', err);
    res.status(500).json({ error: 'Failed to fetch bill' });
  }
});

// PUT /api/bills/:id — update bill
router.put('/bills/:id', async (req, res) => {
  const validationError = validateBillFields(req.body);
  if (validationError) {
    return res.status(400).json({ error: validationError });
  }

  const {
    name,
    amount,
    due_day,
    assigned_paycheck,
    category = 'General',
    active = true,
    variable_amount = false,
  } = req.body;

  try {
    const result = await pool.query(
      `UPDATE bills
       SET name = $1, amount = $2, due_day = $3, assigned_paycheck = $4,
           category = $5, active = $6, variable_amount = $7
       WHERE id = $8
       RETURNING *`,
      [
        name.toString().trim(),
        Number(amount) || 0,
        parseInt(due_day, 10),
        parseInt(assigned_paycheck, 10),
        category || 'General',
        active !== undefined ? active : true,
        Boolean(variable_amount),
        req.params.id,
      ]
    );
    if (result.rows.length === 0) {
      return res.status(404).json({ error: 'Bill not found' });
    }
    res.json(result.rows[0]);
  } catch (err) {
    console.error('PUT /api/bills/:id error:', err);
    res.status(500).json({ error: 'Failed to update bill' });
  }
});

// DELETE /api/bills/:id — hard delete
router.delete('/bills/:id', async (req, res) => {
  try {
    const result = await pool.query(
      'DELETE FROM bills WHERE id = $1 RETURNING id',
      [req.params.id]
    );
    if (result.rows.length === 0) {
      return res.status(404).json({ error: 'Bill not found' });
    }
    res.json({ deleted: true, id: result.rows[0].id });
  } catch (err) {
    console.error('DELETE /api/bills/:id error:', err);
    res.status(500).json({ error: 'Failed to delete bill' });
  }
});

// PATCH /api/bills/:id/toggle — toggle active field
router.patch('/bills/:id/toggle', async (req, res) => {
  try {
    const result = await pool.query(
      'UPDATE bills SET active = NOT active WHERE id = $1 RETURNING *',
      [req.params.id]
    );
    if (result.rows.length === 0) {
      return res.status(404).json({ error: 'Bill not found' });
    }
    res.json(result.rows[0]);
  } catch (err) {
    console.error('PATCH /api/bills/:id/toggle error:', err);
    res.status(500).json({ error: 'Failed to toggle bill' });
  }
});

module.exports = router;
module.exports.validateBillFields = validateBillFields;