const express = require('express');
const { standardizeError } = require('../middleware/errorFormatter');
const router = express.Router();
const { getDb, ensureUserDefaultCategories } = require('../db/database');

// GET /api/categories
router.get('/', (req, res) => {
  const db = getDb();
  ensureUserDefaultCategories(req.user.id);

  const categories = db.prepare(`
    SELECT id, user_id, name, sort_order, created_at, updated_at
    FROM categories
    WHERE user_id = ?
      AND deleted_at IS NULL
    ORDER BY CASE WHEN sort_order IS NULL THEN 1 ELSE 0 END,
      sort_order ASC,
      name COLLATE NOCASE ASC
  `).all(req.user.id);

  const billsByCategory = db.prepare(`
    SELECT
      b.id,
      b.category_id,
      b.name,
      b.active,
      b.expected_amount,
      b.due_day,
      COUNT(p.id) AS payment_count,
      COALESCE(SUM(p.amount), 0) AS total_paid,
      MAX(p.paid_date) AS last_paid_date
    FROM bills b
    LEFT JOIN payments p
      ON p.bill_id = b.id
     AND p.deleted_at IS NULL
    WHERE b.user_id = ?
      AND b.category_id = ?
      AND b.deleted_at IS NULL
    GROUP BY b.id
    ORDER BY b.active DESC, b.due_day ASC, b.name COLLATE NOCASE ASC
  `);

  const shaped = categories.map(category => {
    const bills = billsByCategory.all(req.user.id, category.id).map(bill => ({
      ...bill,
      active: !!bill.active,
      payment_count: Number(bill.payment_count || 0),
      total_paid: Number(bill.total_paid || 0),
      last_paid_date: bill.last_paid_date || null,
    }));

    const activeBillCount = bills.filter(bill => bill.active).length;
    const inactiveBillCount = bills.length - activeBillCount;
    const paymentCount = bills.reduce((sum, bill) => sum + bill.payment_count, 0);

    return {
      ...category,
      bill_count: activeBillCount,
      active_bill_count: activeBillCount,
      inactive_bill_count: inactiveBillCount,
      payment_count: paymentCount,
      bill_names: bills.map(bill => bill.name),
      bills,
    };
  });

  res.json(shaped);
});

// PUT /api/categories/reorder
router.put('/reorder', (req, res) => {
  const db = getDb();
  const entries = Object.entries(req.body || {}).map(([categoryId, sortOrder]) => ({
    categoryId: Number(categoryId),
    sortOrder: Number(sortOrder),
  }));

  if (entries.length === 0) {
    return res.status(400).json(standardizeError('At least one category order is required', 'VALIDATION_ERROR', 'reorder'));
  }

  const invalid = entries.find(({ categoryId, sortOrder }) => (
    !Number.isInteger(categoryId) || categoryId <= 0 || !Number.isInteger(sortOrder) || sortOrder < 0
  ));
  if (invalid) {
    return res.status(400).json(standardizeError('Reorder payload must map category ids to non-negative integer positions', 'VALIDATION_ERROR', 'reorder'));
  }

  const ids = entries.map(item => item.categoryId);
  const placeholders = ids.map(() => '?').join(',');
  const owned = db.prepare(`
    SELECT id
    FROM categories
    WHERE user_id = ? AND deleted_at IS NULL AND id IN (${placeholders})
  `).all(req.user.id, ...ids);
  if (owned.length !== ids.length) {
    return res.status(404).json(standardizeError('One or more categories were not found', 'NOT_FOUND', 'category_id'));
  }

  const update = db.prepare("UPDATE categories SET sort_order = ?, updated_at = datetime('now') WHERE id = ? AND user_id = ?");
  db.transaction((items) => {
    for (const item of items) update.run(item.sortOrder, item.categoryId, req.user.id);
  })(entries);

  res.json({ success: true });
});

// POST /api/categories
router.post('/', (req, res) => {
  const db = getDb();
  const { name } = req.body;
  if (!name) return res.status(400).json(standardizeError('name is required', 'VALIDATION_ERROR', 'name'));

  try {
    const result = db.prepare('INSERT INTO categories (user_id, name) VALUES (?, ?)').run(req.user.id, name.trim());
    const created = db.prepare('SELECT * FROM categories WHERE id = ?').get(result.lastInsertRowid);
    res.status(201).json(created);
  } catch (e) {
    if (e.message.includes('UNIQUE')) {
      return res.status(409).json(standardizeError('Category already exists', 'CONFLICT', 'name'));
    }
    throw e;
  }
});

// PUT /api/categories/:id
router.put('/:id', (req, res) => {
  const db = getDb();
  const { name } = req.body;
  if (!name) return res.status(400).json(standardizeError('name is required', 'VALIDATION_ERROR', 'name'));

  const cat = db.prepare('SELECT id FROM categories WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(req.params.id, req.user.id);
  if (!cat) return res.status(404).json(standardizeError('Category not found', 'NOT_FOUND', 'id'));

  try {
    db.prepare("UPDATE categories SET name = ?, updated_at = datetime('now') WHERE id = ? AND user_id = ?")
      .run(name.trim(), req.params.id, req.user.id);
    res.json(db.prepare('SELECT * FROM categories WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(req.params.id, req.user.id));
  } catch (e) {
    if (e.message.includes('UNIQUE')) {
      return res.status(409).json(standardizeError('Category already exists', 'CONFLICT', 'name'));
    }
    throw e;
  }
});

// DELETE /api/categories/:id
router.delete('/:id', (req, res) => {
  const db = getDb();
  const cat = db.prepare('SELECT id, name FROM categories WHERE id = ? AND user_id = ? AND deleted_at IS NULL').get(req.params.id, req.user.id);
  if (!cat) return res.status(404).json(standardizeError('Category not found', 'NOT_FOUND', 'id'));

  const deleted = db.prepare("UPDATE categories SET deleted_at = datetime('now'), updated_at = datetime('now') WHERE id = ? AND user_id = ? AND deleted_at IS NULL")
    .run(req.params.id, req.user.id);

  res.json({
    success: true,
    deleted: deleted.changes,
    deleted_category_id: cat.id,
    deleted_category_name: cat.name,
    recoverable_until_days: 30,
  });
});

// POST /api/categories/:id/restore — undo category soft delete
router.post('/:id/restore', (req, res) => {
  const db = getDb();
  const cat = db.prepare('SELECT id, name FROM categories WHERE id = ? AND user_id = ? AND deleted_at IS NOT NULL').get(req.params.id, req.user.id);
  if (!cat) return res.status(404).json(standardizeError('Deleted category not found', 'NOT_FOUND', 'id'));

  db.prepare("UPDATE categories SET deleted_at = NULL, updated_at = datetime('now') WHERE id = ? AND user_id = ?")
    .run(req.params.id, req.user.id);
  res.json(db.prepare('SELECT * FROM categories WHERE id = ? AND user_id = ?').get(req.params.id, req.user.id));
});

module.exports = router;