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

function getOrderWithItems(db, id) {
  const order = db.prepare(`
    SELECT o.*, c.name as customer_name
    FROM orders o
    LEFT JOIN customers c ON c.id = o.customer_id
    WHERE o.id = ?
  `).get(id);
  if (!order) return null;
  const items = db.prepare(`
    SELECT oi.*, p.name as product_name
    FROM order_items oi
    JOIN products p ON p.id = oi.product_id
    WHERE oi.order_id = ?
  `).all(id);
  return { ...order, items };
}

function deductStockForOrder(db, orderId, newItems, existingItemsOverride) {
  const existing = existingItemsOverride !== undefined
    ? existingItemsOverride
    : db.prepare('SELECT product_id, quantity FROM order_items WHERE order_id = ?').all(orderId);
  const byProduct = {};
  for (const e of existing) byProduct[e.product_id] = (byProduct[e.product_id] || 0) + e.quantity;
  for (const it of newItems) {
    const pid = it.product_id;
    const qty = Number(it.quantity) || 0;
    byProduct[pid] = (byProduct[pid] || 0) - qty;
  }
  for (const [productId, delta] of Object.entries(byProduct)) {
    if (delta === 0) continue;
    const product = db.prepare('SELECT quantity_on_hand FROM products WHERE id = ?').get(productId);
    if (!product) throw new Error(`Product ${productId} not found`);
    const newQty = product.quantity_on_hand + delta;
    if (newQty < 0) throw new Error(`Insufficient stock for product id ${productId}`);
    db.prepare('UPDATE products SET quantity_on_hand = ? WHERE id = ?').run(newQty, productId);
  }
}

function applyOrderItems(db, orderId, items) {
  db.prepare('DELETE FROM order_items WHERE order_id = ?').run(orderId);
  const productRows = db.prepare('SELECT id, price FROM products').all();
  const priceByProduct = {};
  for (const p of productRows) priceByProduct[p.id] = p.price;
  for (const it of items) {
    const price = it.price_at_sale != null ? it.price_at_sale : (priceByProduct[it.product_id] || 0);
    db.prepare(
      'INSERT INTO order_items (order_id, product_id, quantity, price_at_sale) VALUES (?, ?, ?, ?)'
    ).run(orderId, it.product_id, it.quantity, price);
  }
}

router.get('/', (req, res) => {
  try {
    const db = getDb();
    const rows = db.prepare(`
      SELECT o.*, c.name as customer_name
      FROM orders o
      LEFT JOIN customers c ON c.id = o.customer_id
      ORDER BY o.created_at DESC
    `).all();
    res.json(rows);
  } catch (err) {
    res.status(500).json({ error: err.message });
  }
});

router.get('/:id', (req, res) => {
  try {
    const db = getDb();
    const order = getOrderWithItems(db, req.params.id);
    if (!order) return res.status(404).json({ error: 'Order not found' });
    res.json(order);
  } catch (err) {
    res.status(500).json({ error: err.message });
  }
});

router.post('/', (req, res) => {
  try {
    const db = getDb();
    const { customer_id, status = 'pending', notes, items = [] } = req.body;
    if (!Array.isArray(items) || items.length === 0) {
      return res.status(400).json({ error: 'At least one order item is required' });
    }
    for (const it of items) {
      const product = db.prepare('SELECT id, quantity_on_hand, price FROM products WHERE id = ?').get(it.product_id);
      if (!product) return res.status(400).json({ error: `Product ${it.product_id} not found` });
      const qty = Number(it.quantity) || 0;
      if (qty <= 0) return res.status(400).json({ error: 'Quantity must be positive' });
      if (product.quantity_on_hand < qty) {
        return res.status(400).json({ error: `Insufficient stock for ${product.id}` });
      }
    }
    const result = db.prepare(
      'INSERT INTO orders (customer_id, status, notes) VALUES (?, ?, ?)'
    ).run(customer_id || null, status, notes || null);
    const orderId = result.lastInsertRowid;
    applyOrderItems(db, orderId, items);
    deductStockForOrder(db, orderId, items, []);
    db.prepare('UPDATE orders SET updated_at = datetime(\'now\') WHERE id = ?').run(orderId);
    const order = getOrderWithItems(db, orderId);
    res.status(201).json(order);
  } catch (err) {
    res.status(500).json({ error: err.message });
  }
});

router.put('/:id', (req, res) => {
  try {
    const db = getDb();
    const order = db.prepare('SELECT * FROM orders WHERE id = ?').get(req.params.id);
    if (!order) return res.status(404).json({ error: 'Order not found' });
    const { customer_id, status, notes, items } = req.body;
    if (items !== undefined) {
      if (!Array.isArray(items)) return res.status(400).json({ error: 'items must be an array' });
      const existingItems = db.prepare('SELECT product_id, quantity FROM order_items WHERE order_id = ?').all(req.params.id);
      const newItems = items.map(it => ({ product_id: it.product_id, quantity: Number(it.quantity) || 0 }));
      for (const it of newItems) {
        const product = db.prepare('SELECT id, quantity_on_hand FROM products WHERE id = ?').get(it.product_id);
        if (!product) return res.status(400).json({ error: `Product ${it.product_id} not found` });
      }
      deductStockForOrder(db, req.params.id, newItems, existingItems);
      applyOrderItems(db, req.params.id, items);
    }
    const cid = customer_id !== undefined ? (customer_id || null) : order.customer_id;
    const st = status !== undefined ? status : order.status;
    const no = notes !== undefined ? notes : order.notes;
    db.prepare('UPDATE orders SET customer_id = ?, status = ?, notes = ?, updated_at = datetime(\'now\') WHERE id = ?')
      .run(cid, st, no, req.params.id);
    const updated = getOrderWithItems(db, req.params.id);
    res.json(updated);
  } catch (err) {
    res.status(500).json({ error: err.message });
  }
});

router.delete('/:id', (req, res) => {
  try {
    const db = getDb();
    const order = db.prepare('SELECT * FROM orders WHERE id = ?').get(req.params.id);
    if (!order) return res.status(404).json({ error: 'Order not found' });
    const items = db.prepare('SELECT product_id, quantity FROM order_items WHERE order_id = ?').all(req.params.id);
    for (const it of items) {
      db.prepare('UPDATE products SET quantity_on_hand = quantity_on_hand + ? WHERE id = ?')
        .run(it.quantity, it.product_id);
    }
    db.prepare('DELETE FROM order_items WHERE order_id = ?').run(req.params.id);
    db.prepare('DELETE FROM orders WHERE id = ?').run(req.params.id);
    res.status(204).send();
  } catch (err) {
    res.status(500).json({ error: err.message });
  }
});

module.exports = router;