import { useEffect, useState, useCallback } from 'react';
import { useParams, Link } from 'react-router-dom';
import { api } from '../api';

export default function OrderDetail() {
  const { id } = useParams();
  const [order, setOrder] = useState(null);
  const [products, setProducts] = useState([]);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);
  const [editing, setEditing] = useState(false);
  const [status, setStatus] = useState('pending');
  const [notes, setNotes] = useState('');
  const [paymentMethod, setPaymentMethod] = useState('');
  const [amountPaid, setAmountPaid] = useState('');
  const [items, setItems] = useState([]);

  const load = useCallback(() => {
    Promise.all([
      api(`/orders/${id}`).then((r) => (r.ok ? r.json() : Promise.reject(new Error('Not found')))),
      api('/products').then((r) => r.json()),
    ])
      .then(([o, p]) => {
        setOrder(o);
        setProducts(p);
        setStatus(o.status);
        setNotes(o.notes || '');
        setPaymentMethod(o.payment_method || '');
        setAmountPaid(o.amount_paid != null ? String(o.amount_paid) : '0');
        setItems(o.items?.map((i) => ({ product_id: i.product_id, quantity: i.quantity, price_at_sale: i.price_at_sale })) || []);
      })
      .catch((e) => setError(e.message))
      .finally(() => setLoading(false));
  }, [id]);

  useEffect(() => {
    load();
  }, [load]);

  function handleUpdate(e) {
    e.preventDefault();
    const payload = {
      status,
      payment_method: paymentMethod || null,
      amount_paid: amountPaid !== '' ? Number(amountPaid) : 0,
      notes: notes.trim() || null,
      items: items.map((line) => ({
        product_id: line.product_id,
        quantity: Number(line.quantity) || 0,
        price_at_sale: line.price_at_sale,
      })).filter((line) => line.quantity > 0),
    };
    if (payload.items.length === 0) {
      setError('Order must have at least one item.');
      return;
    }
    api(`/orders/${id}`, {
      method: 'PUT',
      body: payload,
    })
      .then((r) => {
        if (!r.ok) return r.json().then((e) => Promise.reject(new Error(e.error || 'Failed')));
        return r.json();
      })
      .then(setOrder)
      .then(() => setEditing(false))
      .then(load)
      .catch((e) => setError(e.message));
  }

  function addLine() {
    const productId = products[0]?.id;
    if (!productId) return;
    const p = products.find((x) => x.id === productId);
    setItems((prev) => [...prev, { product_id: productId, quantity: 1, price_at_sale: p?.price }]);
  }

  function updateLine(index, field, value) {
    setItems((prev) => prev.map((line, i) => (i === index ? { ...line, [field]: value } : line)));
  }

  function removeLine(index) {
    setItems((prev) => prev.filter((_, i) => i !== index));
  }

  if (loading) return <p className="text-muted">Loading...</p>;
  if (error && !order) return <p className="error">{error}</p>;
  if (!order) return null;

  const productById = Object.fromEntries(products.map((p) => [p.id, p]));
  let total = 0;
  for (const line of items) {
    const price = line.price_at_sale != null ? line.price_at_sale : productById[line.product_id]?.price;
    total += (price || 0) * (Number(line.quantity) || 0);
  }

  return (
    <>
      <h1 className="page-title">Order #{order.id}</h1>
      {error && <p className="error">{error}</p>}

      {!editing ? (
        <div className="card">
          <p><strong>Customer:</strong> {order.customer_id ? (order.customer_name || `#${order.customer_id}`) : 'Walk-in'}</p>
          <p><strong>Status:</strong> {order.status}</p>
          <p><strong>Created:</strong> {new Date(order.created_at).toLocaleString()}</p>
          {order.notes && <p><strong>Notes:</strong> {order.notes}</p>}
          <p><strong>Payment:</strong> {order.payment_method ? order.payment_method.charAt(0).toUpperCase() + order.payment_method.slice(1) : 'Not set'}</p>
          <p><strong>Amount paid:</strong> ${Number(order.amount_paid || 0).toFixed(2)}</p>
          {(() => {
            const orderTotal = (order.items || []).reduce((s, i) => s + i.quantity * i.price_at_sale, 0);
            const balance = orderTotal - (order.amount_paid || 0);
            return balance > 0.005 ? <p style={{ color: 'var(--danger, #e53e3e)', fontWeight: 600 }}>Balance due: ${balance.toFixed(2)}</p> : null;
          })()}
          <div className="table-wrap" style={{ marginTop: '1rem' }}>
            <table>
              <thead>
                <tr>
                  <th>Product</th>
                  <th>Qty</th>
                  <th>Price</th>
                  <th>Subtotal</th>
                </tr>
              </thead>
              <tbody>
                {(order.items || []).map((line) => (
                  <tr key={line.id}>
                    <td>{line.product_name}</td>
                    <td>{line.quantity}</td>
                    <td>${Number(line.price_at_sale).toFixed(2)}</td>
                    <td>${(line.quantity * line.price_at_sale).toFixed(2)}</td>
                  </tr>
                ))}
              </tbody>
            </table>
          </div>
          <p style={{ fontWeight: 600, marginTop: '1rem' }}>
            Total: ${(order.items || []).reduce((s, i) => s + i.quantity * i.price_at_sale, 0).toFixed(2)}
          </p>
          <div style={{ marginTop: '1rem', display: 'flex', gap: '0.5rem' }}>
            <button type="button" className="secondary" onClick={() => setEditing(true)}>Edit</button>
            <Link to="/orders"><button type="button" className="secondary">Back to orders</button></Link>
          </div>
        </div>
      ) : (
        <form onSubmit={handleUpdate} className="card">
          <div className="form-group">
            <label>Status</label>
            <select value={status} onChange={(e) => setStatus(e.target.value)}>
              <option value="pending">Pending</option>
              <option value="paid">Paid</option>
              <option value="delivered">Delivered</option>
            </select>
          </div>
          <div className="form-group">
            <label>Notes</label>
            <textarea value={notes} onChange={(e) => setNotes(e.target.value)} rows={2} />
          </div>
          <div className="form-row">
            <div className="form-group">
              <label>Payment method</label>
              <select value={paymentMethod} onChange={(e) => {
                setPaymentMethod(e.target.value);
                if (e.target.value && amountPaid === '0') setAmountPaid(total.toFixed(2));
              }}>
                <option value="">None</option>
                <option value="cash">Cash</option>
                <option value="card">Card</option>
                <option value="venmo">Venmo</option>
                <option value="check">Check</option>
                <option value="other">Other</option>
              </select>
            </div>
            <div className="form-group">
              <label>Amount paid</label>
              <input
                type="number"
                step="0.01"
                min="0"
                value={amountPaid}
                onChange={(e) => setAmountPaid(e.target.value)}
                placeholder={total.toFixed(2)}
              />
            </div>
          </div>
          <div className="form-group">
            <div style={{ display: 'flex', justifyContent: 'space-between', alignItems: 'center', marginBottom: '0.5rem' }}>
              <label style={{ marginBottom: 0 }}>Items</label>
              <button type="button" className="secondary" onClick={addLine}>Add line</button>
            </div>
            {items.map((line, i) => (
              <div key={i} className="form-row" style={{ alignItems: 'center', gap: '0.5rem', marginBottom: '0.5rem' }}>
                <select
                  value={line.product_id}
                  onChange={(e) => {
                    const newId = Number(e.target.value);
                    const p = products.find((x) => x.id === newId);
                    setItems((prev) => prev.map((ln, idx) => idx === i ? { ...ln, product_id: newId, price_at_sale: p?.price ?? ln.price_at_sale } : ln));
                  }}
                  style={{ flex: 2, minWidth: 0 }}
                >
                  {products.map((p) => (
                    <option key={p.id} value={p.id}>{p.name}</option>
                  ))}
                </select>
                <input
                  type="number"
                  min="1"
                  value={line.quantity}
                  onChange={(e) => updateLine(i, 'quantity', e.target.value)}
                  style={{ width: 80 }}
                />
                <input
                  type="number"
                  step="0.01"
                  value={line.price_at_sale ?? ''}
                  onChange={(e) => updateLine(i, 'price_at_sale', parseFloat(e.target.value) || 0)}
                  style={{ width: 80 }}
                  placeholder="Price"
                />
                <button type="button" className="secondary" onClick={() => removeLine(i)}>Remove</button>
              </div>
            ))}
          </div>
          <p style={{ fontWeight: 600 }}>Total: ${total.toFixed(2)}</p>
          <div style={{ display: 'flex', gap: '0.5rem', marginTop: '1rem' }}>
            <button type="submit">Save</button>
            <button type="button" className="secondary" onClick={() => setEditing(false)}>Cancel</button>
          </div>
        </form>
      )}
    </>
  );
}