<?php
require_once __DIR__ . '/../db/config.php';
header('Content-Type: application/json');

$action = $_GET['action'] ?? '';
$pdo = db();

try {
    switch ($action) {
        case 'get_stock':
            // List all drugs with total stock quantity
            $sql = "SELECT d.id, d.name_en, d.name_ar, d.min_stock_level, d.reorder_level, d.unit, 
                           COALESCE(SUM(b.quantity), 0) as total_stock
                    FROM drugs d
                    LEFT JOIN pharmacy_batches b ON d.id = b.drug_id AND b.quantity > 0 AND b.expiry_date >= CURDATE()
                    GROUP BY d.id
                    ORDER BY d.name_en ASC";
            $stmt = $pdo->query($sql);
            echo json_encode($stmt->fetchAll(PDO::FETCH_ASSOC));
            break;

        case 'get_batches':
            $drug_id = $_GET['drug_id'] ?? 0;
            if (!$drug_id) throw new Exception("Drug ID required");
            
            $sql = "SELECT b.*, s.name_en as supplier_name 
                    FROM pharmacy_batches b
                    LEFT JOIN suppliers s ON b.supplier_id = s.id
                    WHERE b.drug_id = ? AND b.quantity > 0
                    ORDER BY b.expiry_date ASC";
            $stmt = $pdo->prepare($sql);
            $stmt->execute([$drug_id]);
            echo json_encode($stmt->fetchAll(PDO::FETCH_ASSOC));
            break;

        case 'add_stock':
            if ($_SERVER['REQUEST_METHOD'] !== 'POST') throw new Exception("Invalid method");
            
            $drug_id = $_POST['drug_id'] ?? 0;
            $batch_number = $_POST['batch_number'] ?? '';
            $expiry_date = $_POST['expiry_date'] ?? '';
            $quantity = $_POST['quantity'] ?? 0;
            $cost_price = $_POST['cost_price'] ?? 0;
            $sale_price = $_POST['sale_price'] ?? 0;
            $supplier_id = !empty($_POST['supplier_id']) ? $_POST['supplier_id'] : null;

            if (!$drug_id || !$batch_number || !$expiry_date || !$quantity) {
                throw new Exception("Missing required fields");
            }

            $stmt = $pdo->prepare("INSERT INTO pharmacy_batches 
                (drug_id, batch_number, expiry_date, quantity, cost_price, sale_price, supplier_id, received_date) 
                VALUES (?, ?, ?, ?, ?, ?, ?, CURDATE())");
            $stmt->execute([$drug_id, $batch_number, $expiry_date, $quantity, $cost_price, $sale_price, $supplier_id]);
            
            echo json_encode(['success' => true, 'message' => 'Stock added successfully']);
            break;

        case 'search_drugs':
            $q = $_GET['q'] ?? '';
            $sql = "SELECT d.id, d.name_en, d.name_ar, d.sku, d.price as default_price, 
                           (SELECT sale_price FROM pharmacy_batches pb WHERE pb.drug_id = d.id AND pb.quantity > 0 AND pb.expiry_date >= CURDATE() ORDER BY pb.expiry_date ASC LIMIT 1) as batch_price,
                           COALESCE(SUM(b.quantity), 0) as stock
                    FROM drugs d
                    LEFT JOIN pharmacy_batches b ON d.id = b.drug_id AND b.quantity > 0 AND b.expiry_date >= CURDATE()
                    WHERE (d.name_en LIKE ? OR d.name_ar LIKE ? OR d.sku LIKE ?)
                    GROUP BY d.id
                    LIMIT 20";
            $stmt = $pdo->prepare($sql);
            $term = "%$q%";
            $stmt->execute([$term, $term, $term]);
            echo json_encode($stmt->fetchAll(PDO::FETCH_ASSOC));
            break;

        case 'create_sale':
            if ($_SERVER['REQUEST_METHOD'] !== 'POST') throw new Exception("Invalid method");
            $input = json_decode(file_get_contents('php://input'), true);
            
            if (empty($input['items'])) throw new Exception("No items in sale");
            
            $pdo->beginTransaction();
            
            try {
                // Create Sale Record
                $stmt = $pdo->prepare("INSERT INTO pharmacy_sales (patient_id, visit_id, total_amount, payment_method, status) VALUES (?, ?, ?, ?, 'completed')");
                $stmt->execute([
                    $input['patient_id'] ?? null,
                    $input['visit_id'] ?? null,
                    $input['total_amount'] ?? 0,
                    $input['payment_method'] ?? 'cash'
                ]);
                $sale_id = $pdo->lastInsertId();
                
                // Process Items
                foreach ($input['items'] as $item) {
                    $drug_id = $item['drug_id'];
                    $qty_needed = $item['quantity'];
                    $unit_price = $item['price']; // Or fetch from batch? Use provided price for now.
                    
                    // Fetch available batches (FIFO)
                    $batch_stmt = $pdo->prepare("SELECT id, quantity FROM pharmacy_batches WHERE drug_id = ? AND quantity > 0 ORDER BY expiry_date ASC FOR UPDATE");
                    $batch_stmt->execute([$drug_id]);
                    $batches = $batch_stmt->fetchAll(PDO::FETCH_ASSOC);
                    
                    $qty_remaining = $qty_needed;
                    
                    foreach ($batches as $batch) {
                        if ($qty_remaining <= 0) break;
                        
                        $take = min($batch['quantity'], $qty_remaining);
                        
                        // Deduct from batch
                        $update = $pdo->prepare("UPDATE pharmacy_batches SET quantity = quantity - ? WHERE id = ?");
                        $update->execute([$take, $batch['id']]);
                        
                        // Add to sale items
                        $item_stmt = $pdo->prepare("INSERT INTO pharmacy_sale_items (sale_id, drug_id, batch_id, quantity, unit_price, total_price) VALUES (?, ?, ?, ?, ?, ?)");
                        $item_stmt->execute([$sale_id, $drug_id, $batch['id'], $take, $unit_price, $take * $unit_price]);
                        
                        $qty_remaining -= $take;
                    }
                    
                    if ($qty_remaining > 0) {
                        throw new Exception("Insufficient stock for drug ID: $drug_id");
                    }
                }
                
                $pdo->commit();
                echo json_encode(['success' => true, 'sale_id' => $sale_id]);
                
            } catch (Exception $e) {
                $pdo->rollBack();
                throw $e;
            }
            break;

        case 'get_sales':
            // List recent sales
            $sql = "SELECT s.*, p.name as patient_name 
                    FROM pharmacy_sales s
                    LEFT JOIN patients p ON s.patient_id = p.id
                    ORDER BY s.created_at DESC LIMIT 50";
            $stmt = $pdo->query($sql);
            echo json_encode($stmt->fetchAll(PDO::FETCH_ASSOC));
            break;

        case 'get_sale_details':
            $sale_id = $_GET['sale_id'] ?? 0;
            if (!$sale_id) throw new Exception("Sale ID required");
            
            $stmt = $pdo->prepare("SELECT s.*, p.name as patient_name FROM pharmacy_sales s LEFT JOIN patients p ON s.patient_id = p.id WHERE s.id = ?");
            $stmt->execute([$sale_id]);
            $sale = $stmt->fetch(PDO::FETCH_ASSOC);
            
            if (!$sale) throw new Exception("Sale not found");
            
            $items_stmt = $pdo->prepare("SELECT i.*, d.name_en as drug_name 
                                         FROM pharmacy_sale_items i 
                                         JOIN drugs d ON i.drug_id = d.id 
                                         WHERE i.sale_id = ?");
            $items_stmt->execute([$sale_id]);
            $sale['items'] = $items_stmt->fetchAll(PDO::FETCH_ASSOC);
            
            echo json_encode($sale);
            break;

        default:
            throw new Exception("Invalid action");
    }
} catch (Exception $e) {
    http_response_code(400);
    echo json_encode(['error' => $e->getMessage()]);
}