<?php

/**
 * PurchaseOrderManager
 *
 * Handles all read and write operations for td_purchase_order
 * and the downstream stock-in effects on td_stock_<warehouse_id> tables.
 *
 * Method order:
 *   Transaction basis  → getPoList, getPoById, generatePoNumber,
 *                        savePo, confirmPo, receivePo, cancelPo
 *
 * Key design decisions:
 *   - PO items are stored as a JSON array in td_purchase_order.items.
 *     Same pattern as td_order. No separate child table.
 *   - receivePo() calls StockManager::saveStockIn() for each received line
 *     with source='po' and source_id=po_id. This means received goods appear
 *     in the existing Stock In list automatically under source='po'.
 *   - stock_in_id is written back into the items JSON after each receive call,
 *     same pattern as stock_out_id in OrderManager::confirmOrder().
 *   - Partial receipt is supported: receivePo() can be called multiple times
 *     until all items are fully received, advancing status 1→2 (partial) or 1/2→3 (completed).
 *   - cancelPo() is blocked if any linked stock-in rows have been approved (status=1),
 *     because those have already modified rack and balance.
 *   - Write methods do NOT manage their own DB transactions.
 *     Callers must wrap multi-step operations inside dbTransaction().
 *
 * Security: All SQL uses PDO prepared statements with bound parameters.
 * Dynamic stock table names are derived only from md_warehouse.id.
 */
class PurchaseOrderManager {

    private PDO $pdo;
    private int $company_id;

    public function __construct(PDO $pdo, int $company_id) {
        $this->pdo        = $pdo;
        $this->company_id = $company_id;
    }

    // ─────────────────────────────────────────────────────────────
    // Private helpers
    // ─────────────────────────────────────────────────────────────

    private function buildLogEntry(string $action): array {
        return [
            'user_id' => $_SESSION['login_user_id'] ?? null,
            'dt'      => date('Y-m-d H:i:s'),
            'login'   => isset($_SESSION['otpTime'])
                         ? date('Y-m-d H:i:s', $_SESSION['otpTime'])
                         : null,
            'action'  => $action,
        ];
    }

    /**
     * Generate next sequential PO number in PO-YYYYMMDD-XXXX format.
     */
    private function generatePoNumber(): string
    {
        $prefix = 'PO-' . date('Ymd') . '-';

        $sth = $this->pdo->prepare(
            "SELECT po_number FROM td_purchase_order
             WHERE company_id   = :company_id
               AND po_number LIKE :prefix
             ORDER BY po_number DESC
             LIMIT 1"
        );
        $sth->execute([
            ':company_id' => $this->company_id,
            ':prefix'     => $prefix . '%',
        ]);

        $last = $sth->fetchColumn();
        $seq  = $last ? ((int)substr($last, -4) + 1) : 1;

        return $prefix . str_pad($seq, 4, '0', STR_PAD_LEFT);
    }

    private function stockTableNameFromWarehouseId(int $warehouse_id): string
    {
        if ($warehouse_id <= 0) {
            throw new Exception("Invalid warehouse id.");
        }

        return 'td_stock_' . $warehouse_id;
    }

    // ─────────────────────────────────────────────────────────────
    // TRANSACTION BASIS — Read
    // ─────────────────────────────────────────────────────────────

    /**
     * Return all POs for the company, ordered by created_at DESC.
     * Joins md_contact for supplier name display.
     */
    public function getPoList(): array
    {
        $sth = $this->pdo->prepare(
            "SELECT p.*,
                    COALESCE(c.contact_name, '') AS contact_name
             FROM td_purchase_order p
             LEFT JOIN md_contact c
                 ON  c.company_id = p.company_id
                 AND c.id         = p.contact_id
             WHERE p.company_id = :company_id
             ORDER BY p.created_at DESC"
        );
        $sth->execute([':company_id' => $this->company_id]);
        return $sth->fetchAll(PDO::FETCH_ASSOC);
    }

    /**
     * Fetch a single PO by its primary key.
     * Returns the row with items decoded as a PHP array.
     */
    public function getPoById(int $id): array|false
    {
        $sth = $this->pdo->prepare(
            "SELECT p.*,
                    COALESCE(c.contact_name, '') AS contact_name
             FROM td_purchase_order p
             LEFT JOIN md_contact c
                 ON  c.company_id = p.company_id
                 AND c.id         = p.contact_id
             WHERE p.company_id = :company_id
               AND p.id         = :id"
        );
        $sth->execute([':company_id' => $this->company_id, ':id' => $id]);
        $row = $sth->fetch(PDO::FETCH_ASSOC);

        if (!$row) return false;

        $row['items'] = json_decode($row['items'] ?? '[]', true) ?: [];
        return $row;
    }

    // ─────────────────────────────────────────────────────────────
    // TRANSACTION BASIS — Write
    // ─────────────────────────────────────────────────────────────

    /**
     * Insert a new PO (draft) or update metadata on an existing draft.
     *
     * Insert (id=0): generates po_number, sets status=0, payment_status=0.
     * Update (id>0): only allowed while status=0 (draft).
     *
     * @param array  $data     Keys: id, contact_id, po_date, expected_date,
     *                         warehouse_id, items (array), discount, tax,
     *                         shipping_fee, notes.
     * @param array  $logging  Audit entry.
     * @return int  New td_purchase_order.id on insert, 0 on update.
     */
    public function savePo(array $data, array $logging): int
    {
        $id    = (int)($data['id'] ?? 0);
        $items = $data['items'] ?? [];

        $subtotal = array_reduce($items, fn($carry, $item) =>
            $carry + (float)($item['total_price'] ?? 0), 0.0
        );
        $discount     = (float)($data['discount']     ?? 0);
        $tax          = (float)($data['tax']          ?? 0);
        $shipping_fee = (float)($data['shipping_fee'] ?? 0);
        $grand_total  = $subtotal - $discount + $tax + $shipping_fee;

        if ($id > 0) {

            $sth = $this->pdo->prepare(
                "SELECT status, `log` FROM td_purchase_order
                 WHERE company_id = :company_id AND id = :id"
            );
            $sth->execute([':company_id' => $this->company_id, ':id' => $id]);
            $row = $sth->fetch(PDO::FETCH_ASSOC);

            if (!$row) throw new Exception("Purchase order not found.");
            if ((int)$row['status'] !== 0) throw new Exception("Only draft POs can be edited.");

            $log   = json_decode($row['log'] ?? '[]', true) ?: [];
            $log[] = $logging;

            $this->pdo->prepare(
                "UPDATE td_purchase_order SET
                    contact_id    = :contact_id,
                    po_date       = :po_date,
                    expected_date = :expected_date,
                    warehouse_id  = :warehouse_id,
                    items         = :items,
                    subtotal      = :subtotal,
                    discount      = :discount,
                    tax           = :tax,
                    shipping_fee  = :shipping_fee,
                    grand_total   = :grand_total,
                    notes         = :notes,
                    `log`         = :log
                 WHERE id = :id AND company_id = :company_id"
            )->execute([
                ':contact_id'    => (int)($data['contact_id']   ?? 0),
                ':po_date'       => $data['po_date']            ?? date('Y-m-d'),
                ':expected_date' => $data['expected_date']      ?: null,
                ':warehouse_id'  => (int)($data['warehouse_id'] ?? 0),
                ':items'         => json_encode($items, JSON_UNESCAPED_UNICODE),
                ':subtotal'      => $subtotal,
                ':discount'      => $discount,
                ':tax'           => $tax,
                ':shipping_fee'  => $shipping_fee,
                ':grand_total'   => $grand_total,
                ':notes'         => $data['notes'] ?? '',
                ':log'           => json_encode($log),
                ':id'            => $id,
                ':company_id'    => $this->company_id,
            ]);

            return 0;

        } else {

            $log = [$logging];

            $this->pdo->prepare(
                "INSERT INTO td_purchase_order
                    (company_id, uuid, po_number, contact_id, po_date, expected_date,
                     warehouse_id, status, payment_status, subtotal, discount, tax,
                     shipping_fee, grand_total, items, notes, `log`, created_at)
                 VALUES
                    (:company_id, :uuid, :po_number, :contact_id, :po_date, :expected_date,
                     :warehouse_id, 0, 0, :subtotal, :discount, :tax,
                     :shipping_fee, :grand_total, :items, :notes, :log, :created_at)"
            )->execute([
                ':company_id'    => $this->company_id,
                ':uuid'          => bin2hex(random_bytes(16)),
                ':po_number'     => $this->generatePoNumber(),
                ':contact_id'    => (int)($data['contact_id']   ?? 0),
                ':po_date'       => $data['po_date']            ?? date('Y-m-d'),
                ':expected_date' => $data['expected_date']      ?: null,
                ':warehouse_id'  => (int)($data['warehouse_id'] ?? 0),
                ':subtotal'      => $subtotal,
                ':discount'      => $discount,
                ':tax'           => $tax,
                ':shipping_fee'  => $shipping_fee,
                ':grand_total'   => $grand_total,
                ':items'         => json_encode($items, JSON_UNESCAPED_UNICODE),
                ':notes'         => $data['notes'] ?? '',
                ':log'           => json_encode($log),
                ':created_at'    => date('Y-m-d H:i:s'),
            ]);

            return (int)$this->pdo->lastInsertId();
        }
    }

    /**
     * Confirm a draft PO — advance status 0 → 1.
     * No stock rows are created at this stage; receipt happens via receivePo().
     *
     * @throws Exception  If PO not found or not in draft.
     */
    public function confirmPo(int $po_id, array $logging): void
    {
        $sth = $this->pdo->prepare(
            "SELECT * FROM td_purchase_order
             WHERE company_id = :company_id AND id = :id"
        );
        $sth->execute([':company_id' => $this->company_id, ':id' => $po_id]);
        $po = $sth->fetch(PDO::FETCH_ASSOC);

        if (!$po) throw new Exception("Purchase order not found.");
        if ((int)$po['status'] !== 0) throw new Exception("Only draft POs can be confirmed.");

        $log   = json_decode($po['log'] ?? '[]', true) ?: [];
        $log[] = array_merge($logging, ['action' => 'confirm']);

        $this->pdo->prepare(
            "UPDATE td_purchase_order SET
                status = 1,
                `log`  = :log
             WHERE id = :id AND company_id = :company_id"
        )->execute([
            ':log'        => json_encode($log),
            ':id'         => $po_id,
            ':company_id' => $this->company_id,
        ]);
    }

    /**
     * Receive goods against a confirmed PO — creates draft stock-in rows.
     *
     * Flow per received line:
     *   1. Calls StockManager::saveStockIn() with source='po', source_id=po_id.
     *   2. Writes stock_in_id back into the PO item object (same as stock_out_id in orders).
     *   3. Increments received_qty on the item.
     *
     * After all lines:
     *   4. If all items are fully received → status = 3 (completed).
     *   5. If partially received → status = 2 (partial).
     *
     * Can be called multiple times for partial deliveries.
     * If auto_approve=true (from company settings), approveStock() is also called.
     *
     * @param int    $po_id          td_purchase_order.id
     * @param array  $receive_items  Each item: { item_id, product_sku, warehouse_id,
     *                               quantity, zone, aisle, rack, lot_number,
     *                               expiry_date, serial_number, contact_id }
     * @param string $uuid           UUID prefix for stock-in rows.
     * @param array  $logging        Audit entry.
     * @param bool   $auto_approve   Auto-approve stock-in rows immediately.
     */
    public function receivePo(
        int    $po_id,
        array  $receive_items,
        string $uuid,
        array  $logging,
        bool   $auto_approve = false
    ): void {
        $sth = $this->pdo->prepare(
            "SELECT * FROM td_purchase_order
             WHERE company_id = :company_id AND id = :id"
        );
        $sth->execute([':company_id' => $this->company_id, ':id' => $po_id]);
        $po = $sth->fetch(PDO::FETCH_ASSOC);

        if (!$po) throw new Exception("Purchase order not found.");

        $status = (int)$po['status'];
        if ($status === -1) throw new Exception("Cannot receive against a cancelled PO.");
        if ($status === 0)  throw new Exception("Confirm the PO before receiving goods.");
        if ($status === 3)  throw new Exception("This PO is already fully received.");

        if (empty($receive_items)) {
            throw new Exception("No items provided to receive.");
        }

        $po_items = json_decode($po['items'] ?? '[]', true) ?: [];

        // Index PO items by item_id for quick lookup
        $po_items_by_id = [];
        foreach ($po_items as $i => $item) {
            $po_items_by_id[(int)($item['item_id'] ?? $i)] = $i;
        }

        $stock  = new StockManager($this->pdo, $this->company_id);
        $whMgmt = new WarehouseManager($this->pdo, $this->company_id);

        foreach ($receive_items as $j => $recv) {
            $item_id      = (int)($recv['item_id'] ?? -1);
            $product_sku  = $recv['product_sku'] ?? '';
            $warehouse_id = (int)($recv['warehouse_id'] ?? $po['warehouse_id']);
            $quantity     = (float)($recv['quantity'] ?? 0);

            if ($quantity <= 0) continue;
            if (!$product_sku) throw new Exception("Item #{$j}: missing product_sku.");
            if (!$warehouse_id) throw new Exception("Item #{$j}: missing warehouse_id.");

            $item_uuid = $uuid . '_' . $j;
            $item_log  = array_merge($logging, ['action' => 'receive_item']);

            $rack  = $recv['rack']  ?? '';
            $zone  = $recv['zone']  ?? '';
            $aisle = $recv['aisle'] ?? '';

            // Simple location mode: zone and aisle must mirror the rack value
            // (same convention as manage_stock_in.php).
            // occupyRack() looks up md_rack WHERE zone=:zone AND aisle=:aisle AND rack=:rack,
            // so all three must match — a blank zone/aisle produces "Rack --b does not exist".
            if ($zone === '' && $rack !== '') $zone  = $rack;
            if ($aisle === '' && $rack !== '') $aisle = $rack;

            // Resolve unit_price: prefer the receive-time override, fall back to PO item price
            $po_item_price = 0;
            if ($item_id >= 0 && isset($po_items_by_id[$item_id])) {
                $po_item_price = (float)($po_items[$po_items_by_id[$item_id]]['unit_price'] ?? 0);
            }
            $unit_price = (float)($recv['unit_price'] ?? $po_item_price);

            $stock_data = [
                'id'            => 0,
                'warehouse'     => $warehouse_id,
                'product_sku'   => $product_sku,
                'quantity'      => $quantity,
                'price'         => $unit_price,
                'zone'          => $zone,
                'aisle'         => $aisle,
                'rack'          => $rack,
                'lot_number'    => $recv['lot_number']    ?? '',
                'expiry_date'   => $recv['expiry_date']   ?? '',
                'serial_number' => $recv['serial_number'] ?? '',
                'contact_id'    => (int)($recv['contact_id'] ?? $po['contact_id'] ?? 0),
                'description'   => $po['po_number'],
                'source'        => 'po',
                'source_id'     => $po_id,
            ];

            $new_stock_in_id = $stock->saveStockIn($stock_data, $item_log, $item_uuid);

            if ($new_stock_in_id > 0) {
                // saveStockIn() does not write source/source_id — stamp them here.
                // This links the stock-in row back to this PO for cancellation guards
                // and makes it appear under the "PO" source tab on the Stock In list.
                $table = $this->stockTableNameFromWarehouseId($warehouse_id);
                $this->pdo->prepare(
                    "UPDATE `{$table}` SET source = 'po', source_id = :po_id
                     WHERE id = :id AND company_id = :company_id"
                )->execute([
                    ':po_id'      => $po_id,
                    ':id'         => $new_stock_in_id,
                    ':company_id' => $this->company_id,
                ]);

                // approveStock() handles balance updates. saveStockIn() has
                // already reserved the rack so draft receipts cannot be reused.
                if ($auto_approve) {
                    $stock->approveStock($new_stock_in_id, $warehouse_id, 'in', $whMgmt);
                }
            }

            // Write stock_in_id + received qty back into PO item
            if ($item_id >= 0 && isset($po_items_by_id[$item_id])) {
                $idx = $po_items_by_id[$item_id];
                $already_received = (float)($po_items[$idx]['received_qty'] ?? 0);
                $po_items[$idx]['received_qty']  = $already_received + $quantity;
                $po_items[$idx]['stock_in_id']   = $new_stock_in_id;
                $po_items[$idx]['receive_wh']    = $warehouse_id;
                $po_items[$idx]['receive_zone']  = $zone;
                $po_items[$idx]['receive_aisle'] = $aisle;
                $po_items[$idx]['receive_rack']  = $rack;
            }
        }

        // Determine new PO status
        $all_received = true;
        foreach ($po_items as $item) {
            $ordered  = (float)($item['quantity']     ?? 0);
            $received = (float)($item['received_qty'] ?? 0);
            if ($received < $ordered) {
                $all_received = false;
                break;
            }
        }
        $new_status = $all_received ? 3 : 2;

        $log   = json_decode($po['log'] ?? '[]', true) ?: [];
        $log[] = array_merge($logging, ['action' => 'receive', 'new_status' => $new_status]);

        $this->pdo->prepare(
            "UPDATE td_purchase_order SET
                status = :status,
                items  = :items,
                `log`  = :log
             WHERE id = :id AND company_id = :company_id"
        )->execute([
            ':status'     => $new_status,
            ':items'      => json_encode($po_items, JSON_UNESCAPED_UNICODE),
            ':log'        => json_encode($log),
            ':id'         => $po_id,
            ':company_id' => $this->company_id,
        ]);
    }

    /**
     * Update payment status on a PO.
     * Allowed for status >= 1 (confirmed, partial, completed).
     *
     * @param int   $po_id          td_purchase_order.id
     * @param int   $payment_status 0=unpaid, 1=paid, 2=partial
     * @param array $logging        Audit entry.
     */
    public function updatePaymentStatus(int $po_id, int $payment_status, array $logging): void
    {
        $sth = $this->pdo->prepare(
            "SELECT status, `log` FROM td_purchase_order
             WHERE company_id = :company_id AND id = :id"
        );
        $sth->execute([':company_id' => $this->company_id, ':id' => $po_id]);
        $po = $sth->fetch(PDO::FETCH_ASSOC);

        if (!$po) throw new Exception("Purchase order not found.");
        if ((int)$po['status'] < 1) throw new Exception("Confirm the PO before updating payment.");
        if ((int)$po['status'] === -1) throw new Exception("Cannot update a cancelled PO.");

        if (!in_array($payment_status, [0, 1, 2], true)) {
            throw new Exception("Invalid payment status.");
        }

        $log   = json_decode($po['log'] ?? '[]', true) ?: [];
        $log[] = array_merge($logging, ['action' => 'update_payment', 'payment_status' => $payment_status]);

        $this->pdo->prepare(
            "UPDATE td_purchase_order SET
                payment_status = :payment_status,
                `log`          = :log
             WHERE id = :id AND company_id = :company_id"
        )->execute([
            ':payment_status' => $payment_status,
            ':log'            => json_encode($log),
            ':id'             => $po_id,
            ':company_id'     => $this->company_id,
        ]);
    }

    /**
     * Cancel a PO.
     *
     * Blocked if any linked stock-in rows have already been approved (status=1)
     * because those have modified rack occupancy and balance.
     *
     * For draft stock-in rows (status=0), they are soft-deleted (status=-1).
     *
     * @throws Exception
     */
    public function cancelPo(int $po_id, array $logging): void
    {
        $sth = $this->pdo->prepare(
            "SELECT * FROM td_purchase_order
             WHERE company_id = :company_id AND id = :id"
        );
        $sth->execute([':company_id' => $this->company_id, ':id' => $po_id]);
        $po = $sth->fetch(PDO::FETCH_ASSOC);

        if (!$po) throw new Exception("Purchase order not found.");

        $status = (int)$po['status'];
        if ($status === -1) throw new Exception("PO is already cancelled.");
        if ($status === 3)  throw new Exception("Cannot cancel a completed PO.");

        // Guard: block if any approved stock-in rows exist for this PO
        $sth = $this->pdo->prepare(
            "SELECT table_name FROM information_schema.tables
             WHERE table_schema = DATABASE()
               AND table_name LIKE 'td_stock_%'"
        );
        $sth->execute();
        $tables = $sth->fetchAll(PDO::FETCH_COLUMN);

        foreach ($tables as $table) {
            $sth  = $this->pdo->prepare(
                "SELECT COUNT(*) FROM `{$table}`
                 WHERE company_id = :company_id
                   AND source     = 'po'
                   AND source_id  = :po_id
                   AND status     = 1"
            );
            $sth->execute([':company_id' => $this->company_id, ':po_id' => $po_id]);
            if ((int)$sth->fetchColumn() > 0) {
                throw new Exception(
                    "Cannot cancel — stock from this PO has already been approved and received. " .
                    "Please adjust stock manually if needed."
                );
            }
        }

        $whMgmt = new WarehouseManager($this->pdo, $this->company_id);

        // Soft-delete draft stock-in rows and release their rack reservations.
        foreach ($tables as $table) {
            if (!preg_match('/^td_stock_(\d+)$/', $table, $m)) {
                continue;
            }
            $warehouse_id = (int)$m[1];

            $sth = $this->pdo->prepare(
                "SELECT id, zone, aisle, rack
                 FROM `{$table}`
                 WHERE company_id = :company_id
                   AND source     = 'po'
                   AND source_id  = :po_id
                   AND status     = 0"
            );
            $sth->execute([':company_id' => $this->company_id, ':po_id' => $po_id]);
            $draft_rows = $sth->fetchAll(PDO::FETCH_ASSOC);

            foreach ($draft_rows as $row) {
                $this->pdo->prepare(
                    "UPDATE `{$table}` SET status = -1
                     WHERE id = :id AND company_id = :company_id"
                )->execute([
                    ':id'         => (int)$row['id'],
                    ':company_id' => $this->company_id,
                ]);

                $whMgmt->releaseRack(
                    $warehouse_id,
                    $row['zone'],
                    $row['aisle'],
                    $row['rack']
                );
            }
        }

        $log   = json_decode($po['log'] ?? '[]', true) ?: [];
        $log[] = array_merge($logging, ['action' => 'cancel']);

        $this->pdo->prepare(
            "UPDATE td_purchase_order SET
                status = -1,
                `log`  = :log
             WHERE id = :id AND company_id = :company_id"
        )->execute([
            ':log'        => json_encode($log),
            ':id'         => $po_id,
            ':company_id' => $this->company_id,
        ]);
    }
}