<?php

/**
 * BarcodeManager
 *
 * Centralises all md_barcode operations: creating, printing, enabling/disabling,
 * and resolving SKU and location barcode labels.
 *
 * Method order:
 *   Private helpers     → product lookup, lot resolution, label fetch, location validation
 *   SKU label basis     → create / list for product (SKU) barcodes
 *   Location label      → create / list for warehouse location barcodes
 *   Shared operations   → recordPrint / setStatus (both types)
 *   Lookup basis        → resolve any barcode string to its type and fields
 *   Dropdown basis      → lot and product lists for label creation UI
 *
 * Note: operates entirely on $pdo2 (the client database, wms2).
 *       The $advancedLocation flag needed by lookup() must be resolved by the
 *       caller via CompanySettingManager($pdo1) — keeps this class scoped to wms2.
 *
 * Security: all SQL uses PDO prepared statements with bound parameters.
 * No user input is ever interpolated directly into a query string.
 */
class BarcodeManager {

    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 stockTableName(int $warehouse_id): string {
        return 'td_stock_' . $warehouse_id;
    }

    /**
     * Fetch a single active product row by SKU.
     */
    private function findProduct(string $sku): array|false {
        $sth = $this->pdo->prepare(
            "SELECT sku, product_name, uom
             FROM md_product
             WHERE company_id = :company_id
               AND sku = :sku
               AND status > 0
             LIMIT 1"
        );
        $sth->execute([':company_id' => $this->company_id, ':sku' => $sku]);
        return $sth->fetch(PDO::FETCH_ASSOC);
    }

    /**
     * When a serial is provided, verify it does not already map to a different lot
     * across any active warehouse stock table.
     *
     * Throws if the serial is claimed by a different lot, otherwise returns silently.
     */
    private function validateLotSerial(string $sku, string $lot, string $serial): void {
        if ($serial === '') return;

        $warehouses = $this->pdo->prepare(
            "SELECT id FROM md_warehouse
             WHERE company_id = :company_id AND status = 1"
        );
        $warehouses->execute([':company_id' => $this->company_id]);

        foreach ($warehouses->fetchAll(PDO::FETCH_COLUMN) as $warehouse_id) {
            $table = $this->stockTableName((int)$warehouse_id);
            $sth   = $this->pdo->prepare(
                "SELECT lot_number
                 FROM `{$table}`
                 WHERE company_id = :company_id
                   AND product_sku = :sku
                   AND serial_number = :serial
                   AND status != -1
                 LIMIT 1"
            );
            $sth->execute([
                ':company_id' => $this->company_id,
                ':sku'        => $sku,
                ':serial'     => $serial,
            ]);
            $existing_lot = $sth->fetchColumn();
            if ($existing_lot !== false && (string)$existing_lot !== $lot) {
                throw new Exception('Serial number belongs to a different lot.');
            }
        }
    }

    /**
     * Fetch a barcode row from md_barcode by barcode string and type.
     *
     * Returns false if the row does not exist.
     * Throws if the row exists but is disabled (status != 1).
     */
    private function findPreparedLabel(string $barcode, string $type): array|false {
        $sth = $this->pdo->prepare(
            "SELECT *
             FROM md_barcode
             WHERE company_id = :company_id
               AND barcode = :barcode
               AND barcode_type = :barcode_type
             LIMIT 1"
        );
        $sth->execute([
            ':company_id'   => $this->company_id,
            ':barcode'      => $barcode,
            ':barcode_type' => $type,
        ]);
        $row = $sth->fetch(PDO::FETCH_ASSOC);
        if ($row && (int)$row['status'] !== 1) {
            throw new Exception('Barcode is disabled.');
        }
        return $row ?: false;
    }

    /**
     * Confirm a rack row exists for the given warehouse + zone + aisle + rack.
     * Throws if not found.
     */
    private function validateLocation(int $warehouse_id, string $zone, string $aisle, string $rack): void {
        $sth = $this->pdo->prepare(
            "SELECT 1 FROM md_rack
             WHERE company_id    = :company_id
               AND warehouse     = :warehouse
               AND COALESCE(zone,  '') = :zone
               AND COALESCE(aisle,'') = :aisle
               AND rack          = :rack
             LIMIT 1"
        );
        $sth->execute([
            ':company_id' => $this->company_id,
            ':warehouse'  => $warehouse_id,
            ':zone'       => $zone,
            ':aisle'      => $aisle,
            ':rack'       => $rack,
        ]);
        if (!$sth->fetchColumn()) throw new Exception('Location not found.');
    }

    /**
     * Check whether any warehouse stock table has a positive balance for a given SKU + lot.
     * Used as a fallback when a lot row is missing from md_lot.
     */
    private function activeStockLotExists(string $sku, string $lot): bool {
        $warehouses = $this->pdo->prepare(
            "SELECT id FROM md_warehouse
             WHERE company_id = :company_id AND status = 1"
        );
        $warehouses->execute([':company_id' => $this->company_id]);

        foreach ($warehouses->fetchAll(PDO::FETCH_COLUMN) as $warehouse_id) {
            $table = $this->stockTableName((int)$warehouse_id);
            $sth   = $this->pdo->prepare(
                "SELECT ROUND(SUM(COALESCE(`in`, 0)) - SUM(COALESCE(`out`, 0)), 2) AS balance
                 FROM `{$table}`
                 WHERE company_id = :company_id
                   AND product_sku = :product_sku
                   AND lot_number = :lot_number
                   AND status = 1"
            );
            $sth->execute([
                ':company_id'  => $this->company_id,
                ':product_sku' => $sku,
                ':lot_number'  => $lot,
            ]);
            if ((float)$sth->fetchColumn() > 0) return true;
        }
        return false;
    }

    /**
     * Look up a lot by SKU + lot number.
     *
     * Tries md_lot first; falls back to synthesising a row from active stock
     * (handles the case where stock was entered without an md_lot record).
     * Returns false if neither source yields a result.
     */
    private function findLot(string $sku, string $lot): array|false {
        $sth = $this->pdo->prepare(
            "SELECT
                l.product_sku,
                l.lot_number,
                l.expiry_date,
                p.product_name,
                p.uom
             FROM md_lot l
             INNER JOIN md_product p
                ON p.company_id = l.company_id
               AND p.sku = l.product_sku
             WHERE l.company_id = :company_id
               AND l.product_sku = :product_sku
               AND l.lot_number = :lot_number
               AND p.status > 0
             LIMIT 1"
        );
        $sth->execute([
            ':company_id'  => $this->company_id,
            ':product_sku' => $sku,
            ':lot_number'  => $lot,
        ]);
        $row = $sth->fetch(PDO::FETCH_ASSOC);
        if ($row) return $row;

        $product = $this->findProduct($sku);
        if (!$product || !$this->activeStockLotExists($sku, $lot)) return false;

        return [
            'product_sku'  => $product['sku'],
            'lot_number'   => $lot,
            'expiry_date'  => null,
            'product_name' => $product['product_name'],
            'uom'          => $product['uom'],
        ];
    }

    // ─────────────────────────────────────────────────────────────
    // SKU LABEL BASIS
    // ─────────────────────────────────────────────────────────────

    /**
     * Return all SKU barcode labels, optionally filtered by SKU and/or lot.
     *
     * Joined to md_product for product_name. Ordered newest first.
     *
     * @param string $sku  Filter by product SKU (empty = all).
     * @param string $lot  Filter by lot number (empty = all).
     * @return array
     */
    public function listSkuLabels(string $sku = '', string $lot = ''): array {
        $params = [':company_id' => $this->company_id];
        $where  = 'WHERE b.company_id = :company_id';

        if ($sku !== '') {
            $where .= ' AND b.product_sku = :product_sku';
            $params[':product_sku'] = $sku;
        }
        if ($lot !== '') {
            $where .= ' AND b.lot_number = :lot_number';
            $params[':lot_number'] = $lot;
        }

        $sth = $this->pdo->prepare(
            "SELECT
                b.id,
                b.product_sku,
                b.lot_number,
                b.serial_number,
                b.barcode,
                b.status,
                b.print_count,
                b.last_printed_dt,
                b.created_dt,
                p.product_name
             FROM md_barcode b
             LEFT JOIN md_product p
                ON p.company_id = b.company_id
               AND p.sku = b.product_sku
             {$where}
               AND b.barcode_type = 'sku'
             ORDER BY b.created_dt DESC, b.id DESC"
        );
        $sth->execute($params);
        return $sth->fetchAll(PDO::FETCH_ASSOC);
    }

    /**
     * Create a new SKU barcode label (or re-activate a previously disabled one).
     *
     * Validates that the lot exists (or active stock exists for it).
     * When $allowUnlisted is true, skips the lot requirement and only checks
     * that the product SKU is valid — intended for pre-labelling before goods arrive.
     *
     * @param string $sku            Product SKU.
     * @param string $lot            Lot number.
     * @param string $serial         Serial number (unique within lot/sku).
     * @param bool   $allowUnlisted  Allow creating a label for a lot not yet in md_lot or stock.
     * @return array  Keys: product_sku, product_name, lot_number, serial_number, barcode.
     * @throws Exception  On validation failure.
     */
    public function createSkuLabel(string $sku, string $lot, string $serial, bool $allowUnlisted = false): array {
        $lot_row = $this->findLot($sku, $lot);

        if (!$lot_row) {
            if (!$allowUnlisted) throw new Exception('Lot not found.');

            $product = $this->findProduct($sku);
            if (!$product) throw new Exception('SKU not found.');

            $lot_row = [
                'product_sku'  => $product['sku'],
                'lot_number'   => $lot,
                'expiry_date'  => null,
                'product_name' => $product['product_name'],
                'uom'          => $product['uom'],
            ];
        }

        $barcode = "SKU|{$sku}|{$lot}|{$serial}";

        $this->pdo->prepare(
            "INSERT INTO md_barcode
                (company_id, barcode_type, barcode, product_sku, lot_number, serial_number)
             VALUES
                (:company_id, 'sku', :barcode, :product_sku, :lot_number, :serial_number)
             ON DUPLICATE KEY UPDATE
                barcode_type  = VALUES(barcode_type),
                product_sku   = VALUES(product_sku),
                lot_number    = VALUES(lot_number),
                serial_number = VALUES(serial_number),
                status = 1"
        )->execute([
            ':company_id'    => $this->company_id,
            ':barcode'       => $barcode,
            ':product_sku'   => $sku,
            ':lot_number'    => $lot,
            ':serial_number' => $serial,
        ]);

        return [
            'product_sku'   => $sku,
            'product_name'  => $lot_row['product_name'],
            'lot_number'    => $lot,
            'serial_number' => $serial,
            'barcode'       => $barcode,
        ];
    }

    // ─────────────────────────────────────────────────────────────
    // LOCATION LABEL BASIS
    // ─────────────────────────────────────────────────────────────

    /**
     * Return all location barcode labels for this company.
     *
     * @return array
     */
    public function listLocationLabels(): array {
        $sth = $this->pdo->prepare(
            "SELECT barcode, warehouse_id, zone, aisle, rack, status, print_count, last_printed_dt
             FROM md_barcode
             WHERE company_id = :company_id
               AND barcode_type = 'loc'"
        );
        $sth->execute([':company_id' => $this->company_id]);
        return $sth->fetchAll(PDO::FETCH_ASSOC);
    }

    /**
     * Create a new location barcode label (or re-activate a previously disabled one).
     *
     * Validates that the rack exists in md_rack before inserting.
     *
     * @param string $barcode      Full barcode string (e.g. "LOC|1|A|1|R1").
     * @param int    $warehouse_id Warehouse ID.
     * @param string $zone         Zone code.
     * @param string $aisle        Aisle code.
     * @param string $rack         Rack code.
     * @return array  Keys: barcode, warehouse_id, zone, aisle, rack.
     * @throws Exception  If the location is not found in md_rack.
     */
    public function createLocationLabel(string $barcode, int $warehouse_id, string $zone, string $aisle, string $rack): array {
        $this->validateLocation($warehouse_id, $zone, $aisle, $rack);

        $this->pdo->prepare(
            "INSERT INTO md_barcode
                (company_id, barcode_type, barcode, warehouse_id, zone, aisle, rack)
             VALUES
                (:company_id, 'loc', :barcode, :warehouse_id, :zone, :aisle, :rack)
             ON DUPLICATE KEY UPDATE
                barcode_type = VALUES(barcode_type),
                warehouse_id = VALUES(warehouse_id),
                zone         = VALUES(zone),
                aisle        = VALUES(aisle),
                rack         = VALUES(rack),
                status = 1"
        )->execute([
            ':company_id'   => $this->company_id,
            ':barcode'      => $barcode,
            ':warehouse_id' => $warehouse_id,
            ':zone'         => $zone,
            ':aisle'        => $aisle,
            ':rack'         => $rack,
        ]);

        return [
            'barcode'      => $barcode,
            'warehouse_id' => $warehouse_id,
            'zone'         => $zone,
            'aisle'        => $aisle,
            'rack'         => $rack,
        ];
    }

    // ─────────────────────────────────────────────────────────────
    // SHARED LABEL OPERATIONS
    // ─────────────────────────────────────────────────────────────

    /**
     * Increment print_count and update last_printed_dt for an active barcode.
     *
     * @param string $barcode  Barcode string.
     * @param string $type     'sku' or 'loc'.
     */
    public function recordPrint(string $barcode, string $type): void {
        $this->pdo->prepare(
            "UPDATE md_barcode
             SET print_count = print_count + 1,
                 last_printed_dt = NOW()
             WHERE company_id = :company_id
               AND barcode = :barcode
               AND barcode_type = :barcode_type
               AND status = 1"
        )->execute([
            ':company_id'   => $this->company_id,
            ':barcode'      => $barcode,
            ':barcode_type' => $type,
        ]);
    }

    /**
     * Set the status of a barcode label (0 = disabled, 1 = active).
     *
     * @param string $barcode  Barcode string.
     * @param string $type     'sku' or 'loc'.
     * @param int    $status   Target status value.
     */
    public function setStatus(string $barcode, string $type, int $status): void {
        $this->pdo->prepare(
            "UPDATE md_barcode
             SET status = :status
             WHERE company_id = :company_id
               AND barcode = :barcode
               AND barcode_type = :barcode_type"
        )->execute([
            ':company_id'   => $this->company_id,
            ':barcode'      => $barcode,
            ':barcode_type' => $type,
            ':status'       => $status,
        ]);
    }

    // ─────────────────────────────────────────────────────────────
    // LOOKUP / RESOLUTION BASIS
    // ─────────────────────────────────────────────────────────────

    /**
     * Resolve a barcode string to its type and fields.
     *
     * Dispatch order:
     *   1. SKU| prefix → validated SKU label
     *   2. LOC| prefix → validated location label
     *   3. Fallback    → raw product barcode or SKU field match in md_product
     *
     * Returns an array with 'type' set to 'sku', 'loc', or 'raw' plus
     * the type-specific fields.
     *
     * The $advancedLocation flag controls how LOC barcodes are parsed;
     * resolve it from the caller via CompanySettingManager::get('advanced_location').
     *
     * @param string $barcode           Full barcode string to resolve.
     * @param bool   $advancedLocation  True = zone/aisle/rack parts; false = rack only.
     * @return array
     * @throws Exception  On parse or validation failure.
     */
    public function lookup(string $barcode, bool $advancedLocation): array {
        $parts      = explode('|', $barcode);
        $label_type = strtoupper($parts[0] ?? '');

        if ($label_type === 'SKU') {
            if (count($parts) !== 4) throw new Exception('Invalid SKU label format.');
            [, $sku, $lot, $serial] = $parts;
            $sku    = trim($sku);
            $lot    = trim($lot);
            $serial = trim($serial);
            if ($sku === '' || $lot === '' || $serial === '') {
                throw new Exception('SKU, lot, and serial are required.');
            }

            $label = $this->findPreparedLabel($barcode, 'sku');
            if (!$label) throw new Exception('SKU barcode label was not prepared.');
            if (
                $label['product_sku']   !== $sku ||
                $label['lot_number']    !== $lot ||
                $label['serial_number'] !== $serial
            ) {
                throw new Exception('SKU barcode label does not match its registry.');
            }

            $product = $this->findProduct($sku);
            if (!$product) throw new Exception('SKU not found.');
            $this->validateLotSerial($sku, $lot, $serial);

            return [
                'type'          => 'sku',
                'sku'           => $product['sku'],
                'product_name'  => $product['product_name'],
                'uom'           => $product['uom'] ?? 'pcs',
                'lot_number'    => $lot,
                'serial_number' => $serial,
            ];
        }

        if ($label_type === 'LOC') {
            if ($advancedLocation && count($parts) !== 5) throw new Exception('Invalid advanced location label format.');
            if (!$advancedLocation && count($parts) !== 3) throw new Exception('Invalid location label format.');

            $warehouse_id = (int)($parts[1] ?? 0);
            if ($advancedLocation) {
                $zone  = trim($parts[2]);
                $aisle = trim($parts[3]);
                $rack  = trim($parts[4]);
            } else {
                $rack  = trim($parts[2]);
                $zone  = $rack;
                $aisle = $rack;
            }
            if (!$warehouse_id || $zone === '' || $aisle === '' || $rack === '') {
                throw new Exception('Location label is incomplete.');
            }

            $label = $this->findPreparedLabel($barcode, 'loc');
            if (!$label) throw new Exception('Location barcode label was not prepared.');
            if (
                (int)$label['warehouse_id'] !== $warehouse_id ||
                $label['zone']              !== $zone          ||
                $label['aisle']             !== $aisle         ||
                $label['rack']              !== $rack
            ) {
                throw new Exception('Location barcode label does not match its registry.');
            }

            $this->validateLocation($warehouse_id, $zone, $aisle, $rack);

            return [
                'type'         => 'loc',
                'warehouse_id' => $warehouse_id,
                'zone'         => $zone,
                'aisle'        => $aisle,
                'rack'         => $rack,
            ];
        }

        // Fallback: match against md_product's barcode or sku fields
        $sth = $this->pdo->prepare(
            "SELECT sku, product_name, uom
             FROM md_product
             WHERE company_id = :company_id
               AND (barcode = :barcode OR sku = :sku)
               AND status > 0
             ORDER BY (barcode = :barcode_order) DESC
             LIMIT 1"
        );
        $sth->execute([
            ':company_id'    => $this->company_id,
            ':barcode'       => $barcode,
            ':sku'           => $barcode,
            ':barcode_order' => $barcode,
        ]);
        $product = $sth->fetch(PDO::FETCH_ASSOC);

        if (!$product) throw new Exception('Barcode not found.');

        return [
            'type'         => 'raw',
            'sku'          => $product['sku'],
            'product_name' => $product['product_name'],
            'uom'          => $product['uom'] ?? 'pcs',
        ];
    }

    // ─────────────────────────────────────────────────────────────
    // DROPDOWN BASIS
    // ─────────────────────────────────────────────────────────────

    /**
     * Return a merged list of lots for the SKU label creation UI.
     *
     * Combines three sources in priority order, deduplicating by SKU+lot:
     *   1. md_lot rows (canonical lot master)
     *   2. Active stock rows whose lot is not in md_lot
     *   3. Existing barcode rows whose lot is not covered by 1 or 2
     *
     * Each row is augmented with barcode_active_count and barcode_disabled_count.
     * Sorted by product_sku → lot_number.
     *
     * @return array
     */
    public function getLabelLots(): array {
        $sth = $this->pdo->prepare(
            "SELECT
                l.id,
                l.product_sku,
                l.lot_number,
                l.expiry_date,
                l.description,
                p.product_name,
                p.uom,
                'md_lot' AS source
             FROM md_lot l
             INNER JOIN md_product p
                ON p.company_id = l.company_id
               AND p.sku = l.product_sku
             WHERE l.company_id = :company_id
               AND p.status > 0
             ORDER BY l.product_sku ASC, l.lot_number ASC"
        );
        $sth->execute([':company_id' => $this->company_id]);
        $rows = $sth->fetchAll(PDO::FETCH_ASSOC);
        $seen = [];
        foreach ($rows as $row) {
            $seen[$row['product_sku'] . '|' . $row['lot_number']] = true;
        }

        // Supplement from active stock tables
        $warehouses = $this->pdo->prepare(
            "SELECT id FROM md_warehouse
             WHERE company_id = :company_id AND status = 1"
        );
        $warehouses->execute([':company_id' => $this->company_id]);

        foreach ($warehouses->fetchAll(PDO::FETCH_COLUMN) as $warehouse_id) {
            $table = $this->stockTableName((int)$warehouse_id);
            $stock = $this->pdo->prepare(
                "SELECT
                    s.product_sku,
                    s.lot_number,
                    p.product_name,
                    p.uom,
                    ROUND(SUM(COALESCE(s.`in`, 0)) - SUM(COALESCE(s.`out`, 0)), 2) AS balance
                 FROM `{$table}` s
                 INNER JOIN md_product p
                    ON p.company_id = s.company_id
                   AND p.sku = s.product_sku
                 WHERE s.company_id = :company_id
                   AND s.status = 1
                   AND s.lot_number IS NOT NULL
                   AND s.lot_number <> ''
                   AND p.status > 0
                 GROUP BY s.product_sku, s.lot_number, p.product_name, p.uom
                 HAVING balance > 0"
            );
            $stock->execute([':company_id' => $this->company_id]);

            foreach ($stock->fetchAll(PDO::FETCH_ASSOC) as $row) {
                $key = $row['product_sku'] . '|' . $row['lot_number'];
                if (isset($seen[$key])) continue;
                $seen[$key] = true;
                $rows[] = [
                    'id'           => null,
                    'product_sku'  => $row['product_sku'],
                    'lot_number'   => $row['lot_number'],
                    'expiry_date'  => null,
                    'description'  => 'Found in active stock; missing md_lot row.',
                    'product_name' => $row['product_name'],
                    'uom'          => $row['uom'],
                    'source'       => 'active_stock',
                ];
            }
        }

        // Supplement from existing barcode rows
        $barcodes = $this->pdo->prepare(
            "SELECT
                b.product_sku,
                b.lot_number,
                b.serial_number,
                b.barcode,
                b.status,
                b.created_dt,
                p.product_name,
                p.uom
             FROM md_barcode b
             INNER JOIN md_product p
                ON p.company_id = b.company_id
               AND p.sku = b.product_sku
             WHERE b.company_id = :company_id
               AND b.barcode_type = 'sku'
               AND b.product_sku IS NOT NULL AND b.product_sku <> ''
               AND b.lot_number IS NOT NULL AND b.lot_number <> ''
               AND p.status > 0
             ORDER BY b.created_dt DESC, b.id DESC"
        );
        $barcodes->execute([':company_id' => $this->company_id]);

        foreach ($barcodes->fetchAll(PDO::FETCH_ASSOC) as $row) {
            $key = $row['product_sku'] . '|' . $row['lot_number'];
            if (isset($seen[$key])) continue;
            $seen[$key] = true;
            $rows[] = [
                'id'            => null,
                'product_sku'   => $row['product_sku'],
                'lot_number'    => $row['lot_number'],
                'expiry_date'   => null,
                'description'   => 'Prepared barcode exists; missing md_lot row.',
                'product_name'  => $row['product_name'],
                'uom'           => $row['uom'],
                'source'        => 'md_barcode',
                'serial_number' => $row['serial_number'],
                'barcode'       => $row['barcode'],
            ];
        }

        // Attach per-lot label counts
        $status_rows = $this->pdo->prepare(
            "SELECT
                product_sku,
                lot_number,
                SUM(CASE WHEN status = 1 THEN 1 ELSE 0 END)  AS active_count,
                SUM(CASE WHEN status <> 1 THEN 1 ELSE 0 END) AS disabled_count
             FROM md_barcode
             WHERE company_id = :company_id
               AND barcode_type = 'sku'
               AND product_sku IS NOT NULL AND product_sku <> ''
               AND lot_number IS NOT NULL AND lot_number <> ''
             GROUP BY product_sku, lot_number"
        );
        $status_rows->execute([':company_id' => $this->company_id]);

        $label_status = [];
        foreach ($status_rows->fetchAll(PDO::FETCH_ASSOC) as $row) {
            $label_status[$row['product_sku'] . '|' . $row['lot_number']] = [
                'active_count'   => (int)$row['active_count'],
                'disabled_count' => (int)$row['disabled_count'],
            ];
        }

        foreach ($rows as &$row) {
            $status                        = $label_status[$row['product_sku'] . '|' . $row['lot_number']] ?? null;
            $row['barcode_active_count']   = $status['active_count']   ?? 0;
            $row['barcode_disabled_count'] = $status['disabled_count'] ?? 0;
        }
        unset($row);

        usort($rows, fn($a, $b) => [$a['product_sku'], $a['lot_number']] <=> [$b['product_sku'], $b['lot_number']]);

        return $rows;
    }

    /**
     * Return all active products for the label creation product dropdown.
     *
     * @return array  Each row: sku, product_name, uom.
     */
    public function getLabelProducts(): array {
        $sth = $this->pdo->prepare(
            "SELECT sku, product_name, uom
             FROM md_product
             WHERE company_id = :company_id
               AND status > 0
             ORDER BY sku ASC"
        );
        $sth->execute([':company_id' => $this->company_id]);
        return $sth->fetchAll(PDO::FETCH_ASSOC);
    }
}