<?php

/**
 * InvoiceManager
 *
 * Handles all read and write operations for td_invoice.
 * Supports three doc_type values: invoice | credit_note | debit_note
 *
 * Method order:
 *   Transaction basis  → getInvoiceList, getInvoiceById,
 *                        generateInvoiceNumber, saveInvoice,
 *                        createFromOrder, createCreditNote,
 *                        voidInvoice
 *
 * Key design decisions:
 *   - invoice.items is a JSON snapshot of td_order.items at issue time.
 *     credit_note.items contains only the items being corrected.
 *   - grand_total is positive for invoice/debit_note, negative for credit_note.
 *   - createFromOrder() is called by confirmOrder() when auto_invoice=1,
 *     or manually from the order detail page. Always creates status=0 (draft).
 *   - createCreditNote() is called by ReturnManager::approveReturn() —
 *     never directly by the user.
 *   - voidInvoice() only works on invoices with no approved credit notes
 *     summing to grand_total (partial credit notes must be resolved first).
 *
 * Note: 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.
 */
class InvoiceManager {

    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 document number.
     *
     * @param string $doc_type  'invoice' | 'credit_note' | 'debit_note'
     * @return string  e.g. "INV-20260502-0001" | "CN-20260502-0001" | "DN-20260502-0001"
     */
    private function generateInvoiceNumber(string $doc_type): string
    {
        $prefix_map = [
            'invoice'     => 'INV',
            'credit_note' => 'CN',
            'debit_note'  => 'DN',
        ];
        $prefix = ($prefix_map[$doc_type] ?? 'INV') . '-' . date('Ymd') . '-';

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

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

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

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

    /**
     * Return all invoices for the company ordered by id DESC.
     * Optionally filter by order_id or doc_type.
     *
     * @param int    $order_id  Filter by td_order.id (0 = all)
     * @param string $doc_type  Filter by doc_type ('' = all)
     * @return array
     */
    public function getInvoiceList(int $order_id = 0, string $doc_type = ''): array
    {
        $where  = ['i.company_id = :company_id'];
        $params = [':company_id' => $this->company_id];

        if ($order_id > 0) {
            $where[]             = 'i.order_id = :order_id';
            $params[':order_id'] = $order_id;
        }
        if ($doc_type !== '') {
            $where[]             = 'i.doc_type = :doc_type';
            $params[':doc_type'] = $doc_type;
        }

        $sth = $this->pdo->prepare(
            "SELECT i.*,
                    COALESCE(c.contact_name, '') AS contact_name,
                    o.order_number
             FROM td_invoice i
             LEFT JOIN md_contact c
                 ON  c.company_id = i.company_id
                 AND c.id         = i.contact_id
             LEFT JOIN td_order o
                 ON  o.company_id = i.company_id
                 AND o.id         = i.order_id
             WHERE " . implode(' AND ', $where) . "
             ORDER BY i.id DESC"
        );
        $sth->execute($params);
        return $sth->fetchAll(PDO::FETCH_ASSOC);
    }

    /**
     * Fetch a single invoice by id, with items decoded.
     *
     * @param int $id  td_invoice.id
     * @return array|false
     */
    public function getInvoiceById(int $id): array|false
    {
        $sth = $this->pdo->prepare(
            "SELECT i.*,
                    COALESCE(c.contact_name, '') AS contact_name,
                    o.order_number
             FROM td_invoice i
             LEFT JOIN md_contact c
                 ON  c.company_id = i.company_id
                 AND c.id         = i.contact_id
             LEFT JOIN td_order o
                 ON  o.company_id = i.company_id
                 AND o.id         = i.order_id
             WHERE i.company_id = :company_id
               AND i.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
    // ─────────────────────────────────────────────────────────────

    /**
     * Create a draft invoice from a confirmed order.
     *
     * Snapshots td_order.items into td_invoice.items.
     * Copies totals from the order directly.
     * Always creates status=0 (draft) — user must manually issue.
     *
     * Called by:
     *   - confirmOrder() engine when auto_invoice=1
     *   - "Proceed to Invoice" button on order detail page (manual)
     *
     * Must be called inside dbTransaction() by the caller.
     *
     * @param int   $order_id  td_order.id
     * @param array $logging   Audit entry.
     * @return int  New td_invoice.id
     * @throws Exception  If order not found or invoice already exists for this order.
     */
    public function createFromOrder(int $order_id, array $logging): int
    {
        // Load order
        $sth = $this->pdo->prepare(
            "SELECT * FROM td_order
             WHERE company_id = :company_id AND id = :id"
        );
        $sth->execute([':company_id' => $this->company_id, ':id' => $order_id]);
        $order = $sth->fetch(PDO::FETCH_ASSOC);

        if (!$order) {
            throw new Exception("Order not found.");
        }
        if ((int)$order['status'] < 1) {
            throw new Exception("Invoice can only be created for confirmed orders.");
        }

        // Block duplicate invoice for same order
        $sth = $this->pdo->prepare(
            "SELECT COUNT(*) FROM td_invoice
             WHERE company_id = :company_id
               AND order_id   = :order_id
               AND doc_type   = 'invoice'
               AND status    != 4"
        );
        $sth->execute([':company_id' => $this->company_id, ':order_id' => $order_id]);
        if ((int)$sth->fetchColumn() > 0) {
            throw new Exception("An active invoice already exists for this order.");
        }

        $log = [array_merge($logging, ['action' => 'create_from_order'])];

        $this->pdo->prepare(
            "INSERT INTO td_invoice
                (company_id, uuid, doc_type, invoice_number, ref_invoice_id,
                 order_id, contact_id, issued_date, due_date,
                 subtotal, discount, tax, shipping_fee, grand_total,
                 items, status, notes, `log`)
             VALUES
                (:company_id, :uuid, 'invoice', :invoice_number, 0,
                 :order_id, :contact_id, :issued_date, NULL,
                 :subtotal, :discount, :tax, :shipping_fee, :grand_total,
                 :items, 0, '', :log)"
        )->execute([
            ':company_id'      => $this->company_id,
            ':uuid'            => bin2hex(random_bytes(16)),
            ':invoice_number'  => $this->generateInvoiceNumber('invoice'),
            ':order_id'        => $order_id,
            ':contact_id'      => (int)$order['contact_id'],
            ':issued_date'     => date('Y-m-d'),
            ':subtotal'        => $order['subtotal'],
            ':discount'        => $order['discount'],
            ':tax'             => $order['tax'],
            ':shipping_fee'    => $order['shipping_fee'],
            ':grand_total'     => $order['grand_total'],
            ':items'           => $order['items'], // already JSON string
            ':log'             => json_encode($log),
        ]);

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

    /**
     * Update metadata on an existing draft invoice.
     *
     * Only allowed while status = 0 (draft).
     * Editable fields: due_date, notes.
     * Totals are not editable — they snapshot from the order.
     *
     * Must be called inside dbTransaction() by the caller.
     *
     * @param array $data     Keys: id, due_date, notes.
     * @param array $logging  Audit entry.
     * @throws Exception  If invoice not found or not in draft status.
     */
    public function saveInvoice(array $data, array $logging): void
    {
        $id = (int)($data['id'] ?? 0);

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

        if (!$row) {
            throw new Exception("Invoice not found.");
        }
        if ((int)$row['status'] !== 0) {
            throw new Exception("Only draft invoices can be edited.");
        }

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

        $this->pdo->prepare(
            "UPDATE td_invoice SET
                due_date = :due_date,
                notes    = :notes,
                `log`    = :log
             WHERE id = :id AND company_id = :company_id"
        )->execute([
            ':due_date'    => $data['due_date'] ?: null,
            ':notes'       => $data['notes'] ?? '',
            ':log'         => json_encode($log),
            ':id'          => $id,
            ':company_id'  => $this->company_id,
        ]);
    }

    /**
     * Issue a draft invoice (status 0 → 1).
     *
     * @param int   $id       td_invoice.id
     * @param array $logging  Audit entry.
     * @throws Exception  If not found or not draft.
     */
    public function issueInvoice(int $id, array $logging): void
    {
        $sth = $this->pdo->prepare(
            "SELECT status, `log` FROM td_invoice
             WHERE company_id = :company_id AND id = :id"
        );
        $sth->execute([':company_id' => $this->company_id, ':id' => $id]);
        $row = $sth->fetch(PDO::FETCH_ASSOC);

        if (!$row) throw new Exception("Invoice not found.");
        if ((int)$row['status'] !== 0) throw new Exception("Only draft invoices can be issued.");

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

        $this->pdo->prepare(
            "UPDATE td_invoice SET
                status      = 1,
                issued_date = :issued_date,
                `log`       = :log
             WHERE id = :id AND company_id = :company_id"
        )->execute([
            ':issued_date' => date('Y-m-d'),
            ':log'         => json_encode($log),
            ':id'          => $id,
            ':company_id'  => $this->company_id,
        ]);
    }

    /**
     * Create a credit note linked to a parent invoice.
     *
     * Called automatically by ReturnManager::approveReturn().
     * grand_total is stored as negative value for net-balance queries.
     *
     * Must be called inside dbTransaction() by the caller.
     *
     * @param int   $ref_invoice_id  Parent td_invoice.id
     * @param array $items           Items being credited (subset of invoice items)
     * @param float $amount          Credit amount (positive — stored as negative internally)
     * @param array $logging         Audit entry.
     * @return int  New td_invoice.id (credit note)
     * @throws Exception  If parent invoice not found or not issued.
     */
    public function createCreditNote(int $ref_invoice_id, array $items, float $amount, array $logging): int
    {
        $sth = $this->pdo->prepare(
            "SELECT * FROM td_invoice
             WHERE company_id = :company_id AND id = :id AND doc_type = 'invoice'"
        );
        $sth->execute([':company_id' => $this->company_id, ':id' => $ref_invoice_id]);
        $parent = $sth->fetch(PDO::FETCH_ASSOC);

        if (!$parent) {
            throw new Exception("Parent invoice not found.");
        }
        if ((int)$parent['status'] < 1) {
            throw new Exception("Cannot credit a draft invoice. Issue it first.");
        }

        $log = [array_merge($logging, ['action' => 'create_credit_note'])];

        $this->pdo->prepare(
            "INSERT INTO td_invoice
                (company_id, uuid, doc_type, invoice_number, ref_invoice_id,
                 order_id, contact_id, issued_date, due_date,
                 subtotal, discount, tax, shipping_fee, grand_total,
                 items, status, notes, `log`)
             VALUES
                (:company_id, :uuid, 'credit_note', :invoice_number, :ref_invoice_id,
                 :order_id, :contact_id, :issued_date, NULL,
                 :amount, 0, 0, 0, :grand_total,
                 :items, 1, '', :log)"
        )->execute([
            ':company_id'      => $this->company_id,
            ':uuid'            => bin2hex(random_bytes(16)),
            ':invoice_number'  => $this->generateInvoiceNumber('credit_note'),
            ':ref_invoice_id'  => $ref_invoice_id,
            ':order_id'        => (int)$parent['order_id'],
            ':contact_id'      => (int)$parent['contact_id'],
            ':issued_date'     => date('Y-m-d'),
            ':amount'          => $amount,
            ':grand_total'     => -abs($amount), // negative for net-balance queries
            ':items'           => json_encode($items, JSON_UNESCAPED_UNICODE),
            ':log'             => json_encode($log),
        ]);

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

    /**
     * Void an invoice (status → 4).
     *
     * Only allowed if no issued credit notes exist for this invoice,
     * or the sum of credit notes equals the full grand_total.
     *
     * @param int   $id       td_invoice.id
     * @param array $logging  Audit entry.
     * @throws Exception
     */
    public function voidInvoice(int $id, array $logging): void
    {
        $sth = $this->pdo->prepare(
            "SELECT * FROM td_invoice
             WHERE company_id = :company_id AND id = :id"
        );
        $sth->execute([':company_id' => $this->company_id, ':id' => $id]);
        $row = $sth->fetch(PDO::FETCH_ASSOC);

        if (!$row) throw new Exception("Invoice not found.");
        if ((int)$row['status'] === 4) throw new Exception("Invoice is already void.");

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

        $this->pdo->prepare(
            "UPDATE td_invoice SET status = 4, `log` = :log
             WHERE id = :id AND company_id = :company_id"
        )->execute([
            ':log'        => json_encode($log),
            ':id'         => $id,
            ':company_id' => $this->company_id,
        ]);
    }
}