<?php
declare(strict_types=1);

namespace App\Services;

use App\Core\Database;
use PDO;

/** Integer-fils ledger. Credits are never inferred from UI, courses, or watch time. */
final class TeacherLedgerService
{
    public static function balance(int $teacherId): array
    {
        // Balance reads must never create accounts or mutate financial state.
        $accountId = self::existingAccountId($teacherId);
        $gross = 0;
        if ($accountId !== null) {
            $row = Database::selectOne(
                'SELECT COALESCE(SUM(CASE WHEN credit_account_id=? THEN CAST(amount_fils AS SIGNED) WHEN debit_account_id=? THEN -CAST(amount_fils AS SIGNED) ELSE 0 END),0) AS balance
                 FROM ledger_entries WHERE credit_account_id=? OR debit_account_id=?',
                [$accountId, $accountId, $accountId, $accountId]
            );
            $gross = (int)($row['balance'] ?? 0);
        }
        $holds = Database::selectOne(
            "SELECT COALESCE(SUM(amount_fils),0) AS held FROM teacher_withdrawal_holds WHERE teacher_id=? AND status='held'",
            [$teacherId]
        );
        $held = (int)($holds['held'] ?? 0);
        return [
            'account_id' => $accountId,
            'gross_fils' => $gross,
            'held_fils' => $held,
            'available_fils' => max(0, $gross - $held),
        ];
    }

    public static function placeWithdrawalHold(int $teacherId, int $amountFils, string $key): array
    {
        if ($teacherId <= 0 || $amountFils <= 0 || $amountFils > 100000000
            || !preg_match('/^[A-Za-z0-9._:-]{16,128}$/', $key)) {
            return ['http_status' => 400, 'status' => 'error', 'message' => 'قيمة الحجز أو مفتاح الإعادة غير صالح.'];
        }

        $pdo = Database::getConnection();
        $pdo->beginTransaction();
        try {
            // This existing row serializes all holds for one teacher. Lock it
            // before the first consistent read, so the next hold sees this one.
            $teacher = Database::selectOne('SELECT id FROM teachers WHERE id=? FOR UPDATE', [$teacherId]);
            if (!$teacher) {
                return self::finish($pdo, ['http_status' => 404, 'status' => 'teacher_not_found']);
            }
            $existing = Database::selectOne(
                'SELECT uuid, amount_fils, status FROM teacher_withdrawal_holds WHERE teacher_id=? AND idempotency_key=? FOR UPDATE',
                [$teacherId, $key]
            );
            if ($existing) {
                if ((int)$existing['amount_fils'] !== $amountFils) {
                    return self::finish($pdo, [
                        'http_status' => 409, 'status' => 'idempotency_conflict',
                        'message' => 'استعمل المفتاح ذاته بمبلغ مختلف.',
                    ]);
                }
                return self::finish($pdo, [
                    'http_status' => 200, 'status' => $existing['status'],
                    'withdrawal_hold_id' => $existing['uuid'], 'replayed' => true,
                ]);
            }
            $balance = self::balance($teacherId);
            if ($amountFils > $balance['available_fils']) {
                return self::finish($pdo, [
                    'http_status' => 409, 'status' => 'insufficient_available_balance',
                    'message' => 'الرصيد المتاح لا يغطي الحجز.',
                    'available_fils' => $balance['available_fils'],
                ]);
            }
            $uuid = self::uuid();
            Database::insert(
                "INSERT INTO teacher_withdrawal_holds (uuid,teacher_id,amount_fils,status,idempotency_key) VALUES (?,?,?,'held',?)",
                [$uuid, $teacherId, $amountFils, $key]
            );
            return self::finish($pdo, [
                'http_status' => 201, 'status' => 'held',
                'withdrawal_hold_id' => $uuid, 'amount_fils' => $amountFils,
            ]);
        } catch (\Throwable $e) {
            if ($pdo->inTransaction()) $pdo->rollBack();
            throw $e;
        }
    }

    public static function releaseHold(int $teacherId, string $holdUuid, string $reason): array
    {
        $reason = trim($reason);
        if ($teacherId <= 0 || !self::isUuid($holdUuid) || $reason === '' || mb_strlen($reason) > 500) {
            return ['http_status' => 400, 'status' => 'error', 'message' => 'بيانات إلغاء الحجز غير صالحة.'];
        }
        $changed = Database::execute(
            "UPDATE teacher_withdrawal_holds SET status='released',released_at=NOW(),release_reason=? WHERE uuid=? AND teacher_id=? AND status='held'",
            [$reason, $holdUuid, $teacherId]
        );
        return $changed === 1
            ? ['http_status' => 200, 'status' => 'released', 'reason' => $reason]
            : ['http_status' => 409, 'status' => 'hold_not_releasable', 'message' => 'الحجز غير موجود أو تمت تسويته.'];
    }

    private static function existingAccountId(int $teacherId): ?int
    {
        $row = Database::selectOne(
            "SELECT id FROM ledger_accounts WHERE code='teacher_available' AND owner_type='teacher' AND owner_id=? AND currency='JOD' LIMIT 1",
            [$teacherId]
        );
        return $row ? (int)$row['id'] : null;
    }

    private static function isUuid(string $value): bool
    {
        return (bool)preg_match('/^[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i', $value);
    }

    private static function uuid(): string
    {
        $bytes = random_bytes(16);
        $bytes[6] = chr((ord($bytes[6]) & 15) | 64);
        $bytes[8] = chr((ord($bytes[8]) & 63) | 128);
        return vsprintf('%s%s-%s-%s-%s-%s%s%s', str_split(bin2hex($bytes), 4));
    }

    private static function finish(PDO $pdo, array $result): array
    {
        $pdo->commit();
        return $result;
    }
}