<?php

declare(strict_types=1);

/**
 * Calculate number of business days between two dates (skip Sat/Sun)
 */
function calculateBusinessDays(string $dateFrom, string $dateTo): int
{
    $start = new DateTime($dateFrom);
    $end = new DateTime($dateTo);
    $end->modify('+1 day'); // include the end date

    $days = 0;
    $period = new DatePeriod($start, new DateInterval('P1D'), $end);
    foreach ($period as $date) {
        $dayOfWeek = (int)$date->format('N'); // 1=Mon, 7=Sun
        if ($dayOfWeek <= 5) {
            $days++;
        }
    }
    return $days;
}

/**
 * Get leave balance for user (reuse logic from attendance.php)
 *
 * @return array<string, mixed>
 */
function getLeaveBalanceForRequest(PDO $pdo, int $userId, ?int $year = null): array
{
    $year = $year ?: (int)date('Y');

    $stmt = $pdo->prepare(
        'SELECT id, user_id, year, vacation_total, vacation_used, sick_used
        FROM leave_balances WHERE user_id = ? AND year = ?'
    );
    $stmt->execute([$userId, $year]);
    $balance = $stmt->fetch();

    if (!$balance) {
        return [
            'vacation_total' => 160,
            'vacation_used' => 0,
            'vacation_remaining' => 160,
            'sick_used' => 0,
        ];
    }

    return [
        'vacation_total' => (float)$balance['vacation_total'],
        'vacation_used' => (float)$balance['vacation_used'],
        'vacation_remaining' => (float)$balance['vacation_total'] - (float)$balance['vacation_used'],
        'sick_used' => (float)$balance['sick_used'],
    ];
}

/**
 * Get hours already locked in pending requests for vacation
 */
function getPendingVacationHours(PDO $pdo, int $userId, int $year): float
{
    $stmt = $pdo->prepare("
        SELECT COALESCE(SUM(total_hours), 0) as pending_hours
        FROM leave_requests
        WHERE user_id = ? AND leave_type = 'vacation' AND status = 'pending'
          AND YEAR(date_from) = ?
    ");
    $stmt->execute([$userId, $year]);
    return (float)$stmt->fetchColumn();
}

// ============================================================================
// GET Handlers
// ============================================================================

/**
 * GET - Own leave requests
 */
function handleGetMyRequests(PDO $pdo, int $userId): void
{
    $stmt = $pdo->prepare("
        SELECT lr.id, lr.user_id, lr.leave_type, lr.date_from, lr.date_to,
               lr.total_hours, lr.total_days, lr.notes, lr.status,
               lr.reviewer_id, lr.reviewer_note, lr.reviewed_at, lr.created_at,
               CONCAT(u.first_name, ' ', u.last_name) as reviewer_name
        FROM leave_requests lr
        LEFT JOIN users u ON lr.reviewer_id = u.id
        WHERE lr.user_id = ?
        ORDER BY lr.created_at DESC
    ");
    $stmt->execute([$userId]);
    $requests = $stmt->fetchAll();

    successResponse($requests);
}

/**
 * GET - All pending requests (for approver)
 */
function handleGetPending(PDO $pdo): void
{
    $stmt = $pdo->prepare("
        SELECT lr.id, lr.user_id, lr.leave_type, lr.date_from, lr.date_to,
               lr.total_hours, lr.total_days, lr.notes, lr.status,
               lr.reviewer_id, lr.reviewer_note, lr.reviewed_at, lr.created_at,
               CONCAT(u.first_name, ' ', u.last_name) as employee_name,
               CONCAT(rv.first_name, ' ', rv.last_name) as reviewer_name
        FROM leave_requests lr
        JOIN users u ON lr.user_id = u.id
        LEFT JOIN users rv ON lr.reviewer_id = rv.id
        WHERE lr.status = 'pending'
        ORDER BY lr.created_at ASC
    ");
    $stmt->execute();
    $requests = $stmt->fetchAll();

    successResponse([
        'requests' => $requests,
        'count' => count($requests),
    ]);
}

/**
 * GET - All requests with filters (for approver)
 */
function handleGetAll(PDO $pdo): void
{
    $status = $_GET['status'] ?? '';
    $userId = isset($_GET['user_id']) ? (int)$_GET['user_id'] : null;

    $where = [];
    $params = [];

    if ($status && in_array($status, ['pending', 'approved', 'rejected', 'cancelled'])) {
        $where[] = 'lr.status = ?';
        $params[] = $status;
    }

    if ($userId) {
        $where[] = 'lr.user_id = ?';
        $params[] = $userId;
    }

    $whereClause = $where ? 'WHERE ' . implode(' AND ', $where) : '';

    $stmt = $pdo->prepare("
        SELECT lr.id, lr.user_id, lr.leave_type, lr.date_from, lr.date_to,
               lr.total_hours, lr.total_days, lr.notes, lr.status,
               lr.reviewer_id, lr.reviewer_note, lr.reviewed_at, lr.created_at,
               CONCAT(u.first_name, ' ', u.last_name) as employee_name,
               CONCAT(rv.first_name, ' ', rv.last_name) as reviewer_name
        FROM leave_requests lr
        JOIN users u ON lr.user_id = u.id
        LEFT JOIN users rv ON lr.reviewer_id = rv.id
        $whereClause
        ORDER BY lr.created_at DESC
        LIMIT 200
    ");
    $stmt->execute($params);
    $requests = $stmt->fetchAll();

    successResponse($requests);
}

// ============================================================================
// POST Handlers
// ============================================================================

/**
 * POST - Submit new leave request
 */
function handleSubmitRequest(PDO $pdo, int $userId): void
{
    $input = getJsonInput();

    $leaveType = $input['leave_type'] ?? '';
    $dateFrom = $input['date_from'] ?? '';
    $dateTo = $input['date_to'] ?? '';
    $notes = trim($input['notes'] ?? '');

    if (!$leaveType || !$dateFrom || !$dateTo) {
        errorResponse('Vyplňte všechna povinná pole');
    }

    if (!in_array($leaveType, ['vacation', 'sick', 'unpaid'])) {
        errorResponse('Neplatný typ nepřítomnosti');
    }

    // Validate dates
    $from = new DateTime($dateFrom);
    $to = new DateTime($dateTo);
    if ($to < $from) {
        errorResponse('Datum "do" nesmí být před datem "od"');
    }

    // Calculate business days
    $businessDays = calculateBusinessDays($dateFrom, $dateTo);
    if ($businessDays === 0) {
        errorResponse('Zvolené období neobsahuje žádné pracovní dny');
    }

    $totalHours = $businessDays * 8;

    // Check vacation balance
    if ($leaveType === 'vacation') {
        $year = (int)$from->format('Y');
        $balance = getLeaveBalanceForRequest($pdo, $userId, $year);
        $pendingHours = getPendingVacationHours($pdo, $userId, $year);
        $availableHours = $balance['vacation_remaining'] - $pendingHours;

        if ($availableHours < $totalHours) {
            errorResponse(
                "Nemáte dostatek hodin dovolené. Dostupné: {$availableHours}h"
                . " (zbývá {$balance['vacation_remaining']}h, v čekajících žádostech: {$pendingHours}h),"
                . " požadujete: {$totalHours}h."
            );
        }
    }

    // Check overlapping requests
    $stmt = $pdo->prepare("
        SELECT id FROM leave_requests
        WHERE user_id = ? AND status IN ('pending', 'approved')
          AND date_from <= ? AND date_to >= ?
    ");
    $stmt->execute([$userId, $dateTo, $dateFrom]);
    if ($stmt->fetch()) {
        errorResponse('Pro toto období již existuje žádost o nepřítomnost');
    }

    // Insert request
    $stmt = $pdo->prepare("
        INSERT INTO leave_requests (user_id, leave_type, date_from, date_to, total_hours, total_days, notes, status)
        VALUES (?, ?, ?, ?, ?, ?, ?, 'pending')
    ");
    $stmt->execute([$userId, $leaveType, $dateFrom, $dateTo, $totalHours, $businessDays, $notes ?: null]);

    $requestId = (int)$pdo->lastInsertId();

    AuditLog::logCreate('leave_request', $requestId, [
        'leave_type' => $leaveType,
        'date_from' => $dateFrom,
        'date_to' => $dateTo,
        'total_days' => $businessDays,
        'total_hours' => $totalHours,
    ], "Podána žádost o nepřítomnost: $leaveType ($dateFrom - $dateTo)");

    // Send email notification
    try {
        $stmt = $pdo->prepare("SELECT CONCAT(first_name, ' ', last_name) as name FROM users WHERE id = ?");
        $stmt->execute([$userId]);
        $employeeName = $stmt->fetchColumn() ?: 'Neznámý';

        LeaveNotification::notifyNewRequest([
            'leave_type' => $leaveType,
            'date_from' => $dateFrom,
            'date_to' => $dateTo,
            'total_days' => $businessDays,
            'total_hours' => $totalHours,
            'notes' => $notes,
        ], $employeeName);
    } catch (\Exception $e) {
        error_log('Leave notification error: ' . $e->getMessage());
    }

    successResponse(['id' => $requestId], 'Žádost byla odeslána ke schválení');
}

/**
 * POST - Cancel own pending request
 */
function handleCancelRequest(PDO $pdo, int $userId): void
{
    $input = getJsonInput();
    $requestId = (int)($input['request_id'] ?? 0);

    if (!$requestId) {
        errorResponse('ID žádosti je povinné');
    }

    $stmt = $pdo->prepare(
        'SELECT id, user_id, leave_type, date_from, date_to, total_hours,
                total_days, notes, status
        FROM leave_requests WHERE id = ? AND user_id = ?'
    );
    $stmt->execute([$requestId, $userId]);
    $request = $stmt->fetch();

    if (!$request) {
        errorResponse('Žádost nebyla nalezena');
    }

    if ($request['status'] !== 'pending') {
        errorResponse('Lze zrušit pouze čekající žádosti');
    }

    $stmt = $pdo->prepare("UPDATE leave_requests SET status = 'cancelled' WHERE id = ?");
    $stmt->execute([$requestId]);

    AuditLog::logUpdate(
        'leave_request',
        $requestId,
        ['status' => 'pending'],
        ['status' => 'cancelled'],
        'Žádost o nepřítomnost zrušena zaměstnancem'
    );

    successResponse(null, 'Žádost byla zrušena');
}

/**
 * POST - Approve a leave request
 *
 * @param array<string, mixed> $authData
 */
function handleApproveRequest(PDO $pdo, int $reviewerId, array $authData): void
{
    $input = getJsonInput();
    $requestId = (int)($input['request_id'] ?? 0);

    if (!$requestId) {
        errorResponse('ID žádosti je povinné');
    }

    $stmt = $pdo->prepare(
        'SELECT id, user_id, leave_type, date_from, date_to, total_hours,
                total_days, status
        FROM leave_requests WHERE id = ?'
    );
    $stmt->execute([$requestId]);
    $request = $stmt->fetch();

    if (!$request) {
        errorResponse('Žádost nebyla nalezena');
    }

    if ($request['status'] !== 'pending') {
        errorResponse('Lze schválit pouze čekající žádosti');
    }

    if ((int)$request['user_id'] === $reviewerId && !($authData['user']['is_admin'] ?? false)) {
        errorResponse('Nemůžete schválit vlastní žádost', 403);
    }

    // Re-check vacation balance
    if ($request['leave_type'] === 'vacation') {
        $year = (int)date('Y', strtotime($request['date_from']));
        $balance = getLeaveBalanceForRequest($pdo, (int)$request['user_id'], $year);

        if ($balance['vacation_remaining'] < (float)$request['total_hours']) {
            errorResponse(
                "Zaměstnanec nemá dostatek hodin dovolené."
                . " Zbývá: {$balance['vacation_remaining']}h, požadováno: {$request['total_hours']}h."
            );
        }
    }

    // Begin transaction
    $pdo->beginTransaction();

    try {
        // Create attendance records for each business day
        $start = new DateTime($request['date_from']);
        $end = new DateTime($request['date_to']);
        $end->modify('+1 day');

        $period = new DatePeriod($start, new DateInterval('P1D'), $end);
        $insertStmt = $pdo->prepare('
            INSERT INTO attendance (user_id, shift_date, leave_type, leave_hours, notes)
            VALUES (?, ?, ?, 8, ?)
        ');

        $leaveNote = "Schválená žádost #$requestId";
        $totalBusinessDays = 0;

        foreach ($period as $date) {
            $dayOfWeek = (int)$date->format('N');
            if ($dayOfWeek <= 5) {
                $shiftDate = $date->format('Y-m-d');
                $insertStmt->execute([
                    $request['user_id'],
                    $shiftDate,
                    $request['leave_type'],
                    $leaveNote,
                ]);
                $totalBusinessDays++;
            }
        }

        // Update leave balance ONCE with total hours (was N queries, one per day)
        if ($totalBusinessDays > 0) {
            updateLeaveBalance(
                $pdo,
                (int)$request['user_id'],
                $request['date_from'],
                $request['leave_type'],
                (float)($totalBusinessDays * 8)
            );
        }

        // Update request status
        $stmt = $pdo->prepare("
            UPDATE leave_requests
            SET status = 'approved', reviewer_id = ?, reviewed_at = NOW()
            WHERE id = ?
        ");
        $stmt->execute([$reviewerId, $requestId]);

        $pdo->commit();

        AuditLog::logUpdate(
            'leave_request',
            $requestId,
            ['status' => 'pending'],
            ['status' => 'approved', 'reviewer_id' => $reviewerId],
            'Žádost o nepřítomnost schválena'
        );

        successResponse(null, 'Žádost byla schválena');
    } catch (\Exception $e) {
        $pdo->rollBack();
        error_log('Approve request error: ' . $e->getMessage());
        errorResponse('Chyba při schvalování žádosti', 500);
    }
}

/**
 * POST - Reject a leave request
 *
 * @param array<string, mixed> $authData
 */
function handleRejectRequest(PDO $pdo, int $reviewerId, array $authData): void
{
    $input = getJsonInput();
    $requestId = (int)($input['request_id'] ?? 0);
    $note = trim($input['note'] ?? '');

    if (!$requestId) {
        errorResponse('ID žádosti je povinné');
    }

    if (!$note) {
        errorResponse('Důvod zamítnutí je povinný');
    }

    $stmt = $pdo->prepare(
        'SELECT id, user_id, status FROM leave_requests WHERE id = ?'
    );
    $stmt->execute([$requestId]);
    $request = $stmt->fetch();

    if (!$request) {
        errorResponse('Žádost nebyla nalezena');
    }

    if ($request['status'] !== 'pending') {
        errorResponse('Lze zamítnout pouze čekající žádosti');
    }

    if ((int)$request['user_id'] === $reviewerId && !($authData['user']['is_admin'] ?? false)) {
        errorResponse('Nemůžete zamítnout vlastní žádost', 403);
    }

    $stmt = $pdo->prepare("
        UPDATE leave_requests
        SET status = 'rejected', reviewer_id = ?, reviewer_note = ?, reviewed_at = NOW()
        WHERE id = ?
    ");
    $stmt->execute([$reviewerId, $note, $requestId]);

    AuditLog::logUpdate(
        'leave_request',
        $requestId,
        ['status' => 'pending'],
        ['status' => 'rejected', 'reviewer_id' => $reviewerId, 'reviewer_note' => $note],
        "Žádost o nepřítomnost zamítnuta: $note"
    );

    successResponse(null, 'Žádost byla zamítnuta');
}