<?php
session_start();
header('Content-Type: application/json');
require_once '../db/config.php';

if (!isset($_GET['coach_id'])) {
    echo json_encode(['error' => 'Coach ID is required']);
    exit;
}

$coach_id = $_GET['coach_id'];
$start_date_str = isset($_GET['start']) ? $_GET['start'] : 'first day of this month';
$end_date_str = isset($_GET['end']) ? $_GET['end'] : 'last day of this month';

// Fetch coach data
$coach_stmt = db()->prepare("SELECT buffer_time, timezone FROM coaches WHERE id = ?");
$coach_stmt->execute([$coach_id]);
$coach = $coach_stmt->fetch();
$buffer_time = $coach ? (int)$coach['buffer_time'] : 0;
$coach_timezone = new DateTimeZone($coach ? $coach['timezone'] : 'UTC');

// Fetch client timezone
$client_timezone_str = 'UTC'; // Default
if (isset($_SESSION['user_id'])) {
    $client_stmt = db()->prepare("SELECT timezone FROM clients WHERE id = ?");
    $client_stmt->execute([$_SESSION['user_id']]);
    $client = $client_stmt->fetch();
    if ($client && $client['timezone']) {
        $client_timezone_str = $client['timezone'];
    }
}
$client_timezone = new DateTimeZone($client_timezone_str);

$start_date = new DateTime($start_date_str, $client_timezone);
$end_date = new DateTime($end_date_str, $client_timezone);

$response = [
    'availability' => [],
    'bookings' => []
];

// Helper function to convert time
function convert_time($time_str, $from_tz, $to_tz) {
    $dt = new DateTime($time_str, $from_tz);
    $dt->setTimezone($to_tz);
    return $dt->format('Y-m-d H:i:s');
}

// Fetch one-off availability
$stmt_availability = db()->prepare("SELECT start_time, end_time FROM coach_availability WHERE coach_id = ? AND start_time BETWEEN ? AND ?");
$stmt_availability->execute([$coach_id, $start_date->format('Y-m-d H:i:s'), $end_date->format('Y-m-d H:i:s')]);
$one_off_availability = $stmt_availability->fetchAll(PDO::FETCH_ASSOC);

foreach ($one_off_availability as $slot) {
    $response['availability'][] = [
        'start_time' => convert_time($slot['start_time'], $coach_timezone, $client_timezone),
        'end_time' => convert_time($slot['end_time'], $coach_timezone, $client_timezone)
    ];
}


// Fetch recurring availability and generate slots
$stmt_recurring = db()->prepare("SELECT day_of_week, start_time, end_time FROM coach_recurring_availability WHERE coach_id = ?");
$stmt_recurring->execute([$coach_id]);
$recurring_availability = $stmt_recurring->fetchAll(PDO::FETCH_ASSOC);

$interval = new DateInterval('P1D');
$period = new DatePeriod($start_date, $interval, $end_date->modify('+1 day'));

foreach ($period as $date) {
    $day_of_week = $date->format('w');
    foreach ($recurring_availability as $rule) {
        if ((int)$rule['day_of_week'] === (int)$day_of_week) {
            $start_time_str = $date->format('Y-m-d') . ' ' . $rule['start_time'];
            $end_time_str = $date->format('Y-m-d') . ' ' . $rule['end_time'];
            
            $start_dt = new DateTime($start_time_str, $coach_timezone);

            if ($start_dt >= new DateTime('now', $coach_timezone)) {
                 $response['availability'][] = [
                    'start_time' => convert_time($start_time_str, $coach_timezone, $client_timezone),
                    'end_time' => convert_time($end_time_str, $coach_timezone, $client_timezone)
                ];
            }
        }
    }
}

// Fetch confirmed and pending bookings
$stmt_bookings = db()->prepare("SELECT booking_time FROM bookings WHERE coach_id = ? AND (status = 'confirmed' OR status = 'pending') AND booking_time BETWEEN ? AND ?");
$stmt_bookings->execute([$coach_id, $start_date->format('Y-m-d H:i:s'), $end_date->format('Y-m-d H:i:s')]);
$bookings = $stmt_bookings->fetchAll(PDO::FETCH_ASSOC);

// Assume each booking is for one hour and add buffer
foreach ($bookings as $booking) {
    $start_booking_time = new DateTime($booking['booking_time'], $coach_timezone);
    $end_booking_time = clone $start_booking_time;
    $end_booking_time->add(new DateInterval('PT1H')); // Assuming 1-hour bookings
    $end_booking_time->add(new DateInterval('PT' . $buffer_time . 'M'));

    $response['bookings'][] = [
        'start_time' => $start_booking_time->setTimezone($client_timezone)->format('Y-m-d H:i:s'),
        'end_time' => $end_booking_time->setTimezone($client_timezone)->format('Y-m-d H:i:s')
    ];
}

echo json_encode($response);