<?php

/**
 * Helper per la gestione della lista d'attesa (waiting list).
 */

/**
 * La scuola ha attivato la lista d'attesa?
 * Legge l'unico record della tabella option.
 */
function isWaitingListEnabled(mysqli $conn): bool
{
    $res = $conn->query("SELECT waitinglist_enabled FROM `option` LIMIT 1");
    if ($res && ($row = $res->fetch_assoc())) {
        return $row['waitinglist_enabled'] === 'Y';
    }
    return false;
}

/**
 * Capienza, posti impegnati (booked + pending) e posti liberi di una classe.
 *
 * @return array{maxcapacity:int, occupied:int, free:int}
 */
function getClassOccupancy(mysqli $conn, int $idserviceschedule): array
{
    // Capienza (da service via serviceschedule)
    $cap = 0;
    $stmt = $conn->prepare(
        "SELECT s.maxcapacity
         FROM serviceschedule ss
         JOIN service s ON ss.idservice = s.idservice
         WHERE ss.idserviceschedule = ?"
    );
    $stmt->bind_param("i", $idserviceschedule);
    $stmt->execute();
    $res = $stmt->get_result();
    if ($rowCap = $res->fetch_assoc()) {
        $cap = (int) $rowCap['maxcapacity'];
    }
    $stmt->close();

    // Posti impegnati: booked + pending
    $occupied = 0;
    $stmt = $conn->prepare(
        "SELECT COUNT(*) AS occupied
         FROM bookingclass
         WHERE idserviceschedule = ?
           AND status IN ('booked', 'pending')"
    );
    $stmt->bind_param("i", $idserviceschedule);
    $stmt->execute();
    $res = $stmt->get_result();
    if ($rowOcc = $res->fetch_assoc()) {
        $occupied = (int) $rowOcc['occupied'];
    }
    $stmt->close();

    $free = $cap - $occupied;

    return [
        'maxcapacity' => $cap,
        'occupied'    => $occupied,
        'free'        => $free < 0 ? 0 : $free,
    ];
}

/**
 * Decide lo stato di una nuova prenotazione:
 *  - 'pending'  -> c'è posto (flusso normale, insegnante approva)
 *  - 'waiting'  -> classe piena E waiting list attiva
 *  - 'full'     -> classe piena E waiting list disattivata (NON prenotabile)
 */
function decideBookingStatus(mysqli $conn, int $idserviceschedule): string
{
    $occ = getClassOccupancy($conn, $idserviceschedule);

    if ($occ['free'] > 0) {
        return 'pending';
    }

    return isWaitingListEnabled($conn) ? 'waiting' : 'full';
}

/**
 * Posizione (1-based) di un utente nella coda waiting di una classe.
 * 0 se non è in coda.
 */
function getWaitingPosition(mysqli $conn, int $idserviceschedule, int $iduser): int
{
    $stmt = $conn->prepare(
        "SELECT COUNT(*) AS pos
         FROM bookingclass
         WHERE idserviceschedule = ?
           AND status = 'waiting'
           AND created_at <= (
               SELECT created_at FROM bookingclass
               WHERE idserviceschedule = ? AND iduser = ? AND status = 'waiting'
               ORDER BY created_at ASC LIMIT 1
           )"
    );
    $stmt->bind_param("iii", $idserviceschedule, $idserviceschedule, $iduser);
    $stmt->execute();
    $res = $stmt->get_result();
    $pos = 0;
    if ($row = $res->fetch_assoc()) {
        $pos = (int) $row['pos'];
    }
    $stmt->close();
    return $pos;
}