<?php
/**
 * availability.php — on-demand IRCTC seat availability (irctc1 / RapidAPI).
 * Only called on an explicit "Check availability" tap, never automatically.
 *
 * Quota protections (7,000 calls/month hard cap):
 *   - learns which classes a train does NOT have, and short-circuits future
 *     checks for those (no API call, no credit)
 *   - 10-min cache per (train, from, to, class, quota, date)
 *   - every completed call is counted; monthly budget guard stops at the limit
 */
require __DIR__ . '/app/config.php';
header('Content-Type: application/json; charset=utf-8');

const AVAIL_HOST     = 'irctc1.p.rapidapi.com';
const AVAIL_ENDPOINT = 'https://irctc1.p.rapidapi.com/api/v1/checkSeatAvailability';
const AVAIL_CACHE_TTL      = 600;
const AVAIL_MONTHLY_BUDGET = 6500;

function avail_out(array $a): void {
    echo json_encode($a, JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE);
    exit;
}

$train = preg_replace('/[^0-9]/', '', $_GET['train'] ?? '');
$from  = strtoupper(preg_replace('/[^0-9A-Za-z]/', '', $_GET['from'] ?? ''));
$to    = strtoupper(preg_replace('/[^0-9A-Za-z]/', '', $_GET['to'] ?? ''));
$cls   = strtoupper(preg_replace('/[^0-9A-Za-z]/', '', $_GET['class'] ?? 'SL'));
$quota = strtoupper(preg_replace('/[^0-9A-Za-z]/', '', $_GET['quota'] ?? 'GN'));
$date  = $_GET['date'] ?? '';

if (!preg_match('/^\d{4}-\d{2}-\d{2}$/', $date)) avail_out(['status' => false, 'message' => 'Invalid date.']);
if ($train === '' || $from === '' || $to === '')  avail_out(['status' => false, 'message' => 'Missing parameters.']);
if (!in_array($cls, ['SL', '3A', '2A', '1A', 'CC', 'EC', '2S', '3E', 'FC'], true)) $cls = 'SL';

$pdo = db();
$pdo->exec("CREATE TABLE IF NOT EXISTS avail_cache (ckey CHAR(40) PRIMARY KEY, payload MEDIUMTEXT, created_at INT)");
$pdo->exec("CREATE TABLE IF NOT EXISTS rapidapi_usage (ym CHAR(6) PRIMARY KEY, calls INT NOT NULL DEFAULT 0)");
$pdo->exec("CREATE TABLE IF NOT EXISTS train_classes (train_no VARCHAR(10), class VARCHAR(4), valid TINYINT, updated_at INT, PRIMARY KEY (train_no, class))");

/* ---- analytics: count this availability check (cached/short-circuited ones count too) ---- */
$__an = __DIR__ . '/app/analytics.php';
if (is_file($__an)) { require_once $__an; rr_track('availability', ['train_no' => $train, 'from_code' => $from, 'to_code' => $to, 'jdate' => $date, 'note' => $cls . '/' . $quota]); }

/* ---- short-circuit: we already learned this train has no such class ---- */
$kc = $pdo->prepare("SELECT valid FROM train_classes WHERE train_no = ? AND class = ?");
$kc->execute([$train, $cls]);
$known = $kc->fetchColumn();
if ($known !== false && (int) $known === 0) {
    avail_out(['status' => false, 'noclass' => true, 'message' => "This train doesn't have $cls class."]);
}

/* ---- cache (success or cached rejection), per exact query ---- */
$ckey = sha1("$train|$from|$to|$cls|$quota|$date");
$cr = $pdo->prepare("SELECT payload, created_at FROM avail_cache WHERE ckey = ?");
$cr->execute([$ckey]);
$c = $cr->fetch(PDO::FETCH_ASSOC);
if ($c && (time() - (int) $c['created_at'] < AVAIL_CACHE_TTL)) {
    $p = json_decode($c['payload'], true);
    if (!empty($p['ok'])) avail_out(['status' => true, 'cached' => true, 'class' => $cls, 'data' => $p['data']]);
    avail_out(['status' => false, 'cached' => true, 'apierror' => true,
        'message' => $p['err'] ?? 'This train/segment can\'t be checked here.']);
}

/* ---- monthly budget guard ---- */
$ym = date('Ym');
$uq = $pdo->prepare("SELECT calls FROM rapidapi_usage WHERE ym = ?");
$uq->execute([$ym]);
$used = (int) ($uq->fetchColumn() ?: 0);
if ($used >= AVAIL_MONTHLY_BUDGET) {
    avail_out(['status' => false, 'budget' => true,
        'message' => 'Live availability is paused for this month. Please check on the RailOne app or IRCTC.']);
}

$apiKey = defined('RAPIDAPI_KEY') ? RAPIDAPI_KEY : (getenv('RAPIDAPI_KEY') ?: '');
if ($apiKey === '') avail_out(['status' => false, 'message' => 'Availability service not configured.']);

$qs = http_build_query([
    'classType' => $cls, 'fromStationCode' => $from, 'quota' => $quota,
    'toStationCode' => $to, 'trainNo' => $train, 'date' => $date,
]);
$ch = curl_init(AVAIL_ENDPOINT . '?' . $qs);
curl_setopt_array($ch, [
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_TIMEOUT        => 15,
    CURLOPT_HTTPHEADER     => ['x-rapidapi-key: ' . $apiKey, 'x-rapidapi-host: ' . AVAIL_HOST],
]);
$resp = curl_exec($ch);
$code = (int) curl_getinfo($ch, CURLINFO_HTTP_CODE);
curl_close($ch);

if ($resp === false) {
    avail_out(['status' => false, 'message' => 'Could not reach the availability service. Try again, or check on RailOne / IRCTC.']);
}
if ($code === 429) {
    avail_out(['status' => false, 'budget' => true,
        'message' => 'Availability is busy right now. Please check on the RailOne app or IRCTC.']);
}
$json = json_decode($resp, true);
if ($code >= 400 || !is_array($json)) {
    avail_out(['status' => false, 'http' => $code,
        'message' => 'Could not fetch availability right now. Try again, or check on RailOne / IRCTC.']);
}

/* A JSON body came back (HTTP 200) — this spends one call. Count it. */
$pdo->prepare("INSERT INTO rapidapi_usage (ym, calls) VALUES (?, 1)
               ON DUPLICATE KEY UPDATE calls = calls + 1")->execute([$ym]);

if (empty($json['status'])) {
    $raw = (string) ($json['message'] ?? '');

    /* Learn "class does not exist" so we never spend another credit on it. */
    if (stripos($raw, 'class') !== false && (stripos($raw, 'exist') !== false || stripos($raw, 'not available') !== false)) {
        $pdo->prepare("REPLACE INTO train_classes (train_no, class, valid, updated_at) VALUES (?, ?, 0, ?)")
            ->execute([$train, $cls, time()]);
        avail_out(['status' => false, 'noclass' => true, 'message' => "This train doesn't have $cls class."]);
    }

    $msg = (stripos($raw, 'valid train') !== false || $raw === '')
        ? 'Live availability isn\'t available for this train/segment here. You can check on IRCTC or the RailOne app.'
        : $raw;
    $pdo->prepare("REPLACE INTO avail_cache (ckey, payload, created_at) VALUES (?, ?, ?)")
        ->execute([$ckey, json_encode(['ok' => false, 'err' => $msg]), time()]);
    avail_out(['status' => false, 'apierror' => true, 'message' => $msg]);
}

/* Success — remember this class is valid for the train. */
$pdo->prepare("REPLACE INTO train_classes (train_no, class, valid, updated_at) VALUES (?, ?, 1, ?)")
    ->execute([$train, $cls, time()]);

$data = $json['data'] ?? [];
$pdo->prepare("REPLACE INTO avail_cache (ckey, payload, created_at) VALUES (?, ?, ?)")
    ->execute([$ckey, json_encode(['ok' => true, 'data' => $data]), time()]);
avail_out(['status' => true, 'cached' => false, 'class' => $cls, 'data' => $data]);