<?php
// /var/www/html/common.php
// Gemeinsame Helfer für Token-Validierung, Key-Derivation (HKDF) und AES (CBC, IV vorangestellt).

/**
 * Load KEY=value pairs from .env in the project root.
 * Does not override variables already set in the real environment.
 */
function qdb_load_dotenv(string $path): void {
    if (!is_readable($path)) {
        return;
    }
    $lines = file($path, FILE_IGNORE_NEW_LINES);
    if ($lines === false) {
        return;
    }
    foreach ($lines as $line) {
        $line = trim($line);
        if ($line === '' || $line[0] === '#') {
            continue;
        }
        $eq = strpos($line, '=');
        if ($eq === false) {
            continue;
        }
        $name = trim(substr($line, 0, $eq));
        $value = trim(substr($line, $eq + 1));
        if ($name === '') {
            continue;
        }
        $len = strlen($value);
        if ($len >= 2) {
            $q = $value[0];
            if (($q === '"' && $value[$len - 1] === '"') || ($q === "'" && $value[$len - 1] === "'")) {
                $value = substr($value, 1, -1);
            }
        }
        $existing = getenv($name);
        if ($existing !== false && $existing !== '') {
            continue;
        }
        putenv("$name=$value");
        $_ENV[$name] = $value;
    }
}

qdb_load_dotenv(__DIR__ . '/.env');

// --- MASTER-KEY (Server-seitig zum Speichern der DB) ---
// Per ENV 'QDB_MASTER_KEY' (Base64- oder ASCII-String) oder Fallback auf bisherigen Wert.
function get_master_key_bytes(): string {
    $env = getenv('QDB_MASTER_KEY');
    if (!$env || $env === '') {
        throw new RuntimeException('QDB_MASTER_KEY environment variable is not set. Cannot proceed without a master key.');
    }
    $b = base64_decode($env, true);
    if ($b !== false && strlen($b) > 0) {
        return str_pad(substr($b, 0, 32), 32, "\0");
    }
    return str_pad(substr($env, 0, 32), 32, "\0");
}

// --- HKDF (SHA-256) über Token -> Session-Key (32 Byte) ---
// Kompatibel zu Android-Implementierung: salt = leer, info = "qdb-aes"
function hkdf_session_key_from_token(string $tokenHex, string $info = 'qdb-aes', int $len = 32): string {
    $ikm = @hex2bin(trim($tokenHex));
    if ($ikm === false) $ikm = $tokenHex; // Falls bereits binär
    if (function_exists('hash_hkdf')) {
        return hash_hkdf('sha256', $ikm, $len, $info, '');
    }
    // Fallback: eigene HKDF-Implementierung
    $hashLen = 32;
    $salt = str_repeat("\0", $hashLen);
    $prk = hash_hmac('sha256', $ikm, $salt, true);
    $okm = '';
    $t = '';
    $n = (int)ceil($len / $hashLen);
    for ($i = 1; $i <= $n; $i++) {
        $t = hash_hmac('sha256', $t . $info . chr($i), $prk, true);
        $okm .= $t;
    }
    return substr($okm, 0, $len);
}

// --- Token-Storage (DB-backed via session table) ---

function token_add(string $token, int $ttlSeconds = 86400, array $extra = []): void {
    require_once __DIR__ . '/db_init.php';
    [$pdo, $tmpDb, $lockFp] = qdb_open(true);
    $now = time();
    $pdo->prepare(
        "INSERT INTO session (token, userID, role, entityID, createdAt, expiresAt, temp)
         VALUES (:t, :uid, :role, :eid, :ca, :ea, :tmp)"
    )->execute([
        ':t'    => $token,
        ':uid'  => $extra['userID']   ?? '',
        ':role' => $extra['role']     ?? '',
        ':eid'  => $extra['entityID'] ?? '',
        ':ca'   => $now,
        ':ea'   => $now + $ttlSeconds,
        ':tmp'  => (int)(!empty($extra['temp'])),
    ]);
    // Opportunistic cleanup: remove expired sessions
    $pdo->prepare("DELETE FROM session WHERE expiresAt < :now")->execute([':now' => $now]);
    qdb_save($tmpDb, $lockFp);
}

function token_get_record(string $token): ?array {
    require_once __DIR__ . '/db_init.php';
    [$pdo, $tmpDb, $lockFp] = qdb_open(false);
    $stmt = $pdo->prepare("SELECT * FROM session WHERE token = :t AND expiresAt >= :now");
    $stmt->execute([':t' => $token, ':now' => time()]);
    $row = $stmt->fetch(PDO::FETCH_ASSOC);
    qdb_discard($tmpDb, $lockFp);
    if (!$row) return null;
    // Map DB columns to the keys the rest of the codebase expects
    return [
        'token'    => $row['token'],
        'role'     => $row['role'],
        'entityID' => $row['entityID'],
        'userID'   => $row['userID'],
        'created'  => (int)$row['createdAt'],
        'exp'      => (int)$row['expiresAt'],
        'temp'     => (int)$row['temp'],
    ];
}

function token_revoke(string $token): void {
    require_once __DIR__ . '/db_init.php';
    [$pdo, $tmpDb, $lockFp] = qdb_open(true);
    $pdo->prepare("DELETE FROM session WHERE token = :t")->execute([':t' => $token]);
    qdb_save($tmpDb, $lockFp);
}

// --- Auth helpers for endpoints ---
function get_bearer_token(): ?string {
    $auth = $_SERVER['HTTP_AUTHORIZATION'] ?? ($_SERVER['Authorization'] ?? '');
    if (stripos($auth, 'Bearer ') === 0) {
        return substr($auth, 7);
    }
    return null;
}

function qdb_auth_abort(array $body, int $status): never {
    if (defined('QDB_TESTING') && QDB_TESTING) {
        require_once __DIR__ . '/lib/QdbHttpResponse.php';
        throw new QdbHttpResponse($body, $status);
    }
    http_response_code($status);
    header('Content-Type: application/json; charset=UTF-8');
    echo json_encode($body);
    exit;
}

function require_valid_token(): array {
    $token = get_bearer_token();
    if (!$token) {
        qdb_auth_abort(["error" => "Missing Bearer token"], 401);
    }
    $rec = token_get_record($token);
    if (!$rec) {
        qdb_auth_abort(["error" => "Invalid or expired token"], 403);
    }
    if (!empty($rec['temp'])) {
        qdb_auth_abort(["error" => "Password change required before access"], 403);
    }
    $rec['_token'] = $token;
    return $rec;
}

function require_role(array $allowed, array $tokenRecord): void {
    $role = $tokenRecord['role'] ?? '';
    if (!in_array($role, $allowed, true)) {
        qdb_auth_abort(["error" => "Insufficient permissions"], 403);
    }
}

/**
 * Build a SQL WHERE clause fragment that restricts client visibility by role.
 * Returns [string $clause, array $params].
 * $clientAlias is the table alias or name that has a coachID column (e.g. 'client').
 */
function rbac_client_filter(array $tokenRecord, string $clientAlias = 'client'): array {
    $role     = $tokenRecord['role'] ?? '';
    $entityID = $tokenRecord['entityID'] ?? '';
    switch ($role) {
        case 'admin':
            return ['1=1', []];
        case 'supervisor':
            return [
                "$clientAlias.coachID IN (SELECT coachID FROM coach WHERE supervisorID = :rbac_eid)",
                [':rbac_eid' => $entityID]
            ];
        case 'coach':
            return [
                "$clientAlias.coachID = :rbac_eid",
                [':rbac_eid' => $entityID]
            ];
        default:
            return ['0=1', []];
    }
}

// --- AES-256-CBC: IV(16) + CIPHERTEXT ---
function aes256_cbc_encrypt_bytes(string $plain, string $key): string {
    $key = str_pad(substr($key, 0, 32), 32, "\0");
    $iv = random_bytes(16);
    $cipher = openssl_encrypt($plain, 'AES-256-CBC', $key, OPENSSL_RAW_DATA, $iv);
    if ($cipher === false) throw new Exception('openssl_encrypt failed');
    return $iv . $cipher;
}
function aes256_cbc_decrypt_bytes(string $data, string $key): string {
    if (strlen($data) < 16) throw new Exception('cipher too short');
    $key = str_pad(substr($key, 0, 32), 32, "\0");
    $iv = substr($data, 0, 16);
    $ct = substr($data, 16);
    $plain = openssl_decrypt($ct, 'AES-256-CBC', $key, OPENSSL_RAW_DATA, $iv);
    if ($plain === false) throw new Exception('openssl_decrypt failed');
    return $plain;
}