<?php
/**
 * Shaarli utilities
 */

/**
 *  Returns the small hash of a string, using RFC 4648 base64url format
 *
 *  Small hashes:
 *   - are unique (well, as unique as crc32, at last)
 *   - are always 6 characters long.
 *   - only use the following characters: a-z A-Z 0-9 - _ @
 *   - are NOT cryptographically secure (they CAN be forged)
 *
 *  In Shaarli, they are used as a tinyurl-like link to individual entries,
 *  e.g. smallHash('20111006_131924') --> yZH23w
 */
function smallHash($text)
{
    $t = rtrim(base64_encode(hash('crc32', $text, true)), '=');
    return strtr($t, '+/', '-_');
}

/**
 * Tells if a string start with a substring
 */
function startsWith($haystack, $needle, $case=true)
{
    if ($case) {
        return (strcmp(substr($haystack, 0, strlen($needle)), $needle) === 0);
    }
    return (strcasecmp(substr($haystack, 0, strlen($needle)), $needle) === 0);
}

/**
 * Tells if a string ends with a substring
 */
function endsWith($haystack, $needle, $case=true)
{
    if ($case) {
        return (strcmp(substr($haystack, strlen($haystack) - strlen($needle)), $needle) === 0);
    }
    return (strcasecmp(substr($haystack, strlen($haystack) - strlen($needle)), $needle) === 0);
}

/**
 * Same as nl2br(), but escapes < and >
 */
function nl2br_escaped($html)
{
    return str_replace('>', '&gt;', str_replace('<', '&lt;', nl2br($html)));
}

/**
 * htmlspecialchars wrapper
 */
function escape($str)
{
    return htmlspecialchars($str, ENT_COMPAT, 'UTF-8', false);
}

/**
 * Link sanitization before templating
 */
function sanitizeLink(&$link)
{
    $link['url'] = escape($link['url']); // useful?
    $link['title'] = escape($link['title']);
    $link['description'] = escape($link['description']);
    $link['tags'] = escape($link['tags']);
}

/**
 * Checks if a string represents a valid date
 *
 * @param string        a string-formatted date
 * @param format        the expected DateTime format of the string
 * @return              whether the string is a valid date
 * @see                 http://php.net/manual/en/class.datetime.php
 * @see                 http://php.net/manual/en/datetime.createfromformat.php
 */
function checkDateFormat($format, $string)
{
    $date = DateTime::createFromFormat($format, $string);
    return $date && $date->format($string) == $string;
}

/**
 * Generate a header location from HTTP_REFERER.
 * Make sure the referer is Shaarli itself and prevent redirection loop.
 *
 * @param string $referer - HTTP_REFERER.
 * @param string $host - Server HOST.
 * @param array $loopTerms - Contains list of term to prevent redirection loop.
 *
 * @return string $referer - final referer.
 */
function generateLocation($referer, $host, $loopTerms = array())
{
    $final_referer = '?';

    // No referer if it contains any value in $loopCriteria.
    foreach ($loopTerms as $value) {
        if (strpos($referer, $value) !== false) {
            return $final_referer;
        }
    }

    // Remove port from HTTP_HOST
    if ($pos = strpos($host, ':')) {
        $host = substr($host, 0, $pos);
    }

    if (!empty($referer) && strpos(parse_url($referer, PHP_URL_HOST), $host) !== false) {
        $final_referer = $referer;
    }

    return $final_referer;
}

/**
 * Checks the PHP version to ensure Shaarli can run
 *
 * @param string $minVersion minimum PHP required version
 * @param string $curVersion current PHP version (use PHP_VERSION)
 *
 * @throws Exception    the PHP version is not supported
 */
function checkPHPVersion($minVersion, $curVersion)
{
    if (version_compare($curVersion, $minVersion) < 0) {
        throw new Exception(
            'Your PHP version is obsolete!'
            .' Shaarli requires at least PHP '.$minVersion.', and thus cannot run.'
            .' Your PHP version has known security vulnerabilities and should be'
            .' updated as soon as possible.'
        );
    }
}

/**
 * Validate session ID to prevent Full Path Disclosure.
 *
 * See #298.
 * The session ID's format depends on the hash algorithm set in PHP settings
 *
 * @param string $sessionId Session ID
 *
 * @return true if valid, false otherwise.
 *
 * @see http://php.net/manual/en/function.hash-algos.php
 * @see http://php.net/manual/en/session.configuration.php
 */
function is_session_id_valid($sessionId)
{
    if (empty($sessionId)) {
        return false;
    }

    if (!$sessionId) {
        return false;
    }

    if (!preg_match('/^[a-zA-Z0-9,-]{2,128}$/', $sessionId)) {
        return false;
    }

    return true;
}