<?php
// One cache entry for the public homepage list; request arguments never enter its key.
function txiaw_read_home_news_cache($file)
{
    $raw = @file_get_contents($file);
    if ($raw === false) {
        return false;
    }
    $entry = json_decode($raw, true);
    if (!is_array($entry) || !isset($entry['created'], $entry['items']) ||
        !is_numeric($entry['created']) || !is_array($entry['items']) ||
        $entry['created'] > time() + 5) {
        return false;
    }
    return $entry;
}

function txiaw_home_news_cached($cacheDirectory = null, $loader = null)
{
    if ($cacheDirectory === null) {
        $cacheDirectory = dirname(__DIR__) . '/Runtime/TxiawHomeNews';
    }
    if ($loader === null) {
        $loader = function () {
            return gxl_mysql_news('field:news_id,news_cid,news_name;limit:100;order:news_addtime desc');
        };
    }
    $file = $cacheDirectory . '/news-list-v1.json';
    $entry = txiaw_read_home_news_cache($file);
    if ($entry !== false && time() - $entry['created'] < 60) {
        return $entry['items'];
    }
    if (!is_dir($cacheDirectory) && !@mkdir($cacheDirectory, 0750, true) && !is_dir($cacheDirectory)) {
        return call_user_func($loader);
    }
    $lock = @fopen($cacheDirectory . '/news-list-v1.lock', 'c');
    if ($lock === false) {
        return call_user_func($loader);
    }
    if (!flock($lock, LOCK_EX | LOCK_NB)) {
        fclose($lock);
        // Other requests can use a recently expired value while one request refreshes it.
        if ($entry !== false && time() - $entry['created'] < 300) {
            return $entry['items'];
        }
        // A cold cache gets a bounded wait; never keep an entire PHP pool waiting on a lock.
        for ($attempt = 0; $attempt < 20; $attempt++) {
            usleep(10000);
            $entry = txiaw_read_home_news_cache($file);
            if ($entry !== false && time() - $entry['created'] < 60) {
                return $entry['items'];
            }
        }
        // Preserve page availability if the cache filesystem or refresher fails.
        // The indexed query and Nginx limits still bound database work in this fallback.
        return call_user_func($loader);
    }
    try {
        // Another request may have refreshed between our first read and lock acquisition.
        $latest = txiaw_read_home_news_cache($file);
        if ($latest !== false && time() - $latest['created'] < 60) {
            return $latest['items'];
        }
        try {
            $items = call_user_func($loader);
        } catch (Exception $exception) {
            if ($entry !== false && time() - $entry['created'] < 300) {
                return $entry['items'];
            }
            throw $exception;
        }
        if (is_array($items)) {
            $encoded = json_encode(array('created' => time(), 'items' => $items));
            $temporary = $encoded === false ? false : @tempnam($cacheDirectory, '.news-');
            if ($temporary !== false) {
                @chmod($temporary, 0640);
                $written = @file_put_contents($temporary, $encoded);
                if ($written !== strlen($encoded) || !@rename($temporary, $file)) {
                    @unlink($temporary);
                }
            }
        }
        return $items;
    } finally {
        flock($lock, LOCK_UN);
        fclose($lock);
    }
}