<?php

interface FileTextCache
{
    /**
     * Save extracted content for a given File entity
     *
     * @param File $file
     * @param string $content
     */
    public function save(File $file, $content);

    /**
     * Return any cached extracted content for a given file entity
     *
     * @param File $file
     */
    public function load(File $file);

    /**
     * Invalidate the cache for a given file.
     * Invoked in onBeforeWrite on the file
     *
     * @param File $file
     */
    public function invalidate(File $file);
}

/**
 * Caches the extracted content on the record for the file.
 * Limits the stored file content by default to avoid hitting query size limits.
 */
class FileTextCache_Database implements FileTextCache
{
    public function load(File $file)
    {
        return $file->FileContentCache;
    }

    public function save(File $file, $content)
    {
        $maxLength = Config::inst()->get('FileTextCache_Database', 'max_content_length');
        $file->FileContentCache = ($maxLength) ? substr($content, 0, $maxLength) : $content;
        $file->write();
    }

    public function invalidate(File $file)
    {
        // To prevent writing to the cache from invalidating it
        if (!$file->isChanged('FileContentCache')) {
            $file->FileContentCache = '';
        }
    }
}

/**
 * Uses SS_Cache with a lifetime to cache extracted content
 */
class FileTextCache_SSCache implements FileTextCache, Flushable
{
    /**
     * Lifetime of cache in seconds
     * Null is indefinite
     *
     * @var int|null
     * @config
     */
    private static $lifetime = null;

    /**
     * @return SS_Cache
     */
    protected static function get_cache()
    {
        $lifetime = Config::inst()->get(__CLASS__, 'lifetime');
        $cache = SS_Cache::factory(__CLASS__);
        $cache->setLifetime($lifetime);
        return $cache;
    }

    protected function getKey(File $file)
    {
        return md5($file->getFullPath());
    }

    public function load(File $file)
    {
        $key = $this->getKey($file);
        $cache = self::get_cache();
        return $cache->load($key);
    }

    public function save(File $file, $content)
    {
        $key = $this->getKey($file);
        $cache = self::get_cache();
        return $cache->save($content, $key);
    }

    public static function flush()
    {
        $cache = self::get_cache();
        $cache->clean();
    }

    public function invalidate(File $file)
    {
        $key = $this->getKey($file);
        $cache = self::get_cache();
        return $cache->remove($key);
    }
}