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//
// Getdown - application installer, patcher and launcher
// Copyright (C) 2004-2018 Getdown authors
// https://github.com/threerings/getdown/blob/master/LICENSE

package com.threerings.getdown.cache;

import java.io.File;
import java.io.IOException;

import com.threerings.getdown.util.FileUtil;

/**
 * Maintains a cache of code resources. The cache allows multiple application instances of different
 * versions to open at the same time.
 */
public class ResourceCache
{
    public ResourceCache (File _cacheDir) throws IOException
    {
        this._cacheDir = _cacheDir;
        createDirectoryIfNecessary(_cacheDir);
    }

    private void createDirectoryIfNecessary (File dir) throws IOException
    {
        if (!dir.exists() && !dir.mkdirs()) {
            throw new IOException("unable to create directory: " + dir.getAbsolutePath());
        }
    }

    /**
     * Caches the given file under its {@code digest}.
     * @param fileToCache file to cache.
     * @param cacheSubdir the subdirectory of the cache directory in which to store the cached
     * file. Usually either {@code digest} or a prefix of {@code digest}.
     * @param digest a crypto digest of the cached files contents.
     * @return the cached file.
     */
    public File cacheFile (File fileToCache, String cacheSubdir, String digest) throws IOException
    {
        File cacheLocation = new File(_cacheDir, cacheSubdir);
        createDirectoryIfNecessary(cacheLocation);

        File cachedFile = new File(cacheLocation, digest + getFileSuffix(fileToCache));
        File lastAccessedFile = new File(
                cacheLocation, cachedFile.getName() + LAST_ACCESSED_FILE_SUFFIX);

        if (!cachedFile.exists()) {
            createNewFile(cachedFile);
            FileUtil.copy(fileToCache, cachedFile);
        }

        if (lastAccessedFile.exists()) {
            lastAccessedFile.setLastModified(System.currentTimeMillis());
        } else {
            createNewFile(lastAccessedFile);
        }

        return cachedFile;
    }

    private void createNewFile (File fileToCreate) throws IOException
    {
        if (!fileToCreate.exists() && !fileToCreate.createNewFile()) {
            throw new IOException("unable to create new file: " + fileToCreate.getAbsolutePath());
        }
    }

    private String getFileSuffix (File fileToCache) {
        String fileName = fileToCache.getName();
        int index = fileName.lastIndexOf('.');

        return index > -1 ? fileName.substring(index) : "";
    }

    private final File _cacheDir;

    static final String LAST_ACCESSED_FILE_SUFFIX = ".lastAccessed";
}