/*
Copyright (C) 2013 Red Hat, Inc.

This file is part of IcedTea.

IcedTea is free software; you can redistribute it and/or modify it under the
terms of the GNU General Public License as published by the Free Software
Foundation, version 2.

IcedTea is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with
IcedTea; see the file COPYING. If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is making a
combined work based on this library. Thus, the terms and conditions of the GNU
General Public License cover the whole combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent modules, and
to copy and distribute the resulting executable under terms of your choice,
provided that you also meet, for each linked independent module, the terms and
conditions of the license of that module. An independent module is a module
which is not derived from or based on this library. If you modify this library,
you may extend this exception to your version of the library, but you are not
obligated to do so. If you do not wish to do so, delete this exception
statement from your version.
*/
package net.adoptopenjdk.icedteaweb.lockingfile;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

import static java.nio.charset.StandardCharsets.UTF_8;

/**
 * Process-locked string storage backed by a file.
 * Each string is stored on its own line.
 * Any new-lines must be encoded somehow if they are to be stored.
 */
public abstract class LockingReaderWriter {

    private final LockableFile lockableFile;

    /**
     * Create locking file-backed storage.
     *
     * @param file the storage file
     */
    public LockingReaderWriter(final File file) {
        this.lockableFile = LockableFile.getInstance(file);
    }

    /**
     * Get the underlying file.
     * Any access to this file should use lock() and unlock().
     *
     * @return the file
     */
    public File getBackingFile() {
        return this.lockableFile.getFile();
    }

    public boolean isReadOnly() {
        return this.lockableFile.isReadOnly();
    }

    /**
     * Lock the underlying storage. Lock is reentrant.
     */
    public void lock() {
        try {
            lockableFile.lock();
        } catch (final IOException e) {
            throw new StorageIoException(e);
        }
    }

    /**
     * Unlock the underlying storage. Lock is reentrant.
     */
    public void unlock() {
        try {
            lockableFile.unlock();
        } catch (final IOException e) {
            throw new StorageIoException(e);
        }
    }

    /**
     * Writes stored contents to file. Assumes lock is held.
     *
     * @throws IOException
     */
    protected void writeContents() throws IOException {
        if (!getBackingFile().isFile()) {
            return;
        }
        if (isReadOnly()) {
            return;
        }
        try (final BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(
                new FileOutputStream(getBackingFile()), UTF_8))) {
            writeContent(writer);
            writer.flush();
        }
    }

    /**
     * Reads contents from file. Assumes lock is held.
     *
     * @throws IOException
     */
    protected void readContents() throws IOException {
        if (!getBackingFile().isFile()) {
            return;
        }
        try (final BufferedReader reader = new BufferedReader(new InputStreamReader(
                new FileInputStream(getBackingFile()), UTF_8))) {
            while (true) {
                String line = reader.readLine();
                if (line == null) {
                    break;
                }
                readLine(line);
            }
        }
    }

    /**
     * Write contents to the file, first acquiring a lock.
     *
     * @throws IOException
     */
    protected synchronized void writeContentsLocked() throws IOException {
        doLocked(() -> {
            try {
                writeContents();
            } catch (final IOException ex) {
                throw new StorageIoException(ex);
            }
        });

    }

    protected void doLocked(final Runnable r) {
        lock();
        try {
            r.run();
        } finally {
            unlock();
        }
    }

    protected abstract void writeContent(BufferedWriter writer) throws IOException;

    protected abstract void readLine(String line);
}
