/*
 * @(#)FileCacheImageInputStream.java	1.28 03/12/19
 *
 * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package javax.imageio.stream;

import java.io.DataInput;
import java.io.File;
import java.io.InputStream;
import java.io.IOException;
import java.io.RandomAccessFile;

/**
 * An implementation of <code>ImageInputStream</code> that gets its
 * input from a regular <code>InputStream</code>.  A file is used to
 * cache previously read data.
 *
 * @version 0.5
 */
public class FileCacheImageInputStream extends ImageInputStreamImpl {

    private InputStream stream;

    private File cacheFile;

    private RandomAccessFile cache;

    private static final int BUFFER_LENGTH = 1024;

    private byte[] buf = new byte[BUFFER_LENGTH];

    private long length = 0L;

    private boolean foundEOF = false;

    /**
     * Constructs a <code>FileCacheImageInputStream</code> that will read
     * from a given <code>InputStream</code>.
     *
     * <p> A temporary file is used as a cache.  If
     * <code>cacheDir</code>is non-<code>null</code> and is a
     * directory, the file will be created there.  If it is
     * <code>null</code>, the system-dependent default temporary-file
     * directory will be used (see the documentation for
     * <code>File.createTempFile</code> for details).
     *
     * @param stream an <code>InputStream</code> to read from.
     * @param cacheDir a <code>File</code> indicating where the 
     * cache file should be created, or <code>null</code> to use the
     * system directory.
     *
     * @exception IllegalArgumentException if <code>stream</code> is
     * <code>null</code>.
     * @exception IllegalArgumentException if <code>cacheDir</code> is
     * non-<code>null</code> but is not a directory.
     * @exception IOException if a cache file cannot be created.
     */
    public FileCacheImageInputStream(InputStream stream, File cacheDir)
        throws IOException {
        if (stream == null) {
            throw new IllegalArgumentException("stream == null!");
        }
        if ((cacheDir != null) && !(cacheDir.isDirectory())) {
            throw new IllegalArgumentException("Not a directory!");
        }
        this.stream = stream;
        this.cacheFile =
            File.createTempFile("imageio", ".tmp", cacheDir);
        cacheFile.deleteOnExit();
        this.cache = new RandomAccessFile(cacheFile, "rw");
    }

    /**
     * Ensures that at least <code>pos</code> bytes are cached,
     * or the end of the source is reached.  The return value
     * is equal to the smaller of <code>pos</code> and the
     * length of the source file.
     */
    private long readUntil(long pos) throws IOException {
        // We've already got enough data cached
        if (pos < length) {
            return pos;
        }
        // pos >= length but length isn't getting any bigger, so return it
        if (foundEOF) {
            return length;
        }

        long len = pos - length;
        cache.seek(length);
        while (len > 0) {
            // Copy a buffer's worth of data from the source to the cache
            // BUFFER_LENGTH will always fit into an int so this is safe
            int nbytes =
                stream.read(buf, 0, (int)Math.min(len, (long)BUFFER_LENGTH));
            if (nbytes == -1) {
                foundEOF = true;
                return length;
            }

            cache.write(buf, 0, nbytes);
            len -= nbytes;
            length += nbytes;
        }

        return pos;
    }

    public int read() throws IOException {
        bitOffset = 0;
        long next = streamPos + 1;
        long pos = readUntil(next);
        if (pos >= next) {
            cache.seek(streamPos++);
            return cache.read();
        } else {
            return -1;
        }
    }

    public int read(byte[] b, int off, int len) throws IOException {
        if (b == null) {
            throw new NullPointerException();
        }
        // Fix 4430357 - if off + len < 0, overflow occurred
        if (off < 0 || len < 0 || off + len > b.length || off + len < 0) {
            throw new IndexOutOfBoundsException();
        }
        if (len == 0) {
            return 0;
        }

        checkClosed();

        bitOffset = 0;

        long pos = readUntil(streamPos + len);

        // len will always fit into an int so this is safe
        len = (int)Math.min((long)len, pos - streamPos);
        if (len > 0) {
            cache.seek(streamPos);
            cache.readFully(b, off, len);
            streamPos += len;
            return len;
        } else {
            return -1;
        }
    }

    /**
     * Returns <code>true</code> since this
     * <code>ImageInputStream</code> caches data in order to allow
     * seeking backwards.
     *
     * @return <code>true</code>.
     *
     * @see #isCachedMemory
     * @see #isCachedFile
     */
    public boolean isCached() {
        return true;
    }

    /**
     * Returns <code>true</code> since this
     * <code>ImageInputStream</code> maintains a file cache.
     *
     * @return <code>true</code>.
     *
     * @see #isCached
     * @see #isCachedMemory
     */
    public boolean isCachedFile() {
        return true;
    }

    /**
     * Returns <code>false</code> since this
     * <code>ImageInputStream</code> does not maintain a main memory
     * cache.
     *
     * @return <code>false</code>.
     *
     * @see #isCached
     * @see #isCachedFile
     */
    public boolean isCachedMemory() {
        return false;
    }

    /**
     * Closes this <code>FileCacheImageInputStream</code>, closing
     * and removing the cache file.  The source <code>InputStream</code>
     * is not closed.
     *
     * @exception IOException if an error occurs.
     */
    public void close() throws IOException {
        super.close();
        cache.close();
        cacheFile.delete();
        stream = null;
    }
}