/*
 * Copyright [2013] [Cloud4SOA, www.cloud4soa.eu]
 *
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */


/*
 * Copyright 2009-2012 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.cloudfoundry.client.lib.io;

import java.io.ByteArrayOutputStream;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import org.springframework.util.Assert;

/**
 * InputStream that dynamically loads data on demand as the stream is read. Subclasses must implement the
 * {@link #writeMoreData()} method.
 *
 * @author Phillip Webb
 */
public abstract class DynamicInputStream extends InputStream {

    private BufferedOutputStream outputStream = new BufferedOutputStream();

    private byte[] singleByte = new byte[1];

    @Override
    public int read() throws IOException {
        int s = read(singleByte);
        if (s == 1) {
            return (int) singleByte[0] & 0xFF;
        }
        return -1;
    }

    @Override
    public int read(byte[] b, int off, int len) throws IOException {
        if (b == null) {
            throw new NullPointerException();
        }
        if (off < 0 || len < 0 || len > (b.length - off)) {
            throw new IndexOutOfBoundsException();
        }
        if (len == 0) {
            return 0;
        }
        return doRead(b, off, len, true);
    }

    private int doRead(byte[] b, int off, int len, boolean lastWriteWasSuccessful) throws IOException {
        if (outputStream.getAvailable() > 0) {
            return outputStream.read(b, off, len);
        }
        if (!lastWriteWasSuccessful) {
            return -1;
        }
        outputStream.clear();
        boolean writeSuccess = writeMoreData();
        return doRead(b, off, len, writeSuccess);
    }

    /**
     * Returns the {@link OutputStream} that should be used when {@link #writeMoreData() writing} data. The output
     * stream instance will not change during the life of the object and so can be used as the source to a a
     * {@link FilterInputStream}. This is an in-memory stream so care should be taken to not write large amounts of
     * data.
     *
     * @return the output stream
     * @see #writeMoreData()
     */
    protected final OutputStream getOutputStream() {
        return outputStream;
    }

    /**
     * Called when more data should be written to the {@link #getOutputStream() output stream}. This method can be
     * called many times, implementations should write zero or more bytes to {@link #getOutputStream() output stream} on
     * each call. Generally it is recommended that not more that 4096 bytes are written in a single call.
     *
     * @return <tt>false</tt> when no more data is available to write.
     * @throws IOException
     */
    protected abstract boolean writeMoreData() throws IOException;

    /**
     * Internal buffered {@link OutputStream} implementation.
     */
    private static class BufferedOutputStream extends ByteArrayOutputStream {

        private int offset;

        public int getAvailable() {
            return count - offset;
        }

        public void clear() {
            this.count = 0;
            this.offset = 0;
        }

        public int read(byte[] b, int off, int len) {
            int length = Math.min(getAvailable(), len);
            Assert.state(length > 0, "No data available in buffer");
            System.arraycopy(this.buf, this.offset, b, off, length);
            offset += length;
            return length;
        }
    }

}