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// Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
// Licensed under the MIT License:
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

package org.capnproto;

import java.io.IOException;
import java.nio.channels.ReadableByteChannel;
import java.nio.ByteBuffer;

public final class PackedInputStream implements ReadableByteChannel {
    final BufferedInputStream inner;

    public PackedInputStream(BufferedInputStream input) {
        this.inner = input;
    }

    public int read(ByteBuffer outBuf) throws IOException {

        int len = outBuf.remaining();
        if (len == 0) { return 0; }

        if (len % 8 != 0) {
            throw new Error("PackedInputStream reads must be word-aligned");
        }

        int outPtr = outBuf.position();
        int outEnd = outPtr + len;

        ByteBuffer inBuf = this.inner.getReadBuffer();

        while (true) {

            byte tag = 0;

            if (inBuf.remaining() < 10) {
                if (outBuf.remaining() == 0) {
                    return len;
                }

                if (inBuf.remaining() == 0) {
                    inBuf = this.inner.getReadBuffer();
                    continue;
                }

                //# We have at least 1, but not 10, bytes available. We need to read
                //# slowly, doing a bounds check on each byte.

                tag = inBuf.get();

                for (int i = 0; i < 8; ++i) {
                    if ((tag & (1 << i)) != 0) {
                        if (inBuf.remaining() == 0) {
                            inBuf = this.inner.getReadBuffer();
                        }
                        outBuf.put(inBuf.get());
                    } else {
                        outBuf.put((byte)0);
                    }
                }

                if (inBuf.remaining() == 0 && (tag == 0 || tag == (byte)0xff)) {
                    inBuf = this.inner.getReadBuffer();
                }
            } else {

                tag = inBuf.get();
                for (int n = 0; n < 8; ++n) {
                    boolean isNonzero = (tag & (1 << n)) != 0;
                    outBuf.put((byte)(inBuf.get() & (isNonzero ? -1 : 0)));
                    inBuf.position(inBuf.position() + (isNonzero ? 0 : -1));
                }
            }

            if (tag == 0) {
                if (inBuf.remaining() == 0) {
                    throw new Error("Should always have non-empty buffer here.");
                }

                int runLength = (0xff & (int)inBuf.get()) * 8;

                if (runLength > outEnd - outPtr) {
                    throw new Error("Packed input did not end cleanly on a segment boundary");
                }

                for (int i = 0; i < runLength; ++i) {
                    outBuf.put((byte) 0);
                }
            } else if (tag == (byte)0xff) {

                int runLength = (0xff & (int)inBuf.get()) * 8;

                if (inBuf.remaining() >= runLength) {
                    //# Fast path.
                    ByteBuffer slice = inBuf.slice();
                    slice.limit(runLength);
                    outBuf.put(slice);
                    inBuf.position(inBuf.position() + runLength);
                } else {
                    //# Copy over the first buffer, then do one big read for the rest.
                    runLength -= inBuf.remaining();
                    outBuf.put(inBuf);

                    ByteBuffer slice = outBuf.slice();
                    slice.limit(runLength);

                    this.inner.read(slice);
                    outBuf.position(outBuf.position() + runLength);

                    if (outBuf.remaining() == 0) {
                        return len;
                    } else {
                        inBuf = this.inner.getReadBuffer();
                        continue;
                    }
                }
            }

            if (outBuf.remaining() == 0) {
                return len;
            }
        }
    }

    public void close() throws IOException {
        inner.close();
    }

    public boolean isOpen() {
        return inner.isOpen();
    }
}