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/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project 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:
 *
 *   https://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 io.netty5.handler.stream;

import io.netty5.buffer.Buffer;
import io.netty5.buffer.BufferAllocator;
import io.netty5.channel.FileRegion;

import java.io.File;
import java.io.IOException;
import java.nio.channels.ClosedChannelException;
import java.nio.channels.FileChannel;
import java.nio.file.StandardOpenOption;

import static java.util.Objects.requireNonNull;

/**
 * A {@link ChunkedInput} that fetches data from a file chunk by chunk using
 * NIO {@link FileChannel}.
 * 
 * If your operating system supports
 * zero-copy file transfer
 * such as {@code sendfile()}, you might want to use {@link FileRegion} instead.
 */
public class ChunkedNioFile implements ChunkedInput {

    private final FileChannel in;
    private final long startOffset;
    private final long endOffset;
    private final int chunkSize;
    private long offset;

    /**
     * Creates a new instance that fetches data from the specified file.
     */
    public ChunkedNioFile(File in) throws IOException {
        this(FileChannel.open(in.toPath(), StandardOpenOption.READ));
    }

    /**
     * Creates a new instance that fetches data from the specified file.
     *
     * @param chunkSize the number of bytes to fetch on each {@link #readChunk(BufferAllocator)} call.
     */
    public ChunkedNioFile(File in, int chunkSize) throws IOException {
        this(FileChannel.open(in.toPath(), StandardOpenOption.READ), chunkSize);
    }

    /**
     * Creates a new instance that fetches data from the specified file.
     */
    public ChunkedNioFile(FileChannel in) throws IOException {
        this(in, ChunkedStream.DEFAULT_CHUNK_SIZE);
    }

    /**
     * Creates a new instance that fetches data from the specified file.
     *
     * @param chunkSize the number of bytes to fetch on each {@link #readChunk(BufferAllocator)} call.
     */
    public ChunkedNioFile(FileChannel in, int chunkSize) throws IOException {
        this(in, 0, in.size(), chunkSize);
    }

    /**
     * Creates a new instance that fetches data from the specified file.
     *
     * @param offset the offset of the file where the transfer begins
     * @param length the number of bytes to transfer
     * @param chunkSize the number of bytes to fetch on each {@link #readChunk(BufferAllocator)} call.
     */
    public ChunkedNioFile(FileChannel in, long offset, long length, int chunkSize) throws IOException {
        requireNonNull(in, "in");
        if (offset < 0) {
            throw new IllegalArgumentException(
                    "offset: " + offset + " (expected: 0 or greater)");
        }
        if (length < 0) {
            throw new IllegalArgumentException(
                    "length: " + length + " (expected: 0 or greater)");
        }
        if (chunkSize <= 0) {
            throw new IllegalArgumentException(
                    "chunkSize: " + chunkSize +
                    " (expected: a positive integer)");
        }
        if (!in.isOpen()) {
            throw new ClosedChannelException();
        }
        this.in = in;
        this.chunkSize = chunkSize;
        this.offset = startOffset = offset;
        endOffset = offset + length;
    }

    /**
     * Returns the offset in the file where the transfer began.
     */
    public long startOffset() {
        return startOffset;
    }

    /**
     * Returns the offset in the file where the transfer will end.
     */
    public long endOffset() {
        return endOffset;
    }

    /**
     * Returns the offset in the file where the transfer is happening currently.
     */
    public long currentOffset() {
        return offset;
    }

    @Override
    public boolean isEndOfInput() throws Exception {
        return !(offset < endOffset && in.isOpen());
    }

    @Override
    public void close() throws Exception {
        in.close();
    }

    @Override
    public Buffer readChunk(BufferAllocator allocator) throws Exception {
        long offset = this.offset;
        if (offset >= endOffset) {
            return null;
        }

        int chunkSize = (int) Math.min(this.chunkSize, endOffset - offset);
        Buffer buffer = allocator.allocate(chunkSize);
        boolean release = true;
        try {
            int readBytes = 0;
            for (;;) {
                int localReadBytes = buffer.transferFrom(in, offset + readBytes, chunkSize - readBytes);
                if (localReadBytes < 0) {
                    break;
                }
                readBytes += localReadBytes;
                if (readBytes == chunkSize) {
                    break;
                }
            }
            this.offset += readBytes;
            release = false;
            return buffer;
        } finally {
            if (release) {
                buffer.close();
            }
        }
    }

    @Override
    public long length() {
        return endOffset - startOffset;
    }

    @Override
    public long progress() {
        return offset - startOffset;
    }
}