/*
    * 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.api.Buffer;
  import io.netty5.buffer.api.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}.
   * <p>
   * If your operating system supports
   * <a href="https://en.wikipedia.org/wiki/Zero-copy">zero-copy file transfer</a>
   * such as {@code sendfile()}, you might want to use {@link FileRegion} instead.
   */
  public class ChunkedNioFile implements ChunkedInput<Buffer> {
  
      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;
     }
 }