/*
    * 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 java.io.InputStream;
  import java.io.PushbackInputStream;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * A {@link ChunkedInput} that fetches data from an {@link InputStream} chunk by
   * chunk.
   * <p>
   * Please note that the {@link InputStream} instance that feeds data into
   * {@link ChunkedStream} must implement {@link InputStream#available()} as
   * accurately as possible, rather than using the default implementation.
   * Otherwise, {@link ChunkedStream} will generate many too small chunks or
   * block unnecessarily often.
   */
  public class ChunkedStream implements ChunkedInput<Buffer> {
      static final int DEFAULT_CHUNK_SIZE = 8192;
  
      private final PushbackInputStream in;
      private final int chunkSize;
      private long offset;
      private boolean closed;
      private byte[] cachedArray;
  
      /**
       * Creates a new instance that fetches data from the specified stream.
       */
      public ChunkedStream(InputStream in) {
          this(in, DEFAULT_CHUNK_SIZE);
      }
  
      /**
       * Creates a new instance that fetches data from the specified stream.
       *
       * @param chunkSize the number of bytes to fetch on each {@link #readChunk(BufferAllocator)} call.
       */
      public ChunkedStream(InputStream in, int chunkSize) {
          requireNonNull(in, "in");
          if (chunkSize <= 0) {
              throw new IllegalArgumentException(
                      "chunkSize: " + chunkSize +
                      " (expected: a positive integer)");
          }
  
          if (in instanceof PushbackInputStream) {
              this.in = (PushbackInputStream) in;
          } else {
              this.in = new PushbackInputStream(in);
          }
          this.chunkSize = chunkSize;
      }
  
      /**
       * Returns the number of transferred bytes.
       */
      public long transferredBytes() {
          return offset;
      }
  
      @Override
      public boolean isEndOfInput() throws Exception {
          if (closed) {
              return true;
          }
          if (in.available() > 0) {
              return false;
          }
  
          int b = in.read();
          if (b < 0) {
              return true;
          } else {
              in.unread(b);
              return false;
          }
      }
  
      @Override
      public void close() throws Exception {
         closed = true;
         in.close();
     }
 
     @Override
     public Buffer readChunk(BufferAllocator allocator) throws Exception {
         if (isEndOfInput()) {
             return null;
         }
 
         final int availableBytes = in.available();
         final int chunkSize;
         if (availableBytes <= 0) {
             chunkSize = this.chunkSize;
         } else {
             chunkSize = Math.min(this.chunkSize, in.available());
         }
 
         boolean release = true;
         Buffer buffer = allocator.allocate(chunkSize);
         try {
             // transfer to buffer
             int written;
             try (var iter = buffer.forEachWritable()) {
                 var component = iter.first();
                 if (component.hasWritableArray()) {
                     written = in.read(component.writableArray(),
                             component.writableArrayOffset(),
                             component.writableArrayLength());
                 } else {
                     int size = Math.min(component.writableBytes(), chunkSize);
                     if (cachedArray == null || cachedArray.length < size) {
                         cachedArray = new byte[size];
                     }
                     written = in.read(cachedArray, 0, size);
                     if (written > 0) {
                         buffer.writeBytes(cachedArray, 0, written);
                     }
                 }
             }
             if (written < 0) {
                 return null;
             }
             offset += written;
             release = false;
             return buffer;
         } finally {
             if (release) {
                 buffer.close();
             }
         }
     }
 
     @Override
     public long length() {
         return -1;
     }
 
     @Override
     public long progress() {
         return offset;
     }
 }