/*
    * Copyright 2014 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.netty.handler.codec.compression;
  
  import io.netty.buffer.ByteBuf;
  
  /**
   * An bit reader that allows the reading of single bit booleans, bit strings of
   * arbitrary length (up to 32 bits), and bit aligned 32-bit integers. A single byte
   * at a time is read from the {@link ByteBuf} when more bits are required.
   */
  class Bzip2BitReader {
      /**
       * Maximum count of possible readable bytes to check.
       */
      private static final int MAX_COUNT_OF_READABLE_BYTES = Integer.MAX_VALUE >>> 3;
  
      /**
       * The {@link ByteBuf} from which to read data.
       */
      private ByteBuf in;
  
      /**
       * A buffer of bits read from the input stream that have not yet been returned.
       */
      private long bitBuffer;
  
      /**
       * The number of bits currently buffered in {@link #bitBuffer}.
       */
      private int bitCount;
  
      /**
       * Set the {@link ByteBuf} from which to read data.
       */
      void setByteBuf(ByteBuf in) {
          this.in = in;
      }
  
      /**
       * Reads up to 32 bits from the {@link ByteBuf}.
       * @param count The number of bits to read (maximum {@code 32} as a size of {@code int})
       * @return The bits requested, right-aligned within the integer
       */
      int readBits(final int count) {
          if (count < 0 || count > 32) {
              throw new IllegalArgumentException("count: " + count + " (expected: 0-32 )");
          }
          int bitCount = this.bitCount;
          long bitBuffer = this.bitBuffer;
  
          if (bitCount < count) {
              long readData;
              int offset;
              switch (in.readableBytes()) {
                  case 1: {
                      readData = in.readUnsignedByte();
                      offset = 8;
                      break;
                  }
                  case 2: {
                      readData = in.readUnsignedShort();
                      offset = 16;
                      break;
                  }
                  case 3: {
                      readData = in.readUnsignedMedium();
                      offset = 24;
                      break;
                  }
                  default: {
                      readData = in.readUnsignedInt();
                      offset = 32;
                      break;
                  }
              }
  
              bitBuffer = bitBuffer << offset | readData;
              bitCount += offset;
              this.bitBuffer = bitBuffer;
          }
  
          this.bitCount = bitCount -= count;
          return (int) (bitBuffer >>> bitCount & (count != 32 ? (1 << count) - 1 : 0xFFFFFFFFL));
      }
  
     /**
      * Reads a single bit from the {@link ByteBuf}.
      * @return {@code true} if the bit read was {@code 1}, otherwise {@code false}
      */
     boolean readBoolean() {
         return readBits(1) != 0;
     }
 
     /**
      * Reads 32 bits of input as an integer.
      * @return The integer read
      */
     int readInt() {
         return readBits(32);
     }
 
     /**
      * Refill the {@link ByteBuf} by one byte.
      */
     void refill() {
         int readData = in.readUnsignedByte();
         bitBuffer = bitBuffer << 8 | readData;
         bitCount += 8;
     }
 
     /**
      * Checks that at least one bit is available for reading.
      * @return {@code true} if one bit is available for reading, otherwise {@code false}
      */
     boolean isReadable() {
         return bitCount > 0 || in.isReadable();
     }
 
     /**
      * Checks that the specified number of bits available for reading.
      * @param count The number of bits to check
      * @return {@code true} if {@code count} bits are available for reading, otherwise {@code false}
      */
     boolean hasReadableBits(int count) {
         if (count < 0) {
             throw new IllegalArgumentException("count: " + count + " (expected value greater than 0)");
         }
         return bitCount >= count || (in.readableBytes() << 3 & Integer.MAX_VALUE) >= count - bitCount;
     }
 
     /**
      * Checks that the specified number of bytes available for reading.
      * @param count The number of bytes to check
      * @return {@code true} if {@code count} bytes are available for reading, otherwise {@code false}
      */
     boolean hasReadableBytes(int count) {
         if (count < 0 || count > MAX_COUNT_OF_READABLE_BYTES) {
             throw new IllegalArgumentException("count: " + count
                     + " (expected: 0-" + MAX_COUNT_OF_READABLE_BYTES + ')');
         }
         return hasReadableBits(count << 3);
     }
 }