/*
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF 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
    *
   *     http://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 org.apache.giraph.utils;
  
  /**
   * This Code is adapted from main/java/org/apache/mahout/math/Varint.java
   *
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF 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
   *
   *     http://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.
   */
  
  import java.io.DataInput;
  import java.io.DataOutput;
  import java.io.IOException;
  
  /**
   * <p>
   * Encodes signed and unsigned values using a common variable-length scheme,
   * found for example in <a
   * href="http://code.google.com/apis/protocolbuffers/docs/encoding.html">
   * Google's Protocol Buffers</a>. It uses fewer bytes to encode smaller values,
   * but will use slightly more bytes to encode large values.
   * </p>
   * <p>
   * Signed values are further encoded using so-called zig-zag encoding in order
   * to make them "compatible" with variable-length encoding.
   * </p>
   */
  public final class Varint {
  
    /**
     * private constructor
     */
    private Varint() {
    }
  
    /**
     * Encodes a value using the variable-length encoding from <a
     * href="http://code.google.com/apis/protocolbuffers/docs/encoding.html">
     * Google Protocol Buffers</a>.
     *
     * @param value to encode
     * @param out to write bytes to
     * @throws IOException
     *           if {@link DataOutput} throws {@link IOException}
     */
    private static void writeVarLong(
      long value,
      DataOutput out
    ) throws IOException {
      while (true) {
        int bits = ((int) value) & 0x7f;
        value >>>= 7;
        if (value == 0) {
          out.writeByte((byte) bits);
          return;
        }
        out.writeByte((byte) (bits | 0x80));
      }
    }
  
    /**
     * Encodes a value using the variable-length encoding from <a
     * href="http://code.google.com/apis/protocolbuffers/docs/encoding.html">
     * Google Protocol Buffers</a>.
     *
     * @param value to encode
     * @param out to write bytes to
     * @throws IOException
     *           if {@link DataOutput} throws {@link IOException}
     */
    public static void writeUnsignedVarLong(
     long value,
     DataOutput out
   ) throws IOException {
     if (value < 0) {
       throw new IllegalStateException(
         "Negative value passed into writeUnsignedVarLong - " + value);
     }
     writeVarLong(value, out);
   }
 
   /**
    * Zig-zag encoding for signed longs
    *
    * @param value to encode
    * @param out to write bytes to
    * @throws IOException
    *           if {@link DataOutput} throws {@link IOException}
    */
   public static void writeSignedVarLong(
     long value,
     DataOutput out
   ) throws IOException {
     writeVarLong((value << 1) ^ (value >> 63), out);
   }
 
   /**
    * @see #writeVarLong(long, DataOutput)
    * @param value to encode
    * @param out to write bytes to
    * @throws IOException
    */
   private static void writeVarInt(
     int value,
     DataOutput out
   ) throws IOException {
     while (true) {
       int bits = value & 0x7f;
       value >>>= 7;
       if (value == 0) {
         out.writeByte((byte) bits);
         return;
       }
       out.writeByte((byte) (bits | 0x80));
     }
   }
 
   /**
    * @see #writeVarLong(long, DataOutput)
    * @param value to encode
    * @param out to write bytes to
    * @throws IOException
    */
   public static void writeUnsignedVarInt(
     int value,
     DataOutput out
   ) throws IOException {
     if (value < 0) {
       throw new IllegalStateException(
         "Negative value passed into writeUnsignedVarInt - " + value);
     }
     writeVarInt(value, out);
   }
 
   /**
    * Zig-zag encoding for signed ints
    *
    * @see #writeUnsignedVarInt(int, DataOutput)
    * @param value to encode
    * @param out to write bytes to
    * @throws IOException
    */
   public static void writeSignedVarInt(
     int value,
     DataOutput out
   ) throws IOException {
     writeVarInt((value << 1) ^ (value >> 31), out);
   }
 
   /**
    * @param in to read bytes from
    * @return decode value
    * @throws IOException
    *           if {@link DataInput} throws {@link IOException}
    */
   public static long readUnsignedVarLong(DataInput in) throws IOException {
     long tmp;
     // CHECKSTYLE: stop InnerAssignment
     if ((tmp = in.readByte()) >= 0) {
       return tmp;
     }
     long result = tmp & 0x7f;
     if ((tmp = in.readByte()) >= 0) {
       result |= tmp << 7;
     } else {
       result |= (tmp & 0x7f) << 7;
       if ((tmp = in.readByte()) >= 0) {
         result |= tmp << 14;
       } else {
         result |= (tmp & 0x7f) << 14;
         if ((tmp = in.readByte()) >= 0) {
           result |= tmp << 21;
         } else {
           result |= (tmp & 0x7f) << 21;
           if ((tmp = in.readByte()) >= 0) {
             result |= tmp << 28;
           } else {
             result |= (tmp & 0x7f) << 28;
             if ((tmp = in.readByte()) >= 0) {
               result |= tmp << 35;
             } else {
               result |= (tmp & 0x7f) << 35;
               if ((tmp = in.readByte()) >= 0) {
                 result |= tmp << 42;
               } else {
                 result |= (tmp & 0x7f) << 42;
                 if ((tmp = in.readByte()) >= 0) {
                   result |= tmp << 49;
                 } else {
                   result |= (tmp & 0x7f) << 49;
                   if ((tmp = in.readByte()) >= 0) {
                     result |= tmp << 56;
                   } else {
                     result |= (tmp & 0x7f) << 56;
                     result |= ((long) in.readByte()) << 63;
                   }
                 }
               }
             }
           }
         }
       }
     }
     // CHECKSTYLE: resume InnerAssignment
     return result;
   }
 
   /**
    * @param in to read bytes from
    * @return decode value
    * @throws IOException
    *           if {@link DataInput} throws {@link IOException}
    */
   public static long readSignedVarLong(DataInput in) throws IOException {
     long raw = readUnsignedVarLong(in);
     long temp = (((raw << 63) >> 63) ^ raw) >> 1;
     return temp ^ (raw & (1L << 63));
   }
 
   /**
    * @throws IOException
    *           if {@link DataInput} throws {@link IOException}
    * @param in to read bytes from
    * @return decode value
    */
   public static int readUnsignedVarInt(DataInput in) throws IOException {
     int tmp;
     // CHECKSTYLE: stop InnerAssignment
     if ((tmp = in.readByte()) >= 0) {
       return tmp;
     }
     int result = tmp & 0x7f;
     if ((tmp = in.readByte()) >= 0) {
       result |= tmp << 7;
     } else {
       result |= (tmp & 0x7f) << 7;
       if ((tmp = in.readByte()) >= 0) {
         result |= tmp << 14;
       } else {
         result |= (tmp & 0x7f) << 14;
         if ((tmp = in.readByte()) >= 0) {
           result |= tmp << 21;
         } else {
           result |= (tmp & 0x7f) << 21;
           result |= (in.readByte()) << 28;
         }
       }
     }
     // CHECKSTYLE: resume InnerAssignment
     return result;
   }
 
   /**
    * @throws IOException
    *           if {@link DataInput} throws {@link IOException}
    * @param in to read bytes from
    * @return decode value
    */
   public static int readSignedVarInt(DataInput in) throws IOException {
     int raw = readUnsignedVarInt(in);
     int temp = (((raw << 31) >> 31) ^ raw) >> 1;
     return temp ^ (raw & (1 << 31));
   }
 
   /**
    * Simulation for what will happen when writing an unsigned long value
    * as varlong.
    * @param value to consider
    * @return the number of bytes needed to write value.
    * @throws IOException
    */
   public static long sizeOfUnsignedVarLong(long value) throws IOException {
     int result = 0;
     do {
       result++;
       value >>>= 7;
     } while (value != 0);
     return result;
   }
 
   /**
    * Simulation for what will happen when writing a signed long value
    * as varlong.
    * @param value to consider
    * @return the number of bytes needed to write value.
    * @throws IOException
    */
   public static long sizeOfSignedVarLong(long value) throws IOException {
     return sizeOfUnsignedVarLong((value << 1) ^ (value >> 63));
   }
 
   /**
    * Simulation for what will happen when writing an unsigned int value
    * as varint.
    * @param value to consider
    * @return the number of bytes needed to write value.
    * @throws IOException
    */
   public static int sizeOfUnsignedVarInt(int value) throws IOException {
     int cnt = 0;
     do {
       cnt++;
       value >>>= 7;
     } while (value != 0);
     return cnt;
   }
 
   /**
    * Simulation for what will happen when writing a signed int value
    * as varint.
    * @param value to consider
    * @return the number of bytes needed to write value.
    * @throws IOException
    */
   public static int sizeOfSignedVarInt(int value) throws IOException {
     return sizeOfUnsignedVarInt((value << 1) ^ (value >> 31));
   }
 
 }