/*
    * Copyright (C) 2011 The Guava Authors
    *
    * Licensed 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 com.google.common.primitives;
  
  import static com.google.common.base.Preconditions.checkArgument;
  import static com.google.common.base.Preconditions.checkNotNull;
  
  import com.google.common.annotations.Beta;
  import com.google.common.annotations.GwtCompatible;
  
  import java.util.Arrays;
  import java.util.Comparator;
  
  /**
   * Static utility methods pertaining to {@code int} primitives that interpret values as
   * <i>unsigned</i> (that is, any negative value {@code x} is treated as the positive value
   * {@code 2^32 + x}). The methods for which signedness is not an issue are in {@link Ints}, as well
   * as signed versions of methods for which signedness is an issue.
   *
   * <p>In addition, this class provides several static methods for converting an {@code int} to a
   * {@code String} and a {@code String} to an {@code int} that treat the {@code int} as an unsigned
   * number.
   *
   * <p>Users of these utilities must be <i>extremely careful</i> not to mix up signed and unsigned
   * {@code int} values. When possible, it is recommended that the {@link UnsignedInteger} wrapper
   * class be used, at a small efficiency penalty, to enforce the distinction in the type system.
   *
   * <p>See the Guava User Guide article on <a href=
   * "http://code.google.com/p/guava-libraries/wiki/PrimitivesExplained#Unsigned_support">
   * unsigned primitive utilities</a>.
   *
   * @author Louis Wasserman
   * @since 11.0
   */
  @Beta
  @GwtCompatible
  public final class UnsignedInts {
    static final long INT_MASK = 0xffffffffL;
  
    private UnsignedInts() {}
  
    static int flip(int value) {
      return value ^ Integer.MIN_VALUE;
    }
  
    /**
     * Compares the two specified {@code int} values, treating them as unsigned values between
     * {@code 0} and {@code 2^32 - 1} inclusive.
     *
     * @param a the first unsigned {@code int} to compare
     * @param b the second unsigned {@code int} to compare
     * @return a negative value if {@code a} is less than {@code b}; a positive value if {@code a} is
     *         greater than {@code b}; or zero if they are equal
     */
    public static int compare(int a, int b) {
      return Ints.compare(flip(a), flip(b));
    }
  
    /**
     * Returns the value of the given {@code int} as a {@code long}, when treated as unsigned.
     */
    public static long toLong(int value) {
      return value & INT_MASK;
    }
  
    /**
     * Returns the least value present in {@code array}, treating values as unsigned.
     *
     * @param array a <i>nonempty</i> array of unsigned {@code int} values
     * @return the value present in {@code array} that is less than or equal to every other value in
     *         the array according to {@link #compare}
     * @throws IllegalArgumentException if {@code array} is empty
     */
    public static int min(int... array) {
      checkArgument(array.length > 0);
      int min = flip(array[0]);
      for (int i = 1; i < array.length; i++) {
        int next = flip(array[i]);
        if (next < min) {
          min = next;
        }
      }
      return flip(min);
    }
  
    /**
     * Returns the greatest value present in {@code array}, treating values as unsigned.
    *
    * @param array a <i>nonempty</i> array of unsigned {@code int} values
    * @return the value present in {@code array} that is greater than or equal to every other value
    *         in the array according to {@link #compare}
    * @throws IllegalArgumentException if {@code array} is empty
    */
   public static int max(int... array) {
     checkArgument(array.length > 0);
     int max = flip(array[0]);
     for (int i = 1; i < array.length; i++) {
       int next = flip(array[i]);
       if (next > max) {
         max = next;
       }
     }
     return flip(max);
   }
 
   /**
    * Returns a string containing the supplied unsigned {@code int} values separated by
    * {@code separator}. For example, {@code join("-", 1, 2, 3)} returns the string {@code "1-2-3"}.
    *
    * @param separator the text that should appear between consecutive values in the resulting
    *        string (but not at the start or end)
    * @param array an array of unsigned {@code int} values, possibly empty
    */
   public static String join(String separator, int... array) {
     checkNotNull(separator);
     if (array.length == 0) {
       return "";
     }
 
     // For pre-sizing a builder, just get the right order of magnitude
     StringBuilder builder = new StringBuilder(array.length * 5);
     builder.append(toString(array[0]));
     for (int i = 1; i < array.length; i++) {
       builder.append(separator).append(toString(array[i]));
     }
     return builder.toString();
   }
 
   /**
    * Returns a comparator that compares two arrays of unsigned {@code int} values lexicographically.
    * That is, it compares, using {@link #compare(int, int)}), the first pair of values that follow
    * any common prefix, or when one array is a prefix of the other, treats the shorter array as the
    * lesser. For example, {@code [] < [1] < [1, 2] < [2] < [1 << 31]}.
    *
    * <p>The returned comparator is inconsistent with {@link Object#equals(Object)} (since arrays
    * support only identity equality), but it is consistent with {@link Arrays#equals(int[], int[])}.
    *
    * @see <a href="http://en.wikipedia.org/wiki/Lexicographical_order"> Lexicographical order
    *      article at Wikipedia</a>
    */
   public static Comparator<int[]> lexicographicalComparator() {
     return LexicographicalComparator.INSTANCE;
   }
 
   enum LexicographicalComparator implements Comparator<int[]> {
     INSTANCE;
 
     @Override
     public int compare(int[] left, int[] right) {
       int minLength = Math.min(left.length, right.length);
       for (int i = 0; i < minLength; i++) {
         if (left[i] != right[i]) {
           return UnsignedInts.compare(left[i], right[i]);
         }
       }
       return left.length - right.length;
     }
   }
 
   /**
    * Returns dividend / divisor, where the dividend and divisor are treated as unsigned 32-bit
    * quantities.
    *
    * @param dividend the dividend (numerator)
    * @param divisor the divisor (denominator)
    * @throws ArithmeticException if divisor is 0
    */
   public static int divide(int dividend, int divisor) {
     return (int) (toLong(dividend) / toLong(divisor));
   }
 
   /**
    * Returns dividend % divisor, where the dividend and divisor are treated as unsigned 32-bit
    * quantities.
    *
    * @param dividend the dividend (numerator)
    * @param divisor the divisor (denominator)
    * @throws ArithmeticException if divisor is 0
    */
   public static int remainder(int dividend, int divisor) {
     return (int) (toLong(dividend) % toLong(divisor));
   }
 
   /**
    * Returns the unsigned {@code int} value represented by the given string.
    *
    * Accepts a decimal, hexadecimal, or octal number given by specifying the following prefix:
    *
    * <ul>
    * <li>{@code 0x}<i>HexDigits</i>
    * <li>{@code 0X}<i>HexDigits</i>
    * <li>{@code #}<i>HexDigits</i>
    * <li>{@code 0}<i>OctalDigits</i>
    * </ul>
    *
    * @throws NumberFormatException if the string does not contain a valid unsigned {@code int} value
    * @since 13.0
    */
   public static int decode(String stringValue) {
     ParseRequest request = ParseRequest.fromString(stringValue);
 
     try {
       return parseUnsignedInt(request.rawValue, request.radix);
     } catch (NumberFormatException e) {
       NumberFormatException decodeException =
           new NumberFormatException("Error parsing value: " + stringValue);
       decodeException.initCause(e);
       throw decodeException;
     }
   }
 
   /**
    * Returns the unsigned {@code int} value represented by the given decimal string.
    *
    * @throws NumberFormatException if the string does not contain a valid unsigned {@code int} value
    * @throws NullPointerException if {@code s} is null 
    *         (in contrast to {@link Integer#parseInt(String)})
    */
   public static int parseUnsignedInt(String s) {
     return parseUnsignedInt(s, 10);
   }
 
   /**
    * Returns the unsigned {@code int} value represented by a string with the given radix.
    *
    * @param string the string containing the unsigned integer representation to be parsed.
    * @param radix the radix to use while parsing {@code s}; must be between
    *        {@link Character#MIN_RADIX} and {@link Character#MAX_RADIX}.
    * @throws NumberFormatException if the string does not contain a valid unsigned {@code int}, or
    *         if supplied radix is invalid.
    * @throws NullPointerException if {@code s} is null 
    *         (in contrast to {@link Integer#parseInt(String)})
    */
   public static int parseUnsignedInt(String string, int radix) {
     checkNotNull(string);
     long result = Long.parseLong(string, radix);
     if ((result & INT_MASK) != result) {
       throw new NumberFormatException("Input " + string + " in base " + radix
           + " is not in the range of an unsigned integer");
     }
     return (int) result;
   }
 
   /**
    * Returns a string representation of x, where x is treated as unsigned.
    */
   public static String toString(int x) {
     return toString(x, 10);
   }
 
   /**
    * Returns a string representation of {@code x} for the given radix, where {@code x} is treated
    * as unsigned.
    *
    * @param x the value to convert to a string.
    * @param radix the radix to use while working with {@code x}
    * @throws IllegalArgumentException if {@code radix} is not between {@link Character#MIN_RADIX}
    *         and {@link Character#MAX_RADIX}.
    */
   public static String toString(int x, int radix) {
     long asLong = x & INT_MASK;
     return Long.toString(asLong, radix);
   }
 }