/*
 * 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 static com.google.common.primitives.UnsignedInts.INT_MASK;
import static com.google.common.primitives.UnsignedInts.compare;
import static com.google.common.primitives.UnsignedInts.toLong;

import java.math.BigInteger;

import javax.annotation.CheckReturnValue;
import javax.annotation.Nullable;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;

/**
 * A wrapper class for unsigned {@code int} values, supporting arithmetic
 * operations.
 *
 * <p>
 * In some cases, when speed is more important than code readability, it may be
 * faster simply to treat primitive {@code int} values as unsigned, using the
 * methods from {@link UnsignedInts}.
 *
 * <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
 */
@GwtCompatible(emulated = true)
public final class UnsignedInteger extends Number implements Comparable<UnsignedInteger> {
	public static final UnsignedInteger ZERO = fromIntBits(0);
	public static final UnsignedInteger ONE = fromIntBits(1);
	public static final UnsignedInteger MAX_VALUE = fromIntBits(-1);

	/**
	 * Returns an {@code UnsignedInteger} corresponding to a given bit
	 * representation. The argument is interpreted as an unsigned 32-bit value.
	 * Specifically, the sign bit of {@code bits} is interpreted as a normal bit,
	 * and all other bits are treated as usual.
	 *
	 * <p>
	 * If the argument is nonnegative, the returned result will be equal to
	 * {@code bits}, otherwise, the result will be equal to {@code 2^32 + bits}.
	 *
	 * <p>
	 * To represent unsigned decimal constants, consider {@link #valueOf(long)}
	 * instead.
	 *
	 * @since 14.0
	 */
	public static UnsignedInteger fromIntBits(int bits) {
		return new UnsignedInteger(bits);
	}

	/**
	 * Returns a {@code UnsignedInteger} representing the same value as the
	 * specified {@link BigInteger}. This is the inverse operation of
	 * {@link #bigIntegerValue()}.
	 *
	 * @throws IllegalArgumentException if {@code value} is negative or
	 *                                  {@code value >= 2^32}
	 */
	public static UnsignedInteger valueOf(BigInteger value) {
		checkNotNull(value);
		checkArgument(value.signum() >= 0 && value.bitLength() <= Integer.SIZE,
				"value (%s) is outside the range for an unsigned integer value", value);
		return fromIntBits(value.intValue());
	}

	/**
	 * Returns an {@code UnsignedInteger} that is equal to {@code value}, if
	 * possible. The inverse operation of {@link #longValue()}.
	 */
	public static UnsignedInteger valueOf(long value) {
		checkArgument((value & INT_MASK) == value, "value (%s) is outside the range for an unsigned integer value",
				value);
		return fromIntBits((int) value);
	}

	/**
	 * Returns an {@code UnsignedInteger} holding the value of the specified
	 * {@code String}, parsed as an unsigned {@code int} value.
	 *
	 * @throws NumberFormatException if the string does not contain a parsable
	 *                               unsigned {@code int} value
	 */
	public static UnsignedInteger valueOf(String string) {
		return valueOf(string, 10);
	}

	/**
	 * Returns an {@code UnsignedInteger} holding the value of the specified
	 * {@code String}, parsed as an unsigned {@code int} value in the specified
	 * radix.
	 *
	 * @throws NumberFormatException if the string does not contain a parsable
	 *                               unsigned {@code int} value
	 */
	public static UnsignedInteger valueOf(String string, int radix) {
		return fromIntBits(UnsignedInts.parseUnsignedInt(string, radix));
	}

	private final int value;

	private UnsignedInteger(int value) {
		// GWT doesn't consistently overflow values to make them 32-bit, so we need to
		// force it.
		this.value = value & 0xffffffff;
	}

	/**
	 * Returns the value of this {@code UnsignedInteger} as a {@link BigInteger}.
	 */
	public BigInteger bigIntegerValue() {
		return BigInteger.valueOf(longValue());
	}

	/**
	 * Compares this unsigned integer to another unsigned integer. Returns {@code 0}
	 * if they are equal, a negative number if {@code this < other}, and a positive
	 * number if {@code this > other}.
	 */
	@Override
	public int compareTo(UnsignedInteger other) {
		checkNotNull(other);
		return compare(value, other.value);
	}

	/**
	 * Returns the result of dividing this by {@code val}.
	 *
	 * @throws ArithmeticException if {@code val} is zero
	 * @since 14.0
	 */
	@CheckReturnValue
	public UnsignedInteger dividedBy(UnsignedInteger val) {
		return fromIntBits(UnsignedInts.divide(value, checkNotNull(val).value));
	}

	/**
	 * Returns the value of this {@code UnsignedInteger} as a {@code float},
	 * analogous to a widening primitive conversion from {@code int} to
	 * {@code double}, and correctly rounded.
	 */
	@Override
	public double doubleValue() {
		return longValue();
	}

	@Override
	public boolean equals(@Nullable Object obj) {
		if (obj instanceof UnsignedInteger) {
			UnsignedInteger other = (UnsignedInteger) obj;
			return value == other.value;
		}
		return false;
	}

	/**
	 * Returns the value of this {@code UnsignedInteger} as a {@code float},
	 * analogous to a widening primitive conversion from {@code int} to
	 * {@code float}, and correctly rounded.
	 */
	@Override
	public float floatValue() {
		return longValue();
	}

	@Override
	public int hashCode() {
		return value;
	}

	/**
	 * Returns the value of this {@code UnsignedInteger} as an {@code int}. This is
	 * an inverse operation to {@link #fromIntBits}.
	 *
	 * <p>
	 * Note that if this {@code UnsignedInteger} holds a value {@code >= 2^31}, the
	 * returned value will be equal to {@code this - 2^32}.
	 */
	@Override
	public int intValue() {
		return value;
	}

	/**
	 * Returns the value of this {@code UnsignedInteger} as a {@code long}.
	 */
	@Override
	public long longValue() {
		return toLong(value);
	}

	/**
	 * Returns the result of subtracting this and {@code val}. If the result would
	 * be negative, returns the low 32 bits of the result.
	 *
	 * @since 14.0
	 */
	@CheckReturnValue
	public UnsignedInteger minus(UnsignedInteger val) {
		return fromIntBits(value - checkNotNull(val).value);
	}

	/**
	 * Returns this mod {@code val}.
	 *
	 * @throws ArithmeticException if {@code val} is zero
	 * @since 14.0
	 */
	@CheckReturnValue
	public UnsignedInteger mod(UnsignedInteger val) {
		return fromIntBits(UnsignedInts.remainder(value, checkNotNull(val).value));
	}

	/**
	 * Returns the result of adding this and {@code val}. If the result would have
	 * more than 32 bits, returns the low 32 bits of the result.
	 *
	 * @since 14.0
	 */
	@CheckReturnValue
	public UnsignedInteger plus(UnsignedInteger val) {
		return fromIntBits(this.value + checkNotNull(val).value);
	}

	/**
	 * Returns the result of multiplying this and {@code val}. If the result would
	 * have more than 32 bits, returns the low 32 bits of the result.
	 *
	 * @since 14.0
	 */
	@CheckReturnValue
	@GwtIncompatible("Does not truncate correctly")
	public UnsignedInteger times(UnsignedInteger val) {
		// TODO(user): make this GWT-compatible
		return fromIntBits(value * checkNotNull(val).value);
	}

	/**
	 * Returns a string representation of the {@code UnsignedInteger} value, in base
	 * 10.
	 */
	@Override
	public String toString() {
		return toString(10);
	}

	/**
	 * Returns a string representation of the {@code UnsignedInteger} value, in base
	 * {@code radix}. If {@code radix < Character.MIN_RADIX} or
	 * {@code radix > Character.MAX_RADIX}, the radix {@code 10} is used.
	 */
	public String toString(int radix) {
		return UnsignedInts.toString(value, radix);
	}
}
