/*
 * 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.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.math.BigInteger;
import org.jspecify.annotations.Nullable;

/**
 * A wrapper class for unsigned {@code long} 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 long} values as unsigned, using the methods from {@link UnsignedLongs}.
 *
 * <p>See the Guava User Guide article on <a
 * href="https://github.com/google/guava/wiki/PrimitivesExplained#unsigned-support">unsigned
 * primitive utilities</a>.
 *
 * @author Louis Wasserman
 * @author Colin Evans
 * @since 11.0
 */
@GwtCompatible
public final class UnsignedLong extends Number implements Comparable<UnsignedLong> {

  private static final long UNSIGNED_MASK = 0x7fffffffffffffffL;

  public static final UnsignedLong ZERO = new UnsignedLong(0);
  public static final UnsignedLong ONE = new UnsignedLong(1);
  public static final UnsignedLong MAX_VALUE = new UnsignedLong(-1L);

  private final long value;

  private UnsignedLong(long value) {
    this.value = value;
  }

  /**
   * Returns an {@code UnsignedLong} corresponding to a given bit representation. The argument is
   * interpreted as an unsigned 64-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 2^64 + bits}.
   *
   * <p>To represent decimal constants less than {@code 2^63}, consider {@link #valueOf(long)}
   * instead.
   *
   * @since 14.0
   */
  public static UnsignedLong fromLongBits(long bits) {
    // TODO(lowasser): consider caching small values, like Long.valueOf
    return new UnsignedLong(bits);
  }

  /**
   * Returns an {@code UnsignedLong} representing the same value as the specified {@code long}.
   *
   * @throws IllegalArgumentException if {@code value} is negative
   * @since 14.0
   */
  @CanIgnoreReturnValue
  public static UnsignedLong valueOf(long value) {
    checkArgument(value >= 0, "value (%s) is outside the range for an unsigned long value", value);
    return fromLongBits(value);
  }

  /**
   * Returns a {@code UnsignedLong} representing the same value as the specified {@code BigInteger}.
   * This is the inverse operation of {@link #bigIntegerValue()}.
   *
   * @throws IllegalArgumentException if {@code value} is negative or {@code value >= 2^64}
   */
  @CanIgnoreReturnValue
  public static UnsignedLong valueOf(BigInteger value) {
    checkNotNull(value);
    checkArgument(
        value.signum() >= 0 && value.bitLength() <= Long.SIZE,
        "value (%s) is outside the range for an unsigned long value",
        value);
    return fromLongBits(value.longValue());
  }

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

  /**
   * Returns an {@code UnsignedLong} holding the value of the specified {@code String}, parsed as an
   * unsigned {@code long} value in the specified radix.
   *
   * @throws NumberFormatException if the string does not contain a parsable unsigned {@code long}
   *     value, or {@code radix} is not between {@link Character#MIN_RADIX} and {@link
   *     Character#MAX_RADIX}
   */
  @CanIgnoreReturnValue
  public static UnsignedLong valueOf(String string, int radix) {
    return fromLongBits(UnsignedLongs.parseUnsignedLong(string, radix));
  }

  /**
   * Returns the result of adding this and {@code val}. If the result would have more than 64 bits,
   * returns the low 64 bits of the result.
   *
   * @since 14.0
   */
  public UnsignedLong plus(UnsignedLong val) {
    return fromLongBits(this.value + checkNotNull(val).value);
  }

  /**
   * Returns the result of subtracting this and {@code val}. If the result would have more than 64
   * bits, returns the low 64 bits of the result.
   *
   * @since 14.0
   */
  public UnsignedLong minus(UnsignedLong val) {
    return fromLongBits(this.value - checkNotNull(val).value);
  }

  /**
   * Returns the result of multiplying this and {@code val}. If the result would have more than 64
   * bits, returns the low 64 bits of the result.
   *
   * @since 14.0
   */
  public UnsignedLong times(UnsignedLong val) {
    return fromLongBits(value * checkNotNull(val).value);
  }

  /**
   * Returns the result of dividing this by {@code val}.
   *
   * @since 14.0
   */
  public UnsignedLong dividedBy(UnsignedLong val) {
    return fromLongBits(UnsignedLongs.divide(value, checkNotNull(val).value));
  }

  /**
   * Returns this modulo {@code val}.
   *
   * @since 14.0
   */
  public UnsignedLong mod(UnsignedLong val) {
    return fromLongBits(UnsignedLongs.remainder(value, checkNotNull(val).value));
  }

  /** Returns the value of this {@code UnsignedLong} as an {@code int}. */
  @Override
  public int intValue() {
    return (int) value;
  }

  /**
   * Returns the value of this {@code UnsignedLong} as a {@code long}. This is an inverse operation
   * to {@link #fromLongBits}.
   *
   * <p>Note that if this {@code UnsignedLong} holds a value {@code >= 2^63}, the returned value
   * will be equal to {@code this - 2^64}.
   */
  @Override
  public long longValue() {
    return value;
  }

  /**
   * Returns the value of this {@code UnsignedLong} as a {@code float}, analogous to a widening
   * primitive conversion from {@code long} to {@code float}, and correctly rounded.
   */
  @Override
  public float floatValue() {
    if (value >= 0) {
      return (float) value;
    }
    // The top bit is set, which means that the float value is going to come from the top 24 bits.
    // So we can ignore the bottom 8, except for rounding. See doubleValue() for more.
    return (float) ((value >>> 1) | (value & 1)) * 2f;
  }

  /**
   * Returns the value of this {@code UnsignedLong} as a {@code double}, analogous to a widening
   * primitive conversion from {@code long} to {@code double}, and correctly rounded.
   */
  @Override
  public double doubleValue() {
    if (value >= 0) {
      return (double) value;
    }
    // The top bit is set, which means that the double value is going to come from the top 53 bits.
    // So we can ignore the bottom 11, except for rounding. We can unsigned-shift right 1, aka
    // unsigned-divide by 2, and convert that. Then we'll get exactly half of the desired double
    // value. But in the specific case where the bottom two bits of the original number are 01, we
    // want to replace that with 1 in the shifted value for correct rounding.
    return (double) ((value >>> 1) | (value & 1)) * 2.0;
  }

  /** Returns the value of this {@code UnsignedLong} as a {@link BigInteger}. */
  public BigInteger bigIntegerValue() {
    BigInteger bigInt = BigInteger.valueOf(value & UNSIGNED_MASK);
    if (value < 0) {
      bigInt = bigInt.setBit(Long.SIZE - 1);
    }
    return bigInt;
  }

  @Override
  public int compareTo(UnsignedLong o) {
    checkNotNull(o);
    return UnsignedLongs.compare(value, o.value);
  }

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

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

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

  /**
   * Returns a string representation of the {@code UnsignedLong} 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 UnsignedLongs.toString(value, radix);
  }
}
