/*
 * Copyright (C) 2009 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.collect;

import java.io.Serializable;
import java.math.BigInteger;
import java.util.NoSuchElementException;

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

/**
 * A descriptor for a <i>discrete</i> {@code Comparable} domain such as all
 * {@link Integer} instances. A discrete domain is one that supports the three
 * basic operations: {@link #next}, {@link #previous} and {@link #distance},
 * according to their specifications. The methods {@link #minValue} and
 * {@link #maxValue} should also be overridden for bounded types.
 *
 * <p>
 * A discrete domain always represents the <i>entire</i> set of values of its
 * type; it cannot represent partial domains such as "prime integers" or
 * "strings of length 5."
 *
 * <p>
 * See the Guava User Guide section on <a href=
 * "http://code.google.com/p/guava-libraries/wiki/RangesExplained#Discrete_Domains">
 * {@code DiscreteDomain}</a>.
 *
 * @author Kevin Bourrillion
 * @since 10.0
 */
@GwtCompatible
@Beta
public abstract class DiscreteDomain<C extends Comparable> {

	/**
	 * Returns the discrete domain for values of type {@code Integer}.
	 * 
	 * @since 14.0 (since 10.0 as {@code DiscreteDomains.integers()})
	 */
	public static DiscreteDomain<Integer> integers() {
		return IntegerDomain.INSTANCE;
	}

	private static final class IntegerDomain extends DiscreteDomain<Integer> implements Serializable {
		private static final IntegerDomain INSTANCE = new IntegerDomain();

		@Override
		public Integer next(Integer value) {
			int i = value;
			return (i == Integer.MAX_VALUE) ? null : i + 1;
		}

		@Override
		public Integer previous(Integer value) {
			int i = value;
			return (i == Integer.MIN_VALUE) ? null : i - 1;
		}

		@Override
		public long distance(Integer start, Integer end) {
			return (long) end - start;
		}

		@Override
		public Integer minValue() {
			return Integer.MIN_VALUE;
		}

		@Override
		public Integer maxValue() {
			return Integer.MAX_VALUE;
		}

		private Object readResolve() {
			return INSTANCE;
		}

		@Override
		public String toString() {
			return "DiscreteDomain.integers()";
		}

		private static final long serialVersionUID = 0;
	}

	/**
	 * Returns the discrete domain for values of type {@code Long}.
	 * 
	 * @since 14.0 (since 10.0 as {@code DiscreteDomains.longs()})
	 */
	public static DiscreteDomain<Long> longs() {
		return LongDomain.INSTANCE;
	}

	private static final class LongDomain extends DiscreteDomain<Long> implements Serializable {
		private static final LongDomain INSTANCE = new LongDomain();

		@Override
		public Long next(Long value) {
			long l = value;
			return (l == Long.MAX_VALUE) ? null : l + 1;
		}

		@Override
		public Long previous(Long value) {
			long l = value;
			return (l == Long.MIN_VALUE) ? null : l - 1;
		}

		@Override
		public long distance(Long start, Long end) {
			long result = end - start;
			if (end > start && result < 0) { // overflow
				return Long.MAX_VALUE;
			}
			if (end < start && result > 0) { // underflow
				return Long.MIN_VALUE;
			}
			return result;
		}

		@Override
		public Long minValue() {
			return Long.MIN_VALUE;
		}

		@Override
		public Long maxValue() {
			return Long.MAX_VALUE;
		}

		private Object readResolve() {
			return INSTANCE;
		}

		@Override
		public String toString() {
			return "DiscreteDomain.longs()";
		}

		private static final long serialVersionUID = 0;
	}

	/**
	 * Returns the discrete domain for values of type {@code BigInteger}.
	 *
	 * @since 15.0
	 */
	public static DiscreteDomain<BigInteger> bigIntegers() {
		return BigIntegerDomain.INSTANCE;
	}

	private static final class BigIntegerDomain extends DiscreteDomain<BigInteger> implements Serializable {
		private static final BigIntegerDomain INSTANCE = new BigIntegerDomain();

		private static final BigInteger MIN_LONG = BigInteger.valueOf(Long.MIN_VALUE);
		private static final BigInteger MAX_LONG = BigInteger.valueOf(Long.MAX_VALUE);

		@Override
		public BigInteger next(BigInteger value) {
			return value.add(BigInteger.ONE);
		}

		@Override
		public BigInteger previous(BigInteger value) {
			return value.subtract(BigInteger.ONE);
		}

		@Override
		public long distance(BigInteger start, BigInteger end) {
			return end.subtract(start).max(MIN_LONG).min(MAX_LONG).longValue();
		}

		private Object readResolve() {
			return INSTANCE;
		}

		@Override
		public String toString() {
			return "DiscreteDomain.bigIntegers()";
		}

		private static final long serialVersionUID = 0;
	}

	/** Constructor for use by subclasses. */
	protected DiscreteDomain() {
	}

	/**
	 * Returns the unique least value of type {@code C} that is greater than
	 * {@code value}, or {@code null} if none exists. Inverse operation to
	 * {@link #previous}.
	 *
	 * @param value any value of type {@code C}
	 * @return the least value greater than {@code value}, or {@code null} if
	 *         {@code value} is {@code maxValue()}
	 */
	public abstract C next(C value);

	/**
	 * Returns the unique greatest value of type {@code C} that is less than
	 * {@code value}, or {@code null} if none exists. Inverse operation to
	 * {@link #next}.
	 *
	 * @param value any value of type {@code C}
	 * @return the greatest value less than {@code value}, or {@code null} if
	 *         {@code value} is {@code minValue()}
	 */
	public abstract C previous(C value);

	/**
	 * Returns a signed value indicating how many nested invocations of
	 * {@link #next} (if positive) or {@link #previous} (if negative) are needed to
	 * reach {@code end} starting from {@code start}. For example, if {@code end =
	 * next(next(next(start)))}, then {@code distance(start, end) == 3} and {@code
	 * distance(end, start) == -3}. As well, {@code distance(a, a)} is always zero.
	 *
	 * <p>
	 * Note that this function is necessarily well-defined for any discrete type.
	 *
	 * @return the distance as described above, or {@link Long#MIN_VALUE} or
	 *         {@link Long#MAX_VALUE} if the distance is too small or too large,
	 *         respectively.
	 */
	public abstract long distance(C start, C end);

	/**
	 * Returns the minimum value of type {@code C}, if it has one. The minimum value
	 * is the unique value for which {@link Comparable#compareTo(Object)} never
	 * returns a positive value for any input of type {@code C}.
	 *
	 * <p>
	 * The default implementation throws {@code NoSuchElementException}.
	 *
	 * @return the minimum value of type {@code C}; never null
	 * @throws NoSuchElementException if the type has no (practical) minimum value;
	 *                                for example, {@link java.math.BigInteger}
	 */
	public C minValue() {
		throw new NoSuchElementException();
	}

	/**
	 * Returns the maximum value of type {@code C}, if it has one. The maximum value
	 * is the unique value for which {@link Comparable#compareTo(Object)} never
	 * returns a negative value for any input of type {@code C}.
	 *
	 * <p>
	 * The default implementation throws {@code NoSuchElementException}.
	 *
	 * @return the maximum value of type {@code C}; never null
	 * @throws NoSuchElementException if the type has no (practical) maximum value;
	 *                                for example, {@link java.math.BigInteger}
	 */
	public C maxValue() {
		throw new NoSuchElementException();
	}

}
