/*
 * Copyright (C) 2008 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.checkElementIndex;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkPositionIndexes;

import java.io.Serializable;
import java.util.AbstractList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.RandomAccess;

import javax.annotation.CheckForNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Converter;

/**
 * Static utility methods pertaining to {@code int} primitives, that are not
 * already found in either {@link Integer} or {@link Arrays}.
 *
 * <p>
 * See the Guava User Guide article on
 * <a href= "http://code.google.com/p/guava-libraries/wiki/PrimitivesExplained">
 * primitive utilities</a>.
 *
 * @author Kevin Bourrillion
 * @since 1.0
 */
@GwtCompatible(emulated = true)
public final class Ints {
	private Ints() {
	}

	/**
	 * The number of bytes required to represent a primitive {@code int} value.
	 */
	public static final int BYTES = Integer.SIZE / Byte.SIZE;

	/**
	 * The largest power of two that can be represented as an {@code int}.
	 *
	 * @since 10.0
	 */
	public static final int MAX_POWER_OF_TWO = 1 << (Integer.SIZE - 2);

	/**
	 * Returns a hash code for {@code value}; equal to the result of invoking
	 * {@code ((Integer) value).hashCode()}.
	 *
	 * @param value a primitive {@code int} value
	 * @return a hash code for the value
	 */
	public static int hashCode(int value) {
		return value;
	}

	/**
	 * Returns the {@code int} value that is equal to {@code value}, if possible.
	 *
	 * @param value any value in the range of the {@code int} type
	 * @return the {@code int} value that equals {@code value}
	 * @throws IllegalArgumentException if {@code value} is greater than
	 *                                  {@link Integer#MAX_VALUE} or less than
	 *                                  {@link Integer#MIN_VALUE}
	 */
	public static int checkedCast(long value) {
		int result = (int) value;
		if (result != value) {
			// don't use checkArgument here, to avoid boxing
			throw new IllegalArgumentException("Out of range: " + value);
		}
		return result;
	}

	/**
	 * Returns the {@code int} nearest in value to {@code value}.
	 *
	 * @param value any {@code long} value
	 * @return the same value cast to {@code int} if it is in the range of the
	 *         {@code int} type, {@link Integer#MAX_VALUE} if it is too large, or
	 *         {@link Integer#MIN_VALUE} if it is too small
	 */
	public static int saturatedCast(long value) {
		if (value > Integer.MAX_VALUE) {
			return Integer.MAX_VALUE;
		}
		if (value < Integer.MIN_VALUE) {
			return Integer.MIN_VALUE;
		}
		return (int) value;
	}

	/**
	 * Compares the two specified {@code int} values. The sign of the value returned
	 * is the same as that of {@code ((Integer) a).compareTo(b)}.
	 *
	 * <p>
	 * <b>Note:</b> projects using JDK 7 or later should use the equivalent
	 * {@link Integer#compare} method instead.
	 *
	 * @param a the first {@code int} to compare
	 * @param b the second {@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 (a < b) ? -1 : ((a > b) ? 1 : 0);
	}

	/**
	 * Returns {@code true} if {@code target} is present as an element anywhere in
	 * {@code array}.
	 *
	 * @param array  an array of {@code int} values, possibly empty
	 * @param target a primitive {@code int} value
	 * @return {@code true} if {@code array[i] == target} for some value of {@code
	 *     i}
	 */
	public static boolean contains(int[] array, int target) {
		for (int value : array) {
			if (value == target) {
				return true;
			}
		}
		return false;
	}

	/**
	 * Returns the index of the first appearance of the value {@code target} in
	 * {@code array}.
	 *
	 * @param array  an array of {@code int} values, possibly empty
	 * @param target a primitive {@code int} value
	 * @return the least index {@code i} for which {@code array[i] == target}, or
	 *         {@code -1} if no such index exists.
	 */
	public static int indexOf(int[] array, int target) {
		return indexOf(array, target, 0, array.length);
	}

	// TODO(kevinb): consider making this public
	private static int indexOf(int[] array, int target, int start, int end) {
		for (int i = start; i < end; i++) {
			if (array[i] == target) {
				return i;
			}
		}
		return -1;
	}

	/**
	 * Returns the start position of the first occurrence of the specified {@code
	 * target} within {@code array}, or {@code -1} if there is no such occurrence.
	 *
	 * <p>
	 * More formally, returns the lowest index {@code i} such that {@code
	 * java.util.Arrays.copyOfRange(array, i, i + target.length)} contains exactly
	 * the same elements as {@code target}.
	 *
	 * @param array  the array to search for the sequence {@code target}
	 * @param target the array to search for as a sub-sequence of {@code array}
	 */
	public static int indexOf(int[] array, int[] target) {
		checkNotNull(array, "array");
		checkNotNull(target, "target");
		if (target.length == 0) {
			return 0;
		}

		outer: for (int i = 0; i < array.length - target.length + 1; i++) {
			for (int j = 0; j < target.length; j++) {
				if (array[i + j] != target[j]) {
					continue outer;
				}
			}
			return i;
		}
		return -1;
	}

	/**
	 * Returns the index of the last appearance of the value {@code target} in
	 * {@code array}.
	 *
	 * @param array  an array of {@code int} values, possibly empty
	 * @param target a primitive {@code int} value
	 * @return the greatest index {@code i} for which {@code array[i] == target}, or
	 *         {@code -1} if no such index exists.
	 */
	public static int lastIndexOf(int[] array, int target) {
		return lastIndexOf(array, target, 0, array.length);
	}

	// TODO(kevinb): consider making this public
	private static int lastIndexOf(int[] array, int target, int start, int end) {
		for (int i = end - 1; i >= start; i--) {
			if (array[i] == target) {
				return i;
			}
		}
		return -1;
	}

	/**
	 * Returns the least value present in {@code array}.
	 *
	 * @param array a <i>nonempty</i> array of {@code int} values
	 * @return the value present in {@code array} that is less than or equal to
	 *         every other value in the array
	 * @throws IllegalArgumentException if {@code array} is empty
	 */
	public static int min(int... array) {
		checkArgument(array.length > 0);
		int min = array[0];
		for (int i = 1; i < array.length; i++) {
			if (array[i] < min) {
				min = array[i];
			}
		}
		return min;
	}

	/**
	 * Returns the greatest value present in {@code array}.
	 *
	 * @param array a <i>nonempty</i> array of {@code int} values
	 * @return the value present in {@code array} that is greater than or equal to
	 *         every other value in the array
	 * @throws IllegalArgumentException if {@code array} is empty
	 */
	public static int max(int... array) {
		checkArgument(array.length > 0);
		int max = array[0];
		for (int i = 1; i < array.length; i++) {
			if (array[i] > max) {
				max = array[i];
			}
		}
		return max;
	}

	/**
	 * Returns the values from each provided array combined into a single array. For
	 * example, {@code concat(new int[] {a, b}, new int[] {}, new int[] {c}} returns
	 * the array {@code {a, b, c}}.
	 *
	 * @param arrays zero or more {@code int} arrays
	 * @return a single array containing all the values from the source arrays, in
	 *         order
	 */
	public static int[] concat(int[]... arrays) {
		int length = 0;
		for (int[] array : arrays) {
			length += array.length;
		}
		int[] result = new int[length];
		int pos = 0;
		for (int[] array : arrays) {
			System.arraycopy(array, 0, result, pos, array.length);
			pos += array.length;
		}
		return result;
	}

	/**
	 * Returns a big-endian representation of {@code value} in a 4-element byte
	 * array; equivalent to {@code ByteBuffer.allocate(4).putInt(value).array()}.
	 * For example, the input value {@code 0x12131415} would yield the byte array
	 * {@code {0x12, 0x13, 0x14, 0x15}}.
	 *
	 * <p>
	 * If you need to convert and concatenate several values (possibly even of
	 * different types), use a shared {@link java.nio.ByteBuffer} instance, or use
	 * {@link com.google.common.io.ByteStreams#newDataOutput()} to get a growable
	 * buffer.
	 */
	@GwtIncompatible("doesn't work")
	public static byte[] toByteArray(int value) {
		return new byte[] { (byte) (value >> 24), (byte) (value >> 16), (byte) (value >> 8), (byte) value };
	}

	/**
	 * Returns the {@code int} value whose big-endian representation is stored in
	 * the first 4 bytes of {@code bytes}; equivalent to {@code
	 * ByteBuffer.wrap(bytes).getInt()}. For example, the input byte array
	 * {@code {0x12, 0x13, 0x14, 0x15, 0x33}} would yield the {@code int} value
	 * {@code
	 * 0x12131415}.
	 *
	 * <p>
	 * Arguably, it's preferable to use {@link java.nio.ByteBuffer}; that library
	 * exposes much more flexibility at little cost in readability.
	 *
	 * @throws IllegalArgumentException if {@code bytes} has fewer than 4 elements
	 */
	@GwtIncompatible("doesn't work")
	public static int fromByteArray(byte[] bytes) {
		checkArgument(bytes.length >= BYTES, "array too small: %s < %s", bytes.length, BYTES);
		return fromBytes(bytes[0], bytes[1], bytes[2], bytes[3]);
	}

	/**
	 * Returns the {@code int} value whose byte representation is the given 4 bytes,
	 * in big-endian order; equivalent to {@code Ints.fromByteArray(new byte[] {b1,
	 * b2, b3, b4})}.
	 *
	 * @since 7.0
	 */
	@GwtIncompatible("doesn't work")
	public static int fromBytes(byte b1, byte b2, byte b3, byte b4) {
		return b1 << 24 | (b2 & 0xFF) << 16 | (b3 & 0xFF) << 8 | (b4 & 0xFF);
	}

	private static final class IntConverter extends Converter<String, Integer> implements Serializable {
		static final IntConverter INSTANCE = new IntConverter();

		@Override
		protected Integer doForward(String value) {
			return Integer.decode(value);
		}

		@Override
		protected String doBackward(Integer value) {
			return value.toString();
		}

		@Override
		public String toString() {
			return "Ints.stringConverter()";
		}

		private Object readResolve() {
			return INSTANCE;
		}

		private static final long serialVersionUID = 1;
	}

	/**
	 * Returns a serializable converter object that converts between strings and
	 * integers using {@link Integer#decode} and {@link Integer#toString()}.
	 *
	 * @since 16.0
	 */
	@Beta
	public static Converter<String, Integer> stringConverter() {
		return IntConverter.INSTANCE;
	}

	/**
	 * Returns an array containing the same values as {@code array}, but guaranteed
	 * to be of a specified minimum length. If {@code array} already has a length of
	 * at least {@code minLength}, it is returned directly. Otherwise, a new array
	 * of size {@code minLength + padding} is returned, containing the values of
	 * {@code array}, and zeroes in the remaining places.
	 *
	 * @param array     the source array
	 * @param minLength the minimum length the returned array must guarantee
	 * @param padding   an extra amount to "grow" the array by if growth is
	 *                  necessary
	 * @throws IllegalArgumentException if {@code minLength} or {@code padding} is
	 *                                  negative
	 * @return an array containing the values of {@code array}, with guaranteed
	 *         minimum length {@code minLength}
	 */
	public static int[] ensureCapacity(int[] array, int minLength, int padding) {
		checkArgument(minLength >= 0, "Invalid minLength: %s", minLength);
		checkArgument(padding >= 0, "Invalid padding: %s", padding);
		return (array.length < minLength) ? copyOf(array, minLength + padding) : array;
	}

	// Arrays.copyOf() requires Java 6
	private static int[] copyOf(int[] original, int length) {
		int[] copy = new int[length];
		System.arraycopy(original, 0, copy, 0, Math.min(original.length, length));
		return copy;
	}

	/**
	 * Returns a string containing the supplied {@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 {@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(array[0]);
		for (int i = 1; i < array.length; i++) {
			builder.append(separator).append(array[i]);
		}
		return builder.toString();
	}

	/**
	 * Returns a comparator that compares two {@code int} arrays 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]}.
	 *
	 * <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>
	 * @since 2.0
	 */
	public static Comparator<int[]> lexicographicalComparator() {
		return LexicographicalComparator.INSTANCE;
	}

	private 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++) {
				int result = Ints.compare(left[i], right[i]);
				if (result != 0) {
					return result;
				}
			}
			return left.length - right.length;
		}
	}

	/**
	 * Returns an array containing each value of {@code collection}, converted to a
	 * {@code int} value in the manner of {@link Number#intValue}.
	 *
	 * <p>
	 * Elements are copied from the argument collection as if by {@code
	 * collection.toArray()}. Calling this method is as thread-safe as calling that
	 * method.
	 *
	 * @param collection a collection of {@code Number} instances
	 * @return an array containing the same values as {@code collection}, in the
	 *         same order, converted to primitives
	 * @throws NullPointerException if {@code collection} or any of its elements is
	 *                              null
	 * @since 1.0 (parameter was {@code Collection<Integer>} before 12.0)
	 */
	public static int[] toArray(Collection<? extends Number> collection) {
		if (collection instanceof IntArrayAsList) {
			return ((IntArrayAsList) collection).toIntArray();
		}

		Object[] boxedArray = collection.toArray();
		int len = boxedArray.length;
		int[] array = new int[len];
		for (int i = 0; i < len; i++) {
			// checkNotNull for GWT (do not optimize)
			array[i] = ((Number) checkNotNull(boxedArray[i])).intValue();
		}
		return array;
	}

	/**
	 * Returns a fixed-size list backed by the specified array, similar to
	 * {@link Arrays#asList(Object[])}. The list supports
	 * {@link List#set(int, Object)}, but any attempt to set a value to {@code null}
	 * will result in a {@link NullPointerException}.
	 *
	 * <p>
	 * The returned list maintains the values, but not the identities, of
	 * {@code Integer} objects written to or read from it. For example, whether
	 * {@code list.get(0) == list.get(0)} is true for the returned list is
	 * unspecified.
	 *
	 * @param backingArray the array to back the list
	 * @return a list view of the array
	 */
	public static List<Integer> asList(int... backingArray) {
		if (backingArray.length == 0) {
			return Collections.emptyList();
		}
		return new IntArrayAsList(backingArray);
	}

	@GwtCompatible
	private static class IntArrayAsList extends AbstractList<Integer> implements RandomAccess, Serializable {
		final int[] array;
		final int start;
		final int end;

		IntArrayAsList(int[] array) {
			this(array, 0, array.length);
		}

		IntArrayAsList(int[] array, int start, int end) {
			this.array = array;
			this.start = start;
			this.end = end;
		}

		@Override
		public int size() {
			return end - start;
		}

		@Override
		public boolean isEmpty() {
			return false;
		}

		@Override
		public Integer get(int index) {
			checkElementIndex(index, size());
			return array[start + index];
		}

		@Override
		public boolean contains(Object target) {
			// Overridden to prevent a ton of boxing
			return (target instanceof Integer) && Ints.indexOf(array, (Integer) target, start, end) != -1;
		}

		@Override
		public int indexOf(Object target) {
			// Overridden to prevent a ton of boxing
			if (target instanceof Integer) {
				int i = Ints.indexOf(array, (Integer) target, start, end);
				if (i >= 0) {
					return i - start;
				}
			}
			return -1;
		}

		@Override
		public int lastIndexOf(Object target) {
			// Overridden to prevent a ton of boxing
			if (target instanceof Integer) {
				int i = Ints.lastIndexOf(array, (Integer) target, start, end);
				if (i >= 0) {
					return i - start;
				}
			}
			return -1;
		}

		@Override
		public Integer set(int index, Integer element) {
			checkElementIndex(index, size());
			int oldValue = array[start + index];
			// checkNotNull for GWT (do not optimize)
			array[start + index] = checkNotNull(element);
			return oldValue;
		}

		@Override
		public List<Integer> subList(int fromIndex, int toIndex) {
			int size = size();
			checkPositionIndexes(fromIndex, toIndex, size);
			if (fromIndex == toIndex) {
				return Collections.emptyList();
			}
			return new IntArrayAsList(array, start + fromIndex, start + toIndex);
		}

		@Override
		public boolean equals(Object object) {
			if (object == this) {
				return true;
			}
			if (object instanceof IntArrayAsList) {
				IntArrayAsList that = (IntArrayAsList) object;
				int size = size();
				if (that.size() != size) {
					return false;
				}
				for (int i = 0; i < size; i++) {
					if (array[start + i] != that.array[that.start + i]) {
						return false;
					}
				}
				return true;
			}
			return super.equals(object);
		}

		@Override
		public int hashCode() {
			int result = 1;
			for (int i = start; i < end; i++) {
				result = 31 * result + Ints.hashCode(array[i]);
			}
			return result;
		}

		@Override
		public String toString() {
			StringBuilder builder = new StringBuilder(size() * 5);
			builder.append('[').append(array[start]);
			for (int i = start + 1; i < end; i++) {
				builder.append(", ").append(array[i]);
			}
			return builder.append(']').toString();
		}

		int[] toIntArray() {
			// Arrays.copyOfRange() is not available under GWT
			int size = size();
			int[] result = new int[size];
			System.arraycopy(array, start, result, 0, size);
			return result;
		}

		private static final long serialVersionUID = 0;
	}

	private static final byte[] asciiDigits = new byte[128];

	static {
		Arrays.fill(asciiDigits, (byte) -1);
		for (int i = 0; i <= 9; i++) {
			asciiDigits['0' + i] = (byte) i;
		}
		for (int i = 0; i <= 26; i++) {
			asciiDigits['A' + i] = (byte) (10 + i);
			asciiDigits['a' + i] = (byte) (10 + i);
		}
	}

	private static int digit(char c) {
		return (c < 128) ? asciiDigits[c] : -1;
	}

	/**
	 * Parses the specified string as a signed decimal integer value. The ASCII
	 * character {@code '-'} (<code>'&#92;u002D'</code>) is recognized as the minus
	 * sign.
	 *
	 * <p>
	 * Unlike {@link Integer#parseInt(String)}, this method returns {@code null}
	 * instead of throwing an exception if parsing fails. Additionally, this method
	 * only accepts ASCII digits, and returns {@code null} if non-ASCII digits are
	 * present in the string.
	 *
	 * <p>
	 * Note that strings prefixed with ASCII {@code '+'} are rejected, even under
	 * JDK 7, despite the change to {@link Integer#parseInt(String)} for that
	 * version.
	 *
	 * @param string the string representation of an integer value
	 * @return the integer value represented by {@code string}, or {@code null} if
	 *         {@code string} has a length of zero or cannot be parsed as an integer
	 *         value
	 * @since 11.0
	 */
	@Beta
	@CheckForNull
	@GwtIncompatible("TODO")
	public static Integer tryParse(String string) {
		return tryParse(string, 10);
	}

	/**
	 * Parses the specified string as a signed integer value using the specified
	 * radix. The ASCII character {@code '-'} (<code>'&#92;u002D'</code>) is
	 * recognized as the minus sign.
	 *
	 * <p>
	 * Unlike {@link Integer#parseInt(String, int)}, this method returns
	 * {@code null} instead of throwing an exception if parsing fails. Additionally,
	 * this method only accepts ASCII digits, and returns {@code null} if non-ASCII
	 * digits are present in the string.
	 *
	 * <p>
	 * Note that strings prefixed with ASCII {@code '+'} are rejected, even under
	 * JDK 7, despite the change to {@link Integer#parseInt(String, int)} for that
	 * version.
	 *
	 * @param string the string representation of an integer value
	 * @param radix  the radix to use when parsing
	 * @return the integer value represented by {@code string} using {@code radix},
	 *         or {@code null} if {@code string} has a length of zero or cannot be
	 *         parsed as an integer value
	 * @throws IllegalArgumentException if {@code radix < Character.MIN_RADIX} or
	 *                                  {@code radix > Character.MAX_RADIX}
	 */
	@CheckForNull
	@GwtIncompatible("TODO")
	static Integer tryParse(String string, int radix) {
		if (checkNotNull(string).isEmpty()) {
			return null;
		}
		if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX) {
			throw new IllegalArgumentException("radix must be between MIN_RADIX and MAX_RADIX but was " + radix);
		}
		boolean negative = string.charAt(0) == '-';
		int index = negative ? 1 : 0;
		if (index == string.length()) {
			return null;
		}
		int digit = digit(string.charAt(index++));
		if (digit < 0 || digit >= radix) {
			return null;
		}
		int accum = -digit;

		int cap = Integer.MIN_VALUE / radix;

		while (index < string.length()) {
			digit = digit(string.charAt(index++));
			if (digit < 0 || digit >= radix || accum < cap) {
				return null;
			}
			accum *= radix;
			if (accum < Integer.MIN_VALUE + digit) {
				return null;
			}
			accum -= digit;
		}

		if (negative) {
			return accum;
		} else if (accum == Integer.MIN_VALUE) {
			return null;
		} else {
			return -accum;
		}
	}
}
