/*
 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package java.lang;

import java.util.NoSuchElementException;
import java.util.PrimitiveIterator;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.IntConsumer;
import java.util.stream.IntStream;
import java.util.stream.StreamSupport;

/**
 * A <tt>CharSequence</tt> is a readable sequence of <code>char</code> values. This
 * interface provides uniform, read-only access to many different kinds of
 * <code>char</code> sequences.
 * A <code>char</code> value represents a character in the <i>Basic
 * Multilingual Plane (BMP)</i> or a surrogate. Refer to <a
 * href="Character.html#unicode">Unicode Character Representation</a> for details.
 *
 * <p> This interface does not refine the general contracts of the {@link
 * java.lang.Object#equals(java.lang.Object) equals} and {@link
 * java.lang.Object#hashCode() hashCode} methods. The result of comparing two
 * objects that implement <tt>CharSequence</tt> is therefore, in general,
 * undefined. Each object may be implemented by a different class, and there
 * is no guarantee that each class will be capable of testing its instances
 * for equality with those of the other. It is therefore inappropriate to use
 * arbitrary <tt>CharSequence</tt> instances as elements in a set or as keys in
 * a map. </p>
 *
 * @author Mike McCloskey
 * @since 1.4
 * @spec JSR-51
 */

public interface CharSequence {

 /**
 * Returns the length of this character sequence. The length is the number
 * of 16-bit <code>char</code>s in the sequence.
 *
 * @return the number of <code>char</code>s in this sequence
 */
 int length();

 /**
 * Returns the <code>char</code> value at the specified index. An index ranges from zero
 * to <tt>length() - 1</tt>. The first <code>char</code> value of the sequence is at
 * index zero, the next at index one, and so on, as for array
 * indexing.
 *
 * <p>If the <code>char</code> value specified by the index is a
 * <a href="{@docRoot}/java/lang/Character.html#unicode">surrogate</a>, the surrogate
 * value is returned.
 *
 * @param index the index of the <code>char</code> value to be returned
 *
 * @return the specified <code>char</code> value
 *
 * @throws IndexOutOfBoundsException
 * if the <tt>index</tt> argument is negative or not less than
 * <tt>length()</tt>
 */
 char charAt(int index);

 /**
 * Returns a <code>CharSequence</code> that is a subsequence of this sequence.
 * The subsequence starts with the <code>char</code> value at the specified index and
 * ends with the <code>char</code> value at index <tt>end - 1</tt>. The length
 * (in <code>char</code>s) of the
 * returned sequence is <tt>end - start</tt>, so if <tt>start == end</tt>
 * then an empty sequence is returned.
 *
 * @param start the start index, inclusive
 * @param end the end index, exclusive
 *
 * @return the specified subsequence
 *
 * @throws IndexOutOfBoundsException
 * if <tt>start</tt> or <tt>end</tt> are negative,
 * if <tt>end</tt> is greater than <tt>length()</tt>,
 * or if <tt>start</tt> is greater than <tt>end</tt>
 */
 CharSequence subSequence(int start, int end);

 /**
 * Returns a string containing the characters in this sequence in the same
 * order as this sequence. The length of the string will be the length of
 * this sequence.
 *
 * @return a string consisting of exactly this sequence of characters
 */
 public String toString();

 /**
 * Returns a stream of {@code int} zero-extending the {@code char} values
 * from this sequence. Any char which maps to a <a
 * href="{@docRoot}/java/lang/Character.html#unicode">surrogate code
 * point</a> is passed through uninterpreted.
 *
 * <p>If the sequence is mutated while the stream is being read, the
 * result is undefined.
 *
 * @return an IntStream of char values from this sequence
 * @since 1.8
 */
 public default IntStream chars() {
 class CharIterator implements PrimitiveIterator.OfInt {
 int cur = 0;

 public boolean hasNext() {
 return cur < length();
 }

 public int nextInt() {
 if (hasNext()) {
 return charAt(cur++);
 } else {
 throw new NoSuchElementException();
 }
 }

 @Override
 public void forEachRemaining(IntConsumer block) {
 for (; cur < length(); cur++) {
 block.accept(charAt(cur));
 }
 }
 }

 return StreamSupport.intStream(() ->
 Spliterators.spliterator(
 new CharIterator(),
 length(),
 Spliterator.ORDERED),
 Spliterator.SUBSIZED | Spliterator.SIZED | Spliterator.ORDERED,
 false);
 }

 /**
 * Returns a stream of code point values from this sequence. Any surrogate
 * pairs encountered in the sequence are combined as if by {@linkplain
 * Character#toCodePoint Character.toCodePoint} and the result is passed
 * to the stream. Any other code units, including ordinary BMP characters,
 * unpaired surrogates, and undefined code units, are zero-extended to
 * {@code int} values which are then passed to the stream.
 *
 * <p>If the sequence is mutated while the stream is being read, the result
 * is undefined.
 *
 * @return an IntStream of Unicode code points from this sequence
 * @since 1.8
 */
 public default IntStream codePoints() {
 class CodePointIterator implements PrimitiveIterator.OfInt {
 int cur = 0;

 @Override
 public void forEachRemaining(IntConsumer block) {
 final int length = length();
 int i = cur;
 try {
 while (i < length) {
 char c1 = charAt(i++);
 if (!Character.isHighSurrogate(c1) || i >= length) {
 block.accept(c1);
 } else {
 char c2 = charAt(i);
 if (Character.isLowSurrogate(c2)) {
 i++;
 block.accept(Character.toCodePoint(c1, c2));
 } else {
 block.accept(c1);
 }
 }
 }
 } finally {
 cur = i;
 }
 }

 public boolean hasNext() {
 return cur < length();
 }

 public int nextInt() {
 final int length = length();

 if (cur >= length) {
 throw new NoSuchElementException();
 }
 char c1 = charAt(cur++);
 if (Character.isHighSurrogate(c1) && cur < length) {
 char c2 = charAt(cur);
 if (Character.isLowSurrogate(c2)) {
 cur++;
 return Character.toCodePoint(c1, c2);
 }
 }
 return c1;
 }
 }

 return StreamSupport.intStream(() ->
 Spliterators.spliteratorUnknownSize(
 new CodePointIterator(),
 Spliterator.ORDERED),
 Spliterator.ORDERED,
 false);
 }
}