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package java.lang;

import java.util.NoSuchElementException;
import java.util.Objects;
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 {@code CharSequence} is a readable sequence of {@code char} values. This
 * interface provides uniform, read-only access to many different kinds of
 * {@code char} sequences.
 * A {@code char} 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 testing two objects
 * that implement {@code CharSequence} for equality 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 {@code CharSequence} 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}s in the sequence.
 *
 * @return the number of {@code char}s in this sequence
 */
 int length();

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

 /**
 * Returns a {@code CharSequence} that is a subsequence of this sequence.
 * The subsequence starts with the {@code char} value at the specified index and
 * ends with the {@code char} value at index {@code end - 1}. The length
 * (in {@code char}s) of the
 * returned sequence is {@code end - start}, so if {@code start == end}
 * 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 {@code start} or {@code end} are negative,
 * if {@code end} is greater than {@code length()},
 * or if {@code start} is greater than {@code end}
 */
 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.base/java/lang/Character.html#unicode">surrogate code
 * point</a> is passed through uninterpreted.
 *
 * <p>The stream binds to this sequence when the terminal stream operation
 * commences (specifically, for mutable sequences the spliterator for the
 * stream is <a href="../util/Spliterator.html#binding"><em>late-binding</em></a>).
 * If the sequence is modified during that operation then 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>The stream binds to this sequence when the terminal stream operation
 * commences (specifically, for mutable sequences the spliterator for the
 * stream is <a href="../util/Spliterator.html#binding"><em>late-binding</em></a>).
 * If the sequence is modified during that operation then 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);
 }

 /**
 * Compares two {@code CharSequence} instances lexicographically. Returns a
 * negative value, zero, or a positive value if the first sequence is lexicographically
 * less than, equal to, or greater than the second, respectively.
 *
 * <p>
 * The lexicographical ordering of {@code CharSequence} is defined as follows.
 * Consider a {@code CharSequence} <i>cs</i> of length <i>len</i> to be a
 * sequence of char values, <i>cs[0]</i> to <i>cs[len-1]</i>. Suppose <i>k</i>
 * is the lowest index at which the corresponding char values from each sequence
 * differ. The lexicographic ordering of the sequences is determined by a numeric
 * comparison of the char values <i>cs1[k]</i> with <i>cs2[k]</i>. If there is
 * no such index <i>k</i>, the shorter sequence is considered lexicographically
 * less than the other. If the sequences have the same length, the sequences are
 * considered lexicographically equal.
 *
 *
 * @param cs1 the first {@code CharSequence}
 * @param cs2 the second {@code CharSequence}
 *
 * @return the value {@code 0} if the two {@code CharSequence} are equal;
 * a negative integer if the first {@code CharSequence}
 * is lexicographically less than the second; or a
 * positive integer if the first {@code CharSequence} is
 * lexicographically greater than the second.
 *
 * @since 11
 */
 @SuppressWarnings("unchecked")
 public static int compare(CharSequence cs1, CharSequence cs2) {
 if (Objects.requireNonNull(cs1) == Objects.requireNonNull(cs2)) {
 return 0;
 }

 if (cs1.getClass() == cs2.getClass() && cs1 instanceof Comparable) {
 return ((Comparable<Object>) cs1).compareTo(cs2);
 }

 for (int i = 0, len = Math.min(cs1.length(), cs2.length()); i < len; i++) {
 char a = cs1.charAt(i);
 char b = cs2.charAt(i);
 if (a != b) {
 return a - b;
 }
 }

 return cs1.length() - cs2.length();
 }

}