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

/**
 * {@code StringJoiner} is used to construct a sequence of characters separated
 * by a delimiter and optionally starting with a supplied prefix
 * and ending with a supplied suffix.
 * <p>
 * Prior to adding something to the {@code StringJoiner}, its
 * {@code sj.toString()} method will, by default, return {@code prefix + suffix}.
 * However, if the {@code setEmptyValue} method is called, the {@code emptyValue}
 * supplied will be returned instead. This can be used, for example, when
 * creating a string using set notation to indicate an empty set, i.e.
 * <code>"{}"</code>, where the {@code prefix} is <code>"{"</code>, the
 * {@code suffix} is <code>"}"</code> and nothing has been added to the
 * {@code StringJoiner}.
 *
 * @apiNote
 * <p>The String {@code "[George:Sally:Fred]"} may be constructed as follows:
 *
 * <pre> {@code
 * StringJoiner sj = new StringJoiner(":", "[", "]");
 * sj.add("George").add("Sally").add("Fred");
 * String desiredString = sj.toString();
 * }</pre>
 * <p>
 * A {@code StringJoiner} may be employed to create formatted output from a
 * {@link java.util.stream.Stream} using
 * {@link java.util.stream.Collectors#joining(CharSequence)}. For example:
 *
 * <pre> {@code
 * List<Integer> numbers = Arrays.asList(1, 2, 3, 4);
 * String commaSeparatedNumbers = numbers.stream()
 * .map(i -> i.toString())
 * .collect(Collectors.joining(", "));
 * }</pre>
 *
 * @see java.util.stream.Collectors#joining(CharSequence)
 * @see java.util.stream.Collectors#joining(CharSequence, CharSequence, CharSequence)
 * @since 1.8
*/
public final class StringJoiner {
 private final String prefix;
 private final String delimiter;
 private final String suffix;

 /*
 * StringBuilder value -- at any time, the characters constructed from the
 * prefix, the added element separated by the delimiter, but without the
 * suffix, so that we can more easily add elements without having to jigger
 * the suffix each time.
 */
 private StringBuilder value;

 /*
 * By default, the string consisting of prefix+suffix, returned by
 * toString(), or properties of value, when no elements have yet been added,
 * i.e. when it is empty. This may be overridden by the user to be some
 * other value including the empty String.
 */
 private String emptyValue;

 /**
 * Constructs a {@code StringJoiner} with no characters in it, with no
 * {@code prefix} or {@code suffix}, and a copy of the supplied
 * {@code delimiter}.
 * If no characters are added to the {@code StringJoiner} and methods
 * accessing the value of it are invoked, it will not return a
 * {@code prefix} or {@code suffix} (or properties thereof) in the result,
 * unless {@code setEmptyValue} has first been called.
 *
 * @param delimiter the sequence of characters to be used between each
 * element added to the {@code StringJoiner} value
 * @throws NullPointerException if {@code delimiter} is {@code null}
 */
 public StringJoiner(CharSequence delimiter) {
 this(delimiter, "", "");
 }

 /**
 * Constructs a {@code StringJoiner} with no characters in it using copies
 * of the supplied {@code prefix}, {@code delimiter} and {@code suffix}.
 * If no characters are added to the {@code StringJoiner} and methods
 * accessing the string value of it are invoked, it will return the
 * {@code prefix + suffix} (or properties thereof) in the result, unless
 * {@code setEmptyValue} has first been called.
 *
 * @param delimiter the sequence of characters to be used between each
 * element added to the {@code StringJoiner}
 * @param prefix the sequence of characters to be used at the beginning
 * @param suffix the sequence of characters to be used at the end
 * @throws NullPointerException if {@code prefix}, {@code delimiter}, or
 * {@code suffix} is {@code null}
 */
 public StringJoiner(CharSequence delimiter,
 CharSequence prefix,
 CharSequence suffix) {
 Objects.requireNonNull(prefix, "The prefix must not be null");
 Objects.requireNonNull(delimiter, "The delimiter must not be null");
 Objects.requireNonNull(suffix, "The suffix must not be null");
 // make defensive copies of arguments
 this.prefix = prefix.toString();
 this.delimiter = delimiter.toString();
 this.suffix = suffix.toString();
 this.emptyValue = this.prefix + this.suffix;
 }

 /**
 * Sets the sequence of characters to be used when determining the string
 * representation of this {@code StringJoiner} and no elements have been
 * added yet, that is, when it is empty. A copy of the {@code emptyValue}
 * parameter is made for this purpose. Note that once an add method has been
 * called, the {@code StringJoiner} is no longer considered empty, even if
 * the element(s) added correspond to the empty {@code String}.
 *
 * @param emptyValue the characters to return as the value of an empty
 * {@code StringJoiner}
 * @return this {@code StringJoiner} itself so the calls may be chained
 * @throws NullPointerException when the {@code emptyValue} parameter is
 * {@code null}
 */
 public StringJoiner setEmptyValue(CharSequence emptyValue) {
 this.emptyValue = Objects.requireNonNull(emptyValue,
 "The empty value must not be null").toString();
 return this;
 }

 /**
 * Returns the current value, consisting of the {@code prefix}, the values
 * added so far separated by the {@code delimiter}, and the {@code suffix},
 * unless no elements have been added in which case, the
 * {@code prefix + suffix} or the {@code emptyValue} characters are returned
 *
 * @return the string representation of this {@code StringJoiner}
 */
 @Override
 public String toString() {
 if (value == null) {
 return emptyValue;
 } else {
 if (suffix.equals("")) {
 return value.toString();
 } else {
 int initialLength = value.length();
 String result = value.append(suffix).toString();
 // reset value to pre-append initialLength
 value.setLength(initialLength);
 return result;
 }
 }
 }

 /**
 * Adds a copy of the given {@code CharSequence} value as the next
 * element of the {@code StringJoiner} value. If {@code newElement} is
 * {@code null}, then {@code "null"} is added.
 *
 * @param newElement The element to add
 * @return a reference to this {@code StringJoiner}
 */
 public StringJoiner add(CharSequence newElement) {
 prepareBuilder().append(newElement);
 return this;
 }

 /**
 * Adds the contents of the given {@code StringJoiner} without prefix and
 * suffix as the next element if it is non-empty. If the given {@code
 * StringJoiner} is empty, the call has no effect.
 *
 * <p>A {@code StringJoiner} is empty if {@link #add(CharSequence) add()}
 * has never been called, and if {@code merge()} has never been called
 * with a non-empty {@code StringJoiner} argument.
 *
 * <p>If the other {@code StringJoiner} is using a different delimiter,
 * then elements from the other {@code StringJoiner} are concatenated with
 * that delimiter and the result is appended to this {@code StringJoiner}
 * as a single element.
 *
 * @param other The {@code StringJoiner} whose contents should be merged
 * into this one
 * @throws NullPointerException if the other {@code StringJoiner} is null
 * @return This {@code StringJoiner}
 */
 public StringJoiner merge(StringJoiner other) {
 Objects.requireNonNull(other);
 if (other.value != null) {
 final int length = other.value.length();
 // lock the length so that we can seize the data to be appended
 // before initiate copying to avoid interference, especially when
 // merge 'this'
 StringBuilder builder = prepareBuilder();
 builder.append(other.value, other.prefix.length(), length);
 }
 return this;
 }

 private StringBuilder prepareBuilder() {
 if (value != null) {
 value.append(delimiter);
 } else {
 value = new StringBuilder().append(prefix);
 }
 return value;
 }

 /**
 * Returns the length of the {@code String} representation
 * of this {@code StringJoiner}. Note that if
 * no add methods have been called, then the length of the {@code String}
 * representation (either {@code prefix + suffix} or {@code emptyValue})
 * will be returned. The value should be equivalent to
 * {@code toString().length()}.
 *
 * @return the length of the current value of {@code StringJoiner}
 */
 public int length() {
 // Remember that we never actually append the suffix unless we return
 // the full (present) value or some sub-string or length of it, so that
 // we can add on more if we need to.
 return (value != null ? value.length() + suffix.length() :
 emptyValue.length());
 }
}