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/*
* Copyright 2010 The Closure Compiler 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.javascript.jscomp;
/**
* Guava code that will eventually be open-sourced properly. Package-private
* until they're able to do that. A lot of these methods are discouraged
* anyways.
*
* @author [email protected] (Nick Santos)
*/
class Strings {
private Strings() {} // All static
/**
* If this given string is of length {@code maxLength} or less, it will
* be returned as-is.
* Otherwise, it will be truncated to {@code maxLength}, regardless of whether
* there are any space characters in the String. If an ellipsis is requested
* to be appended to the truncated String, the String will be truncated so
* that the ellipsis will also fit within maxLength.
* If no truncation was necessary, no ellipsis will be added.
* @param source the String to truncate if necessary
* @param maxLength the maximum number of characters to keep
* @param addEllipsis if true, and if the String had to be truncated,
* add "..." to the end of the String before returning. Additionally,
* the ellipsis will only be added if maxLength is greater than 3.
* @return the original string if it's length is less than or equal to
* maxLength, otherwise a truncated string as mentioned above
*/
static String truncateAtMaxLength(String source, int maxLength,
boolean addEllipsis) {
if (source.length() <= maxLength) {
return source;
}
if (addEllipsis && maxLength > 3) {
return unicodePreservingSubstring(source, 0, maxLength - 3) + "...";
}
return unicodePreservingSubstring(source, 0, maxLength);
}
/**
* Normalizes {@code index} such that it respects Unicode character
* boundaries in {@code str}.
*
* If {@code index} is the low surrogate of a Unicode character,
* the method returns {@code index - 1}. Otherwise, {@code index} is
* returned.
*
*
In the case in which {@code index} falls in an invalid surrogate pair
* (e.g. consecutive low surrogates, consecutive high surrogates), or if
* if it is not a valid index into {@code str}, the original value of
* {@code index} is returned.
*
* @param str the String
* @param index the index to be normalized
* @return a normalized index that does not split a Unicode character
*/
private static int unicodePreservingIndex(String str, int index) {
if (index > 0 && index < str.length()) {
if (Character.isHighSurrogate(str.charAt(index - 1)) &&
Character.isLowSurrogate(str.charAt(index))) {
return index - 1;
}
}
return index;
}
/**
* Returns a substring of {@code str} that respects Unicode character
* boundaries.
*
*
The string will never be split between a [high, low] surrogate pair,
* as defined by {@link Character#isHighSurrogate} and
* {@link Character#isLowSurrogate}.
*
*
If {@code begin} or {@code end} are the low surrogate of a Unicode
* character, it will be offset by -1.
*
*
This behavior guarantees that
* {@code str.equals(StringUtil.unicodePreservingSubstring(str, 0, n) +
* StringUtil.unicodePreservingSubstring(str, n, str.length())) } is
* true for all {@code n}.
*
This means that unlike {@link String#substring(int, int)}, the length of
* the returned substring may not necessarily be equivalent to
* {@code end - begin}.
*
* @param str the original String
* @param begin the beginning index, inclusive
* @param end the ending index, exclusive
* @return the specified substring, possibly adjusted in order to not
* split Unicode surrogate pairs
* @throws IndexOutOfBoundsException if the {@code begin} is negative,
* or {@code end} is larger than the length of {@code str}, or
* {@code begin} is larger than {@code end}
*/
private static String unicodePreservingSubstring(
String str, int begin, int end) {
return str.substring(unicodePreservingIndex(str, begin),
unicodePreservingIndex(str, end));
}
}