86 lines
3.2 KiB
Scala
86 lines
3.2 KiB
Scala
package com.twitter.tweetypie.tweettext
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/**
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* An efficient converter of indices between code points and code units.
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*/
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class IndexConverter(text: String) {
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// Keep track of a single corresponding pair of code unit and code point
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// offsets so that we can re-use counting work if the next requested
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// entity is near the most recent entity.
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private var codePointIndex = 0
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// The code unit index should never split a surrogate pair.
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private var charIndex = 0
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/**
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* @param offset Index into the string measured in code units.
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* @return The code point index that corresponds to the specified character index.
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*/
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def toCodePoints(offset: Offset.CodeUnit): Offset.CodePoint =
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Offset.CodePoint(codeUnitsToCodePoints(offset.toInt))
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/**
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* @param charIndex Index into the string measured in code units.
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* @return The code point index that corresponds to the specified character index.
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*/
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def codeUnitsToCodePoints(charIndex: Int): Int = {
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if (charIndex < this.charIndex) {
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this.codePointIndex -= text.codePointCount(charIndex, this.charIndex)
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} else {
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this.codePointIndex += text.codePointCount(this.charIndex, charIndex)
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}
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this.charIndex = charIndex
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// Make sure that charIndex never points to the second code unit of a
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// surrogate pair.
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if (charIndex > 0 && Character.isSupplementaryCodePoint(text.codePointAt(charIndex - 1))) {
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this.charIndex -= 1
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this.codePointIndex -= 1
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}
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this.codePointIndex
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}
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/**
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* @param offset Index into the string measured in code points.
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* @return the corresponding code unit index
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*/
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def toCodeUnits(offset: Offset.CodePoint): Offset.CodeUnit = {
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this.charIndex = text.offsetByCodePoints(charIndex, offset.toInt - this.codePointIndex)
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this.codePointIndex = offset.toInt
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Offset.CodeUnit(this.charIndex)
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}
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/**
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* @param codePointIndex Index into the string measured in code points.
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* @return the corresponding code unit index
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*/
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def codePointsToCodeUnits(codePointIndex: Int): Int =
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toCodeUnits(Offset.CodePoint(codePointIndex)).toInt
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/**
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* Returns a substring which begins at the specified code point `from` and extends to the
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* code point `to`. Since String.substring only works with character, the method first
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* converts code point offset to code unit offset.
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*/
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def substring(from: Offset.CodePoint, to: Offset.CodePoint): String =
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text.substring(toCodeUnits(from).toInt, toCodeUnits(to).toInt)
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/**
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* Returns a substring which begins at the specified code point `from` and extends to the
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* code point `to`. Since String.substring only works with character, the method first
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* converts code point offset to code unit offset.
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*/
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def substringByCodePoints(from: Int, to: Int): String =
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substring(Offset.CodePoint(from), Offset.CodePoint(to))
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/**
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* Returns a substring which begins at the specified code point `from` and extends to the
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* end of the string. Since String.substring only works with character, the method first
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* converts code point offset to code unit offset.
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*/
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def substringByCodePoints(from: Int): String = {
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val charFrom = codePointsToCodeUnits(from)
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text.substring(charFrom)
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}
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}
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