70 lines
2.6 KiB
JavaScript
70 lines
2.6 KiB
JavaScript
/*
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* Copyright (C) 2022 Yomichan Authors
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <https://www.gnu.org/licenses/>.
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*/
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/**
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* Class containing generic string utility functions.
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*/
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class StringUtil {
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/**
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* Reads code points from a string in the forward direction.
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* @param {string} text The text to read the code points from.
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* @param {number} position The index of the first character to read.
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* @param {number} count The number of code points to read.
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* @returns {string} The code points from the string.
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*/
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static readCodePointsForward(text, position, count) {
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let result = '';
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for (; count > 0; --count) {
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const char = text[position];
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const charCode = char.charCodeAt(0);
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result += char;
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if (charCode >= 0xd800 && charCode < 0xdc00 && ++position < text.length) {
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const char2 = text[position];
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const charCode2 = char2.charCodeAt(0);
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if (charCode2 >= 0xdc00 && charCode2 < 0xe000) {
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result += char2;
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}
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}
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}
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return result;
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}
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/**
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* Reads code points from a string in the backward direction.
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* @param {string} text The text to read the code points from.
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* @param {number} position The index of the first character to read.
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* @param {number} count The number of code points to read.
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* @returns {string} The code points from the string.
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*/
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static readCodePointsBackward(text, position, count) {
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let result = '';
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for (; count > 0; --count) {
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const char = text[position];
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const charCode = char.charCodeAt(0);
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result = char + result;
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if (charCode >= 0xdc00 && charCode < 0xe000 && position > 0) {
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const char2 = text[position - 1];
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const charCode2 = char2.charCodeAt(0);
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if (charCode2 >= 0xd800 && charCode2 < 0xdc00) {
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result = char2 + result;
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}
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}
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}
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return result;
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}
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}
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