/* * Copyright (C) 2023-2024 Yomitan Authors * Copyright (C) 2022 Yomichan Authors * * This program is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see <https://www.gnu.org/licenses/>. */ /** * Class containing generic string utility functions. */ export class StringUtil { /** * Reads code points from a string in the forward direction. * @param {string} text The text to read the code points from. * @param {number} position The index of the first character to read. * @param {number} count The number of code points to read. * @returns {string} The code points from the string. */ static readCodePointsForward(text, position, count) { const textLength = text.length; let result = ''; for (; count > 0; --count) { const char = text[position]; result += char; if (++position >= textLength) { break; } const charCode = char.charCodeAt(0); if (charCode >= 0xd800 && charCode < 0xdc00) { // charCode is a high surrogate code const char2 = text[position]; const charCode2 = char2.charCodeAt(0); if (charCode2 >= 0xdc00 && charCode2 < 0xe000) { // charCode2 is a low surrogate code result += char2; if (++position >= textLength) { break; } } } } return result; } /** * Reads code points from a string in the backward direction. * @param {string} text The text to read the code points from. * @param {number} position The index of the first character to read. * @param {number} count The number of code points to read. * @returns {string} The code points from the string. */ static readCodePointsBackward(text, position, count) { let result = ''; for (; count > 0; --count) { const char = text[position]; result = char + result; if (--position < 0) { break; } const charCode = char.charCodeAt(0); if (charCode >= 0xdc00 && charCode < 0xe000) { // charCode is a low surrogate code const char2 = text[position]; const charCode2 = char2.charCodeAt(0); if (charCode2 >= 0xd800 && charCode2 < 0xdc00) { // charCode2 is a high surrogate code result = char2 + result; if (--position < 0) { break; } } } } return result; } }