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+/*
+ * 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.
+ */
+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) {
+ let result = '';
+ for (; count > 0; --count) {
+ const char = text[position];
+ const charCode = char.charCodeAt(0);
+ result += char;
+ if (charCode >= 0xd800 && charCode < 0xdc00 && ++position < text.length) {
+ const char2 = text[position];
+ const charCode2 = char2.charCodeAt(0);
+ if (charCode2 >= 0xdc00 && charCode2 < 0xe000) {
+ result += char2;
+ }
+ }
+ }
+ 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];
+ const charCode = char.charCodeAt(0);
+ result = char + result;
+ if (charCode >= 0xdc00 && charCode < 0xe000 && position > 0) {
+ const char2 = text[position - 1];
+ const charCode2 = char2.charCodeAt(0);
+ if (charCode2 >= 0xd800 && charCode2 < 0xdc00) {
+ result = char2 + result;
+ }
+ }
+ }
+ return result;
+ }
+}