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/*
* 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/>.
*/
/**
* 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.
*/
export function 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.
*/
export function 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;
}
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