source: imaps-frontend/node_modules/es-abstract/2020/CodePointAt.js

'use strict';

var $TypeError = require('es-errors/type');
var callBound = require('call-bind/callBound');
var isLeadingSurrogate = require('../helpers/isLeadingSurrogate');
var isTrailingSurrogate = require('../helpers/isTrailingSurrogate');

var UTF16DecodeSurrogatePair = require('./UTF16DecodeSurrogatePair');

var $charAt = callBound('String.prototype.charAt');
var $charCodeAt = callBound('String.prototype.charCodeAt');

// https://262.ecma-international.org/11.0/#sec-codepointat

module.exports = function CodePointAt(string, position) {
        if (typeof string !== 'string') {
                throw new $TypeError('Assertion failed: `string` must be a String');
        }
        var size = string.length;
        if (position < 0 || position >= size) {
                throw new $TypeError('Assertion failed: `position` must be >= 0, and < the length of `string`');
        }
        var first = $charCodeAt(string, position);
        var cp = $charAt(string, position);
        var firstIsLeading = isLeadingSurrogate(first);
        var firstIsTrailing = isTrailingSurrogate(first);
        if (!firstIsLeading && !firstIsTrailing) {
                return {
                        '[[CodePoint]]': cp,
                        '[[CodeUnitCount]]': 1,
                        '[[IsUnpairedSurrogate]]': false
                };
        }
        if (firstIsTrailing || (position + 1 === size)) {
                return {
                        '[[CodePoint]]': cp,
                        '[[CodeUnitCount]]': 1,
                        '[[IsUnpairedSurrogate]]': true
                };
        }
        var second = $charCodeAt(string, position + 1);
        if (!isTrailingSurrogate(second)) {
                return {
                        '[[CodePoint]]': cp,
                        '[[CodeUnitCount]]': 1,
                        '[[IsUnpairedSurrogate]]': true
                };
        }

        return {
                '[[CodePoint]]': UTF16DecodeSurrogatePair(first, second),
                '[[CodeUnitCount]]': 2,
                '[[IsUnpairedSurrogate]]': false
        };
};