overleaf/services/web/public/js/ace/autocomplete/text_completer.js

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define(function(require, exports, module) {
    var Range = require("ace/range").Range;
    
    var splitRegex = /[^a-zA-Z_0-9\$\-]+/;

    function getWordIndex(doc, pos) {
        var textBefore = doc.getTextRange(Range.fromPoints({row: 0, column:0}, pos));
        return textBefore.split(splitRegex).length - 1;
    }

    /**
     * Does a distance analysis of the word `prefix` at position `pos` in `doc`.
     * @return Map
     */
    function wordDistance(doc, pos) {
        var prefixPos = getWordIndex(doc, pos);
        var words = doc.getValue().split(splitRegex);
        var wordScores = Object.create(null);
        
        var currentWord = words[prefixPos];

        words.forEach(function(word, idx) {
            if (!word || word === currentWord) return;

            var distance = Math.abs(prefixPos - idx);
            var score = words.length - distance;
            if (wordScores[word]) {
                wordScores[word] = Math.max(score, wordScores[word]);
            } else {
                wordScores[word] = score;
            }
        });
        return wordScores;
    }

    exports.getCompletions = function(editor, session, pos, prefix, callback) {
        var wordScore = wordDistance(session, pos, prefix);
        var wordList = Object.keys(wordScore);
        callback(null, wordList.map(function(word) {
            return {
                name: word,
                value: word,
                score: wordScore[word],
                meta: "local"
            };
        }));
    };
});