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Filename : utils.js
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/**
 * @fileoverview Define utility functions for token store.
 * @author Toru Nagashima
 */
"use strict";

//------------------------------------------------------------------------------
// Exports
//------------------------------------------------------------------------------

/**
 * Finds the index of the first token which is after the given location.
 * If it was not found, this returns `tokens.length`.
 * @param {(Token|Comment)[]} tokens It searches the token in this list.
 * @param {number} location The location to search.
 * @returns {number} The found index or `tokens.length`.
 */
exports.search = function search(tokens, location) {
    for (let minIndex = 0, maxIndex = tokens.length - 1; minIndex <= maxIndex;) {

        /*
         * Calculate the index in the middle between minIndex and maxIndex.
         * `| 0` is used to round a fractional value down to the nearest integer: this is similar to
         * using `Math.trunc()` or `Math.floor()`, but performance tests have shown this method to
         * be faster.
         */
        const index = (minIndex + maxIndex) / 2 | 0;
        const token = tokens[index];
        const tokenStartLocation = token.range[0];

        if (location <= tokenStartLocation) {
            if (index === minIndex) {
                return index;
            }
            maxIndex = index;
        } else {
            minIndex = index + 1;
        }
    }
    return tokens.length;
};

/**
 * Gets the index of the `startLoc` in `tokens`.
 * `startLoc` can be the value of `node.range[1]`, so this checks about `startLoc - 1` as well.
 * @param {(Token|Comment)[]} tokens The tokens to find an index.
 * @param {Object} indexMap The map from locations to indices.
 * @param {number} startLoc The location to get an index.
 * @returns {number} The index.
 */
exports.getFirstIndex = function getFirstIndex(tokens, indexMap, startLoc) {
    if (startLoc in indexMap) {
        return indexMap[startLoc];
    }
    if ((startLoc - 1) in indexMap) {
        const index = indexMap[startLoc - 1];
        const token = tokens[index];

        // If the mapped index is out of bounds, the returned cursor index will point after the end of the tokens array.
        if (!token) {
            return tokens.length;
        }

        /*
         * For the map of "comment's location -> token's index", it points the next token of a comment.
         * In that case, +1 is unnecessary.
         */
        if (token.range[0] >= startLoc) {
            return index;
        }
        return index + 1;
    }
    return 0;
};

/**
 * Gets the index of the `endLoc` in `tokens`.
 * The information of end locations are recorded at `endLoc - 1` in `indexMap`, so this checks about `endLoc - 1` as well.
 * @param {(Token|Comment)[]} tokens The tokens to find an index.
 * @param {Object} indexMap The map from locations to indices.
 * @param {number} endLoc The location to get an index.
 * @returns {number} The index.
 */
exports.getLastIndex = function getLastIndex(tokens, indexMap, endLoc) {
    if (endLoc in indexMap) {
        return indexMap[endLoc] - 1;
    }
    if ((endLoc - 1) in indexMap) {
        const index = indexMap[endLoc - 1];
        const token = tokens[index];

        // If the mapped index is out of bounds, the returned cursor index will point before the end of the tokens array.
        if (!token) {
            return tokens.length - 1;
        }

        /*
         * For the map of "comment's location -> token's index", it points the next token of a comment.
         * In that case, -1 is necessary.
         */
        if (token.range[1] > endLoc) {
            return index - 1;
        }
        return index;
    }
    return tokens.length - 1;
};