faridv/hop

/**
 * @license
 * Copyright Google LLC All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */

const LF_CHAR = 10;
const CR_CHAR = 13;
const LINE_SEP_CHAR = 8232;
const PARAGRAPH_CHAR = 8233;

/** Gets the line and character for the given position from the line starts map. */
export function getLineAndCharacterFromPosition(lineStartsMap: number[], position: number) {
    const lineIndex = findClosestLineStartPosition(lineStartsMap, position);
    return {character: position - lineStartsMap[lineIndex], line: lineIndex};
}

/**
 * Computes the line start map of the given text. This can be used in order to
 * retrieve the line and character of a given text position index.
 */
export function computeLineStartsMap(text: string): number[] {
    const result: number[] = [0];
    let pos = 0;
    while (pos < text.length) {
        const char = text.charCodeAt(pos++);
        // Handles the "CRLF" line break. In that case we peek the character
        // after the "CR" and check if it is a line feed.
        if (char === CR_CHAR) {
            if (text.charCodeAt(pos) === LF_CHAR) {
                pos++;
            }
            result.push(pos);
        } else if (char === LF_CHAR || char === LINE_SEP_CHAR || char === PARAGRAPH_CHAR) {
            result.push(pos);
        }
    }
    result.push(pos);
    return result;
}

/** Finds the closest line start for the given position. */
function findClosestLineStartPosition<T>(
    linesMap: T[], position: T, low = 0, high = linesMap.length - 1) {
    while (low <= high) {
        const pivotIdx = Math.floor((low + high) / 2);
        const pivotEl = linesMap[pivotIdx];

        if (pivotEl === position) {
            return pivotIdx;
        } else if (position > pivotEl) {
            low = pivotIdx + 1;
        } else {
            high = pivotIdx - 1;
        }
    }

    // In case there was no exact match, return the closest "lower" line index. We also
    // subtract the index by one because want the index of the previous line start.
    return low - 1;
}