CyberChef/src/core/lib/FuzzySearch.mjs

/**
 * LICENSE
 *
 *   This software is dual-licensed to the public domain and under the following
 *   license: you are granted a perpetual, irrevocable license to copy, modify,
 *   publish, and distribute this file as you see fit.
 *
 * VERSION
 *   0.1.0  (2016-03-28)  Initial release
 *
 * AUTHOR
 *   Forrest Smith
 *
 * CONTRIBUTORS
 *   J<EFBFBD>rgen Tjern<EFBFBD> - async helper
 *   Anurag Awasthi - updated to 0.2.0
 */

const SEQUENTIAL_BONUS = 15; // bonus for adjacent matches
const SEPARATOR_BONUS = 30; // bonus if match occurs after a separator
const CAMEL_BONUS = 30; // bonus if match is uppercase and prev is lower
const FIRST_LETTER_BONUS = 15; // bonus if the first letter is matched

const LEADING_LETTER_PENALTY = -5; // penalty applied for every letter in str before the first match
const MAX_LEADING_LETTER_PENALTY = -15; // maximum penalty for leading letters
const UNMATCHED_LETTER_PENALTY = -1;

/**
 * Does a fuzzy search to find pattern inside a string.
 * @param {*} pattern string        pattern to search for
 * @param {*} str     string        string which is being searched
 * @returns [boolean, number]       a boolean which tells if pattern was
 *                                  found or not and a search score
 */
export function fuzzyMatch(pattern, str) {
    const recursionCount = 0;
    const recursionLimit = 10;
    const matches = [];
    const maxMatches = 256;

    return fuzzyMatchRecursive(
        pattern,
        str,
        0 /* patternCurIndex */,
        0 /* strCurrIndex */,
        null /* srcMatces */,
        matches,
        maxMatches,
        0 /* nextMatch */,
        recursionCount,
        recursionLimit
    );
}

/**
 * Recursive helper function
 */
function fuzzyMatchRecursive(
    pattern,
    str,
    patternCurIndex,
    strCurrIndex,
    srcMatches,
    matches,
    maxMatches,
    nextMatch,
    recursionCount,
    recursionLimit
) {
    let outScore = 0;

    // Return if recursion limit is reached.
    if (++recursionCount >= recursionLimit) {
        return [false, outScore];
    }

    // Return if we reached ends of strings.
    if (patternCurIndex === pattern.length || strCurrIndex === str.length) {
        return [false, outScore];
    }

    // Recursion params
    let recursiveMatch = false;
    let bestRecursiveMatches = [];
    let bestRecursiveScore = 0;

    // Loop through pattern and str looking for a match.
    let firstMatch = true;
    while (patternCurIndex < pattern.length && strCurrIndex < str.length) {
        // Match found.
        if (
            pattern[patternCurIndex].toLowerCase() === str[strCurrIndex].toLowerCase()
        ) {
            if (nextMatch >= maxMatches) {
                return [false, outScore];
            }

            if (firstMatch && srcMatches) {
                matches = [...srcMatches];
                firstMatch = false;
            }

            const recursiveMatches = [];
            const [matched, recursiveScore] = fuzzyMatchRecursive(
                pattern,
                str,
                patternCurIndex,
                strCurrIndex + 1,
                matches,
                recursiveMatches,
                maxMatches,
                nextMatch,
                recursionCount,
                recursionLimit
            );

            if (matched) {
                // Pick best recursive score.
                if (!recursiveMatch || recursiveScore > bestRecursiveScore) {
                    bestRecursiveMatches = [...recursiveMatches];
                    bestRecursiveScore = recursiveScore;
                }
                recursiveMatch = true;
            }

            matches[nextMatch++] = strCurrIndex;
            ++patternCurIndex;
        }
        ++strCurrIndex;
    }

    const matched = patternCurIndex === pattern.length;

    if (matched) {
        outScore = 100;

        // Apply leading letter penalty
        let penalty = LEADING_LETTER_PENALTY * matches[0];
        penalty =
            penalty < MAX_LEADING_LETTER_PENALTY ?
                MAX_LEADING_LETTER_PENALTY :
                penalty;
        outScore += penalty;

        // Apply unmatched penalty
        const unmatched = str.length - nextMatch;
        outScore += UNMATCHED_LETTER_PENALTY * unmatched;

        // Apply ordering bonuses
        for (let i = 0; i < nextMatch; i++) {
            const currIdx = matches[i];

            if (i > 0) {
                const prevIdx = matches[i - 1];
                if (currIdx === prevIdx + 1) {
                    outScore += SEQUENTIAL_BONUS;
                }
            }

            // Check for bonuses based on neighbor character value.
            if (currIdx > 0) {
                // Camel case
                const neighbor = str[currIdx - 1];
                const curr = str[currIdx];
                if (
                    neighbor !== neighbor.toUpperCase() &&
                    curr !== curr.toLowerCase()
                ) {
                    outScore += CAMEL_BONUS;
                }
                const isNeighbourSeparator = neighbor === "_" || neighbor === " ";
                if (isNeighbourSeparator) {
                    outScore += SEPARATOR_BONUS;
                }
            } else {
                // First letter
                outScore += FIRST_LETTER_BONUS;
            }
        }

        // Return best result
        if (recursiveMatch && (!matched || bestRecursiveScore > outScore)) {
            // Recursive score is better than "this"
            outScore = bestRecursiveScore;
            return [true, outScore, calcMatchRanges(matches)];
        } else if (matched) {
            // "this" score is better than recursive
            return [true, outScore, calcMatchRanges(matches)];
        } else {
            return [false, outScore];
        }
    }
    return [false, outScore];
}

/**
 * Turns a list of match indexes into a list of match ranges
 *
 * @author n1474335 [n1474335@gmail.com]
 * @param [number] matches
 * @returns [[number]]
 */
function calcMatchRanges(matches) {
    const ranges = [];
    let start = matches[0],
        curr = start;

    matches.forEach(m => {
        if (m === curr || m === curr + 1) curr = m;
        else {
            ranges.push([start, curr - start + 1]);
            start = m;
            curr = m;
        }
    });

    ranges.push([start, curr - start + 1]);
    return ranges;
}