lnav/src/fts_fuzzy_match.cc

// 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.

#include <cstring>  // memcpy

#include "fts_fuzzy_match.hh"

#include <ctype.h>  // ::tolower, ::toupper

#include "config.h"

namespace fts {

// Forward declarations for "private" implementation
namespace fuzzy_internal {
static bool fuzzy_match_recursive(const char* pattern,
                                  const char* str,
                                  int& outScore,
                                  const char* strBegin,
                                  uint8_t const* srcMatches,
                                  uint8_t* newMatches,
                                  int maxMatches,
                                  int nextMatch,
                                  int& recursionCount,
                                  int recursionLimit);
}

// Public interface
bool
fuzzy_match_simple(char const* pattern, char const* str)
{
    while (*pattern != '\0' && *str != '\0') {
        if (tolower(*pattern) == tolower(*str))
            ++pattern;
        ++str;
    }

    return *pattern == '\0' ? true : false;
}

bool
fuzzy_match(char const* pattern, char const* str, int& outScore)
{
    uint8_t matches[256];
    return fuzzy_match(pattern, str, outScore, matches, sizeof(matches));
}

bool
fuzzy_match(char const* pattern,
            char const* str,
            int& outScore,
            uint8_t* matches,
            int maxMatches)
{
    int recursionCount = 0;
    int recursionLimit = 10;

    return fuzzy_internal::fuzzy_match_recursive(pattern,
                                                 str,
                                                 outScore,
                                                 str,
                                                 nullptr,
                                                 matches,
                                                 maxMatches,
                                                 0,
                                                 recursionCount,
                                                 recursionLimit);
}

// Private implementation
static bool
fuzzy_internal::fuzzy_match_recursive(const char* pattern,
                                      const char* str,
                                      int& outScore,
                                      const char* strBegin,
                                      uint8_t const* srcMatches,
                                      uint8_t* matches,
                                      int maxMatches,
                                      int nextMatch,
                                      int& recursionCount,
                                      int recursionLimit)
{
    // Count recursions
    ++recursionCount;
    if (recursionCount >= recursionLimit)
        return false;

    // Detect end of strings
    if (*pattern == '\0' || *str == '\0')
        return false;

    // Recursion params
    bool recursiveMatch = false;
    uint8_t bestRecursiveMatches[256];
    int bestRecursiveScore = 0;

    // Loop through pattern and str looking for a match
    bool first_match = true;
    while (*pattern != '\0' && *str != '\0') {
        // Found match
        if (tolower(*pattern) == tolower(*str)) {
            // Supplied matches buffer was too short
            if (nextMatch >= maxMatches)
                return false;

            // "Copy-on-Write" srcMatches into matches
            if (first_match && srcMatches) {
                memcpy(matches, srcMatches, nextMatch);
                first_match = false;
            }

            // Recursive call that "skips" this match
            uint8_t recursiveMatches[256];
            int recursiveScore;
            if (fuzzy_match_recursive(pattern,
                                      str + 1,
                                      recursiveScore,
                                      strBegin,
                                      matches,
                                      recursiveMatches,
                                      sizeof(recursiveMatches),
                                      nextMatch,
                                      recursionCount,
                                      recursionLimit))
            {
                // Pick best recursive score
                if (!recursiveMatch || recursiveScore > bestRecursiveScore) {
                    memcpy(bestRecursiveMatches, recursiveMatches, 256);
                    bestRecursiveScore = recursiveScore;
                }
                recursiveMatch = true;
            }

            // Advance
            matches[nextMatch++] = (uint8_t) (str - strBegin);
            ++pattern;
        }
        ++str;
    }

    // Determine if full pattern was matched
    bool matched = *pattern == '\0' ? true : false;

    // Calculate score
    if (matched) {
        const int sequential_bonus = 15;  // bonus for adjacent matches
        const int separator_bonus
            = 30;  // bonus if match occurs after a separator
        const int camel_bonus
            = 30;  // bonus if match is uppercase and prev is lower
        const int first_letter_bonus
            = 15;  // bonus if the first letter is matched

        const int leading_letter_penalty
            = -5;  // penalty applied for every letter in str before the first
                   // match
        const int max_leading_letter_penalty
            = -15;  // maximum penalty for leading letters
        const int unmatched_letter_penalty
            = -1;  // penalty for every letter that doesn't matter

        // Iterate str to end
        while (*str != '\0')
            ++str;

        // Initialize score
        outScore = 100;

        // Apply leading letter penalty
        int penalty = leading_letter_penalty * matches[0];
        if (penalty < max_leading_letter_penalty)
            penalty = max_leading_letter_penalty;
        outScore += penalty;

        // Apply unmatched penalty
        int unmatched = (int) (str - strBegin) - nextMatch;
        outScore += unmatched_letter_penalty * unmatched;

        // Apply ordering bonuses
        for (int i = 0; i < nextMatch; ++i) {
            uint8_t currIdx = matches[i];

            if (i > 0) {
                uint8_t prevIdx = matches[i - 1];

                // Sequential
                if (currIdx == (prevIdx + 1))
                    outScore += sequential_bonus;
            }

            // Check for bonuses based on neighbor character value
            if (currIdx > 0) {
                // Camel case
                char neighbor = strBegin[currIdx - 1];
                char curr = strBegin[currIdx];
                if (::islower(neighbor) && ::isupper(curr))
                    outScore += camel_bonus;

                // Separator
                bool neighborSeparator = neighbor == '_' || neighbor == ' ';
                if (neighborSeparator)
                    outScore += separator_bonus;
            } else {
                // First letter
                outScore += first_letter_bonus;
            }
        }
    }

    // Return best result
    if (recursiveMatch && (!matched || bestRecursiveScore > outScore)) {
        // Recursive score is better than "this"
        memcpy(matches, bestRecursiveMatches, maxMatches);
        outScore = bestRecursiveScore;
        return true;
    } else if (matched) {
        // "this" score is better than recursive
        return true;
    } else {
        // no match
        return false;
    }
}
}  // namespace fts