Flow.Launcher/Flow.Launcher.Infrastructure/StringMatcher.cs

using Flow.Launcher.Plugin.SharedModels;
using System;
using System.Collections.Generic;
using System.Linq;

namespace Flow.Launcher.Infrastructure
{
    public class StringMatcher
    {
        private readonly MatchOption _defaultMatchOption = new MatchOption();

        public SearchPrecisionScore UserSettingSearchPrecision { get; set; }

        private readonly IAlphabet _alphabet;

        public StringMatcher(IAlphabet alphabet = null)
        {
            _alphabet = alphabet;
        }

        public static StringMatcher Instance { get; internal set; }

        public static MatchResult FuzzySearch(string query, string stringToCompare)
        {
            return Instance.FuzzyMatch(query, stringToCompare);
        }

        public MatchResult FuzzyMatch(string query, string stringToCompare)
        {
            return FuzzyMatch(query, stringToCompare, _defaultMatchOption);
        }

        /// <summary>
        /// Current method includes two part, Acronym Match and Fuzzy Search:
        /// 
        /// Acronym Match:
        /// Charater lists below will be considered as Acronym
        /// 1. Character on index 0
        /// 2. Character appears after a space
        /// 3. Character that is UpperCase
        /// 4. Character that is number
        /// 
        /// Acronym Search will match all query when meeting with Acronyms in the stringToCompare
        /// If any of the character in Query isn't matched with the string, Acronym Search fail.
        /// Score will be calculated based on the number of mismatched acronym before all query has been matched
        /// 
        /// Fuzzy Search:
        /// Character matching + substring matching;
        /// 1. Query search string is split into substrings, separator is whitespace.
        /// 2. Check each query substring's characters against full compare string,
        /// 3. if a character in the substring is matched, loop back to verify the previous character.
        /// 4. If previous character also matches, and is the start of the substring, update list.
        /// 5. Once the previous character is verified, move on to the next character in the query substring.
        /// 6. Move onto the next substring's characters until all substrings are checked.
        /// 7. Consider success and move onto scoring if every char or substring without whitespaces matched
        /// </summary>
        public MatchResult FuzzyMatch(string query, string stringToCompare, MatchOption opt)
        {
            if (string.IsNullOrEmpty(stringToCompare) || string.IsNullOrEmpty(query))
                return new MatchResult(false, UserSettingSearchPrecision);

            query = query.Trim();
            TranslationMapping translationMapping;
            (stringToCompare, translationMapping) = _alphabet?.Translate(stringToCompare) ?? (stringToCompare, null);

            var currentAcronymQueryIndex = 0;
            var acronymMatchData = new List<int>();

            decimal acronymsTotalCount = 0;
            decimal acronymsMatched = 0;

            var fullStringToCompareWithoutCase = opt.IgnoreCase ? stringToCompare.ToLower() : stringToCompare;
            var queryWithoutCase = opt.IgnoreCase ? query.ToLower() : query;

            var querySubstrings = queryWithoutCase.Split(new[] {' '}, StringSplitOptions.RemoveEmptyEntries);
            int currentQuerySubstringIndex = 0;
            var currentQuerySubstring = querySubstrings[currentQuerySubstringIndex];
            var currentQuerySubstringCharacterIndex = 0;

            var firstMatchIndex = -1;
            var firstMatchIndexInWord = -1;
            var lastMatchIndex = 0;
            bool allQuerySubstringsMatched = false;
            bool matchFoundInPreviousLoop = false;
            bool allSubstringsContainedInCompareString = true;

            var indexList = new List<int>();
            List<int> spaceIndices = new List<int>();

            for (var compareStringIndex = 0; compareStringIndex < fullStringToCompareWithoutCase.Length; compareStringIndex++)
            {
                // If acronyms matching successfully finished, this gets the remaining not matched acronyms for score calculation
                if (currentAcronymQueryIndex >= query.Length && acronymsMatched == query.Length)
                {
                    if (IsAcronym(stringToCompare, compareStringIndex))
                        acronymsTotalCount++;
                    continue;
                }

                if (currentAcronymQueryIndex >= query.Length ||
                    currentAcronymQueryIndex >= query.Length && allQuerySubstringsMatched)
                    break;

                // To maintain a list of indices which correspond to spaces in the string to compare
                // To populate the list only for the first query substring
                if (fullStringToCompareWithoutCase[compareStringIndex] == ' ' && currentQuerySubstringIndex == 0)
                    spaceIndices.Add(compareStringIndex);

                // Acronym check
                if (IsAcronym(stringToCompare, compareStringIndex))
                {
                    if (fullStringToCompareWithoutCase[compareStringIndex] ==
                        queryWithoutCase[currentAcronymQueryIndex])
                    {
                        acronymMatchData.Add(compareStringIndex);
                        acronymsMatched++;

                        currentAcronymQueryIndex++;
                    }

                    acronymsTotalCount++;
                }
                // Acronym end

                if (allQuerySubstringsMatched || fullStringToCompareWithoutCase[compareStringIndex] !=
                    currentQuerySubstring[currentQuerySubstringCharacterIndex])
                {
                    matchFoundInPreviousLoop = false;

                    continue;
                }

                if (firstMatchIndex < 0)
                {
                    // first matched char will become the start of the compared string
                    firstMatchIndex = compareStringIndex;
                }

                if (currentQuerySubstringCharacterIndex == 0)
                {
                    // first letter of current word
                    matchFoundInPreviousLoop = true;
                    firstMatchIndexInWord = compareStringIndex;
                }
                else if (!matchFoundInPreviousLoop)
                {
                    // we want to verify that there is not a better match if this is not a full word
                    // in order to do so we need to verify all previous chars are part of the pattern
                    var startIndexToVerify = compareStringIndex - currentQuerySubstringCharacterIndex;

                    if (AllPreviousCharsMatched(startIndexToVerify, currentQuerySubstringCharacterIndex,
                        fullStringToCompareWithoutCase, currentQuerySubstring))
                    {
                        matchFoundInPreviousLoop = true;

                        // if it's the beginning character of the first query substring that is matched then we need to update start index
                        firstMatchIndex = currentQuerySubstringIndex == 0 ? startIndexToVerify : firstMatchIndex;

                        indexList = GetUpdatedIndexList(startIndexToVerify, currentQuerySubstringCharacterIndex,
                            firstMatchIndexInWord, indexList);
                    }
                }

                lastMatchIndex = compareStringIndex + 1;
                indexList.Add(compareStringIndex);

                currentQuerySubstringCharacterIndex++;

                // if finished looping through every character in the current substring
                if (currentQuerySubstringCharacterIndex == currentQuerySubstring.Length)
                {
                    // if any of the substrings was not matched then consider as all are not matched
                    allSubstringsContainedInCompareString =
                        matchFoundInPreviousLoop && allSubstringsContainedInCompareString;

                    currentQuerySubstringIndex++;

                    allQuerySubstringsMatched =
                        AllQuerySubstringsMatched(currentQuerySubstringIndex, querySubstrings.Length);

                    if (allQuerySubstringsMatched)
                        continue;

                    // otherwise move to the next query substring
                    currentQuerySubstring = querySubstrings[currentQuerySubstringIndex];
                    currentQuerySubstringCharacterIndex = 0;
                }
            }

            // return acronym match if all query char matched
            if (acronymsMatched > 0 && acronymsMatched == query.Length)
            {
                int acronymScore = (int)(acronymsMatched / acronymsTotalCount * 100);

                if (acronymScore >= (int)UserSettingSearchPrecision)
                {
                    acronymMatchData = acronymMatchData.Select(x => translationMapping?.MapToOriginalIndex(x) ?? x).Distinct().ToList();
                    return new MatchResult(true, UserSettingSearchPrecision, acronymMatchData, acronymScore);
                }
            }

            // proceed to calculate score if every char or substring without whitespaces matched
            if (allQuerySubstringsMatched)
            {
                var nearestSpaceIndex = CalculateClosestSpaceIndex(spaceIndices, firstMatchIndex);
                var score = CalculateSearchScore(query, stringToCompare, firstMatchIndex - nearestSpaceIndex - 1,
                    lastMatchIndex - firstMatchIndex, allSubstringsContainedInCompareString);

                var resultList = indexList.Select(x => translationMapping?.MapToOriginalIndex(x) ?? x).Distinct().ToList();
                return new MatchResult(true, UserSettingSearchPrecision, resultList, score);
            }

            return new MatchResult(false, UserSettingSearchPrecision);
        }

        private bool IsAcronym(string stringToCompare, int compareStringIndex)
        {
            if (char.IsUpper(stringToCompare[compareStringIndex]) ||
                    char.IsNumber(stringToCompare[compareStringIndex]) ||
                    char.IsDigit(stringToCompare[compareStringIndex]))
                return true;

            if (compareStringIndex == 0)
                return true;

            if (compareStringIndex != 0 && char.IsWhiteSpace(stringToCompare[compareStringIndex - 1]))
                return true;

            return false;
        }

        // To get the index of the closest space which preceeds the first matching index
        private int CalculateClosestSpaceIndex(List<int> spaceIndices, int firstMatchIndex)
        {
            if (spaceIndices.Count == 0)
            {
                return -1;
            }
            else
            {
                int? ind = spaceIndices.OrderBy(item => (firstMatchIndex - item))
                    .FirstOrDefault(item => firstMatchIndex > item);
                int closestSpaceIndex = ind ?? -1;
                return closestSpaceIndex;
            }
        }

        private static bool AllPreviousCharsMatched(int startIndexToVerify, int currentQuerySubstringCharacterIndex,
            string fullStringToCompareWithoutCase, string currentQuerySubstring)
        {
            var allMatch = true;
            for (int indexToCheck = 0; indexToCheck < currentQuerySubstringCharacterIndex; indexToCheck++)
            {
                if (fullStringToCompareWithoutCase[startIndexToVerify + indexToCheck] !=
                    currentQuerySubstring[indexToCheck])
                {
                    allMatch = false;
                }
            }

            return allMatch;
        }

        private static List<int> GetUpdatedIndexList(int startIndexToVerify, int currentQuerySubstringCharacterIndex,
            int firstMatchIndexInWord, List<int> indexList)
        {
            var updatedList = new List<int>();

            indexList.RemoveAll(x => x >= firstMatchIndexInWord);

            updatedList.AddRange(indexList);

            for (int indexToCheck = 0; indexToCheck < currentQuerySubstringCharacterIndex; indexToCheck++)
            {
                updatedList.Add(startIndexToVerify + indexToCheck);
            }

            return updatedList;
        }

        private static bool AllQuerySubstringsMatched(int currentQuerySubstringIndex, int querySubstringsLength)
        {
            // Acronym won't utilize the substring to match
            return currentQuerySubstringIndex >= querySubstringsLength;
        }

        private static int CalculateSearchScore(string query, string stringToCompare, int firstIndex, int matchLen,
            bool allSubstringsContainedInCompareString)
        {
            // A match found near the beginning of a string is scored more than a match found near the end
            // A match is scored more if the characters in the patterns are closer to each other, 
            // while the score is lower if they are more spread out
            var score = 100 * (query.Length + 1) / ((1 + firstIndex) + (matchLen + 1));

            // A match with less characters assigning more weights
            if (stringToCompare.Length - query.Length < 5)
            {
                score += 20;
            }
            else if (stringToCompare.Length - query.Length < 10)
            {
                score += 10;
            }

            if (allSubstringsContainedInCompareString)
            {
                int count = query.Count(c => !char.IsWhiteSpace(c));
                //10 per char is too much for long query strings, this threshhold is to avoid where long strings will override the other results too much
                int threshold = 4;
                if (count <= threshold)
                {
                    score += count * 10;
                }
                else
                {
                    score += threshold * 10 + (count - threshold) * 5;
                }
            }

            return score;
        }
    }

    public class MatchOption
    {
        public bool IgnoreCase { get; set; } = true;
    }
}