Tusker/Tusker/FuzzyMatcher.swift

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//
// FuzzyMatcher.swift
// Tusker
//
// Created by Shadowfacts on 10/10/20.
// Copyright © 2020 Shadowfacts. All rights reserved.
//
import Foundation
struct FuzzyMatcher {
private init() {}
/// Rudimentary string fuzzy matching algorithm.
///
/// Operates on UTF-8 code points, so attempting to match strings which include characters composed of
/// multiple code points may produce unexpected results.
///
/// Scoring is as follows:
/// +2 points for every char in `pattern` that occurs in `str` sequentially
/// -2 points for every char in `pattern` that does not occur in `str` sequentially
/// -1 point for every char in `str` skipped between matching chars from the `pattern`
static func match(pattern: String, str: String) -> (matched: Bool, score: Int) {
let pattern = pattern.lowercased()
let str = str.lowercased()
var patternIndex = pattern.utf8.startIndex
var lastStrMatchIndex: String.UTF8View.Index?
var strIndex = str.utf8.startIndex
var score = 0
while patternIndex < pattern.utf8.endIndex && strIndex < str.utf8.endIndex {
let patternChar = pattern.utf8[patternIndex]
let strChar = str.utf8[strIndex]
if patternChar == strChar {
let distance = str.utf8.distance(from: lastStrMatchIndex ?? str.utf8.startIndex, to: strIndex)
if distance > 1 {
score -= distance - 1
}
patternIndex = pattern.utf8.index(after: patternIndex)
lastStrMatchIndex = strIndex
strIndex = str.utf8.index(after: strIndex)
score += 2
} else {
strIndex = str.utf8.index(after: strIndex)
if strIndex >= str.utf8.endIndex {
patternIndex = pattern.utf8.index(after: patternIndex)
strIndex = str.utf8.index(after: lastStrMatchIndex ?? str.utf8.startIndex)
score -= 2
}
}
}
return (score > 0, score)
}
}