Compact occurrences of characters to given maximum in Swift

String+compactOccurences.swift

//  Created by Umur Gedik on 27.12.2023.

import Foundation

public extension StringProtocol {
    func compact(occurencesOf needle: Character, to maxNeedles: Int) -> String {
        var parts: [Self.SubSequence] = []
        var cursor: String.Index = startIndex
        while let needleIndex = self[cursor...].firstIndex(of: needle) {
            if needleIndex != cursor {
                parts.append(self[cursor..<needleIndex])
            }

            let nextNonNeedleIndex = self[needleIndex...]
                .dropFirst()
                .firstIndex(where: { $0 != needle }) ?? endIndex

            let numNeedles = distance(from: needleIndex, to: nextNonNeedleIndex)
            let inclusiveIndex = index(needleIndex, offsetBy: Swift.min(numNeedles, maxNeedles))
            parts.append(self[needleIndex..<inclusiveIndex])

            cursor = nextNonNeedleIndex
        }

        if cursor < endIndex {
            parts.append(self[cursor..<endIndex])
        }

        return parts.joined()
    }
}