StringEndIndex

StringEndIndex.swift

extension Array where Element == UInt8 {
    func stringEndIndex(from startIndex: Int = 0) -> Int? {
        findStringEndIndex(from: startIndex)
    }

    // Method to calculate the end index of string
    private func findStringEndIndex(from startIndex: Int, to endIndex: Int? = nil) -> Int? {
        guard (endIndex == .none) || (endIndex != nil && endIndex! <= startIndex && endIndex! < count) 
        
        else { return nil } // Not a valid string

        guard startIndex < count else { return endIndex }

        var arraySlice = self[0...startIndex]
        guard !arraySlice.contains(where: { 0...31 ~= $0 }) else { return endIndex }
        
        if String(data: Data(arraySlice), encoding: .utf8) != nil {
            return findStringEndIndex(from: startIndex + 1, to: startIndex)
        }

        guard startIndex + 1 < count else { return endIndex }
        arraySlice = self[0 ... startIndex + 1]
        
        guard !arraySlice.contains(where: { 0...31 ~= $0 }) else { return endIndex }
        
        if String(data: Data(arraySlice), encoding: .utf8) != nil {
            return findStringEndIndex(from: startIndex + 2, to: startIndex + 1)
        }

        guard startIndex + 3 < count else { return endIndex }
        arraySlice = self[0 ... startIndex + 3]
        
        guard !arraySlice.contains(where: { 0...31 ~= $0 }) else { return endIndex }
        
        if String(data: Data(arraySlice), encoding: .utf8) != nil {
            return findStringEndIndex(from: startIndex + 4, to: startIndex + 3)
        }

        return endIndex
    }
}