ReadDataLines.swift

// Swift
//
// Intent: Process a simple memory-resident ASCII-style string in UTF8 format.
//
// Reads Data as a string, line by line,
// similar to how FileHandle works with a file pointer index.
// There are better ways to do this.
//
// By Andrew Kingdom
// MIT license
// 
import Foundation

class ReadDataLines {

// The 'searchIndex' parameter should normally be initialised to 0 (the first character index)
    // When there is no more data, a null result is returned.
    static func readLine(from data: Data, searchIndex: inout Int) throws -> String? {
        
        var startIndex = searchIndex
        
        if(startIndex < 0 || startIndex >= data.count) { return nil }
        
        // Find the next newline character in the data starting from the given index.
        if(!findNextOccurrence(of: 0x0a, in: data, index: &searchIndex)) {
            
            // If we reach the end of the data without finding a newline character, return the remaining data as the line.
            let remainder = String(data: data[startIndex..<data.count], encoding: .utf8)
            return remainder
        } else {
            
            // newline found -- return the line up to the newline character.
            let line = String(data: data[startIndex..<searchIndex], encoding: .utf8)
            
            // Update the index pointer to point to the character after the newline character.
            searchIndex += 1
            
            return line
        }
    }

    // index should be initialised to 0.
    // Result is false if there was no found match.
    static func findNextOccurrence(of character: UInt8, in data: Data, index: inout Int) -> Bool {
        for i in index..<data.count {
            if data[i] == character {
                index = i
                return true
            }
        }
        index = data.count
        return false
    }


}