TextStreams.swift

//  
//  TextStreams.swift
//  
//  Created by Matthias Zenger on 05/06/2016.
//  Copyright © 2016 ObjectHub. All rights reserved.
//  

import Foundation

class ByteGenerator: GeneratorType {
  typealias Element = UInt8
  let input: NSInputStream
  var buffer: [UInt8]
  var index: Int = 0
  var eof: Bool = true
  
  init?(path: String, capacity: Int = 1024) {
    guard let input = NSInputStream(fileAtPath: path) else {
      return nil
    }
    self.buffer = [UInt8](count: capacity, repeatedValue: 0)
    input.open()
    if input.hasBytesAvailable {
      self.eof = input.read(&self.buffer, maxLength: self.buffer.count * sizeof(UInt8)) <= 0
    }
    self.input = input
  }
  
  deinit {
    input.close()
  }
  
  func next() -> UInt8? {
    guard !self.eof else {
      return nil
    }
    if self.index >= self.buffer.count {
      self.index = 0
      self.eof = !input.hasBytesAvailable ||
                 input.read(&self.buffer, maxLength: self.buffer.count * sizeof(UInt8)) <= 0
      guard !self.eof else {
        return nil
      }
    }
    self.index += 1
    return self.buffer[self.index - 1]
  }
}

struct CharacterGenerator<G: GeneratorType, U: UnicodeCodecType where G.Element == U.CodeUnit>: GeneratorType {
  typealias Element = Character
  var source: G
  var decoder: U
  
  mutating func next() -> Character? {
    guard case .Result(let scalar) = self.decoder.decode(&self.source) else {
      return nil
    }
    return Character(scalar)
  }
}

struct LineGenerator<G: GeneratorType where G.Element == Character>: GeneratorType {
  typealias Element = String
  var source: G
  
  mutating func next() -> String? {
    guard let fst = source.next() else {
      return nil
    }
    guard fst != "\n" else {
      return ""
    }
    var line = String(fst)
    while let ch = source.next() {
      if (ch == "\n") {
        return line
      }
      line.append(ch)
    }
    return line
  }
}

if let input = ByteGenerator(path: "/Users/username/Desktop/filename.txt") {
  var generator = LineGenerator(source: CharacterGenerator(source: input, decoder: UTF8()))
  var i = 0
  while let line = generator.next() {
    print("\(i): \(line)")
    i += 1
  }
}