buffer.swift

//
//  buffer.swift
//
//  Created by H.J. Banken on 06/10/2015.
//  Copyright (c) 2015 Q42 Internet B.V. All rights reserved.
//

public class BufferList<T> {
  private let maker: (Int -> T?)
  private let offset: Int
  let length: Int

  private let bufferSize: Int
  private var bufferPointers: [Int] = []
  private var buffer: [Int:T?] = [:]

  public init(maker: (Int -> T?), length:Int, offset:Int = 0, bufferSize: Int = -1){
    self.maker = maker
    self.offset = offset
    self.length = length
    self.bufferSize = bufferSize
  }

  public func map<V>(mapper:T->V)->BufferList<V> {
    return BufferList<V>(
      maker: { index in
        if let outer = self[index] {
          return mapper(outer)
        }
        return nil
      },
      length: self.length,
      offset: self.offset
    )
  }

  public func map<V>(mapper:T->V?)->BufferList<V> {
    return BufferList<V>(
      maker: { index in
        if let outer = self[index] {
          return mapper(outer)
        }
        return nil
      },
      length: self.length,
      offset: self.offset
    )
  }

  public subscript(i:Int)->T? {
    if (0 <= i && i < length) {
      if let val = buffer[i] {
        // Buffered
        return val
      } else {
        // Unbuffered, make
        let val = maker(i)

        // Shrink buffer
        while (bufferSize >= 0 && bufferPointers.count > 0 && bufferPointers.count > bufferSize) {
          if let index = buffer.indexForKey(bufferPointers[0]) {
            buffer.removeAtIndex(index)
          }
          bufferPointers.removeAtIndex(0)
        }

        if (bufferSize > 0) {
          buffer[i] = val
        }

        return val
      }
    }

    return nil
  }

  public static func empty() -> BufferList<T> {
    return bufferlist(0, 0) { index in nil }
  }

  public func interleave(element: T) -> BufferList<T> {
    return bufferlist(length * 2, bufferSize * 2) { index in
      index % 2 == 1 ? element : self.maker(index / 2)
    }
  }
}

public func bufferlist<T>(count:Int, makerone: Int->T?)->BufferList<T> {
  return BufferList (
    maker: makerone,
    length: count,
    offset: 0,
    bufferSize: count
  )
}

public func bufferlist<T>(count:Int, bufferSize:Int, makerone: Int->T?)->BufferList<T> {
  return BufferList (
    maker: makerone,
    length: count,
    offset: 0,
    bufferSize: bufferSize
  )
}