SWCompression/Sources/DataWithPointer.swift

//
//  DataWithPointer.swift
//  SWCompression
//
//  Created by Timofey Solomko on 01.11.16.
//  Copyright © 2016 Timofey Solomko. All rights reserved.
//

import Foundation

enum BitOrder {
    case straight
    case reversed
}

class DataWithPointer {

    private let bitOrder: BitOrder
    private let bitArray: [UInt8]
    var index: Int = 0
    private(set) var bitMask: UInt8

    init(data: Data, bitOrder: BitOrder) {
        self.bitOrder = bitOrder
        self.bitArray = data.toArray(type: UInt8.self)

        switch self.bitOrder {
        case .reversed:
            self.bitMask = 1
        case .straight:
            self.bitMask = 128
        }
    }

    func bits(count: Int) -> [UInt8] {
        guard count > 0 else { return [] }

        var array: [UInt8] = Array(repeating: 0, count: count)
        for i in 0..<count {
            array[i] = self.bitArray[self.index] & self.bitMask > 0 ? 1 : 0

            switch self.bitOrder {
            case .reversed:
                if self.bitMask == 128 {
                    self.index += 1
                    self.bitMask = 1
                } else {
                    self.bitMask <<= 1
                }
            case .straight:
                if self.bitMask == 1 {
                    self.index += 1
                    self.bitMask = 128
                } else {
                    self.bitMask >>= 1
                }
            }
        }

        return array
    }

    func intFromBits(count: Int) -> Int {
        guard count > 0 else { return 0 }

        var result = 0
        for i in 0..<count {
            let power: Int
            switch self.bitOrder {
            case .straight:
                power = count - i - 1
            case .reversed:
                power = i
            }

            let bit = self.bitArray[self.index] & self.bitMask > 0 ? 1 : 0
            result += Int(pow(Double(2), Double(power))) * bit

            switch self.bitOrder {
            case .reversed:
                if self.bitMask == 128 {
                    self.index += 1
                    self.bitMask = 1
                } else {
                    self.bitMask <<= 1
                }
            case .straight:
                if self.bitMask == 1 {
                    self.index += 1
                    self.bitMask = 128
                } else {
                    self.bitMask >>= 1
                }
            }
        }

        return result
    }

    func bit() -> UInt8 {
        return self.bits(count: 1).first!
    }

    func alignedByte() -> UInt8 {
        self.skipUntilNextByte()
        self.index += 1
        return self.bitArray[self.index - 1]
    }

    // MARK: Manipulations with index and bitShift

    func skipUntilNextByte() {
        switch self.bitOrder {
        case .reversed:
            guard self.bitMask != 1 else { return }
            self.bitMask = 1
        case .straight:
            guard self.bitMask != 128 else { return }
            self.bitMask = 128
        }
        self.index += 1
    }

}