//
//  CryptoSwift
//
//  Copyright (C) 2014-2017 Marcin Krzyżanowski <marcin@krzyzanowskim.com>
//  This software is provided 'as-is', without any express or implied warranty.
//
//  In no event will the authors be held liable for any damages arising from the use of this software.
//
//  Permission is granted to anyone to use this software for any purpose,including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions:
//
//  - The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation is required.
//  - Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
//  - This notice may not be removed or altered from any source or binary distribution.
//

public final class MD5: DigestType {
  static let blockSize: Int = 64
  static let digestLength: Int = 16 // 128 / 8
  fileprivate static let hashInitialValue: Array<UInt32> = [0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476]

  fileprivate var accumulated = Array<UInt8>()
  fileprivate var processedBytesTotalCount: Int = 0
  fileprivate var accumulatedHash: Array<UInt32> = MD5.hashInitialValue

  /** specifies the per-round shift amounts */
  private let s: Array<UInt32> = [
    7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22,
    5, 9, 14, 20, 5, 9, 14, 20, 5, 9, 14, 20, 5, 9, 14, 20,
    4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23,
    6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21
  ]

  /** binary integer part of the sines of integers (Radians) */
  private let k: Array<UInt32> = [
    0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee,
    0xf57c0faf, 0x4787c62a, 0xa8304613, 0xfd469501,
    0x698098d8, 0x8b44f7af, 0xffff5bb1, 0x895cd7be,
    0x6b901122, 0xfd987193, 0xa679438e, 0x49b40821,
    0xf61e2562, 0xc040b340, 0x265e5a51, 0xe9b6c7aa,
    0xd62f105d, 0x2441453, 0xd8a1e681, 0xe7d3fbc8,
    0x21e1cde6, 0xc33707d6, 0xf4d50d87, 0x455a14ed,
    0xa9e3e905, 0xfcefa3f8, 0x676f02d9, 0x8d2a4c8a,
    0xfffa3942, 0x8771f681, 0x6d9d6122, 0xfde5380c,
    0xa4beea44, 0x4bdecfa9, 0xf6bb4b60, 0xbebfbc70,
    0x289b7ec6, 0xeaa127fa, 0xd4ef3085, 0x4881d05,
    0xd9d4d039, 0xe6db99e5, 0x1fa27cf8, 0xc4ac5665,
    0xf4292244, 0x432aff97, 0xab9423a7, 0xfc93a039,
    0x655b59c3, 0x8f0ccc92, 0xffeff47d, 0x85845dd1,
    0x6fa87e4f, 0xfe2ce6e0, 0xa3014314, 0x4e0811a1,
    0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391
  ]

  public init() {
  }

  public func calculate(for bytes: Array<UInt8>) -> Array<UInt8> {
    do {
      return try update(withBytes: bytes.slice, isLast: true)
    } catch {
      fatalError()
    }
  }

  // mutating currentHash in place is way faster than returning new result
  fileprivate func process(block chunk: ArraySlice<UInt8>, currentHash: inout Array<UInt32>) {
    assert(chunk.count == 16 * 4)

    // Initialize hash value for this chunk:
    var A: UInt32 = currentHash[0]
    var B: UInt32 = currentHash[1]
    var C: UInt32 = currentHash[2]
    var D: UInt32 = currentHash[3]

    var dTemp: UInt32 = 0

    // Main loop
    for j in 0..<self.k.count {
      var g = 0
      var F: UInt32 = 0

      switch j {
        case 0...15:
          F = (B & C) | ((~B) & D)
          g = j
        case 16...31:
          F = (D & B) | (~D & C)
          g = (5 * j + 1) % 16
        case 32...47:
          F = B ^ C ^ D
          g = (3 * j + 5) % 16
        case 48...63:
          F = C ^ (B | (~D))
          g = (7 * j) % 16
        default:
          break
      }
      dTemp = D
      D = C
      C = B

      // break chunk into sixteen 32-bit words M[j], 0 ≤ j ≤ 15 and get M[g] value
      let gAdvanced = g << 2

      var Mg = UInt32(chunk[chunk.startIndex &+ gAdvanced])
      Mg |= UInt32(chunk[chunk.startIndex &+ gAdvanced &+ 1]) << 8
      Mg |= UInt32(chunk[chunk.startIndex &+ gAdvanced &+ 2]) << 16
      Mg |= UInt32(chunk[chunk.startIndex &+ gAdvanced &+ 3]) << 24

      B = B &+ rotateLeft(A &+ F &+ self.k[j] &+ Mg, by: self.s[j])
      A = dTemp
    }

    currentHash[0] = currentHash[0] &+ A
    currentHash[1] = currentHash[1] &+ B
    currentHash[2] = currentHash[2] &+ C
    currentHash[3] = currentHash[3] &+ D
  }
}

extension MD5: Updatable {
  public func update(withBytes bytes: ArraySlice<UInt8>, isLast: Bool = false) throws -> Array<UInt8> {
    self.accumulated += bytes

    if isLast {
      let lengthInBits = (processedBytesTotalCount + self.accumulated.count) * 8
      let lengthBytes = lengthInBits.bytes(totalBytes: 64 / 8) // A 64-bit representation of b

      // Step 1. Append padding
      bitPadding(to: &self.accumulated, blockSize: MD5.blockSize, allowance: 64 / 8)

      // Step 2. Append Length a 64-bit representation of lengthInBits
      self.accumulated += lengthBytes.reversed()
    }

    var processedBytes = 0
    for chunk in self.accumulated.batched(by: MD5.blockSize) {
      if isLast || (self.accumulated.count - processedBytes) >= MD5.blockSize {
        self.process(block: chunk, currentHash: &self.accumulatedHash)
        processedBytes += chunk.count
      }
    }
    self.accumulated.removeFirst(processedBytes)
    self.processedBytesTotalCount += processedBytes

    // output current hash
    var result = Array<UInt8>()
    result.reserveCapacity(MD5.digestLength)

    for hElement in self.accumulatedHash {
      let hLE = hElement.littleEndian
      result += Array<UInt8>(arrayLiteral: UInt8(hLE & 0xff), UInt8((hLE >> 8) & 0xff), UInt8((hLE >> 16) & 0xff), UInt8((hLE >> 24) & 0xff))
    }

    // reset hash value for instance
    if isLast {
      self.accumulatedHash = MD5.hashInitialValue
    }

    return result
  }
}
