//
//  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.
//

//  TODO: generic for process32/64 (UInt32/UInt64)
//

public final class SHA2: DigestType {
  @usableFromInline
  let variant: Variant

  @usableFromInline
  let size: Int

  @usableFromInline
  let blockSize: Int

  @usableFromInline
  let digestLength: Int

  private let k: Array<UInt64>

  @usableFromInline
  var accumulated = Array<UInt8>()

  @usableFromInline
  var processedBytesTotalCount: Int = 0

  @usableFromInline
  var accumulatedHash32 = Array<UInt32>()

  @usableFromInline
  var accumulatedHash64 = Array<UInt64>()

  public enum Variant: RawRepresentable {
    case sha224, sha256, sha384, sha512

    public var digestLength: Int {
      self.rawValue / 8
    }

    public var blockSize: Int {
      switch self {
        case .sha224, .sha256:
          return 64
        case .sha384, .sha512:
          return 128
      }
    }

    public typealias RawValue = Int
    public var rawValue: RawValue {
      switch self {
        case .sha224:
          return 224
        case .sha256:
          return 256
        case .sha384:
          return 384
        case .sha512:
          return 512
      }
    }

    public init?(rawValue: RawValue) {
      switch rawValue {
        case 224:
          self = .sha224
        case 256:
          self = .sha256
        case 384:
          self = .sha384
        case 512:
          self = .sha512
        default:
          return nil
      }
    }

    @usableFromInline
    var h: Array<UInt64> {
      switch self {
        case .sha224:
          return [0xc1059ed8, 0x367cd507, 0x3070dd17, 0xf70e5939, 0xffc00b31, 0x68581511, 0x64f98fa7, 0xbefa4fa4]
        case .sha256:
          return [0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19]
        case .sha384:
          return [0xcbbb9d5dc1059ed8, 0x629a292a367cd507, 0x9159015a3070dd17, 0x152fecd8f70e5939, 0x67332667ffc00b31, 0x8eb44a8768581511, 0xdb0c2e0d64f98fa7, 0x47b5481dbefa4fa4]
        case .sha512:
          return [0x6a09e667f3bcc908, 0xbb67ae8584caa73b, 0x3c6ef372fe94f82b, 0xa54ff53a5f1d36f1, 0x510e527fade682d1, 0x9b05688c2b3e6c1f, 0x1f83d9abfb41bd6b, 0x5be0cd19137e2179]
      }
    }

    @usableFromInline
    var finalLength: Int {
      switch self {
        case .sha224:
          return 7
        case .sha384:
          return 6
        default:
          return Int.max
      }
    }
  }

  public init(variant: SHA2.Variant) {
    self.variant = variant
    switch self.variant {
      case .sha224, .sha256:
        self.accumulatedHash32 = variant.h.map { UInt32($0) } // FIXME: UInt64 for process64
        self.blockSize = variant.blockSize
        self.size = variant.rawValue
        self.digestLength = variant.digestLength
        self.k = [
          0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
          0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
          0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
          0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
          0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
          0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
          0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
          0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
        ]
      case .sha384, .sha512:
        self.accumulatedHash64 = variant.h
        self.blockSize = variant.blockSize
        self.size = variant.rawValue
        self.digestLength = variant.digestLength
        self.k = [
          0x428a2f98d728ae22, 0x7137449123ef65cd, 0xb5c0fbcfec4d3b2f, 0xe9b5dba58189dbbc, 0x3956c25bf348b538,
          0x59f111f1b605d019, 0x923f82a4af194f9b, 0xab1c5ed5da6d8118, 0xd807aa98a3030242, 0x12835b0145706fbe,
          0x243185be4ee4b28c, 0x550c7dc3d5ffb4e2, 0x72be5d74f27b896f, 0x80deb1fe3b1696b1, 0x9bdc06a725c71235,
          0xc19bf174cf692694, 0xe49b69c19ef14ad2, 0xefbe4786384f25e3, 0x0fc19dc68b8cd5b5, 0x240ca1cc77ac9c65,
          0x2de92c6f592b0275, 0x4a7484aa6ea6e483, 0x5cb0a9dcbd41fbd4, 0x76f988da831153b5, 0x983e5152ee66dfab,
          0xa831c66d2db43210, 0xb00327c898fb213f, 0xbf597fc7beef0ee4, 0xc6e00bf33da88fc2, 0xd5a79147930aa725,
          0x06ca6351e003826f, 0x142929670a0e6e70, 0x27b70a8546d22ffc, 0x2e1b21385c26c926, 0x4d2c6dfc5ac42aed,
          0x53380d139d95b3df, 0x650a73548baf63de, 0x766a0abb3c77b2a8, 0x81c2c92e47edaee6, 0x92722c851482353b,
          0xa2bfe8a14cf10364, 0xa81a664bbc423001, 0xc24b8b70d0f89791, 0xc76c51a30654be30, 0xd192e819d6ef5218,
          0xd69906245565a910, 0xf40e35855771202a, 0x106aa07032bbd1b8, 0x19a4c116b8d2d0c8, 0x1e376c085141ab53,
          0x2748774cdf8eeb99, 0x34b0bcb5e19b48a8, 0x391c0cb3c5c95a63, 0x4ed8aa4ae3418acb, 0x5b9cca4f7763e373,
          0x682e6ff3d6b2b8a3, 0x748f82ee5defb2fc, 0x78a5636f43172f60, 0x84c87814a1f0ab72, 0x8cc702081a6439ec,
          0x90befffa23631e28, 0xa4506cebde82bde9, 0xbef9a3f7b2c67915, 0xc67178f2e372532b, 0xca273eceea26619c,
          0xd186b8c721c0c207, 0xeada7dd6cde0eb1e, 0xf57d4f7fee6ed178, 0x06f067aa72176fba, 0x0a637dc5a2c898a6,
          0x113f9804bef90dae, 0x1b710b35131c471b, 0x28db77f523047d84, 0x32caab7b40c72493, 0x3c9ebe0a15c9bebc,
          0x431d67c49c100d4c, 0x4cc5d4becb3e42b6, 0x597f299cfc657e2a, 0x5fcb6fab3ad6faec, 0x6c44198c4a475817
        ]
    }
  }

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

  @usableFromInline
  func process64(block chunk: ArraySlice<UInt8>, currentHash hh: inout Array<UInt64>) {
    // break chunk into sixteen 64-bit words M[j], 0 ≤ j ≤ 15, big-endian
    // Extend the sixteen 64-bit words into eighty 64-bit words:
    let M = UnsafeMutablePointer<UInt64>.allocate(capacity: self.k.count)
    M.initialize(repeating: 0, count: self.k.count)
    defer {
      M.deinitialize(count: self.k.count)
      M.deallocate()
    }
    for x in 0..<self.k.count {
      switch x {
        case 0...15:
          let start = chunk.startIndex.advanced(by: x * 8) // * MemoryLayout<UInt64>.size
          M[x] = UInt64(bytes: chunk, fromIndex: start)
        default:
          let s0 = rotateRight(M[x - 15], by: 1) ^ rotateRight(M[x - 15], by: 8) ^ (M[x - 15] >> 7)
          let s1 = rotateRight(M[x - 2], by: 19) ^ rotateRight(M[x - 2], by: 61) ^ (M[x - 2] >> 6)
          M[x] = M[x - 16] &+ s0 &+ M[x - 7] &+ s1
      }
    }

    var A = hh[0]
    var B = hh[1]
    var C = hh[2]
    var D = hh[3]
    var E = hh[4]
    var F = hh[5]
    var G = hh[6]
    var H = hh[7]

    // Main loop
    for j in 0..<self.k.count {
      let s0 = rotateRight(A, by: 28) ^ rotateRight(A, by: 34) ^ rotateRight(A, by: 39)
      let maj = (A & B) ^ (A & C) ^ (B & C)
      let t2 = s0 &+ maj
      let s1 = rotateRight(E, by: 14) ^ rotateRight(E, by: 18) ^ rotateRight(E, by: 41)
      let ch = (E & F) ^ ((~E) & G)
      let t1 = H &+ s1 &+ ch &+ self.k[j] &+ UInt64(M[j])

      H = G
      G = F
      F = E
      E = D &+ t1
      D = C
      C = B
      B = A
      A = t1 &+ t2
    }

    hh[0] = (hh[0] &+ A)
    hh[1] = (hh[1] &+ B)
    hh[2] = (hh[2] &+ C)
    hh[3] = (hh[3] &+ D)
    hh[4] = (hh[4] &+ E)
    hh[5] = (hh[5] &+ F)
    hh[6] = (hh[6] &+ G)
    hh[7] = (hh[7] &+ H)
  }

  // mutating currentHash in place is way faster than returning new result
  @usableFromInline
  func process32(block chunk: ArraySlice<UInt8>, currentHash hh: inout Array<UInt32>) {
    // break chunk into sixteen 32-bit words M[j], 0 ≤ j ≤ 15, big-endian
    // Extend the sixteen 32-bit words into sixty-four 32-bit words:
    let M = UnsafeMutablePointer<UInt32>.allocate(capacity: self.k.count)
    M.initialize(repeating: 0, count: self.k.count)
    defer {
      M.deinitialize(count: self.k.count)
      M.deallocate()
    }

    for x in 0..<self.k.count {
      switch x {
        case 0...15:
          let start = chunk.startIndex.advanced(by: x * 4) // * MemoryLayout<UInt32>.size
          M[x] = UInt32(bytes: chunk, fromIndex: start)
        default:
          let s0 = rotateRight(M[x - 15], by: 7) ^ rotateRight(M[x - 15], by: 18) ^ (M[x - 15] >> 3)
          let s1 = rotateRight(M[x - 2], by: 17) ^ rotateRight(M[x - 2], by: 19) ^ (M[x - 2] >> 10)
          M[x] = M[x - 16] &+ s0 &+ M[x - 7] &+ s1
      }
    }

    var A = hh[0]
    var B = hh[1]
    var C = hh[2]
    var D = hh[3]
    var E = hh[4]
    var F = hh[5]
    var G = hh[6]
    var H = hh[7]

    // Main loop
    for j in 0..<self.k.count {
      let s0 = rotateRight(A, by: 2) ^ rotateRight(A, by: 13) ^ rotateRight(A, by: 22)
      let maj = (A & B) ^ (A & C) ^ (B & C)
      let t2 = s0 &+ maj
      let s1 = rotateRight(E, by: 6) ^ rotateRight(E, by: 11) ^ rotateRight(E, by: 25)
      let ch = (E & F) ^ ((~E) & G)
      let t1 = H &+ s1 &+ ch &+ UInt32(self.k[j]) &+ M[j]

      H = G
      G = F
      F = E
      E = D &+ t1
      D = C
      C = B
      B = A
      A = t1 &+ t2
    }

    hh[0] = hh[0] &+ A
    hh[1] = hh[1] &+ B
    hh[2] = hh[2] &+ C
    hh[3] = hh[3] &+ D
    hh[4] = hh[4] &+ E
    hh[5] = hh[5] &+ F
    hh[6] = hh[6] &+ G
    hh[7] = hh[7] &+ H
  }
}

extension SHA2: Updatable {

  @inlinable
  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: self.blockSize / 8) // A 64-bit/128-bit representation of b. blockSize fit by accident.

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

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

    var processedBytes = 0
    for chunk in self.accumulated.batched(by: self.blockSize) {
      if isLast || (self.accumulated.count - processedBytes) >= self.blockSize {
        switch self.variant {
          case .sha224, .sha256:
            self.process32(block: chunk, currentHash: &self.accumulatedHash32)
          case .sha384, .sha512:
            self.process64(block: chunk, currentHash: &self.accumulatedHash64)
          @unknown default:
            preconditionFailure()
          }
        processedBytes += chunk.count
      }
    }
    self.accumulated.removeFirst(processedBytes)
    self.processedBytesTotalCount += processedBytes

    // output current hash
    var result = Array<UInt8>(repeating: 0, count: variant.digestLength)
    switch self.variant {
      case .sha224, .sha256:
        var pos = 0
        for idx in 0..<self.accumulatedHash32.count where idx < self.variant.finalLength {
          let h = accumulatedHash32[idx]
          result[pos + 0] = UInt8((h >> 24) & 0xff)
          result[pos + 1] = UInt8((h >> 16) & 0xff)
          result[pos + 2] = UInt8((h >> 8) & 0xff)
          result[pos + 3] = UInt8(h & 0xff)
          pos += 4
        }
      case .sha384, .sha512:
        var pos = 0
        for idx in 0..<self.accumulatedHash64.count where idx < self.variant.finalLength {
          let h = accumulatedHash64[idx]
          result[pos + 0] = UInt8((h >> 56) & 0xff)
          result[pos + 1] = UInt8((h >> 48) & 0xff)
          result[pos + 2] = UInt8((h >> 40) & 0xff)
          result[pos + 3] = UInt8((h >> 32) & 0xff)
          result[pos + 4] = UInt8((h >> 24) & 0xff)
          result[pos + 5] = UInt8((h >> 16) & 0xff)
          result[pos + 6] = UInt8((h >> 8) & 0xff)
          result[pos + 7] = UInt8(h & 0xff)
          pos += 8
        }
      @unknown default:
          preconditionFailure()
    }

    // reset hash value for instance
    if isLast {
      switch self.variant {
        case .sha224, .sha256:
          self.accumulatedHash32 = self.variant.h.lazy.map { UInt32($0) } // FIXME: UInt64 for process64
        case .sha384, .sha512:
          self.accumulatedHash64 = self.variant.h
        @unknown default:
          preconditionFailure()
      }
    }

    return result
  }
}
