//
//  Crypto+Utils.swift
//  H2OPal Demo App
//
//  Created by Matic Kunaver on 19/02/2017.
//  Copyright © 2017 Out of Galaxy, Inc. All rights reserved.
//

import Foundation

enum CryptoAlgorithm {
  case MD5, SHA1, SHA224, SHA256, SHA384, SHA512

  var HMACAlgorithm: CCHmacAlgorithm {
    var result: Int = 0
    switch self {
    case .MD5:      result = kCCHmacAlgMD5
    case .SHA1:     result = kCCHmacAlgSHA1
    case .SHA224:   result = kCCHmacAlgSHA224
    case .SHA256:   result = kCCHmacAlgSHA256
    case .SHA384:   result = kCCHmacAlgSHA384
    case .SHA512:   result = kCCHmacAlgSHA512
    }
    return CCHmacAlgorithm(result)
  }

  var digestLength: Int {
    var result: Int32 = 0
    switch self {
    case .MD5:      result = CC_MD5_DIGEST_LENGTH
    case .SHA1:     result = CC_SHA1_DIGEST_LENGTH
    case .SHA224:   result = CC_SHA224_DIGEST_LENGTH
    case .SHA256:   result = CC_SHA256_DIGEST_LENGTH
    case .SHA384:   result = CC_SHA384_DIGEST_LENGTH
    case .SHA512:   result = CC_SHA512_DIGEST_LENGTH
    }
    return Int(result)
  }
}

extension String {

  func hmac(algorithm: CryptoAlgorithm, key: String) -> String {
    let str = self.cString(using: String.Encoding.utf8)
    let strLen = Int(self.lengthOfBytes(using: String.Encoding.utf8))
    let digestLen = algorithm.digestLength
    let result = UnsafeMutablePointer<CUnsignedChar>.allocate(capacity: digestLen)
    let keyStr = key.cString(using: String.Encoding.utf8)
    let keyLen = Int(key.lengthOfBytes(using: String.Encoding.utf8))

    CCHmac(algorithm.HMACAlgorithm, keyStr!, keyLen, str!, strLen, result)

    let digest = stringFromResult(result: result, length: digestLen)

    result.deallocate(capacity: digestLen)

    return digest
  }

  private func stringFromResult(result: UnsafeMutablePointer<CUnsignedChar>, length: Int) -> String {
    let hash = NSMutableString()
    for i in 0..<length {
      hash.appendFormat("%02x", result[i])
    }
    return String(hash)
  }

}
