// Copyright 2023 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import CryptoKit
import Foundation

/// Set of utility APIs for generating cryptographical artifacts.
enum CryptoUtils {
  enum NonceGenerationError: Error {
    case generationFailure(status: OSStatus)
  }

  static func randomNonceString(length: Int = 32) throws -> String {
    precondition(length > 0)
    var randomBytes = [UInt8](repeating: 0, count: length)
    let errorCode = SecRandomCopyBytes(kSecRandomDefault, randomBytes.count, &randomBytes)
    if errorCode != errSecSuccess {
      throw NonceGenerationError.generationFailure(status: errorCode)
    }

    let charset: [Character] =
      Array("0123456789ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz-._")

    let nonce = randomBytes.map { byte in
      // Pick a random character from the set, wrapping around if needed.
      charset[Int(byte) % charset.count]
    }

    return String(nonce)
  }

  static func sha256(_ input: String) -> String {
    let inputData = Data(input.utf8)
    let hashedData = SHA256.hash(data: inputData)
    let hashString = hashedData.compactMap {
      String(format: "%02x", $0)
    }.joined()

    return hashString
  }
}