// Copyright 2016 The Fuchsia Authors
//
// 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.

#ifndef COBALT_ENCODER_CLIENT_SECRET_H_
#define COBALT_ENCODER_CLIENT_SECRET_H_

#include <string>
#include <utility>
#include <vector>

#include "util/crypto_util/random.h"
#include "util/crypto_util/types.h"

namespace cobalt {
namespace encoder {

using crypto::byte;

// A ClientSecret is a wrapper around an array of bytes containing
// random bytes from a CSPRNG. Clients should invoke GenerateNewSecret()
// once, and then permanently and securely save the token returned by
// GetToken(). After that clients should reconstruct the token using
// FromToken().
//
// Tokens are passed into several different methods in the Encoder API.
class ClientSecret {
 public:
  // Move constructor
  ClientSecret(ClientSecret&& other) { bytes_ = std::move(other.bytes_); }

  // Copy constructor
  ClientSecret(const ClientSecret& other) { bytes_ = other.bytes_; }

  bool operator==(const ClientSecret& other) const {
    if (!valid() || !other.valid()) {
      return false;
    }
    return bytes_ == other.bytes_;
  }

  bool operator!=(const ClientSecret& other) const {
    return !operator==(other);
  }

  // Returns a ClientSecret with freshly generated bytes.
  static ClientSecret GenerateNewSecret();

  // Returns a ClientSecret with bytes decoded from |token|. If token is not
  // valid then the returned ClientSecret will have valid() == false.
  static ClientSecret FromToken(const std::string& token);

  // Is this ClientSecret valid? An invalid ClientSecret may occur when an
  // invalid token is passed to FromToken(), or after a move occurs.
  bool valid() const { return !bytes_.empty(); }

  // Returns a token that may be used to reconstitute this ClientSecret
  // using the FromToken() function. Returns the empty string if this
  // ClientSecret is not valid.
  //
  // This method is not thread safe.
  std::string GetToken();

  const byte* data() const { return bytes_.data(); }

  static const size_t kNumSecretBytes = 16;

  // For internal testing use only. Does not take ownership of |rand|.
  // Uses |rand| to generate the new secret.
  static ClientSecret GenerateNewSecret(crypto::Random* rand);

 private:
  // Private default constructor
  ClientSecret() {}
  std::vector<byte> bytes_;
};

}  // namespace encoder
}  // namespace cobalt

#endif  // COBALT_ENCODER_CLIENT_SECRET_H_