//
//
// Copyright 2015 gRPC 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 GRPC_SRC_CORE_LIB_SECURITY_TRANSPORT_AUTH_FILTERS_H
#define GRPC_SRC_CORE_LIB_SECURITY_TRANSPORT_AUTH_FILTERS_H

#include "absl/status/statusor.h"

#include <grpc/credentials.h>
#include <grpc/grpc_security.h>
#include <grpc/grpc_security_constants.h>
#include <grpc/support/port_platform.h>

#include "src/core/lib/channel/channel_args.h"
#include "src/core/lib/channel/channel_fwd.h"
#include "src/core/lib/channel/channel_stack.h"
#include "src/core/lib/channel/promise_based_filter.h"
#include "src/core/lib/gprpp/ref_counted_ptr.h"
#include "src/core/lib/promise/arena_promise.h"
#include "src/core/lib/security/credentials/credentials.h"
#include "src/core/lib/security/security_connector/security_connector.h"
#include "src/core/lib/transport/transport.h"

namespace grpc_core {

// Handles calling out to credentials to fill in metadata per call.
class ClientAuthFilter final : public ChannelFilter {
 public:
  static const grpc_channel_filter kFilter;

  ClientAuthFilter(
      RefCountedPtr<grpc_channel_security_connector> security_connector,
      RefCountedPtr<grpc_auth_context> auth_context);

  static absl::StatusOr<std::unique_ptr<ClientAuthFilter>> Create(
      const ChannelArgs& args, ChannelFilter::Args);

  // Construct a promise for one call.
  ArenaPromise<ServerMetadataHandle> MakeCallPromise(
      CallArgs call_args, NextPromiseFactory next_promise_factory) override;

 private:
  ArenaPromise<absl::StatusOr<CallArgs>> GetCallCredsMetadata(
      CallArgs call_args);

  // Contains refs to security connector and auth context.
  grpc_call_credentials::GetRequestMetadataArgs args_;
};

class ServerAuthFilter final : public ImplementChannelFilter<ServerAuthFilter> {
 private:
  class RunApplicationCode {
   public:
    RunApplicationCode(ServerAuthFilter* filter, ClientMetadata& metadata);

    RunApplicationCode(const RunApplicationCode&) = delete;
    RunApplicationCode& operator=(const RunApplicationCode&) = delete;
    RunApplicationCode(RunApplicationCode&& other) noexcept
        : state_(std::exchange(other.state_, nullptr)) {}
    RunApplicationCode& operator=(RunApplicationCode&& other) noexcept {
      state_ = std::exchange(other.state_, nullptr);
      return *this;
    }

    Poll<absl::Status> operator()();

   private:
    // Called from application code.
    static void OnMdProcessingDone(void* user_data,
                                   const grpc_metadata* consumed_md,
                                   size_t num_consumed_md,
                                   const grpc_metadata* response_md,
                                   size_t num_response_md,
                                   grpc_status_code status,
                                   const char* error_details);

    struct State;
    State* state_;
  };

 public:
  static const grpc_channel_filter kFilter;

  ServerAuthFilter(RefCountedPtr<grpc_server_credentials> server_credentials,
                   RefCountedPtr<grpc_auth_context> auth_context);

  static absl::StatusOr<std::unique_ptr<ServerAuthFilter>> Create(
      const ChannelArgs& args, ChannelFilter::Args);

  class Call {
   public:
    explicit Call(ServerAuthFilter* filter);
    auto OnClientInitialMetadata(ClientMetadata& md, ServerAuthFilter* filter) {
      return If(
          filter->server_credentials_ == nullptr ||
              filter->server_credentials_->auth_metadata_processor().process ==
                  nullptr,
          ImmediateOkStatus(),
          [filter, md = &md]() { return RunApplicationCode(filter, *md); });
    }
    static const NoInterceptor OnServerInitialMetadata;
    static const NoInterceptor OnClientToServerMessage;
    static const NoInterceptor OnServerToClientMessage;
    static const NoInterceptor OnServerTrailingMetadata;
    static const NoInterceptor OnFinalize;
  };

 private:
  ArenaPromise<absl::StatusOr<CallArgs>> GetCallCredsMetadata(
      CallArgs call_args);

  RefCountedPtr<grpc_server_credentials> server_credentials_;
  RefCountedPtr<grpc_auth_context> auth_context_;
};

}  // namespace grpc_core

// Exposed for testing purposes only.
// Check if the channel's security level is higher or equal to
// that of call credentials to make a decision whether the transfer
// of call credentials should be allowed or not.
bool grpc_check_security_level(grpc_security_level channel_level,
                               grpc_security_level call_cred_level);

#endif  // GRPC_SRC_CORE_LIB_SECURITY_TRANSPORT_AUTH_FILTERS_H