// Copyright 2025 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef QUICHE_QUIC_MASQUE_MASQUE_OHTTP_CLIENT_H_
#define QUICHE_QUIC_MASQUE_MASQUE_OHTTP_CLIENT_H_

#include <functional>
#include <memory>
#include <optional>
#include <string>
#include <utility>
#include <vector>

#include "absl/base/nullability.h"
#include "absl/container/flat_hash_map.h"
#include "absl/status/status.h"
#include "absl/status/statusor.h"
#include "absl/strings/string_view.h"
#include "openssl/base.h"
#include "quiche/quic/core/io/quic_event_loop.h"
#include "quiche/quic/masque/masque_connection_pool.h"
#include "quiche/quic/tools/quic_url.h"
#include "quiche/binary_http/binary_http_message.h"
#include "quiche/common/platform/api/quiche_export.h"
#include "quiche/oblivious_http/buffers/oblivious_http_request.h"
#include "quiche/oblivious_http/common/oblivious_http_chunk_handler.h"
#include "quiche/oblivious_http/oblivious_http_client.h"

namespace quic {

// A client that sends OHTTP requests through a relay/gateway to target URLs.
class QUICHE_EXPORT MasqueOhttpClient
    : public quic::MasqueConnectionPool::Visitor {
 public:
  using RequestId = quic::MasqueConnectionPool::RequestId;
  using Message = quic::MasqueConnectionPool::Message;

  class QUICHE_NO_EXPORT Config {
   public:
    class QUICHE_NO_EXPORT PerRequestConfig {
     public:
      explicit PerRequestConfig(const std::string& url) : url_(url) {}
      // Copyable and movable.
      PerRequestConfig(const PerRequestConfig& other) = default;
      PerRequestConfig& operator=(const PerRequestConfig& other) = default;
      PerRequestConfig(PerRequestConfig&& other) = default;
      PerRequestConfig& operator=(PerRequestConfig&& other) = default;

      void SetPostData(const std::string& post_data) { post_data_ = post_data; }
      void SetMethod(const std::string& method) { method_ = method; }
      absl::Status AddHeaders(const std::vector<std::string>& headers);
      absl::Status AddOuterHeaders(
          const std::vector<std::string>& outer_headers);
      absl::Status AddPrivateToken(const std::string& private_token);
      void SetNumBhttpChunks(int num_chunks) { num_bhttp_chunks_ = num_chunks; }
      void SetNumOhttpChunks(int num_chunks) { num_ohttp_chunks_ = num_chunks; }
      void SetPingPongMode(bool ping_pong_mode) {
        ping_pong_mode_ = ping_pong_mode;
      }
      void SetExpectedGatewayError(const std::string& expected_gateway_error) {
        expected_gateway_error_ = expected_gateway_error;
      }
      void SetExpectedGatewayStatusCode(uint16_t status_code) {
        expected_gateway_status_code_ = status_code;
      }
      void SetExpectedEncapsulatedStatusCode(uint16_t status_code) {
        expected_encapsulated_status_code_ = status_code;
      }
      void SetEncapsulatedResponseBodyCallback(
          std::function<absl::Status(absl::string_view)> callback) {
        encapsulated_response_body_callback_ = std::move(callback);
      }

      std::string url() const { return url_; }
      std::string post_data() const { return post_data_; }
      std::string method() const;
      const std::vector<std::pair<std::string, std::string>>& headers() const {
        return headers_;
      }
      const std::vector<std::pair<std::string, std::string>>& outer_headers()
          const {
        return outer_headers_;
      }
      int num_bhttp_chunks() const { return num_bhttp_chunks_; }
      int num_ohttp_chunks() const { return num_ohttp_chunks_; }
      bool ping_pong_mode() const { return ping_pong_mode_; }
      std::optional<std::string> expected_gateway_error() const {
        return expected_gateway_error_;
      }
      std::optional<uint16_t> expected_gateway_status_code() const {
        return expected_gateway_status_code_;
      }
      std::optional<uint16_t> expected_encapsulated_status_code() const {
        return expected_encapsulated_status_code_;
      }
      const std::function<absl::Status(absl::string_view)> absl_nullable&
      encapsulated_response_body_callback() const {
        return encapsulated_response_body_callback_;
      }

     private:
      std::string url_;
      std::string post_data_;
      std::optional<std::string> method_;
      std::vector<std::pair<std::string, std::string>> headers_;
      std::vector<std::pair<std::string, std::string>> outer_headers_;
      int num_ohttp_chunks_ = 0;
      int num_bhttp_chunks_ = -1;
      bool ping_pong_mode_ = false;
      std::optional<std::string> expected_gateway_error_;
      std::optional<uint16_t> expected_gateway_status_code_;
      std::optional<uint16_t> expected_encapsulated_status_code_;
      std::function<absl::Status(absl::string_view)> absl_nullable
      encapsulated_response_body_callback_ = nullptr;
    };

    explicit Config(const std::string& key_fetch_url,
                    const std::string& relay_url)
        : key_fetch_url_(key_fetch_url), relay_url_(relay_url) {}
    // Movable but not copyable.
    Config(const Config& other) = delete;
    Config& operator=(const Config& other) = delete;
    Config(Config&& other) = default;
    Config& operator=(Config&& other) = default;

    absl::Status ConfigureKeyFetchClientCert(
        const std::string& client_cert_file,
        const std::string& client_cert_key_file);
    absl::Status ConfigureKeyFetchClientCertFromData(
        const std::string& client_cert_pem_data,
        const std::string& client_cert_key_data);
    absl::Status ConfigureOhttpMtls(const std::string& client_cert_file,
                                    const std::string& client_cert_key_file);
    absl::Status ConfigureOhttpMtlsFromData(
        const std::string& client_cert_pem_data,
        const std::string& client_cert_key_data);
    void SetDisableCertificateVerification(
        bool disable_certificate_verification) {
      disable_certificate_verification_ = disable_certificate_verification;
    }
    void SetDnsConfig(const MasqueConnectionPool::DnsConfig& dns_config) {
      dns_config_ = dns_config;
    }
    void SetHandleGzipResponse(bool handle_gzip_response) {
      handle_gzip_response_ = handle_gzip_response;
    }
    absl::Status AddKeyFetchHeaders(
        const std::vector<std::string>& key_fetch_headers);
    void AddPerRequestConfig(const PerRequestConfig& per_request_config) {
      per_request_configs_.push_back(per_request_config);
    }

    const std::string& key_fetch_url() const { return key_fetch_url_; }
    const std::string& relay_url() const { return relay_url_; }
    SSL_CTX* key_fetch_ssl_ctx() const { return key_fetch_ssl_ctx_.get(); }
    SSL_CTX* ohttp_ssl_ctx() const { return ohttp_ssl_ctx_.get(); }
    const std::vector<PerRequestConfig>& per_request_configs() const {
      return per_request_configs_;
    }
    bool disable_certificate_verification() const {
      return disable_certificate_verification_;
    }
    const MasqueConnectionPool::DnsConfig& dns_config() const {
      return dns_config_;
    }
    const std::vector<std::pair<std::string, std::string>>& key_fetch_headers()
        const {
      return key_fetch_headers_;
    }
    bool handle_gzip_response() const { return handle_gzip_response_; }

   private:
    std::string key_fetch_url_;
    std::string relay_url_;
    bssl::UniquePtr<SSL_CTX> key_fetch_ssl_ctx_;
    bssl::UniquePtr<SSL_CTX> ohttp_ssl_ctx_;
    bool disable_certificate_verification_ = false;
    MasqueConnectionPool::DnsConfig dns_config_;
    std::vector<std::pair<std::string, std::string>> key_fetch_headers_;
    std::vector<PerRequestConfig> per_request_configs_;
    bool handle_gzip_response_ = false;
  };

  class ResponseVisitor {
   public:
    virtual ~ResponseVisitor() = default;
    virtual void OnRequestStarted(RequestId request_id,
                                  MasqueOhttpClient* client) = 0;
    virtual void OnResponseChunk(RequestId request_id,
                                 absl::string_view chunk) = 0;
    virtual void OnResponseDone(RequestId request_id,
                                const Message& response) = 0;
    virtual void OnError(RequestId request_id, absl::Status status) = 0;
  };

  void set_response_visitor(ResponseVisitor* visitor) {
    response_visitor_ = visitor;
  }

  // Starts by fetching the HPKE keys and then runs the client until all
  // requests are complete or aborted.
  static absl::Status Run(Config config);

  // Sends a body chunk for a chunked OHTTP request.
  absl::Status SendBodyChunk(RequestId request_id, absl::string_view chunk,
                             bool is_final);

  // From quic::MasqueConnectionPool::Visitor.
  void OnPoolResponse(quic::MasqueConnectionPool* /*pool*/,
                      RequestId request_id, absl::StatusOr<Message>&& response,
                      bool end_stream) override;
  void OnPoolData(quic::MasqueConnectionPool* /*pool*/, RequestId request_id,
                  absl::string_view data, bool end_stream) override;

 private:
  // Fetch key from the key URL.
  absl::Status StartKeyFetch(const std::string& url_string);

  // Handles the key response.
  absl::Status HandleKeyResponse(const absl::StatusOr<Message>& response);

  // Handles the key data and starts the OHTTP request.
  absl::Status HandleKeyData(const std::string& key_data);

  // Sends the OHTTP request for the given URL.
  absl::Status SendOhttpRequest(
      const Config::PerRequestConfig& per_request_config);

  // Signals the client to abort.
  void Abort(absl::Status status);

  class QUICHE_NO_EXPORT ChunkHandler
      : public quiche::ObliviousHttpChunkHandler,
        public quiche::BinaryHttpResponse::IndeterminateLengthDecoder::
            MessageSectionHandler {
   public:
    using ResponseChunkCallback = std::function<void(absl::string_view)>;

    explicit ChunkHandler();
    void SetResponseChunkCallback(ResponseChunkCallback callback) {
      response_chunk_callback_ = std::move(callback);
    }
    // Neither copyable nor movable to ensure pointer stability as required for
    // quiche::ObliviousHttpChunkHandler.
    ChunkHandler(const ChunkHandler& other) = delete;
    ChunkHandler& operator=(const ChunkHandler& other) = delete;

    std::optional<quiche::ChunkedObliviousHttpClient>& chunked_client() {
      return chunked_client_;
    }
    ChunkHandler(ChunkHandler&& other) = delete;
    ChunkHandler& operator=(ChunkHandler&& other) = delete;

    // Decrypts a response chunk.
    absl::Status DecryptChunk(absl::string_view encrypted_chunk,
                              bool end_stream);

    void SetChunkedClient(quiche::ChunkedObliviousHttpClient chunked_client) {
      chunked_client_.emplace(std::move(chunked_client));
    }

    Message ExtractResponse() && { return std::move(response_); }

    // From quiche::ObliviousHttpChunkHandler.
    absl::Status OnDecryptedChunk(absl::string_view decrypted_chunk) override;
    absl::Status OnChunksDone() override;

    // From quiche::BinaryHttpResponse::
    // IndeterminateLengthDecoder::MessageSectionHandler.
    absl::Status OnInformationalResponseStatusCode(
        uint16_t status_code) override;
    absl::Status OnInformationalResponseHeader(
        absl::string_view name, absl::string_view value) override;
    absl::Status OnInformationalResponseDone() override;
    absl::Status OnInformationalResponsesSectionDone() override;
    absl::Status OnFinalResponseStatusCode(uint16_t status_code) override;
    absl::Status OnFinalResponseHeader(absl::string_view name,
                                       absl::string_view value) override;
    absl::Status OnFinalResponseHeadersDone() override;
    absl::Status OnBodyChunk(absl::string_view body_chunk) override;
    absl::Status OnBodyChunksDone() override;
    absl::Status OnTrailer(absl::string_view name,
                           absl::string_view value) override;
    absl::Status OnTrailersDone() override;

   private:
    ResponseChunkCallback response_chunk_callback_;
    std::optional<quiche::ChunkedObliviousHttpClient> chunked_client_;
    quiche::BinaryHttpResponse::IndeterminateLengthDecoder decoder_;
    Message response_;
    std::string buffered_binary_response_;
    std::optional<bool> is_chunked_response_;
    size_t decrypted_chunk_count_ = 0;
    size_t body_chunk_count_ = 0;
  };

  struct PendingRequest {
    explicit PendingRequest(const Config::PerRequestConfig& per_request_config)
        : per_request_config(per_request_config) {}

    const Config::PerRequestConfig& per_request_config;
    // `context` is only used for non-chunked OHTTP requests.
    std::optional<quiche::ObliviousHttpRequest::Context> context;
    // `chunk_handler` is only used for chunked OHTTP requests. We use
    // std::unique_ptr to ensure pointer stability since this object is used as
    // a callback target.
    std::unique_ptr<ChunkHandler> chunk_handler;
    std::optional<quiche::BinaryHttpRequest::IndeterminateLengthEncoder>
        encoder;
  };

  explicit MasqueOhttpClient(Config config, quic::QuicEventLoop* event_loop);

  // Starts fetching for the key and sends the OHTTP request.
  absl::Status Start();

  // Returns true if the client has completed all requests.
  bool IsDone();

  absl::StatusOr<Message> TryExtractEncapsulatedResponse(
      RequestId request_id, quiche::ObliviousHttpRequest::Context& context,
      const Message& response);
  absl::Status ProcessOhttpResponse(RequestId request_id,
                                    const absl::StatusOr<Message>& response,
                                    bool end_stream);
  absl::Status CheckStatusAndContentType(
      const Message& response, const std::string& content_type,
      std::optional<uint16_t> expected_status_code);

  Config config_;
  quic::MasqueConnectionPool connection_pool_;
  std::optional<RequestId> key_fetch_request_id_;
  absl::Status status_ = absl::OkStatus();
  std::optional<quiche::ObliviousHttpClient> ohttp_client_;
  quic::QuicUrl relay_url_;
  absl::flat_hash_map<RequestId, PendingRequest> pending_ohttp_requests_;
  ResponseVisitor* response_visitor_ = nullptr;
};
}  // namespace quic

#endif  // QUICHE_QUIC_MASQUE_MASQUE_OHTTP_CLIENT_H_