#ifndef CLIENT_HTTP_HPP
#define CLIENT_HTTP_HPP

#include "utility.hpp"
#include <mutex>
#include <random>
#include <vector>

#ifdef USE_STANDALONE_ASIO
#include <asio.hpp>
namespace SimpleWeb {
  namespace asio = asio;
  using error_code = std::error_code;
  using errc = std::errc;
  using system_error = std::system_error;
  namespace make_error_code = std;
  using string_view = const std::string &; // TODO c++17: use std::string_view
} // namespace SimpleWeb
#else
#include <boost/asio.hpp>
#include <boost/utility/string_ref.hpp>
namespace SimpleWeb {
  namespace asio = boost::asio;
  using error_code = boost::system::error_code;
  namespace errc = boost::system::errc;
  using system_error = boost::system::system_error;
  namespace make_error_code = boost::system::errc;
  using string_view = boost::string_ref;
} // namespace SimpleWeb
#endif

namespace SimpleWeb {
  template <class socket_type>
  class Client;

  template <class socket_type>
  class ClientBase {
  public:
    class Content : public std::istream {
      friend class ClientBase<socket_type>;

    public:
      size_t size() {
        return streambuf.size();
      }
      /// Convenience function to return std::string. Note that the stream buffer is emptied when this functions is used.
      std::string string() {
        std::stringstream ss;
        ss << rdbuf();
        return ss.str();
      }

    private:
      asio::streambuf &streambuf;
      Content(asio::streambuf &streambuf) : std::istream(&streambuf), streambuf(streambuf) {}
    };

    class Response {
      friend class ClientBase<socket_type>;
      friend class Client<socket_type>;

    public:
      std::string http_version, status_code;

      Content content;

      CaseInsensitiveMultimap header;

    private:
      asio::streambuf content_buffer;

      Response() : content(content_buffer) {}
    };

    class Config {
      friend class ClientBase<socket_type>;

    private:
      Config() {}

    public:
      /// Set timeout on requests in seconds. Default value: 0 (no timeout).
      size_t timeout = 0;
      /// Set connect timeout in seconds. Default value: 0 (Config::timeout is then used instead).
      size_t timeout_connect = 0;
      /// Set proxy server (server:port)
      std::string proxy_server;
    };

  protected:
    class Connection {
    public:
      Connection(const std::string &host, unsigned short port, const Config &config, std::unique_ptr<socket_type> &&socket)
          : host(host), port(port), config(config), socket(std::move(socket)) {
        if(config.proxy_server.empty())
          query = std::unique_ptr<asio::ip::tcp::resolver::query>(new asio::ip::tcp::resolver::query(host, std::to_string(port)));
        else {
          auto proxy_host_port = parse_host_port(config.proxy_server, 8080);
          query = std::unique_ptr<asio::ip::tcp::resolver::query>(new asio::ip::tcp::resolver::query(proxy_host_port.first, std::to_string(proxy_host_port.second)));
        }
      }

      std::string host;
      unsigned short port;
      Config config;

      std::unique_ptr<socket_type> socket;
      bool in_use = false;
      bool reconnecting = false;

      std::unique_ptr<asio::ip::tcp::resolver::query> query;
    };

    class Session {
    public:
      Session(const std::shared_ptr<asio::io_service> &io_service, const std::shared_ptr<Connection> &connection, std::unique_ptr<asio::streambuf> &&request_buffer)
          : io_service(io_service), connection(connection), request_buffer(std::move(request_buffer)), response(new Response()) {}
      std::shared_ptr<asio::io_service> io_service;
      std::shared_ptr<Connection> connection;
      std::unique_ptr<asio::streambuf> request_buffer;
      std::shared_ptr<Response> response;
      std::function<void(const error_code &)> callback;
    };

  public:
    /// Set before calling request
    Config config;

    /// If you have your own asio::io_service, store its pointer here before calling request().
    /// When using asynchronous requests, running the io_service is up to the programmer.
    std::shared_ptr<asio::io_service> io_service;

    virtual ~ClientBase() {}

    /// Convenience function to perform synchronous request. The io_service is run within this function.
    /// If reusing the io_service for other tasks, please use the asynchronous request functions instead.
    std::shared_ptr<Response> request(const std::string &method, const std::string &path = std::string("/"),
                                      string_view content = "", const CaseInsensitiveMultimap &header = CaseInsensitiveMultimap()) {
      std::shared_ptr<Response> response;
      request(method, path, content, header, [&response](std::shared_ptr<Response> response_, const error_code &ec) {
        response = response_;
        if(ec)
          throw system_error(ec);
      });

      io_service->reset();
      io_service->run();

      return response;
    }

    /// Convenience function to perform synchronous request. The io_service is run within this function.
    /// If reusing the io_service for other tasks, please use the asynchronous request functions instead.
    std::shared_ptr<Response> request(const std::string &method, const std::string &path, std::istream &content,
                                      const CaseInsensitiveMultimap &header = CaseInsensitiveMultimap()) {
      std::shared_ptr<Response> response;
      request(method, path, content, header, [&response](std::shared_ptr<Response> response_, const error_code &ec) {
        response = response_;
        if(ec)
          throw system_error(ec);
      });

      io_service->reset();
      io_service->run();

      return response;
    }

    /// Asynchronous request where setting and/or running Client's io_service is required.
    void request(const std::string &method, const std::string &path, string_view content, const CaseInsensitiveMultimap &header,
                 std::function<void(std::shared_ptr<Response>, const error_code &)> &&request_callback_) {
      auto session = std::make_shared<Session>(io_service, get_connection(), create_request_header(method, path, header));
      auto connection = session->connection;
      auto response = session->response;
      auto request_callback = std::make_shared<std::function<void(std::shared_ptr<Response>, const error_code &)>>(std::move(request_callback_));
      auto connections = this->connections;
      auto connections_mutex = this->connections_mutex;
      session->callback = [connection, response, request_callback, connections, connections_mutex](const error_code &ec) {
        {
          std::lock_guard<std::mutex> lock(*connections_mutex);
          connection->in_use = false;

          // Remove unused connections, but keep one open for HTTP persistent connection:
          size_t unused_connections = 0;
          for(auto it = connections->begin(); it != connections->end();) {
            if((*it)->in_use)
              ++it;
            else {
              ++unused_connections;
              if(unused_connections > 1)
                it = connections->erase(it);
              else
                ++it;
            }
          }
        }

        if(*request_callback)
          (*request_callback)(response, ec);
      };

      std::ostream write_stream(session->request_buffer.get());
      if(content.size() > 0)
        write_stream << "Content-Length: " << content.size() << "\r\n";
      write_stream << "\r\n"
                   << content;

      Client<socket_type>::connect(session);
    }

    /// Asynchronous request where setting and/or running Client's io_service is required.
    void request(const std::string &method, const std::string &path, string_view content,
                 std::function<void(std::shared_ptr<Response>, const error_code &)> &&request_callback) {
      request(method, path, content, CaseInsensitiveMultimap(), std::move(request_callback));
    }

    /// Asynchronous request where setting and/or running Client's io_service is required.
    void request(const std::string &method, const std::string &path,
                 std::function<void(std::shared_ptr<Response>, const error_code &)> &&request_callback) {
      request(method, path, std::string(), CaseInsensitiveMultimap(), std::move(request_callback));
    }

    /// Asynchronous request where setting and/or running Client's io_service is required.
    void request(const std::string &method, std::function<void(std::shared_ptr<Response>, const error_code &)> &&request_callback) {
      request(method, std::string("/"), std::string(), CaseInsensitiveMultimap(), std::move(request_callback));
    }

    /// Asynchronous request where setting and/or running Client's io_service is required.
    void request(const std::string &method, const std::string &path, std::istream &content, const CaseInsensitiveMultimap &header,
                 std::function<void(std::shared_ptr<Response>, const error_code &)> &&request_callback_) {
      auto session = std::make_shared<Session>(io_service, get_connection(), create_request_header(method, path, header));
      auto connection = session->connection;
      auto response = session->response;
      auto request_callback = std::make_shared<std::function<void(std::shared_ptr<Response>, const error_code &)>>(std::move(request_callback_));
      auto connections = this->connections;
      auto connections_mutex = this->connections_mutex;
      session->callback = [connection, response, request_callback, connections, connections_mutex](const error_code &ec) {
        {
          std::lock_guard<std::mutex> lock(*connections_mutex);
          connection->in_use = false;

          // Remove unused connections, but keep one open for HTTP persistent connection:
          size_t unused_connections = 0;
          for(auto it = connections->begin(); it != connections->end();) {
            if((*it)->in_use)
              ++it;
            else {
              ++unused_connections;
              if(unused_connections > 1)
                it = connections->erase(it);
              else
                ++it;
            }
          }
        }

        if(*request_callback)
          (*request_callback)(response, ec);
      };

      content.seekg(0, std::ios::end);
      auto content_length = content.tellg();
      content.seekg(0, std::ios::beg);
      std::ostream write_stream(session->request_buffer.get());
      if(content_length > 0)
        write_stream << "Content-Length: " << content_length << "\r\n";
      write_stream << "\r\n";
      if(content_length > 0)
        write_stream << content.rdbuf();

      Client<socket_type>::connect(session);
    }

    /// Asynchronous request where setting and/or running Client's io_service is required.
    void request(const std::string &method, const std::string &path, std::istream &content,
                 std::function<void(std::shared_ptr<Response>, const error_code &)> &&request_callback) {
      request(method, path, content, CaseInsensitiveMultimap(), std::move(request_callback));
    }

  protected:
    std::string host;
    unsigned short port;

    std::shared_ptr<std::vector<std::shared_ptr<Connection>>> connections;
    std::shared_ptr<std::mutex> connections_mutex;

    ClientBase(const std::string &host_port, unsigned short default_port)
        : io_service(new asio::io_service()), connections(new std::vector<std::shared_ptr<Connection>>()), connections_mutex(new std::mutex()) {
      auto parsed_host_port = parse_host_port(host_port, default_port);
      host = parsed_host_port.first;
      port = parsed_host_port.second;
    }

    std::shared_ptr<Connection> get_connection() {
      std::shared_ptr<Connection> connection;
      std::lock_guard<std::mutex> lock(*connections_mutex);
      for(auto it = connections->begin(); it != connections->end(); ++it) {
        if(!(*it)->in_use && !connection) {
          connection = *it;
          break;
        }
      }
      if(!connection) {
        connection = create_connection();
        connections->emplace_back(connection);
      }
      connection->reconnecting = false;
      connection->in_use = true;
      return connection;
    }

    virtual std::shared_ptr<Connection> create_connection() = 0;

    std::unique_ptr<asio::streambuf> create_request_header(const std::string &method, const std::string &path, const CaseInsensitiveMultimap &header) const {
      auto corrected_path = path;
      if(corrected_path == "")
        corrected_path = "/";
      if(!config.proxy_server.empty() && std::is_same<socket_type, asio::ip::tcp::socket>::value)
        corrected_path = "http://" + host + ':' + std::to_string(port) + corrected_path;

      std::unique_ptr<asio::streambuf> request_buffer(new asio::streambuf());
      std::ostream write_stream(request_buffer.get());
      write_stream << method << " " << corrected_path << " HTTP/1.1\r\n";
      write_stream << "Host: " << host << "\r\n";
      for(auto &h : header)
        write_stream << h.first << ": " << h.second << "\r\n";
      return request_buffer;
    }

    static std::pair<std::string, unsigned short> parse_host_port(const std::string &host_port, unsigned short default_port) {
      std::pair<std::string, unsigned short> parsed_host_port;
      size_t host_end = host_port.find(':');
      if(host_end == std::string::npos) {
        parsed_host_port.first = host_port;
        parsed_host_port.second = default_port;
      }
      else {
        parsed_host_port.first = host_port.substr(0, host_end);
        parsed_host_port.second = static_cast<unsigned short>(stoul(host_port.substr(host_end + 1)));
      }
      return parsed_host_port;
    }

    static std::shared_ptr<asio::deadline_timer> get_timeout_timer(const std::shared_ptr<Session> &session, size_t timeout = 0) {
      if(timeout == 0)
        timeout = session->connection->config.timeout;
      if(timeout == 0)
        return nullptr;

      auto timer = std::make_shared<asio::deadline_timer>(*session->io_service);
      timer->expires_from_now(boost::posix_time::seconds(timeout));
      timer->async_wait([session](const error_code &ec) {
        if(!ec)
          close(session);
      });
      return timer;
    }

    static void parse_response_header(const std::shared_ptr<Response> &response) {
      std::string line;
      getline(response->content, line);
      size_t version_end = line.find(' ');
      if(version_end != std::string::npos) {
        if(5 < line.size())
          response->http_version = line.substr(5, version_end - 5);
        if((version_end + 1) < line.size())
          response->status_code = line.substr(version_end + 1, line.size() - (version_end + 1) - 1);

        getline(response->content, line);
        size_t param_end;
        while((param_end = line.find(':')) != std::string::npos) {
          size_t value_start = param_end + 1;
          if((value_start) < line.size()) {
            if(line[value_start] == ' ')
              value_start++;
            if(value_start < line.size())
              response->header.insert(std::make_pair(line.substr(0, param_end), line.substr(value_start, line.size() - value_start - 1)));
          }

          getline(response->content, line);
        }
      }
    }

    static void write(const std::shared_ptr<Session> &session) {
      auto timer = get_timeout_timer(session);
      asio::async_write(*session->connection->socket, session->request_buffer->data(), [session, timer](const error_code &ec, size_t /*bytes_transferred*/) {
        if(timer)
          timer->cancel();
        if(!ec)
          read(session);
        else {
          close(session);
          session->callback(ec);
        }
      });
    }

    static void read(const std::shared_ptr<Session> &session) {
      auto timer = get_timeout_timer(session);
      asio::async_read_until(*session->connection->socket, session->response->content_buffer, "\r\n\r\n", [session, timer](const error_code &ec, size_t bytes_transferred) {
        if(timer)
          timer->cancel();
        if(!ec) {
          session->connection->reconnecting = false;

          size_t num_additional_bytes = session->response->content_buffer.size() - bytes_transferred;

          parse_response_header(session->response);

          auto header_it = session->response->header.find("Content-Length");
          if(header_it != session->response->header.end()) {
            auto content_length = stoull(header_it->second);
            if(content_length > num_additional_bytes) {
              auto timer = get_timeout_timer(session);
              asio::async_read(*session->connection->socket, session->response->content_buffer, asio::transfer_exactly(content_length - num_additional_bytes), [session, timer](const error_code &ec, size_t /*bytes_transferred*/) {
                if(timer)
                  timer->cancel();
                if(!ec)
                  session->callback(ec);
                else {
                  close(session);
                  session->callback(ec);
                }
              });
            }
            else
              session->callback(ec);
          }
          else if((header_it = session->response->header.find("Transfer-Encoding")) != session->response->header.end() && header_it->second == "chunked") {
            auto tmp_streambuf = std::make_shared<asio::streambuf>();
            read_chunked(session, tmp_streambuf);
          }
          else if(session->response->http_version < "1.1" || ((header_it = session->response->header.find("Session")) != session->response->header.end() && header_it->second == "close")) {
            auto timer = get_timeout_timer(session);
            asio::async_read(*session->connection->socket, session->response->content_buffer, [session, timer](const error_code &ec, size_t /*bytes_transferred*/) {
              if(timer)
                timer->cancel();
              if(!ec)
                session->callback(ec);
              else {
                close(session);
                if(ec == asio::error::eof) {
                  error_code ec;
                  session->callback(ec);
                }
                else
                  session->callback(ec);
              }
            });
          }
          else
            session->callback(ec);
        }
        else {
          if(!session->connection->reconnecting) {
            session->connection->reconnecting = true;
            close(session);
            Client<socket_type>::connect(session);
          }
          else {
            close(session);
            session->callback(ec);
          }
        }
      });
    }

    static void read_chunked(const std::shared_ptr<Session> &session, const std::shared_ptr<asio::streambuf> &tmp_streambuf) {
      auto timer = get_timeout_timer(session);
      asio::async_read_until(*session->connection->socket, session->response->content_buffer, "\r\n", [session, tmp_streambuf, timer](const error_code &ec, size_t bytes_transferred) {
        if(timer)
          timer->cancel();
        if(!ec) {
          std::string line;
          getline(session->response->content, line);
          bytes_transferred -= line.size() + 1;
          line.pop_back();
          std::streamsize length = stol(line, 0, 16);

          auto num_additional_bytes = static_cast<std::streamsize>(session->response->content_buffer.size() - bytes_transferred);

          auto post_process = [session, tmp_streambuf, length] {
            std::ostream tmp_stream(tmp_streambuf.get());
            if(length > 0) {
              std::vector<char> buffer(static_cast<size_t>(length));
              session->response->content.read(&buffer[0], length);
              tmp_stream.write(&buffer[0], length);
            }

            //Remove "\r\n"
            session->response->content.get();
            session->response->content.get();

            if(length > 0)
              read_chunked(session, tmp_streambuf);
            else {
              std::ostream response_stream(&session->response->content_buffer);
              response_stream << tmp_stream.rdbuf();
              error_code ec;
              session->callback(ec);
            }
          };

          if((2 + length) > num_additional_bytes) {
            auto timer = get_timeout_timer(session);
            asio::async_read(*session->connection->socket, session->response->content_buffer, asio::transfer_exactly(2 + length - num_additional_bytes), [session, post_process, timer](const error_code &ec, size_t /*bytes_transferred*/) {
              if(timer)
                timer->cancel();
              if(!ec)
                post_process();
              else {
                close(session);
                session->callback(ec);
              }
            });
          }
          else
            post_process();
        }
        else {
          close(session);
          session->callback(ec);
        }
      });
    }

    static void close(const std::shared_ptr<Session> &session) {
      error_code ec;
      session->connection->socket->lowest_layer().shutdown(asio::ip::tcp::socket::shutdown_both, ec);
      session->connection->socket->lowest_layer().close(ec);
    }
  };

  template <class socket_type>
  class Client : public ClientBase<socket_type> {};

  typedef asio::ip::tcp::socket HTTP;

  template <>
  class Client<HTTP> : public ClientBase<HTTP> {
  public:
    friend ClientBase<HTTP>;

    Client(const std::string &server_port_path) : ClientBase<HTTP>::ClientBase(server_port_path, 80) {}

  protected:
    std::shared_ptr<Connection> create_connection() override {
      return std::make_shared<Connection>(host, port, config, std::unique_ptr<HTTP>(new HTTP(*io_service)));
    }

    static void connect(const std::shared_ptr<Session> &session) {
      if(!session->connection->socket->lowest_layer().is_open()) {
        auto resolver = std::make_shared<asio::ip::tcp::resolver>(*session->io_service);
        auto timer = get_timeout_timer(session, session->connection->config.timeout_connect);
        resolver->async_resolve(*session->connection->query, [session, timer, resolver](const error_code &ec, asio::ip::tcp::resolver::iterator it) {
          if(timer)
            timer->cancel();
          if(!ec) {
            auto timer = get_timeout_timer(session, session->connection->config.timeout_connect);
            asio::async_connect(*session->connection->socket, it, [session, timer, resolver](const error_code &ec, asio::ip::tcp::resolver::iterator /*it*/) {
              if(timer)
                timer->cancel();
              if(!ec) {
                asio::ip::tcp::no_delay option(true);
                session->connection->socket->set_option(option);
                write(session);
              }
              else {
                close(session);
                session->callback(ec);
              }
            });
          }
          else {
            close(session);
            session->callback(ec);
          }
        });
      }
      else
        write(session);
    }
  };
} // namespace SimpleWeb

#endif /* CLIENT_HTTP_HPP */