//
// Copyright (c) 2017 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// Official repository: https://github.com/boostorg/beast
//

#include "fields_alloc.hpp"

#include "../common/mime_types.hpp"

#include <boost/beast/core.hpp>
#include <boost/beast/http.hpp>
#include <boost/beast/version.hpp>
#include <boost/asio.hpp>
#include <boost/filesystem.hpp>
#include <chrono>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <iostream>
#include <list>
#include <memory>
#include <string>

namespace ip = boost::asio::ip;         // from <boost/asio.hpp>
using tcp = boost::asio::ip::tcp;       // from <boost/asio.hpp>
namespace http = boost::beast::http;    // from <boost/beast/http.hpp>

class http_worker
{
public:
    http_worker(http_worker const&) = delete;
    http_worker& operator=(http_worker const&) = delete;

    http_worker(tcp::acceptor& acceptor, const std::string& doc_root) :
        acceptor_(acceptor),
        doc_root_(doc_root)
    {
    }

    void start()
    {
        accept();
        check_deadline();
    }

private:
    using alloc_t = fields_alloc<char>;
    using request_body_t = http::basic_dynamic_body<boost::beast::flat_static_buffer<1024 * 1024>>;

    // The acceptor used to listen for incoming connections.
    tcp::acceptor& acceptor_;

    // The path to the root of the document directory.
    std::string doc_root_;

    // The socket for the currently connected client.
    tcp::socket socket_{acceptor_.get_io_service()};

    // The buffer for performing reads
    boost::beast::flat_static_buffer<8192> buffer_;

    // The allocator used for the fields in the request and reply.
    alloc_t alloc_{8192};

    // The parser for reading the requests
    boost::optional<http::request_parser<request_body_t, alloc_t>> parser_;

    // The timer putting a time limit on requests.
    boost::asio::basic_waitable_timer<std::chrono::steady_clock> request_deadline_{
        acceptor_.get_io_service(), (std::chrono::steady_clock::time_point::max)()};

    // The string-based response message.
    boost::optional<http::response<http::string_body, http::basic_fields<alloc_t>>> string_response_;

    // The string-based response serializer.
    boost::optional<http::response_serializer<http::string_body, http::basic_fields<alloc_t>>> string_serializer_;

    // The file-based response message.
    boost::optional<http::response<http::file_body, http::basic_fields<alloc_t>>> file_response_;

    // The file-based response serializer.
    boost::optional<http::response_serializer<http::file_body, http::basic_fields<alloc_t>>> file_serializer_;

    void accept()
    {
        // Clean up any previous connection.
        boost::beast::error_code ec;
        socket_.close(ec);
        buffer_.consume(buffer_.size());

        acceptor_.async_accept(
            socket_,
            [this](boost::beast::error_code ec)
            {
                if (ec)
                {
                    accept();
                }
                else
                {
                    // Request must be fully processed within 60 seconds.
                    request_deadline_.expires_from_now(
                        std::chrono::seconds(60));

                    read_request();
                }
            });
    }

    void read_request()
    {
        // On each read the parser needs to be destroyed and
        // recreated. We store it in a boost::optional to
        // achieve that.
        //
        // Arguments passed to the parser constructor are
        // forwarded to the message object. A single argument
        // is forwarded to the body constructor.
        //
        // We construct the dynamic body with a 1MB limit
        // to prevent vulnerability to buffer attacks.
        //
        parser_.emplace(
            std::piecewise_construct,
            std::make_tuple(),
            std::make_tuple(alloc_));

        http::async_read(
            socket_,
            buffer_,
            *parser_,
            [this](boost::beast::error_code ec)
            {
                if (ec)
                    accept();
                else
                    process_request(parser_->get());
            });
    }

    void process_request(http::request<request_body_t, http::basic_fields<alloc_t>> const& req)
    {
        switch (req.method())
        {
        case http::verb::get:
            send_file(req.target());
            break;

        default:
            // We return responses indicating an error if
            // we do not recognize the request method.
            send_bad_response(
                http::status::bad_request,
                "Invalid request-method '" + req.method_string().to_string() + "'\r\n");
            break;
        }
    }

    void send_bad_response(
        http::status status,
        std::string const& error)
    {
        string_response_.emplace(
            std::piecewise_construct,
            std::make_tuple(),
            std::make_tuple(alloc_));

        string_response_->result(status);
        string_response_->set(http::field::server, "Beast");
        string_response_->set(http::field::connection, "close");
        string_response_->set(http::field::content_type, "text/plain");
        string_response_->body = error;
        string_response_->prepare_payload();

        string_serializer_.emplace(*string_response_);

        http::async_write(
            socket_,
            *string_serializer_,
            [this](boost::beast::error_code ec)
            {
                socket_.shutdown(tcp::socket::shutdown_send, ec);
                string_serializer_.reset();
                string_response_.reset();
                accept();
            });
    }

    void send_file(boost::beast::string_view target)
    {
        // Request path must be absolute and not contain "..".
        if (target.empty() || target[0] != '/' || target.find("..") != std::string::npos)
        {
            send_bad_response(
                http::status::not_found,
                "File not found\r\n");
            return;
        }

        std::string full_path = doc_root_;
        full_path.append(
            target.data(),
            target.size());

        http::file_body::value_type file;
        boost::beast::error_code ec;
        file.open(
            full_path.c_str(),
            boost::beast::file_mode::read,
            ec);
        if(ec)
        {
            send_bad_response(
                http::status::not_found,
                "File not found\r\n");
            return;
        }

        file_response_.emplace(
            std::piecewise_construct,
            std::make_tuple(),
            std::make_tuple(alloc_));

        file_response_->result(http::status::ok);
        file_response_->set(http::field::server, "Beast");
        file_response_->set(http::field::connection, "close");
        file_response_->set(http::field::content_type, mime_type(target.to_string()));
        file_response_->body = std::move(file);
        file_response_->prepare_payload();

        file_serializer_.emplace(*file_response_);

        http::async_write(
            socket_,
            *file_serializer_,
            [this](boost::beast::error_code ec)
            {
                socket_.shutdown(tcp::socket::shutdown_send, ec);
                file_serializer_.reset();
                file_response_.reset();
                accept();
            });
    }

    void check_deadline()
    {
        // The deadline may have moved, so check it has really passed.
        if (request_deadline_.expires_at() <= std::chrono::steady_clock::now())
        {
            // Close socket to cancel any outstanding operation.
            boost::beast::error_code ec;
            socket_.close();

            // Sleep indefinitely until we're given a new deadline.
            request_deadline_.expires_at(
                std::chrono::steady_clock::time_point::max());
        }

        request_deadline_.async_wait(
            [this](boost::beast::error_code)
            {
                check_deadline();
            });
    }
};

int main(int argc, char* argv[])
{
    try
    {
        // Check command line arguments.
        if (argc != 6)
        {
            std::cerr << "Usage: http_server_fast <address> <port> <doc_root> <num_workers> {spin|block}\n";
            std::cerr << "  For IPv4, try:\n";
            std::cerr << "    http_server_fast 0.0.0.0 80 . 100 block\n";
            std::cerr << "  For IPv6, try:\n";
            std::cerr << "    http_server_fast 0::0 80 . 100 block\n";
            return EXIT_FAILURE;
        }

        auto address = ip::address::from_string(argv[1]);
        unsigned short port = static_cast<unsigned short>(std::atoi(argv[2]));
        std::string doc_root = argv[3];
        int num_workers = std::atoi(argv[4]);
        bool spin = (std::strcmp(argv[5], "spin") == 0);

        boost::asio::io_service ios{1};
        tcp::acceptor acceptor{ios, {address, port}};

        std::list<http_worker> workers;
        for (int i = 0; i < num_workers; ++i)
        {
            workers.emplace_back(acceptor, doc_root);
            workers.back().start();
        }

        if (spin)
          for (;;) ios.poll();
        else
          ios.run();
    }
    catch (const std::exception& e)
    {
        std::cerr << "Exception: " << e.what() << std::endl;
        return EXIT_FAILURE;
    }
}