#include "web/ng/Server.hpp"

#include "util/Assert.hpp"
#include "util/Spawn.hpp"
#include "util/Taggable.hpp"
#include "util/config/ConfigDefinition.hpp"
#include "util/config/ObjectView.hpp"
#include "util/log/Logger.hpp"
#include "web/ProxyIpResolver.hpp"
#include "web/ng/Connection.hpp"
#include "web/ng/MessageHandler.hpp"
#include "web/ng/ProcessingPolicy.hpp"
#include "web/ng/Response.hpp"
#include "web/ng/impl/HttpConnection.hpp"
#include "web/ng/impl/ServerSslContext.hpp"

#include <boost/asio/detached.hpp>
#include <boost/asio/io_context.hpp>
#include <boost/asio/ip/address.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <boost/asio/socket_base.hpp>
#include <boost/asio/spawn.hpp>
#include <boost/asio/ssl/context.hpp>
#include <boost/asio/ssl/error.hpp>
#include <boost/beast/core/detect_ssl.hpp>
#include <boost/beast/core/error.hpp>
#include <boost/beast/core/flat_buffer.hpp>
#include <boost/beast/core/tcp_stream.hpp>
#include <boost/system/system_error.hpp>
#include <fmt/format.h>

#include <chrono>
#include <cstddef>
#include <functional>
#include <memory>
#include <optional>
#include <string>
#include <utility>

namespace web::ng {

namespace {

std::expected<boost::asio::ip::tcp::endpoint, std::string>
makeEndpoint(util::config::ObjectView const& serverConfig)
{
    auto const ip = serverConfig.get<std::string>("ip");

    boost::system::error_code error;
    auto const address = boost::asio::ip::make_address(ip, error);
    if (error)
        return std::unexpected{fmt::format("Error parsing provided IP: {}", error.message())};

    auto const port = serverConfig.get<unsigned short>("port");
    return boost::asio::ip::tcp::endpoint{address, port};
}

std::expected<boost::asio::ip::tcp::acceptor, std::string>
makeAcceptor(boost::asio::io_context& context, boost::asio::ip::tcp::endpoint const& endpoint)
{
    boost::asio::ip::tcp::acceptor acceptor{context};
    try {
        acceptor.open(endpoint.protocol());
        acceptor.set_option(boost::asio::socket_base::reuse_address(true));
        acceptor.bind(endpoint);
        acceptor.listen(boost::asio::socket_base::max_listen_connections);
    } catch (boost::system::system_error const& error) {
        return std::unexpected{fmt::format("Error creating TCP acceptor: {}", error.what())};
    }
    return acceptor;
}

std::expected<std::string, boost::system::system_error>
extractIp(boost::asio::ip::tcp::socket const& socket)
{
    std::string ip;
    try {
        ip = socket.remote_endpoint().address().to_string();
    } catch (boost::system::system_error const& error) {
        return std::unexpected{error};
    }
    return ip;
}

struct SslDetectionResult {
    boost::asio::ip::tcp::socket socket;
    bool isSsl;
    boost::beast::flat_buffer buffer;
};

std::expected<std::optional<SslDetectionResult>, std::string>
detectSsl(boost::asio::ip::tcp::socket socket, boost::asio::yield_context yield)
{
    boost::beast::tcp_stream tcpStream{std::move(socket)};
    boost::beast::flat_buffer buffer;
    boost::beast::error_code errorCode;
    bool const isSsl = boost::beast::async_detect_ssl(tcpStream, buffer, yield[errorCode]);

    if (errorCode == boost::asio::ssl::error::stream_truncated)
        return std::nullopt;

    if (errorCode)
        return std::unexpected{fmt::format("Detector failed (detect): {}", errorCode.message())};

    return SslDetectionResult{
        .socket = tcpStream.release_socket(), .isSsl = isSsl, .buffer = std::move(buffer)
    };
}

std::expected<impl::UpgradableConnectionPtr, std::optional<std::string>>
makeConnection(
    SslDetectionResult sslDetectionResult,
    std::optional<boost::asio::ssl::context>& sslContext,
    std::string ip,
    util::TagDecoratorFactory& tagDecoratorFactory,
    Server::OnConnectCheck onConnectCheck,
    size_t maxSendingQueueSize,
    boost::asio::yield_context yield
)
{
    impl::UpgradableConnectionPtr connection;
    if (sslDetectionResult.isSsl) {
        if (not sslContext.has_value()) {
            return std::unexpected{
                "Error creating a connection: SSL is not supported by this server"
            };
        }

        auto sslConnection = std::make_unique<impl::SslHttpConnection>(
            std::move(sslDetectionResult.socket),
            std::move(ip),
            std::move(sslDetectionResult.buffer),
            *sslContext,
            tagDecoratorFactory,
            maxSendingQueueSize
        );
        sslConnection->setTimeout(std::chrono::seconds{10});
        auto const expectedSuccess = sslConnection->sslHandshake(yield);
        if (not expectedSuccess.has_value()) {
            return std::unexpected{
                fmt::format("SSL handshake error: {}", expectedSuccess.error().message())
            };
        }

        connection = std::move(sslConnection);
    } else {
        connection = std::make_unique<impl::PlainHttpConnection>(
            std::move(sslDetectionResult.socket),
            std::move(ip),
            std::move(sslDetectionResult.buffer),
            tagDecoratorFactory,
            maxSendingQueueSize
        );
    }

    auto expectedSuccess = onConnectCheck(*connection);
    if (not expectedSuccess.has_value()) {
        connection->send(std::move(expectedSuccess).error(), yield);
        connection->close(yield);
        return std::unexpected{std::nullopt};
    }
    return connection;
}

std::expected<ConnectionPtr, std::string>
tryUpgradeConnection(
    impl::UpgradableConnectionPtr connection,
    util::TagDecoratorFactory& tagDecoratorFactory,
    size_t maxSendingQueueSize,
    boost::asio::yield_context yield
)
{
    auto const expectedIsUpgrade = connection->isUpgradeRequested(yield);
    if (not expectedIsUpgrade.has_value()) {
        return std::unexpected{fmt::format(
            "Error checking whether upgrade requested: {}", expectedIsUpgrade.error().message()
        )};
    }

    if (*expectedIsUpgrade) {
        auto expectedUpgradedConnection =
            connection->upgrade(tagDecoratorFactory, maxSendingQueueSize, yield);
        if (expectedUpgradedConnection.has_value())
            return std::move(expectedUpgradedConnection).value();

        return std::unexpected{
            fmt::format("Error upgrading connection: {}", expectedUpgradedConnection.error().what())
        };
    }

    return connection;
}

}  // namespace

Server::Server(
    boost::asio::io_context& ctx,
    boost::asio::ip::tcp::endpoint endpoint,
    std::optional<boost::asio::ssl::context> sslContext,
    ProcessingPolicy processingPolicy,
    std::optional<size_t> parallelRequestLimit,
    util::TagDecoratorFactory tagDecoratorFactory,
    ProxyIpResolver proxyIpResolver,
    size_t maxSubscriptionSendQueueSize,
    Hooks hooks
)
    : ctx_{ctx}
    , sslContext_{std::move(sslContext)}
    , tagDecoratorFactory_{tagDecoratorFactory}
    , maxSubscriptionSendQueueSize_{maxSubscriptionSendQueueSize}
    , connectionHandler_{processingPolicy, parallelRequestLimit, tagDecoratorFactory_, std::move(proxyIpResolver), std::move(hooks.onDisconnectHook), std::move(hooks.onIpChangeHook)}
    , endpoint_{std::move(endpoint)}
    , onConnectCheck_{std::move(hooks.onConnectCheck)}
{
}

void
Server::onGet(std::string const& target, MessageHandler handler)
{
    ASSERT(not running_, "Adding a GET handler is not allowed when Server is running.");
    connectionHandler_.onGet(target, std::move(handler));
}

void
Server::onPost(std::string const& target, MessageHandler handler)
{
    ASSERT(not running_, "Adding a POST handler is not allowed when Server is running.");
    connectionHandler_.onPost(target, std::move(handler));
}

void
Server::onWs(MessageHandler handler)
{
    ASSERT(not running_, "Adding a Websocket handler is not allowed when Server is running.");
    connectionHandler_.onWs(std::move(handler));
}

std::optional<std::string>
Server::run()
{
    LOG(log_.info()) << "Starting ng::Server";
    auto acceptor = makeAcceptor(ctx_.get(), endpoint_);
    if (not acceptor.has_value())
        return std::move(acceptor).error();

    running_ = true;
    util::spawn(
        ctx_.get(),
        [this, acceptor = std::move(acceptor).value()](boost::asio::yield_context yield) mutable {
            while (true) {
                boost::beast::error_code errorCode;
                boost::asio::ip::tcp::socket socket{ctx_.get().get_executor()};

                acceptor.async_accept(socket, yield[errorCode]);
                LOG(log_.trace()) << "Accepted a new connection";
                if (errorCode) {
                    LOG(log_.debug()) << "Error accepting a connection: " << errorCode.what();
                    continue;
                }

                // Note: This was desigen to use `boost::asio::detached`
                boost::asio::spawn(
                    ctx_.get(),
                    [this, socket = std::move(socket)](boost::asio::yield_context yield) mutable {
                        handleConnection(std::move(socket), yield);
                    },
                    boost::asio::detached
                );
            }
        }
    );
    return std::nullopt;
}

void
Server::stop(boost::asio::yield_context yield)
{
    connectionHandler_.stop(yield);
}

void
Server::handleConnection(boost::asio::ip::tcp::socket socket, boost::asio::yield_context yield)
{
    auto sslDetectionResultExpected = detectSsl(std::move(socket), yield);
    if (not sslDetectionResultExpected) {
        LOG(log_.info()) << sslDetectionResultExpected.error();
        return;
    }
    auto sslDetectionResult = std::move(sslDetectionResultExpected).value();
    if (not sslDetectionResult)
        return;  // stream truncated, probably user disconnected

    auto ip = extractIp(sslDetectionResult->socket);
    if (not ip.has_value()) {
        LOG(log_.info()) << "Cannot get remote endpoint: " << ip.error().what();
        return;
    }

    auto connectionExpected = makeConnection(
        std::move(sslDetectionResult).value(),
        sslContext_,
        std::move(ip).value(),
        tagDecoratorFactory_,
        onConnectCheck_,
        maxSubscriptionSendQueueSize_,
        yield
    );
    if (not connectionExpected.has_value()) {
        if (connectionExpected.error().has_value()) {
            LOG(
                log_.info()
            ) << *connectionExpected.error();  // NOLINT(bugprone-unchecked-optional-access)
        }
        return;
    }
    LOG(log_.trace()) << connectionExpected.value()->tag() << "Connection created";

    if (connectionHandler_.isStopping()) {
        util::spawn(
            ctx_.get(),
            [connection = std::move(connectionExpected).value()](boost::asio::yield_context yield) {
                web::ng::impl::ConnectionHandler::stopConnection(*connection, yield);
            }
        );
        return;
    }

    auto connection = tryUpgradeConnection(
        std::move(connectionExpected).value(),
        tagDecoratorFactory_,
        maxSubscriptionSendQueueSize_,
        yield
    );
    if (not connection.has_value()) {
        LOG(log_.info()) << connection.error();
        return;
    }

    util::spawn(
        ctx_.get(),
        [this,
         connection = std::move(connection).value()](boost::asio::yield_context yield) mutable {
            connectionHandler_.processConnection(std::move(connection), yield);
        }
    );
}

std::expected<Server, std::string>
makeServer(
    util::config::ClioConfigDefinition const& config,
    Server::OnConnectCheck onConnectCheck,
    Server::OnIpChangeHook onIpChangeHook,
    Server::OnDisconnectHook onDisconnectHook,
    boost::asio::io_context& context
)
{
    auto const serverConfig = config.getObject("server");

    auto endpoint = makeEndpoint(serverConfig);
    if (not endpoint.has_value())
        return std::unexpected{std::move(endpoint).error()};

    auto expectedSslContext = impl::makeServerSslContext(config);
    if (not expectedSslContext)
        return std::unexpected{std::move(expectedSslContext).error()};

    ProcessingPolicy processingPolicy{ProcessingPolicy::Parallel};
    std::optional<size_t> parallelRequestLimit;

    auto const processingStrategyStr = serverConfig.get<std::string>("processing_policy");
    if (processingStrategyStr == "sequent") {
        processingPolicy = ProcessingPolicy::Sequential;
    } else if (processingStrategyStr == "parallel") {
        parallelRequestLimit = serverConfig.maybeValue<size_t>("parallel_requests_limit");
    } else {
        return std::unexpected{
            fmt::format("Invalid 'server.processing_strategy': {}", processingStrategyStr)
        };
    }

    auto const maxSubscriptionSendQueueSize = serverConfig.get<size_t>("ws_max_sending_queue_size");

    auto proxyIpResolver = ProxyIpResolver::fromConfig(config);

    return std::expected<Server, std::string>{
        std::in_place,
        context,
        std::move(endpoint).value(),
        std::move(expectedSslContext).value(),
        processingPolicy,
        parallelRequestLimit,
        util::TagDecoratorFactory(config),
        std::move(proxyIpResolver),
        maxSubscriptionSendQueueSize,
        Server::Hooks{
            .onConnectCheck = std::move(onConnectCheck),
            .onIpChangeHook = std::move(onIpChangeHook),
            .onDisconnectHook = std::move(onDisconnectHook)
        }
    };
}

}  // namespace web::ng