/*
 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
 * Copyright (c) 2022, the SerenityOS developers.
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#pragma once

#include <AK/ByteBuffer.h>
#include <AK/Try.h>
#include <LibCore/Event.h>
#include <LibCore/EventLoop.h>
#include <LibCore/Notifier.h>
#include <LibCore/Socket.h>
#include <LibCore/Timer.h>
#include <LibIPC/Forward.h>
#include <LibIPC/Message.h>
#include <errno.h>
#include <stdint.h>
#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>

namespace IPC {

// NOTE: This is an abstraction to allow using IPC::Connection without a Core::EventLoop.
// FIXME: It's not particularly nice, think of something nicer.
struct DeferredInvoker {
    virtual ~DeferredInvoker() = default;
    virtual void schedule(Function<void()>) = 0;
};

class ConnectionBase : public Core::Object {
    C_OBJECT_ABSTRACT(ConnectionBase);

public:
    virtual ~ConnectionBase() override = default;

    void set_fd_passing_socket(NonnullOwnPtr<Core::LocalSocket>);
    void set_deferred_invoker(NonnullOwnPtr<DeferredInvoker>);
    DeferredInvoker& deferred_invoker() { return *m_deferred_invoker; }

    bool is_open() const { return m_socket->is_open(); }
    ErrorOr<void> post_message(Message const&);

    void shutdown();
    virtual void die() { }

    Core::LocalSocket& socket() { return *m_socket; }
    Core::LocalSocket& fd_passing_socket();

protected:
    explicit ConnectionBase(IPC::Stub&, NonnullOwnPtr<Core::LocalSocket>, u32 local_endpoint_magic);

    virtual void may_have_become_unresponsive() { }
    virtual void did_become_responsive() { }
    virtual void try_parse_messages(Vector<u8> const& bytes, size_t& index) = 0;
    virtual void shutdown_with_error(Error const&);

    OwnPtr<IPC::Message> wait_for_specific_endpoint_message_impl(u32 endpoint_magic, int message_id);
    void wait_for_socket_to_become_readable();
    ErrorOr<Vector<u8>> read_as_much_as_possible_from_socket_without_blocking();
    ErrorOr<void> drain_messages_from_peer();

    ErrorOr<void> post_message(MessageBuffer);
    void handle_messages();

    IPC::Stub& m_local_stub;

    NonnullOwnPtr<Core::LocalSocket> m_socket;
    OwnPtr<Core::LocalSocket> m_fd_passing_socket;

    RefPtr<Core::Timer> m_responsiveness_timer;

    Vector<NonnullOwnPtr<Message>> m_unprocessed_messages;
    ByteBuffer m_unprocessed_bytes;

    u32 m_local_endpoint_magic { 0 };

    NonnullOwnPtr<DeferredInvoker> m_deferred_invoker;
};

template<typename LocalEndpoint, typename PeerEndpoint>
class Connection : public ConnectionBase {
public:
    Connection(IPC::Stub& local_stub, NonnullOwnPtr<Core::LocalSocket> socket)
        : ConnectionBase(local_stub, move(socket), LocalEndpoint::static_magic())
    {
        m_socket->on_ready_to_read = [this] {
            NonnullRefPtr protect = *this;
            // FIXME: Do something about errors.
            (void)drain_messages_from_peer();
            handle_messages();
        };
    }

    template<typename MessageType>
    OwnPtr<MessageType> wait_for_specific_message()
    {
        return wait_for_specific_endpoint_message<MessageType, LocalEndpoint>();
    }

    template<typename RequestType, typename... Args>
    NonnullOwnPtr<typename RequestType::ResponseType> send_sync(Args&&... args)
    {
        MUST(post_message(RequestType(forward<Args>(args)...)));
        auto response = wait_for_specific_endpoint_message<typename RequestType::ResponseType, PeerEndpoint>();
        VERIFY(response);
        return response.release_nonnull();
    }

    template<typename RequestType, typename... Args>
    OwnPtr<typename RequestType::ResponseType> send_sync_but_allow_failure(Args&&... args)
    {
        if (post_message(RequestType(forward<Args>(args)...)).is_error())
            return nullptr;
        return wait_for_specific_endpoint_message<typename RequestType::ResponseType, PeerEndpoint>();
    }

protected:
    template<typename MessageType, typename Endpoint>
    OwnPtr<MessageType> wait_for_specific_endpoint_message()
    {
        if (auto message = wait_for_specific_endpoint_message_impl(Endpoint::static_magic(), MessageType::static_message_id()))
            return message.template release_nonnull<MessageType>();
        return {};
    }

    virtual void try_parse_messages(Vector<u8> const& bytes, size_t& index) override
    {
        u32 message_size = 0;
        for (; index + sizeof(message_size) < bytes.size(); index += message_size) {
            memcpy(&message_size, bytes.data() + index, sizeof(message_size));
            if (message_size == 0 || bytes.size() - index - sizeof(uint32_t) < message_size)
                break;
            index += sizeof(message_size);
            auto remaining_bytes = ReadonlyBytes { bytes.data() + index, message_size };

            auto local_message = LocalEndpoint::decode_message(remaining_bytes, fd_passing_socket());
            if (!local_message.is_error()) {
                m_unprocessed_messages.append(local_message.release_value());
                continue;
            }

            auto peer_message = PeerEndpoint::decode_message(remaining_bytes, fd_passing_socket());
            if (!peer_message.is_error()) {
                m_unprocessed_messages.append(peer_message.release_value());
                continue;
            }

            dbgln("Failed to parse a message");
            dbgln("Local endpoint error: {}", local_message.error());
            dbgln("Peer endpoint error: {}", peer_message.error());
            break;
        }
    }
};

}

template<typename LocalEndpoint, typename PeerEndpoint>
struct AK::Formatter<IPC::Connection<LocalEndpoint, PeerEndpoint>> : Formatter<Core::Object> {
};