// GUI frontend (secondary to the TUI - see PLAN.md Decisions). Same
// capture/decode/filter/pcapng pipeline as main.cpp's CLI/TUI modes,
// via packeteer::CaptureSession - not a hand-copied setup path, so it
// can't drift on datalink validation, filter errors, or the
// pcap_breakloop() shutdown hook the way two independent
// implementations eventually would.
//
// Dear ImGui + SDL3 (see CMakeLists.txt for the toolkit decision).

#include <SDL3/SDL.h>
#include <imgui.h>
#include <imgui_impl_sdl3.h>
#include <imgui_impl_sdlrenderer3.h>

#include <atomic>
#include <cstdio>
#include <cstring>
#include <deque>
#include <mutex>
#include <optional>
#include <span>
#include <string>
#include <thread>

#include "packeteer/capture_session.hpp"
#include "packeteer/net/tcp_reassembly.hpp"
#include "packeteer/packet_diagnostics.hpp"
#include "packeteer/search.hpp"
#include "packeteer/summarize.hpp"

namespace {

struct PacketRow {
    std::string summary;
    std::vector<unsigned char> data;
    // -a only: computed once at consume time (reassembly needs
    // in-order state across packets, unlike checksum status below,
    // which is stateless and cheap enough to compute lazily when a row
    // is selected instead of storing it on every row).
    std::optional<std::string> reassembled_http;
};

constexpr std::size_t kMaxRows = 5000;  // cap memory; oldest rows scroll off

struct SharedState {
    std::mutex mutex;
    std::deque<PacketRow> rows;
    std::uint64_t packet_count = 0;
    bool replay_finished = false;  // guarded by mutex, like rows/packet_count
    // Set once the consumer loop drains and exits from an explicit stop
    // (the window's quit action or an external SIGINT/SIGTERM) - but
    // NOT when a replay simply reaches end-of-file on its own, since the
    // point of replaying a file is browsing/searching it afterward, not
    // watching it flash by and vanish. The render loop watches this so
    // an external signal still closes the whole app in every other case
    // - not just the capture, leaving a frozen window behind - the
    // same single shutdown path run_tui() uses.
    std::atomic<bool> capture_alive{true};
};

void consumer_loop(packeteer::CaptureSession& session, packeteer::CaptureQueue& queue,
                    SharedState& state, packeteer::net::TcpReassembler* reassembler) {
    while (auto packet = queue.pop()) {
        std::span<const unsigned char> bytes{packet->data};
        std::string summary = packeteer::summarize_packet(bytes, session.datalink());

        if (auto* writer = session.pcapng_writer()) {
            writer->write_packet(/*interface_id=*/0, packet->ts_sec, packet->ts_usec, bytes,
                                  packet->original_len);
        }

        std::optional<std::string> reassembled_http;
        if (reassembler) {
            reassembled_http = packeteer::reassembled_http_status(bytes, session.datalink(),
                                                                    *reassembler);
        }

        std::lock_guard<std::mutex> lock(state.mutex);
        state.rows.push_back({std::move(summary), std::move(packet->data),
                               std::move(reassembled_http)});
        if (state.rows.size() > kMaxRows) state.rows.pop_front();
        ++state.packet_count;
    }
    if (session.is_replay() && !session.stop_requested()) {
        std::lock_guard<std::mutex> lock(state.mutex);
        state.replay_finished = true;
    } else {
        state.capture_alive.store(false);
    }
}

void print_usage(const char* argv0) {
    std::printf(
        "packeteer - terminal packet capture and analysis tool (GUI)\n"
        "\n"
        "Usage: %s [options] [interface]\n"
        "\n"
        "If no interface is given, the first available device is used.\n"
        "Search is available interactively in the window itself.\n"
        "\n"
        "Options:\n"
        "  -w <file>       Write the capture to <file> as pcapng (Wireshark-compatible)\n"
        "  -r <file>       Replay a saved pcapng file instead of a live device\n"
        "  -f <expr>       Kernel-level capture filter (tcpdump/BPF syntax); also\n"
        "                  applies to what -w writes. Can't be combined with -r.\n"
        "  -c              Show IPv4/TCP/UDP checksum validity for the selected packet.\n"
        "                  Off by default - see the CLI's -h for why (checksum offload).\n"
        "  -a              Reassemble TCP streams and show HTTP requests/responses\n"
        "                  joined across segments for the selected packet, when its\n"
        "                  segment contributed to one. In-order segments only.\n"
        "  -h, --help      Show this help and exit\n"
        "\n"
        "Examples:\n"
        "  %s eth0\n"
        "  %s eth0 -f \"tcp port 443\"\n"
        "  %s -r out.pcapng\n",
        argv0, argv0, argv0, argv0);
}

}  // namespace

int main(int argc, char** argv) {
    for (int i = 1; i < argc; ++i) {
        if (std::strcmp(argv[i], "-h") == 0 || std::strcmp(argv[i], "--help") == 0) {
            print_usage(argv[0]);
            return 0;
        }
    }

    packeteer::CaptureSessionOptions options;
    bool enable_checksums = false;
    bool enable_reassembly = false;
    for (int i = 1; i < argc; ++i) {
        if (std::strcmp(argv[i], "-w") == 0 && i + 1 < argc) {
            options.pcapng_output_path = argv[++i];
        } else if (std::strcmp(argv[i], "-f") == 0 && i + 1 < argc) {
            options.filter_expr = argv[++i];
        } else if (std::strcmp(argv[i], "-r") == 0 && i + 1 < argc) {
            options.replay_input_path = argv[++i];
        } else if (std::strcmp(argv[i], "-c") == 0) {
            enable_checksums = true;
        } else if (std::strcmp(argv[i], "-a") == 0) {
            enable_reassembly = true;
        } else if (options.device.empty()) {
            options.device = argv[i];
        }
    }

    packeteer::CaptureSession session;
    if (auto err = session.open(options)) {
        std::fprintf(stderr, "%s\n", err->c_str());
        return 1;
    }
    session.install_signal_handlers();

    if (!SDL_Init(SDL_INIT_VIDEO)) {
        std::fprintf(stderr, "SDL_Init failed: %s\n", SDL_GetError());
        return 1;
    }

    SDL_Window* window =
        SDL_CreateWindow("packeteer", 1000, 650, SDL_WINDOW_RESIZABLE | SDL_WINDOW_HIDDEN);
    if (window == nullptr) {
        std::fprintf(stderr, "SDL_CreateWindow failed: %s\n", SDL_GetError());
        SDL_Quit();
        return 1;
    }
    SDL_Renderer* renderer = SDL_CreateRenderer(window, nullptr);
    if (renderer == nullptr) {
        std::fprintf(stderr, "SDL_CreateRenderer failed: %s\n", SDL_GetError());
        SDL_DestroyWindow(window);
        SDL_Quit();
        return 1;
    }
    SDL_SetWindowPosition(window, SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED);
    SDL_ShowWindow(window);

    IMGUI_CHECKVERSION();
    ImGui::CreateContext();
    ImGui::GetIO().IniFilename = nullptr;  // no layout file: this is a fixed, simple layout
    ImGui_ImplSDL3_InitForSDLRenderer(window, renderer);
    ImGui_ImplSDLRenderer3_Init(renderer);

    packeteer::CaptureQueue queue(4096);
    SharedState state;
    packeteer::net::TcpReassembler reassembler;
    std::thread capture_thread = session.start_capture_thread(queue);
    std::thread consumer_thread(consumer_loop, std::ref(session), std::ref(queue),
                                 std::ref(state), enable_reassembly ? &reassembler : nullptr);

    int selected_row = -1;
    bool quit = false;
    char search_buf[256] = {};
    ImGuiIO& io = ImGui::GetIO();
    while (!quit && state.capture_alive.load()) {
        SDL_Event event;
        while (SDL_PollEvent(&event)) {
            ImGui_ImplSDL3_ProcessEvent(&event);
            if (event.type == SDL_EVENT_QUIT) {
                quit = true;
                session.request_stop();
            }
            // io.WantCaptureKeyboard reflects whether an ImGui widget
            // (the search box) held keyboard focus as of the last
            // completed frame - without this check, Escape would quit
            // the whole app while the user is just trying to clear a
            // search term, instead of doing what the TUI's Escape does
            // in the same context (clear the term, stay open).
            if (event.type == SDL_EVENT_KEY_DOWN && event.key.key == SDLK_ESCAPE &&
                !io.WantCaptureKeyboard) {
                quit = true;
                session.request_stop();
            }
        }

        ImGui_ImplSDLRenderer3_NewFrame();
        ImGui_ImplSDL3_NewFrame();
        ImGui::NewFrame();

        ImGui::SetNextWindowPos(ImVec2(0, 0));
        ImGui::SetNextWindowSize(io.DisplaySize);
        ImGui::Begin("packeteer", nullptr,
                      ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoResize |
                          ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoCollapse);

        if (session.is_replay()) {
            ImGui::Text("replaying %s (%s)", session.device().c_str(),
                        pcap_datalink_val_to_name(session.datalink()));
        } else {
            ImGui::Text("capturing on %s (%s)", session.device().c_str(),
                        pcap_datalink_val_to_name(session.datalink()));
        }
        ImGui::SameLine();
        ImGui::SetNextItemWidth(300);
        ImGui::InputTextWithHint("##search", "search (display filter, not capture filter)",
                                  search_buf, sizeof(search_buf));
        if (ImGui::IsItemFocused() && ImGui::IsKeyPressed(ImGuiKey_Escape)) {
            search_buf[0] = '\0';  // same behavior as the TUI's Esc-while-searching
        }
        std::string search_term(search_buf);
        ImGui::Separator();

        float details_height = 160.0f;
        std::size_t shown = 0;
        ImGui::BeginChild("packet_list", ImVec2(0, -details_height - 8), ImGuiChildFlags_Borders);
        {
            std::lock_guard<std::mutex> lock(state.mutex);
            for (std::size_t i = 0; i < state.rows.size(); ++i) {
                if (!packeteer::matches_search(state.rows[i].summary, search_term)) continue;
                ++shown;

                // ImGui derives a widget's ID from its label text by
                // default; two rows with identical summary text (e.g.
                // repeated ICMP lines) would otherwise collide on the
                // same ID. PushID(index) makes each row's ID unique
                // regardless of what text it displays.
                ImGui::PushID(static_cast<int>(i));
                bool is_selected = (selected_row == static_cast<int>(i));
                if (ImGui::Selectable(state.rows[i].summary.c_str(), is_selected)) {
                    selected_row = static_cast<int>(i);
                }
                ImGui::PopID();
            }
            // Auto-scroll to the newest row unless the user has scrolled up
            // to look at something (a manual scroll leaves the view short
            // of the max, which is what we check here).
            if (ImGui::GetScrollY() >= ImGui::GetScrollMaxY() - 1.0f) {
                ImGui::SetScrollHereY(1.0f);
            }
        }
        ImGui::EndChild();

        ImGui::BeginChild("packet_details", ImVec2(0, details_height), ImGuiChildFlags_Borders);
        {
            std::lock_guard<std::mutex> lock(state.mutex);
            if (selected_row >= 0 && selected_row < static_cast<int>(state.rows.size())) {
                const auto& row = state.rows[selected_row];
                if (enable_checksums) {
                    std::string status = packeteer::checksum_status(row.data, session.datalink());
                    if (!status.empty()) {
                        ImGui::TextColored(ImVec4(0.6f, 0.8f, 1.0f, 1.0f), "%s", status.c_str());
                    }
                }
                if (row.reassembled_http) {
                    ImGui::TextColored(ImVec4(0.6f, 1.0f, 0.6f, 1.0f), "%s",
                                        row.reassembled_http->c_str());
                }
                for (const auto& line : packeteer::hex_dump_lines(row.data)) {
                    ImGui::TextUnformatted(line.c_str());
                }
            } else {
                ImGui::TextDisabled("select a packet to see its hex dump");
            }
        }
        ImGui::EndChild();

        ImGui::Separator();
        {
            std::lock_guard<std::mutex> lock(state.mutex);
            const char* finished = state.replay_finished ? "  [replay finished]" : "";
            if (search_term.empty()) {
                ImGui::Text("packets: %llu%s  dropped: %llu  (Esc to quit)",
                            static_cast<unsigned long long>(state.packet_count), finished,
                            static_cast<unsigned long long>(queue.dropped()));
            } else {
                ImGui::Text("packets: %llu (%zu shown)%s  dropped: %llu  (Esc to clear search)",
                            static_cast<unsigned long long>(state.packet_count), shown, finished,
                            static_cast<unsigned long long>(queue.dropped()));
            }
        }
        // Kernel/interface-level drops: a traffic spike can drop
        // packets before libpcap ever hands them to our callback,
        // which the queue-side counter above can't see.
        if (auto stats = session.stats()) {
            if (stats->dropped > 0 || stats->if_dropped > 0) {
                ImGui::TextColored(ImVec4(1.0f, 0.6f, 0.2f, 1.0f),
                                    "kernel/interface dropped %u/%u (received %u)", stats->dropped,
                                    stats->if_dropped, stats->received);
            }
        }

        ImGui::End();

        ImGui::Render();
        SDL_SetRenderDrawColor(renderer, 30, 30, 30, 255);
        SDL_RenderClear(renderer);
        ImGui_ImplSDLRenderer3_RenderDrawData(ImGui::GetDrawData(), renderer);
        SDL_RenderPresent(renderer);
    }

    session.request_stop();
    capture_thread.join();
    consumer_thread.join();

    if (queue.dropped() > 0) {
        std::fprintf(stderr, "dropped %llu packets (render side fell behind)\n",
                     static_cast<unsigned long long>(queue.dropped()));
    }

    ImGui_ImplSDLRenderer3_Shutdown();
    ImGui_ImplSDL3_Shutdown();
    ImGui::DestroyContext();
    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    SDL_Quit();
    return 0;
}