// Stage 2 (PLAN.md): Ethernet/IP/TCP/UDP decoders producing a live
// packet-list line per capture. The TUI itself is still an open
// question (PLAN.md), so this prints to stdout for now; -x keeps the
// stage-1 hex dump available underneath each summary.
//
// Stage 3: -w <file> writes the same capture out as pcapng alongside
// the summary, so files stay Wireshark-compatible (PLAN.md).
//
// Stage 4: capture thread -> bounded CaptureQueue -> render loop on
// the main thread (PLAN.md's architecture sketch). The capture thread
// only copies raw bytes into the queue; decoding, printing, and
// pcapng-writing all happen on the consumer side, so a slow render
// path can never block the capture thread - a full queue drops the
// packet and counts it instead.
//
// Stage 5: L7 dissectors register into an L7Registry keyed by port
// (packeteer/l7/dissector.hpp) and get consulted from summarize_packet
// once TCP/UDP decode a port number. DNS is the first one, proving the
// interface against real traffic rather than synthetic bytes.
//
// IPv6: dispatched by version nibble rather than assumed absent --
// every live-capture test so far has shown real IPv6 background
// traffic silently dropped once the decoder only handled IPv4.
//
// Stage 6: -f <expr> compiles a tcpdump-style BPF expression via
// libpcap's own compiler (packeteer/filter.hpp) and installs it with
// pcap_setfilter(), filtering in the kernel before packets ever reach
// userspace - rather than hand-rolling a second BPF parser.
//
// Device-open/datalink-validate/filter/pcapng/signal-handler setup all
// goes through packeteer::CaptureSession (packeteer/capture_session.hpp)
// - the same one gui_main.cpp uses - so the CLI/TUI and GUI frontends
// can't drift apart on that setup path.

#include <pcap.h>

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

#include <ftxui/component/component.hpp>
#include <ftxui/component/screen_interactive.hpp>
#include <ftxui/dom/elements.hpp>

#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 {

// Queue capacity: how many packets can be buffered between the capture
// thread and the render loop before new packets get dropped. Sized as
// a fixed constant rather than a flag - tune later if a real workload
// needs it, not speculatively now.
constexpr std::size_t kQueueCapacity = 4096;

void hex_dump(std::span<const unsigned char> bytes) {
    for (const auto& line : packeteer::hex_dump_lines(bytes)) {
        std::printf("%s\n", line.c_str());
    }
    std::printf("\n");
}

struct RenderOptions {
    bool verbose_hex;
    bool verbose_checksums;
    int datalink;
    packeteer::pcapng::Writer* pcapng_writer;
    std::string search_term;  // display filter - see packeteer/search.hpp
    packeteer::net::TcpReassembler* reassembler;  // -a only; nullptr means disabled
};

void render_packet(const packeteer::CapturedPacket& packet, const RenderOptions& opts) {
    std::span<const unsigned char> bytes{packet.data};

    std::string line = packeteer::summarize_packet(bytes, opts.datalink);

    // -g is a display filter, not a capture filter: still written to
    // -w regardless of whether it matches, since -w should reflect
    // what was actually captured (that's -f's job), not what's shown.
    if (opts.pcapng_writer) {
        opts.pcapng_writer->write_packet(/*interface_id=*/0, packet.ts_sec, packet.ts_usec, bytes,
                                          packet.original_len);
    }

    if (!packeteer::matches_search(line, opts.search_term)) return;

    if (opts.verbose_checksums) {
        std::string status = packeteer::checksum_status(bytes, opts.datalink);
        if (!status.empty()) line += "  " + status;
    }
    std::printf("%s\n", line.c_str());
    if (opts.reassembler) {
        if (auto status = packeteer::reassembled_http_status(bytes, opts.datalink,
                                                               *opts.reassembler)) {
            std::printf("  [%s]\n", status->c_str());
        }
    }
    if (opts.verbose_hex) hex_dump(bytes);

    // Flush per packet: stdout is fully buffered off a tty, and this is
    // a live capture tool, not a batch one.
    std::fflush(stdout);
}

// TUI mode (-t): a scrolling packet list in a full-screen view, built
// with FTXUI (see NAMES.md-adjacent decision: chosen over notcurses for
// pure-C++ portability - no C build-system/dependency chain to fight
// on every platform PLAN.md targets, and genuine Windows console
// support, which notcurses lacks).
//
// A dedicated consumer thread pops from the capture queue and appends
// formatted rows to shared state; the UI thread just redraws on
// Event::Custom. 'q'/Esc triggers the same pcap_breakloop() shutdown
// path as Ctrl-C, so there's one shutdown sequence, not two: breakloop
// -> capture thread's pcap_loop returns -> queue.stop() -> consumer
// drains and calls screen.Exit() -> screen.Loop() returns.
void run_tui(packeteer::CaptureSession& session, packeteer::CaptureQueue& queue,
             RenderOptions& opts) {
    using namespace ftxui;

    constexpr std::size_t kMaxRows = 2000;  // cap memory; oldest rows scroll off

    std::mutex state_mutex;
    std::deque<std::string> rows;
    std::uint64_t packet_count = 0;

    // '/' search: a display filter over `rows`, independent of the
    // capture itself (packeteer/search.hpp) - typed and read only on
    // the UI thread (the consumer thread never touches it), so unlike
    // `rows`/`packet_count` it doesn't need state_mutex.
    bool searching = false;
    std::string search_term;
    bool replay_finished = false;  // guarded by state_mutex, like rows/packet_count

    auto screen = ScreenInteractive::Fullscreen();

    std::thread consumer_thread([&] {
        while (auto packet = queue.pop()) {
            std::span<const unsigned char> bytes{packet->data};
            std::string line = packeteer::summarize_packet(bytes, opts.datalink);

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

            {
                std::lock_guard<std::mutex> lock(state_mutex);
                rows.push_back(std::move(line));
                if (rows.size() > kMaxRows) rows.pop_front();
                ++packet_count;
            }
            screen.PostEvent(Event::Custom);
        }
        // Replay reaching end-of-file on its own (stop_requested() still
        // false) shouldn't close the window - the point of replaying a
        // file is browsing/searching it afterward, not watching it flash
        // by. An explicit stop (q/Esc below, or an external signal, both
        // of which set stop_requested()) always closes, live capture
        // included - that's still the same behavior as before.
        if (session.is_replay() && !session.stop_requested()) {
            {
                std::lock_guard<std::mutex> lock(state_mutex);
                replay_finished = true;
            }
            screen.PostEvent(Event::Custom);  // one more redraw for the final state
        } else {
            screen.Exit();
        }
    });

    auto renderer = Renderer([&] {
        std::lock_guard<std::mutex> lock(state_mutex);
        Elements lines;
        std::size_t shown = 0;
        for (const auto& row : rows) {
            if (!packeteer::matches_search(row, search_term)) continue;
            lines.push_back(text(row));
            ++shown;
        }

        std::string status = "packets: " + std::to_string(packet_count);
        if (!search_term.empty()) status += " (" + std::to_string(shown) + " shown)";
        if (replay_finished) status += "  [replay finished]";
        status += "  dropped: " + std::to_string(queue.dropped()) +
                  (searching ? "  (Enter to apply, Esc to clear)" : "  (/ to search, q to quit)");
        // 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.
        Elements footer = {text(status) | dim};
        if (auto stats = session.stats()) {
            if (stats->dropped > 0 || stats->if_dropped > 0) {
                std::string kernel_status = "kernel/interface dropped " +
                                             std::to_string(stats->dropped) + "/" +
                                             std::to_string(stats->if_dropped) + " (received " +
                                             std::to_string(stats->received) + ")";
                footer.push_back(text(kernel_status) | color(Color::Yellow));
            }
        }
        if (searching || !search_term.empty()) {
            footer.push_back(text("search: " + search_term + (searching ? "_" : "")) |
                              color(Color::Green));
        }
        std::string title = session.is_replay() ? ("packeteer - replaying " + session.device())
                                                 : "packeteer - live capture";
        return vbox({
                   text(title) | bold | color(Color::Cyan),
                   separator(),
                   vbox(std::move(lines)) | yframe | flex,
                   separator(),
                   vbox(std::move(footer)),
               }) |
               border;
    });

    auto component = CatchEvent(renderer, [&](const Event& event) {
        if (searching) {
            if (event == Event::Return) {
                searching = false;
                return true;
            }
            if (event == Event::Escape) {
                searching = false;
                search_term.clear();
                return true;
            }
            if (event == Event::Backspace) {
                if (!search_term.empty()) search_term.pop_back();
                return true;
            }
            if (event.is_character()) {
                search_term += event.character();
                return true;
            }
            return true;  // swallow anything else while typing (don't let it fall through to quit)
        }
        if (event == Event::Character('/')) {
            searching = true;
            return true;
        }
        if (event == Event::Character('q') || event == Event::Escape) {
            session.request_stop();
            // Closes immediately rather than waiting for the capture/
            // replay thread to actually finish and drain the queue --
            // necessary for replay mode specifically (that thread may
            // already be long gone once the user quits after browsing a
            // finished replay, so nothing else would ever call this).
            // main() still joins the thread properly afterward either way.
            screen.Exit();
            return true;
        }
        return false;
    });

    screen.Loop(component);
    consumer_thread.join();
}

void print_usage(const char* argv0) {
    std::printf(
        "packeteer - terminal packet capture and analysis tool\n"
        "\n"
        "Usage: %s [options] [interface]\n"
        "\n"
        "If no interface is given, the first available device is used.\n"
        "\n"
        "Options:\n"
        "  -t, --tui       Launch the interactive TUI instead of plain-text output\n"
        "  -x              Show a hex dump under each summary (plain-text mode only)\n"
        "  -c              Show IPv4/TCP/UDP checksum validity (plain-text mode only).\n"
        "                  Off by default: checksum offload means many outbound and\n"
        "                  loopback packets show as invalid even when nothing is\n"
        "                  actually wrong - the NIC computes the real checksum in\n"
        "                  hardware after most capture points already saw the packet.\n"
        "  -a              Reassemble TCP streams and re-run HTTP parsing on the\n"
        "                  joined bytes (plain-text mode only), catching a\n"
        "                  request/response split across multiple segments that\n"
        "                  single-packet HTTP dissection alone would miss. In-order\n"
        "                  segments only - out-of-order/retransmitted segments are\n"
        "                  dropped rather than buffered for reordering.\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"
        "  -g <term>       Display filter: only show packets whose summary contains\n"
        "                  <term> (case-insensitive). Doesn't affect -w. In TUI mode,\n"
        "                  press '/' to search interactively instead.\n"
        "  -h, --help      Show this help and exit\n"
        "\n"
        "Examples:\n"
        "  %s eth0                            capture on eth0, print each packet\n"
        "  %s eth0 -t                         capture on eth0 in the interactive TUI\n"
        "  %s eth0 -f \"tcp port 443\"          only capture HTTPS traffic\n"
        "  %s eth0 -w out.pcapng              capture and save to out.pcapng\n"
        "  %s -r out.pcapng -t                replay a saved capture in the TUI\n",
        argv0, argv0, 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 tui_mode = false;
    bool enable_reassembly = false;
    RenderOptions opts{.verbose_hex = false,
                        .verbose_checksums = false,
                        .datalink = 0,
                        .pcapng_writer = nullptr,
                        .search_term = "",
                        .reassembler = nullptr};

    for (int i = 1; i < argc; ++i) {
        if (std::strcmp(argv[i], "-x") == 0) {
            opts.verbose_hex = true;
        } else if (std::strcmp(argv[i], "-c") == 0) {
            opts.verbose_checksums = true;
        } else if (std::strcmp(argv[i], "-a") == 0) {
            enable_reassembly = true;
        } else if (std::strcmp(argv[i], "-t") == 0 || std::strcmp(argv[i], "--tui") == 0) {
            tui_mode = true;
        } else 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], "-g") == 0 && i + 1 < argc) {
            opts.search_term = argv[++i];
        } 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;
    }
    opts.datalink = session.datalink();
    opts.pcapng_writer = session.pcapng_writer();
    session.install_signal_handlers();

    packeteer::net::TcpReassembler reassembler;
    if (enable_reassembly) opts.reassembler = &reassembler;

    if (!tui_mode) {
        if (session.is_replay()) {
            std::printf("replaying %s (%s)\n", session.device().c_str(),
                         pcap_datalink_val_to_name(session.datalink()));
        } else {
            std::printf("capturing on %s (%s, ctrl-c to stop)\n", session.device().c_str(),
                         pcap_datalink_val_to_name(session.datalink()));
        }
    }

    packeteer::CaptureQueue queue(kQueueCapacity);
    std::thread capture_thread = session.start_capture_thread(queue);

    if (tui_mode) {
        run_tui(session, queue, opts);
    } else {
        while (auto packet = queue.pop()) {
            render_packet(*packet, opts);
        }
    }

    capture_thread.join();

    if (queue.dropped() > 0) {
        std::fprintf(stderr, "dropped %llu packets (render side fell behind)\n",
                     static_cast<unsigned long long>(queue.dropped()));
    }
    // Kernel-level counters, queried before the session closes its
    // handle: a traffic spike can drop packets before libpcap ever
    // hands them to our callback, which queue.dropped() can't see.
    if (auto stats = session.stats()) {
        if (stats->dropped > 0 || stats->if_dropped > 0) {
            std::fprintf(stderr, "kernel/interface dropped %u/%u packets (received %u)\n",
                         stats->dropped, stats->if_dropped, stats->received);
        }
    }

    return 0;
}