// veloxd — the Velox download-manager daemon.
//
// Wires up both RPC transports (Unix socket + loopback WebSocket), the SQLite store,
// and a dispatcher skeleton so the CLI and GUI have a real server to speak to
// (AGENT-DAEMON.md build order, steps 1 and 3). The scheduler and the engine link land
// next.

#include <csignal>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <string>

#include <sys/socket.h>
#include <sys/un.h>
#include <unistd.h>

#include "rpc/dispatcher.hpp"
#include "rpc/event_loop.hpp"
#include "rpc/pairing.hpp"
#include "rpc/runtime_dir.hpp"
#include "rpc/uds_server.hpp"
#include "rpc/ws_server.hpp"
#include "store/migrations.hpp"
#include "store/sqlite.hpp"
#include "version.hpp"

namespace {

velox::daemon::rpc::EventLoop* g_loop = nullptr;

void on_signal(int) {
    if (g_loop != nullptr) g_loop->stop();  // stop() is async-signal-safe (writes an eventfd)
}

// Single-instance guard: bind an abstract-namespace Unix socket whose name is unique to
// this user. A second daemon gets EADDRINUSE and exits. The kernel reclaims an
// abstract-namespace address when the holding process dies, so a crash never wedges it
// (docs/01 §2). Returns the held fd (kept open for the process lifetime) or -1.
int acquire_single_instance_lock() {
    const int fd = ::socket(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0);
    if (fd < 0) return -1;

    const std::string name = std::string("velox-daemon-") + std::to_string(::geteuid());
    sockaddr_un addr{};
    addr.sun_family = AF_UNIX;
    // Leading NUL selects the abstract namespace; the name follows, not NUL-terminated.
    addr.sun_path[0] = '\0';
    std::memcpy(addr.sun_path + 1, name.c_str(), name.size());
    const socklen_t len =
        static_cast<socklen_t>(offsetof(sockaddr_un, sun_path) + 1 + name.size());

    if (::bind(fd, reinterpret_cast<sockaddr*>(&addr), len) != 0) {
        ::close(fd);
        return -1;
    }
    return fd;
}

}  // namespace

int main() {
    std::cout << "veloxd " << velox::daemon::kDaemonVersion << " (protocol "
              << velox::proto::kProtocolVersion << ")\n";

    const int lock_fd = acquire_single_instance_lock();
    if (lock_fd < 0) {
        std::cerr << "veloxd: another instance is already running for this user\n";
        return 1;
    }

    velox::daemon::rpc::RuntimeDir rt;
    if (const auto ec = velox::daemon::rpc::resolve_runtime_dir(rt)) {
        std::cerr << "veloxd: cannot prepare runtime directory: " << ec.message() << "\n";
        return 1;
    }

    velox::daemon::rpc::EventLoop loop;
    g_loop = &loop;

    struct sigaction sa{};
    sa.sa_handler = on_signal;
    ::sigemptyset(&sa.sa_mask);
    ::sigaction(SIGINT, &sa, nullptr);
    ::sigaction(SIGTERM, &sa, nullptr);
    ::signal(SIGPIPE, SIG_IGN);  // a client vanishing mid-write is EPIPE, never a signal

    std::string data_dir;
    if (const auto ec = velox::daemon::rpc::resolve_data_dir(data_dir)) {
        std::cerr << "veloxd: cannot prepare data directory: " << ec.message() << "\n";
        return 1;
    }
    auto db = velox::daemon::store::Db::open(data_dir + "/velox.db");
    if (!db) {
        std::cerr << "veloxd: cannot open " << data_dir << "/velox.db: "
                  << db.error().to_string() << "\n";
        return 1;
    }
    if (const auto m = velox::daemon::store::migrate_to_head(*db); !m) {
        std::cerr << "veloxd: schema migration failed: " << m.error().to_string() << "\n";
        return 1;
    }

    velox::daemon::rpc::VeloxDispatcher dispatcher;

    velox::daemon::rpc::UdsServer uds(loop, dispatcher, rt.socket_path());
    if (const auto ec = uds.start()) {
        std::cerr << "veloxd: cannot listen on " << rt.socket_path() << ": " << ec.message()
                  << "\n";
        return 1;
    }
    std::cout << "veloxd: listening on " << uds.socket_path() << "\n";

    // The WebSocket transport is the extension's fallback (docs/05 §4); the Unix socket is
    // the primary. If every port in 52000-52016 is taken, log it and carry on rather than
    // refusing to start — capture must fail open, and the GUI/CLI still have the socket.
    // TODO(build step 7): replace EnvAutoApprover with a GUI-dialog / desktop-notification
    // approver. Until then pairing needs VELOX_PAIR_AUTO=1.
    velox::daemon::rpc::EnvAutoApprover approver;
    velox::daemon::rpc::WsServer ws(loop, dispatcher, *db, approver, rt);
    if (const auto ec = ws.start()) {
        std::cerr << "veloxd: WebSocket transport unavailable (" << ec.message()
                  << "); the extension fallback will not work this run\n";
    } else {
        std::cout << "veloxd: WebSocket transport on 127.0.0.1:" << ws.port() << "\n";
    }

    loop.run();
    std::cout << "veloxd: shutting down\n";

    g_loop = nullptr;
    ::close(lock_fd);
    return 0;
}