using GLib;

namespace Spry.Cli {

    /**
     * `spry dev` — build, run and watch the application.
     *
     * Sets up the builddir when absent, builds with ninja, spawns the app
     * binary with the stack's library environment, then watches `src/`,
     * `meson.build` and `web-config.json`. On change it rebuilds
     * incrementally — meson's dependency graph re-runs the statum-mkpstm /
     * statum-mkres code generation automatically — and restarts the binary
     * when the build succeeds. On failure the compiler errors are shown and
     * the previous process keeps running, so the loop is never left dead.
     *
     * Restarts are cheap by design: Statum state is client-carried, the
     * browser transparently recovers via the transmit(retry) protocol, and
     * session identity survives via the static keys in web-config.json —
     * just refresh the page.
     */
    public class Dev : Object {

        /** Delay bundling rapid consecutive saves into one rebuild. */
        private const uint DEBOUNCE_MS = 200;

        /** Grace period after SIGTERM before escalating to SIGKILL. */
        private const uint KILL_GRACE_SECONDS = 3;

        private string app_dir;
        private string app_name;
        private string build_dir;
        private string binary_path;
        private string? libdir;
        private int port;

        private MainLoop loop;
        private SubprocessLauncher launcher;
        private Subprocess? app_process = null;
        private FileMonitor[] monitors = {};
        private uint debounce_source = 0;
        private bool expect_exit = false;
        private bool shutting_down = false;

        /**
         * Runs the dev loop in `app_dir`. Does not return until the user
         * interrupts it (Ctrl-C) or the initial build fails.
         */
        public static int run(string app_dir, string app_name, int port, bool fresh,
                bool no_run, string? libdir) throws Error {
            var dev = new Dev();
            dev.app_dir = app_dir;
            dev.app_name = app_name;
            dev.build_dir = Path.build_filename(app_dir, "builddir");
            dev.binary_path = Path.build_filename(dev.build_dir, app_name);
            dev.libdir = libdir;
            dev.port = port;

            if (fresh) {
                dev.reset_database();
            }

            dev.launcher = new SubprocessLauncher(SubprocessFlags.NONE);
            Tools.apply_env(dev.launcher, libdir);

            if (!FileUtils.test(Path.build_filename(dev.build_dir, "build.ninja"), FileTest.EXISTS)) {
                dev.step("Configuring builddir");
                if (!dev.spawn_sync({ "meson", "setup", ".", "builddir" })) {
                    stderr.printf("[spry] meson setup failed — fix the errors above and re-run spry dev\n");
                    return 1;
                }
            }

            dev.step("Building");
            if (!dev.build()) {
                return 1;
            }
            if (no_run) {
                return 0;
            }

            dev.loop = new MainLoop();
            dev.watch_sources();
            dev.install_signal_handlers();
            dev.spawn_child();

            dev.loop.run();
            return 0;
        }

        // ------------------------------------------------------------------
        // Build / run / restart
        // ------------------------------------------------------------------

        /** Deletes the application's SQLite store (honouring SPRY_DB_PATH). */
        private void reset_database() {
            var configured = Environment.get_variable("SPRY_DB_PATH");
            var path = configured != null && configured.length > 0
                ? configured
                : app_name + ".sqlite";
            if (FileUtils.test(path, FileTest.EXISTS)) {
                FileUtils.remove(path);
                stdout.printf("[spry] Deleted %s\n", path);
            }
        }

        /** Incrementally builds; returns true on success. */
        private bool build() throws Error {
            return spawn_sync({ "ninja", "-C", "builddir" });
        }

        /**
         * Runs a short-lived child that inherits this process's stdio,
         * with the stack's library environment applied.
         */
        private bool spawn_sync(string[] argv) throws Error {
            var process = launcher.spawnv(argv);
            try {
                process.wait_check();
                return true;
            } catch (Error e) {
                return false;
            }
        }

        private void spawn_child() {
            try {
                expect_exit = false;
                app_process = launcher.spawnv({ binary_path, port.to_string() });
                stdout.printf("[spry] Running %s on port %d (Ctrl-C to stop)\n", app_name, port);
                watch_child.begin();
            } catch (Error e) {
                stderr.printf("[spry] Could not run %s: %s\n", binary_path, e.message);
            }
        }

        /**
         * The single lifecycle waiter for the running child: on an expected
         * exit (restart) it spawns the replacement; on an unexpected exit it
         * reports and leaves the loop watching for the next successful
         * rebuild.
         */
        private async void watch_child() {
            var process = app_process;
            if (process == null) {
                return;
            }
            try {
                yield ((!)process).wait_async(null);
            } catch (Error e) {
            }
            if (shutting_down) {
                return;
            }
            if (expect_exit) {
                spawn_child();
            } else {
                app_process = null;
                stdout.printf("[spry] %s exited — save a file to rebuild, or Ctrl-C to quit\n", app_name);
            }
        }

        /** Rebuilds and, on success, replaces the running child. */
        private void rebuild() {
            if (shutting_down) {
                return;
            }
            step("Rebuilding");
            try {
                if (!build()) {
                    stdout.printf("[spry] Build failed — %s is still running\n", app_name);
                    return;
                }
            } catch (Error e) {
                stderr.printf("[spry] Build could not run: %s\n", e.message);
                return;
            }
            restart_child();
        }

        /**
         * Stops the running child (SIGTERM, escalating to SIGKILL after the
         * grace period); the lifecycle waiter spawns the replacement once it
         * observes the exit. When no child is running the replacement starts
         * immediately.
         */
        private void restart_child() {
            var process = app_process;
            if (process == null) {
                spawn_child();
                return;
            }
            expect_exit = true;
            ((!)process).send_signal(ProcessSignal.TERM);
            Timeout.add_seconds(KILL_GRACE_SECONDS, () => {
                if (!shutting_down && app_process == process && !((!)process).get_if_exited()) {
                    stdout.printf("[spry] %s did not exit — killing it\n", app_name);
                    ((!)process).send_signal(ProcessSignal.KILL);
                }
                return false;
            });
        }

        // ------------------------------------------------------------------
        // Watching
        // ------------------------------------------------------------------

        /** Watches the application's sources for changes. */
        private void watch_sources() throws Error {
            watch_tree(File.new_for_path(Path.build_filename(app_dir, "src")));
            watch_file(Path.build_filename(app_dir, "meson.build"));
            watch_file(Path.build_filename(app_dir, "web-config.json"));
        }

        private void watch_tree(File directory) {
            watch_directory(directory);
            try {
                var enumerator = directory.enumerate_children("standard::name,standard::type",
                    FileQueryInfoFlags.NONE);
                FileInfo info;
                while ((info = enumerator.next_file()) != null) {
                    if (info.get_file_type() == FileType.DIRECTORY) {
                        watch_tree(File.new_for_path(
                            Path.build_filename((!) directory.get_path(), info.get_name())));
                    }
                }
            } catch (Error e) {
                stderr.printf("[spry] Could not enumerate %s: %s\n", directory.get_path(), e.message);
            }
        }

        /**
         * Attaches a directory monitor; newly created subdirectories are
         * picked up as well, so `spry add` output is watched without a
         * restart.
         */
        private void watch_directory(File directory) {
            try {
                var monitor = directory.monitor_directory(FileMonitorFlags.NONE);
                monitor.changed.connect((file, other, event) => {
                    if (event == FileMonitorEvent.CREATED && file.query_file_type(FileQueryInfoFlags.NONE) == FileType.DIRECTORY) {
                        watch_tree(file);
                    }
                    if (event != FileMonitorEvent.CHANGES_DONE_HINT) {
                        schedule_rebuild();
                    }
                });
                monitors += monitor;
            } catch (Error e) {
                stderr.printf("[spry] Could not watch %s: %s\n", directory.get_path(), e.message);
            }
        }

        private void watch_file(string path) {
            try {
                var monitor = File.new_for_path(path).monitor_file(FileMonitorFlags.NONE);
                monitor.changed.connect(() => schedule_rebuild());
                monitors += monitor;
            } catch (Error e) {
                stderr.printf("[spry] Could not watch %s: %s\n", path, e.message);
            }
        }

        /** Bundles rapid saves into a single rebuild. */
        private void schedule_rebuild() {
            if (debounce_source != 0) {
                Source.remove(debounce_source);
            }
            debounce_source = Timeout.add(DEBOUNCE_MS, () => {
                debounce_source = 0;
                rebuild();
                return false;
            });
        }

        // ------------------------------------------------------------------
        // Lifecycle
        // ------------------------------------------------------------------

        private void install_signal_handlers() {
            Unix.signal_add(ProcessSignal.INT, () => {
                shutdown();
                return false;
            });
            Unix.signal_add(ProcessSignal.TERM, () => {
                shutdown();
                return false;
            });
        }

        private void shutdown() {
            if (shutting_down) {
                return;
            }
            shutting_down = true;
            stdout.printf("\n[spry] Stopping %s\n", app_name);
            if (app_process != null) {
                ((!)app_process).send_signal(ProcessSignal.TERM);
                Timeout.add_seconds(KILL_GRACE_SECONDS, () => {
                    if (app_process != null && !((!)app_process).get_if_exited()) {
                        ((!)app_process).send_signal(ProcessSignal.KILL);
                    }
                    return false;
                });
            }
            Timeout.add(KILL_GRACE_SECONDS * 1000, () => {
                loop.quit();
                return false;
            });
        }

        private void step(string label) {
            stdout.printf("[spry] %s…\n", label);
        }
    }
}