package space.minecraft;

import com.sun.net.httpserver.HttpExchange;
import com.sun.net.httpserver.HttpServer;
import net.fabricmc.api.ClientModInitializer;
import net.fabricmc.loader.api.FabricLoader;
import net.fabricmc.loader.api.MappingResolver;
import java.lang.reflect.*;
import java.net.InetSocketAddress;
import java.nio.charset.StandardCharsets;
import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicBoolean;

/** Local telemetry/control adapter. Gameplay remains in the upstream AltoClef mod.
 *
 * <p>Threading contract: every read or mutation of Minecraft client state
 * ({@link #snapshot}, {@link #connect}, AltoClef commands) runs ONLY on the
 * Minecraft client thread, reached through {@code Executor} dispatch (the
 * client implements {@code java.util.concurrent.Executor}) with a reflective
 * {@code execute(Runnable)} fallback. Dispatch is never run inline on a
 * telemetry or HTTP thread: a failed dispatch records a diagnostic and the
 * bridge keeps reporting a loading/error heartbeat WITHOUT claiming fresh
 * connected world observations.
 *
 * <p>Freshness contract for /state: {@code heartbeat_at} is refreshed by the
 * scheduler tick itself (bridge alive), while {@code observed_at} is refreshed
 * only by a snapshot that actually ran on the client thread. At most one
 * snapshot is ever queued, so rendering load cannot build a backlog.
 *
 * <p>Connect contract: the client starts at the normal TitleScreen (no
 * {@code --server/--port}, which would bypass it and leave upstream
 * uninitialized) and this bridge connects only on a Title/Disconnected
 * screen with no resource reload overlay (connecting mid-reload NPEs
 * WorldRenderer via ShaderProgram.addSampler), on the client thread only.
 */
public final class SpaceBridge implements ClientModInitializer {
    private static final MappingResolver MAP = FabricLoader.getInstance().getMappingResolver();
    private volatile String state = "{\"connected\":false,\"loading\":true,\"heartbeat_at\":0}";
    private volatile String lastError = "";
    private volatile String lastCommand = "";
    private final AtomicBoolean snapshotPending = new AtomicBoolean(false);
    private long connectAttempt;
    private long connectAttempts;
    private volatile String connectState = "startup";
    private String lastGate = "";
    private long creditsSince;
    private boolean creditsObserved;
    private boolean enteredEnd;
    private String previousDimension = "";

    private static Class<?> mc(String intermediary) throws Exception {
        return Class.forName(MAP.mapClassName("intermediary", "net.minecraft." + intermediary));
    }
    private static Method accessibleMethod(Class<?> owner, String name, Class<?>[] types) throws Exception {
        try {
            return owner.getMethod(name, types);
        } catch (NoSuchMethodException missing) {
            Method fallback = owner.getDeclaredMethod(name, types);
            fallback.setAccessible(true);
            return fallback;
        }
    }
    private static Object method(Object obj, String owner, String id, String desc,
                                 Class<?>[] types, Object... args) throws Exception {
        String name = MAP.mapMethodName("intermediary", "net.minecraft." + owner, id, desc);
        return accessibleMethod(mc(owner), name, types).invoke(obj, args);
    }
    private static Object call(Object obj, String name, Class<?>[] types, Object... args) throws Exception {
        return accessibleMethod(obj.getClass(), name, types).invoke(obj, args);
    }
    private static Object call(Object obj, String name) throws Exception {
        return call(obj, name, new Class<?>[0]);
    }
    private static Object client() throws Exception {
        return method(null, "class_310", "method_1551", "()Lnet/minecraft/class_310;", new Class<?>[0]);
    }
    /** Enqueue on the client thread. Never runs the task inline: throws on failure. */
    private static void dispatchToClient(Object client, Runnable task) throws Exception {
        if (client instanceof Executor) {
            ((Executor) client).execute(task);
            return;
        }
        accessibleMethod(client.getClass(), "execute", new Class<?>[]{Runnable.class}).invoke(client, task);
    }
    private static Object screen(Object client) throws Exception {
        String name = MAP.mapFieldName("intermediary", "net.minecraft.class_310", "field_1755", "Lnet/minecraft/class_437;");
        try {
            return mc("class_310").getField(name).get(client);
        } catch (NoSuchFieldException missing) {
            Field fallback = mc("class_310").getDeclaredField(name);
            fallback.setAccessible(true);
            return fallback.get(client);
        }
    }
    private static void respond(HttpExchange ex, int code, String body) throws Exception {
        byte[] data = body.getBytes(StandardCharsets.UTF_8);
        ex.getResponseHeaders().set("Content-Type", "application/json; charset=utf-8");
        ex.sendResponseHeaders(code, data.length);
        ex.getResponseBody().write(data);
        ex.close();
    }
    /** Loading/error heartbeat: fresh heartbeat_at, no connected observations claimed. */
    private void heartbeat(String detail) {
        Map<String, Object> data = new LinkedHashMap<>();
        data.put("connected", false);
        data.put("loading", true);
        data.put("heartbeat_at", System.currentTimeMillis() / 1000.0);
        data.put("dispatch_error", detail == null ? "" : detail);
        data.put("error", lastError);
        data.put("last_command", lastCommand);
        state = json(data);
    }
    private void queueSnapshot() {
        // At most one pending snapshot: skip the tick when the client thread
        // has not drained the previous one (e.g. under rendering load).
        if (!snapshotPending.compareAndSet(false, true)) {
            heartbeat("snapshot still queued on client thread");
            return;
        }
        boolean queued = false;
        try {
            dispatchToClient(client(), () -> {
                try {
                    snapshot();
                } finally {
                    snapshotPending.set(false);
                }
            });
            queued = true;
        } catch (Exception err) {
            lastError = "client dispatch failed: " + err;
        } finally {
            if (!queued) {
                snapshotPending.set(false);
                heartbeat(lastError);
            }
        }
    }
    @Override public void onInitializeClient() {
        try {
            int port = Integer.parseInt(System.getenv().getOrDefault("ALTOCLEF_BRIDGE_PORT", "3002"));
            HttpServer server = HttpServer.create(new InetSocketAddress("127.0.0.1", port), 8);
            server.createContext("/state", ex -> {
                try { respond(ex, 200, state); } catch (Exception ignored) { ex.close(); }
            });
            server.createContext("/command", ex -> {
                try {
                    if (!"POST".equals(ex.getRequestMethod())) { respond(ex, 405, "{}"); return; }
                    String command = new String(ex.getRequestBody().readNBytes(128), StandardCharsets.UTF_8).trim();
                    if (!Set.of("gamer", "stop", "status").contains(command)) {
                        respond(ex, 400, "{\"error\":\"unsupported command\"}"); return;
                    }
                    try {
                        dispatchToClient(client(), () -> {
                            try {
                                Class<?> alto = Class.forName("adris.altoclef.AltoClef");
                                Object executor = alto.getMethod("getCommandExecutor").invoke(null);
                                if (executor == null) throw new IllegalStateException("AltoClef is not initialized");
                                executor.getClass().getMethod("executeWithPrefix", String.class).invoke(executor, command);
                                lastCommand = command;
                                lastError = "";
                                System.out.println("[space-altoclef] command=" + command);
                            } catch (Exception err) { lastError = err.toString(); }
                        });
                    } catch (Exception err) {
                        lastError = "command dispatch failed: " + err;
                        respond(ex, 503, json(Map.of("error", lastError)));
                        return;
                    }
                    respond(ex, 202, "{\"accepted\":true}");
                } catch (Exception err) {
                    try { respond(ex, 503, json(Map.of("error", err.toString()))); } catch (Exception ignored) { ex.close(); }
                }
            });
            server.setExecutor(Executors.newFixedThreadPool(2));
            server.start();
            Executors.newSingleThreadScheduledExecutor(r -> {
                Thread t = new Thread(r, "space-altoclef-telemetry"); t.setDaemon(true); return t;
            }).scheduleWithFixedDelay(() -> {
                try {
                    queueSnapshot();
                } catch (Throwable err) {
                    lastError = "telemetry scheduler: " + err;
                    heartbeat(lastError);
                }
            }, 2, 1, TimeUnit.SECONDS);
            System.out.println("[space-altoclef] local bridge ready on 127.0.0.1:" + port);
        } catch (Exception err) { throw new RuntimeException("Space bridge failed", err); }
    }
    private void connect(Object client, Object currentScreen) throws Exception {
        // Gated connect: NEVER while a resource/shader reload overlay
        // is up (that NPEs WorldRenderer via ShaderProgram.addSampler on a
        // half-built reload), never while vanilla is already connecting, and
        // never before upstream initialized on the TitleScreen.
        // Pinned Yarn 1.19.4+build.2: METHOD emh ()Lesx; aJ method_18506 getOverlay
        // (owner class_310 MinecraftClient, returns class_4071 Overlay).
        Object overlay = method(client, "class_310", "method_18506", "()Lnet/minecraft/class_4071;",
                                new Class<?>[0]);
        boolean title = currentScreen != null
                && (mc("class_442").isInstance(currentScreen) || mc("class_419").isInstance(currentScreen));
        boolean connecting = currentScreen != null && mc("class_412").isInstance(currentScreen);
        String screenName = currentScreen == null ? "<none>" : currentScreen.getClass().getName();
        if (overlay != null) {
            gate("waiting resource reload (overlay=" + overlay.getClass().getName() + ")");
            return;
        }
        if (connecting) {
            connectState = "connecting (vanilla ConnectScreen)";
            return;
        }
        if (!title) {
            gate("waiting title screen (screen=" + screenName + ")");
            return;
        }
        if (System.currentTimeMillis() - connectAttempt < 30000) {
            connectState = "retry waits 30s throttle (screen=" + screenName + ")";
            return;
        }
        connectAttempt = System.currentTimeMillis();
        connectAttempts++;
        String address = System.getenv().getOrDefault("ALTOCLEF_SERVER", "127.0.0.1:25568");
        Object parsed = method(null, "class_639", "method_2950", "(Ljava/lang/String;)Lnet/minecraft/class_639;",
                               new Class<?>[]{String.class}, address);
        Object info = mc("class_642").getConstructor(String.class, String.class, boolean.class)
                                   .newInstance("Minecraft Friends", address, false);
        method(null, "class_412", "method_36877",
               "(Lnet/minecraft/class_437;Lnet/minecraft/class_310;Lnet/minecraft/class_639;Lnet/minecraft/class_642;)V",
               new Class<?>[]{mc("class_437"), mc("class_310"), mc("class_639"), mc("class_642")},
               screen(client), client, parsed, info);
        connectState = "connecting to " + address + " (attempt " + connectAttempts + ")";
        System.out.println("[space-altoclef] connecting to " + address + " (attempt " + connectAttempts + ")");
    }
    /** Throttled gate diagnostic: log only when the reason changes. */
    private void gate(String reason) {
        connectState = reason;
        if (!reason.equals(lastGate)) {
            lastGate = reason;
            System.out.println("[space-altoclef] connect gated: " + reason);
        }
    }
    private String currentDimension() throws Exception {
        // Upstream WorldHelper.getCurrentDimension is package-private static;
        // resolve it as a declared method so snapshots survive visibility.
        Class<?> helper = Class.forName("adris.altoclef.util.helpers.WorldHelper");
        return String.valueOf(accessibleMethod(helper, "getCurrentDimension", new Class<?>[0]).invoke(null));
    }
    /** Runs ONLY on the Minecraft client thread. Refreshes observed_at. */
    private void snapshot() {
        Map<String,Object> data = new LinkedHashMap<>();
        try {
            Object client = client();
            Class<?> alto = Class.forName("adris.altoclef.AltoClef");
            Object mod = alto.getMethod("getInstance").invoke(null);
            Object executor = alto.getMethod("getCommandExecutor").invoke(null);
            Object player = mod == null ? null : call(mod, "getPlayer");
            data.put("connected", player != null);
            data.put("initialized", executor != null);
            data.put("last_command", lastCommand);
            data.put("error", lastError);
            Object currentScreen = screen(client);
            boolean credits = currentScreen != null && mc("class_445").isInstance(currentScreen);
            if (credits) {
                if (enteredEnd) creditsObserved = true;
                if (creditsSince == 0) creditsSince = System.currentTimeMillis();
                if (System.currentTimeMillis() - creditsSince > 12000) {
                    method(currentScreen, "class_437", "method_25419", "()V", new Class<?>[0]);
                }
            }
            data.put("credits_screen", credits);
            data.put("credits_observed", creditsObserved);
            data.put("entered_end", enteredEnd);
            data.put("connect_state", connectState);
            data.put("connect_attempts", connectAttempts);
            if (player == null) {
                if (executor != null && !credits) connect(client, currentScreen);
            } else {
                String dimension = currentDimension();
                if ("END".equals(dimension)) enteredEnd = true;
                data.put("dimension", dimension);
                data.put("returned_from_end", enteredEnd && "OVERWORLD".equals(dimension));
                if (!dimension.equals(previousDimension)) {
                    System.out.println("[space-altoclef] dimension=" + dimension);
                    previousDimension = dimension;
                }
                data.put("position", Map.of("x", method(player,"class_1297","method_23317","()D",new Class<?>[0]),
                                            "y", method(player,"class_1297","method_23318","()D",new Class<?>[0]),
                                            "z", method(player,"class_1297","method_23321","()D",new Class<?>[0])));
                data.put("health", method(player,"class_1309","method_6032","()F",new Class<?>[0]));
                Object controller = call(mod, "getController");
                data.put("creative", method(controller,"class_636","method_2914","()Z",new Class<?>[0]));
                Object inventory = method(player,"class_1657","method_31548","()Lnet/minecraft/class_1661;",new Class<?>[0]);
                List<Object> items = new ArrayList<>();
                for (int slot = 0; slot < 41; slot++) {
                    Object stack = method(inventory,"class_1263","method_5438","(I)Lnet/minecraft/class_1799;",new Class<?>[]{int.class},slot);
                    int count = (Integer) method(stack,"class_1799","method_7947","()I",new Class<?>[0]);
                    if (count > 0) items.add(Map.of("slot",slot,"item",String.valueOf(method(stack,"class_1799","method_7909","()Lnet/minecraft/class_1792;",new Class<?>[0])),"count",count));
                }
                data.put("inventory", items);
                Object chain = call(mod,"getUserTaskChain");
                if (chain == null) {
                    // Upstream builds the task chain on TitleScreen entry; a
                    // null chain during loading reports initialized=false with
                    // diagnostics, never an NPE, and never a fabricated
                    // task_active.
                    data.put("initialized", false);
                    data.put("task_active", false);
                    data.put("init_note", "taskchain not yet initialized (waiting TitleScreen entry)");
                } else {
                    data.put("task_active", call(chain,"isActive"));
                    data.put("tasks", String.valueOf(call(chain,"getTasks")));
                }
                data.put("entered_end", enteredEnd);
                lastError = "";
                data.put("error", "");
            }
        } catch (Exception err) {
            lastError = err.toString();
            data.put("error", lastError);
        }
        data.put("heartbeat_at", System.currentTimeMillis() / 1000.0);
        data.put("observed_at", System.currentTimeMillis() / 1000.0);
        state = json(data);
    }
    private static String json(Object value) {
        if (value == null) return "null";
        if (value instanceof Boolean || value instanceof Number) return value.toString();
        if (value instanceof Map<?,?> map) {
            StringJoiner parts = new StringJoiner(",", "{", "}");
            map.forEach((k,v) -> parts.add(json(String.valueOf(k)) + ":" + json(v)));
            return parts.toString();
        }
        if (value instanceof Collection<?> list) {
            StringJoiner parts = new StringJoiner(",", "[", "]");
            list.forEach(v -> parts.add(json(v))); return parts.toString();
        }
        return "\"" + value.toString().replace("\\","\\\\").replace("\"","\\\"")
                                     .replace("\n","\\n").replace("\r","\\r").replace("\t","\\t") + "\"";
    }
}