import type { FastifyInstance } from "fastify";
import type { PiProcessManager } from "../pi/pi-process-manager.js";
import type { ThtRunner } from "../tht/tht-runner.js";
import type { SseHub } from "../sse/sse-hub.js";
import type { Settings } from "../settings/settings-store.js";
import { getUser } from "../auth/auth.js";
import type { ReadinessManager } from "../runtime/readiness-manager.js";

const BOOTSTRAP_FAILURE_MESSAGE =
  "Session startup failed. Check configuration and connectivity, then Resume the session.";
const READINESS_FAILURE_MESSAGE =
  "Session services are not ready. Check configuration and connectivity, then try again.";
const RESUME_FAILURE_MESSAGE =
  "Session could not be resumed. Check configuration and connectivity, then try again.";

function eventCursor(...values: unknown[]): number {
  let cursor = 0;
  for (const value of values.flatMap((item) => Array.isArray(item) ? item : [item])) {
    if (typeof value !== "string" || !/^\d+$/.test(value)) continue;
    const parsed = Number(value);
    if (Number.isSafeInteger(parsed)) cursor = Math.max(cursor, parsed);
  }
  return cursor;
}

export function sessionRoutes(
  app: FastifyInstance,
  d: { mgr: PiProcessManager; tht: ThtRunner; hub: SseHub; getSettings: () => Settings; readiness: ReadinessManager },
) {
  const lifecycleTails = new Map<string, Promise<void>>();
  const boundRuntimes = new Map<
    string,
    ReturnType<PiProcessManager["createFor"]>
  >();
  const failurePersistenceClaimed = new WeakSet<
    ReturnType<PiProcessManager["createFor"]>
  >();

  const withSessionLifecycle = async <T>(id: string, work: () => Promise<T>): Promise<T> => {
    const previous = lifecycleTails.get(id) ?? Promise.resolve();
    let release!: () => void;
    const gate = new Promise<void>((resolve) => { release = resolve; });
    const tail = previous.then(() => gate);
    lifecycleTails.set(id, tail);
    await previous;
    try {
      return await work();
    } finally {
      release();
      if (lifecycleTails.get(id) === tail) lifecycleTails.delete(id);
    }
  };

  const info = (id: string, text: string, level = "info") =>
    d.hub.publish(id, "info", { type: "info", level, text });

  const bindRuntime = (id: string, rt: ReturnType<PiProcessManager["createFor"]>) => {
    const previous = boundRuntimes.get(id);
    boundRuntimes.set(id, rt);
    try {
      rt.bridge.onClientEvent((e) => {
        // Child termination is asynchronous. Ignore queued events from a runtime once a newer
        // identity is bound or the session is explicitly closed/deleted. The active identity
        // remains bound after an unexpected exit so its public failure events still reach SSE.
        if (boundRuntimes.get(id) !== rt) return;
        if (e.type === "system_event" && e.event === "session_failed") {
          if (!failurePersistenceClaimed.has(rt)) {
            failurePersistenceClaimed.add(rt);
            void withSessionLifecycle(id, async () => {
              // agent_end can release the old binding before this queued work acquires the lock.
              // Undefined means no replacement; a different identity means Resume won and the
              // old failure must not touch its manifest.
              const bound = boundRuntimes.get(id);
              if (bound !== undefined && bound !== rt) return;
              await d.tht.failSession(id, d.getSettings().workspace).catch(() => undefined);
            }).catch(() => undefined);
          }
        }
        d.hub.publish(id, e.type, e);
        if (
          e.type === "system_event"
          && e.event === "agent_end"
          && d.mgr.get(id) !== rt
          && boundRuntimes.get(id) === rt
        ) {
          boundRuntimes.delete(id);
        }
      });
    } catch (error) {
      if (previous) boundRuntimes.set(id, previous);
      else if (boundRuntimes.get(id) === rt) boundRuntimes.delete(id);
      throw error;
    }
  };

  const bootstrap = (
    id: string,
    rt: ReturnType<PiProcessManager["createFor"]>,
    configure: Promise<void>,
    retrieval: Promise<void> | null,
    start: () => void,
  ) => {
    void (async () => {
      try {
        if (retrieval) info(id, "Preparing retrieval context");
        await Promise.all([configure, retrieval]);
        if (d.mgr.get(id) !== rt) return;
        info(id, "Starting model");
        if (d.mgr.get(id) !== rt) return;
        start();
      } catch {
        void withSessionLifecycle(id, async () => {
          // A bootstrap continuation can settle after Close/Delete or after a replacement was
          // installed. Claim only the runtime identity that actually failed; holding the same
          // lifecycle lock through persistence prevents a Resume from becoming that failure's
          // accidental target.
          if (d.mgr.get(id) !== rt || !d.mgr.teardownIfCurrent(id, rt)) return;
          if (!failurePersistenceClaimed.has(rt)) {
            failurePersistenceClaimed.add(rt);
            await d.tht.failSession(id, d.getSettings().workspace).catch(() => undefined);
          }
          rt.bridge.emitClientEvent({ type: "info", level: "error", text: BOOTSTRAP_FAILURE_MESSAGE });
          rt.bridge.emitClientEvent({ type: "system_event", event: "session_failed" });
          rt.bridge.emitClientEvent({ type: "system_event", event: "agent_end" });
        });
      }
    })();
  };

  app.post("/runtime/prewarm", async (_req, reply) => {
    const workspace = d.getSettings().workspace ?? "";
    void d.readiness.ensure(workspace).catch(() => undefined);
    return reply.code(202).send({ status: "warming" });
  });

  app.post("/sessions", async (req, reply) => {
    const b = req.body as { question: string; name?: string };
    const s = d.getSettings();
    const ensure = await d.readiness.ensure(s.workspace ?? "");
    if (!ensure.ok) return reply.code(503).send({ error: READINESS_FAILURE_MESSAGE });
    // Settings (global) supply workspace/provider/model/thinking. The new-question
    // form sends only the question text. `workspace` selects the tht `-c <config>`.
    const { id } = await d.tht.sessionNew({
      question: b.question,
      name: b.name,
      workspace: s.workspace,
      provider: s.provider,
      model: s.model,
      thinking: s.thinking,
    });
    const options = {
      provider: s.provider,
      model: s.model,
      thinking: s.thinking,
      author: getUser(req).id,
      question: b.question,
    };
    const rt = d.mgr.createFor(id, options);
    bindRuntime(id, rt);
    info(id, "Session created");
    bootstrap(
      id, rt, d.mgr.configure(rt, options),
      d.tht.searchPack(b.question, id, s.workspace),
      () => d.mgr.start(id, rt, options),
    );
    return { id };
  });
  app.get("/sessions", async () => d.tht.sessionList(d.getSettings().workspace));
  app.get("/sessions/:id", async (req) => d.tht.sessionShow((req.params as any).id, d.getSettings().workspace));
  app.post("/sessions/:id/response", async (req, reply) => {
    const id = (req.params as any).id;
    const rt = d.mgr.get(id);
    if (!rt) return reply.code(404).send({ error: "sessione non attiva" });
    rt.bridge.respond((req.body as any).ui_response);
    return reply.code(204).send();
  });
  app.post("/sessions/:id/steer", async (req, reply) => {
    const rt = d.mgr.get((req.params as any).id);
    if (!rt) return reply.code(404).send({ error: "sessione non attiva" });
    rt.bridge.steer((req.body as any).text);
    return reply.code(204).send();
  });
  app.post("/sessions/:id/resume", async (req, reply) => {
    const id = (req.params as any).id;
    return withSessionLifecycle(id, async () => {
      // This check belongs inside the per-session lock: a preceding cold Resume may have
      // installed a running runtime while this request was waiting.
      const existing = d.mgr.get(id);
      if (existing) {
        const state = existing.bridge.turnState();
        if (state === "running" || state === "waiting") {
          return reply.code(200).send({ id, alreadyActive: true });
        }
      }
      const manifest = (await d.tht.sessionShow(id, d.getSettings().workspace)) as { status?: string; archived?: boolean } | null;
      if (manifest?.status === "finalized" || manifest?.archived) {
        return reply.code(409).send({ error: "sessione in sola lettura (finalizzata o archiviata)" });
      }
      const settings = d.getSettings();
      const ensure = await d.readiness.ensure(settings.workspace ?? "");
      if (!ensure.ok) return reply.code(503).send({ error: READINESS_FAILURE_MESSAGE });
      const saved = manifest as { provider?: string; model?: string; thinking?: string } | null;
      const options = {
        provider: saved?.provider,
        model: saved?.model,
        thinking: saved?.thinking ?? settings.thinking,
        author: getUser(req).id,
        mode: "resume" as const,
      };

      // Reopening is validation, not the transport commit point. Keep the old hub intact if
      // persistence cannot be reopened.
      try {
        await d.tht.reopenSession(id, settings.workspace);
      } catch {
        return reply.code(503).send({ error: RESUME_FAILURE_MESSAGE });
      }

      // Re-check immediately before the replacement commit. A lifecycle operation that ran
      // before this request acquired the lock may have changed or removed the runtime.
      const current = d.mgr.get(id);
      if (current) {
        const state = current.bridge.turnState();
        if (state === "running" || state === "waiting") {
          return reply.code(200).send({ id, alreadyActive: true });
        }
      }

      let rt: ReturnType<PiProcessManager["createFor"]> | undefined;
      try {
        if (current) {
          if (boundRuntimes.get(id) === current) boundRuntimes.delete(id);
          d.mgr.teardownIfCurrent(id, current);
        }
        rt = d.mgr.createFor(id, options);
        bindRuntime(id, rt);
      } catch {
        // A created-but-unbound runtime is not usable. The old hub remains attached because
        // clear() has not happened yet.
        if (rt) {
          if (boundRuntimes.get(id) === rt) boundRuntimes.delete(id);
          d.mgr.teardownIfCurrent(id, rt);
        }
        return reply.code(503).send({ error: RESUME_FAILURE_MESSAGE });
      }

      // Commit the replacement only after reopen + runtime creation/binding succeeded, and
      // immediately before the first event produced by the new Resume.
      d.hub.clear(id);
      info(id, "Resuming session");
      bootstrap(id, rt, d.mgr.configure(rt, options), null, () => d.mgr.start(id, rt, options));
      return reply.code(200).send({ id, alreadyActive: false });
    });
  });
  app.post("/sessions/:id/close", async (req) => {
    const id = (req.params as { id: string }).id;
    return withSessionLifecycle(id, async () => {
      // Invalidate the live generation before persistence can yield. Otherwise its deferred
      // bootstrap may start Pi while Close is already in progress.
      const current = d.mgr.get(id);
      boundRuntimes.delete(id);
      if (current) d.mgr.teardownIfCurrent(id, current);
      try {
        await d.tht.closeSession(id, d.getSettings().workspace);
      } finally {
        d.hub.clear(id);
      }
      return { closed: true };
    });
  });
  app.get("/sessions/:id/events", (req, reply) => {
    const id = (req.params as any).id;
    const rt = d.mgr.get(id);
    const afterId = eventCursor(
      req.headers["last-event-id"],
      (req.query as { lastEventId?: unknown }).lastEventId,
    );
    // Add CORS headers manually: reply.raw.writeHead bypasses Fastify's onSend hooks
    // (where @fastify/cors injects headers), so we must set them explicitly here.
    const origin = (req.headers.origin as string | undefined) ?? "*";
    reply.raw.writeHead(200, {
      "Content-Type": "text/event-stream",
      "Cache-Control": "no-cache",
      "X-Accel-Buffering": "no",
      Connection: "keep-alive",
      "Access-Control-Allow-Origin": origin,
      "Access-Control-Allow-Credentials": "true",
    });
    // Send the handshake immediately. Without this, Node waits for the first event body and
    // proxies/clients cannot establish an idle SSE subscription or inspect its headers.
    reply.raw.flushHeaders();
    const send = (event: string, data: object, eventId: number) =>
      reply.raw.write(`id: ${eventId}\nevent: ${event}\ndata: ${JSON.stringify(data)}\n\n`);
    const off = d.hub.subscribe(id, send, {
      afterId,
      pending: rt?.bridge.pendingWidget() ?? null,
      // clear()/forget() end every old transport so native EventSource reconnects with its
      // Last-Event-ID instead of remaining attached to a subscriber callback that no longer exists.
      close: () => {
        if (!reply.raw.writableEnded) reply.raw.end();
      },
    });
    req.raw.on("close", off);
  });
  app.post("/sessions/:id/rename", async (req, reply) => {
    await d.tht.setName((req.params as any).id, (req.body as any).name);
    return reply.code(204).send();
  });
  app.post("/sessions/:id/group", async (req, reply) => {
    await d.tht.setGroup((req.params as any).id, (req.body as any).group);
    return reply.code(204).send();
  });
  app.post("/sessions/:id/archive", async (req, reply) => {
    await d.tht.archive((req.params as any).id);
    return reply.code(204).send();
  });
  app.post("/sessions/:id/unarchive", async (req, reply) => {
    await d.tht.unarchive((req.params as any).id);
    return reply.code(204).send();
  });
  app.delete("/sessions/:id", async (req, reply) => {
    const id = (req.params as any).id;
    return withSessionLifecycle(id, async () => {
      const current = d.mgr.get(id);
      boundRuntimes.delete(id);
      if (current) d.mgr.teardownIfCurrent(id, current);
      await d.tht.deleteSession(id, d.getSettings().workspace);
      d.hub.forget(id);
      return reply.code(204).send();
    });
  });
  app.get("/sessions/:id/documents", async (req) => d.tht.documents((req.params as any).id));
}