import type { Sql } from '../db.js';
import type { FastifyBaseLogger } from 'fastify';
import type { Broker } from '@boocode/server/broker';
import type { Config } from '../config.js';

interface InferenceRunner {
  enqueue: (sessionId: string, chatId: string, assistantId: string, user: string) => void;
  cancel: (sessionId: string, chatId: string) => Promise<boolean>;
  hasActive: (chatId: string) => boolean;
}

interface Deps {
  sql: Sql;
  inference: InferenceRunner;
  broker: Broker;
  log: FastifyBaseLogger;
  config: Config;
}

const POLL_INTERVAL_MS = 5_000;
const COMPLETION_POLL_MS = 2_000;

export function createDispatcher(deps: Deps): { start(): void; stop(): Promise<void> } {
  const { sql, inference, log, config } = deps;
  let timer: ReturnType<typeof setInterval> | null = null;
  let running = false;
  let stopping = false;
  let inflightPromise: Promise<void> | null = null;

  async function poll(): Promise<void> {
    if (running || stopping) return;

    // Grab one pending task
    const rows = await sql<{ id: string; project_id: string; input: string; agent: string | null; model: string | null }[]>`
      SELECT id, project_id, input, agent, model
      FROM tasks
      WHERE state = 'pending'
      ORDER BY created_at
      LIMIT 1
    `;
    if (rows.length === 0) return;

    const task = rows[0]!;
    running = true;
    inflightPromise = runTask(task).finally(() => {
      running = false;
      inflightPromise = null;
    });
  }

  async function runTask(task: { id: string; project_id: string; input: string; agent: string | null; model: string | null }): Promise<void> {
    const taskId = task.id;
    log.info({ taskId }, 'dispatcher: starting task');

    try {
      // Mark running
      await sql`
        UPDATE tasks
        SET state = 'running', started_at = clock_timestamp(), execution_path = 'native'
        WHERE id = ${taskId}
      `;

      // Create session + chat for this task
      const model = task.model ?? config.DEFAULT_MODEL;
      const sessionName = 'Task: ' + task.input.slice(0, 40);

      const [session] = await sql<{ id: string }[]>`
        INSERT INTO sessions (project_id, name, model, status)
        VALUES (${task.project_id}, ${sessionName}, ${model}, 'open')
        RETURNING id
      `;
      const sessionId = session!.id;

      const [chat] = await sql<{ id: string }[]>`
        INSERT INTO chats (session_id, name, status)
        VALUES (${sessionId}, 'Task execution', 'open')
        RETURNING id
      `;
      const chatId = chat!.id;

      // Link task to session
      await sql`UPDATE tasks SET session_id = ${sessionId} WHERE id = ${taskId}`;

      // Create user message + streaming assistant
      await sql<{ id: string }[]>`
        INSERT INTO messages (session_id, chat_id, role, content, status, created_at)
        VALUES (${sessionId}, ${chatId}, 'user', ${task.input}, 'complete', clock_timestamp())
        RETURNING id
      `;
      const [assistantMsg] = await sql<{ id: string }[]>`
        INSERT INTO messages (session_id, chat_id, role, content, status, created_at)
        VALUES (${sessionId}, ${chatId}, 'assistant', '', 'streaming', clock_timestamp())
        RETURNING id
      `;
      const assistantId = assistantMsg!.id;

      // Enqueue inference
      inference.enqueue(sessionId, chatId, assistantId, 'default');

      // Wait for inference to complete (poll message status)
      const finalStatus = await waitForCompletion(assistantId);

      if (stopping) {
        // Graceful shutdown — mark cancelled
        await sql`
          UPDATE tasks
          SET state = 'cancelled', ended_at = clock_timestamp()
          WHERE id = ${taskId}
        `;
        return;
      }

      if (finalStatus === 'complete') {
        // Grab assistant content for output_summary
        const [msg] = await sql<{ content: string | null }[]>`
          SELECT content FROM messages WHERE id = ${assistantId}
        `;
        const summary = (msg?.content ?? '').slice(0, 500);
        await sql`
          UPDATE tasks
          SET state = 'completed', ended_at = clock_timestamp(), output_summary = ${summary}
          WHERE id = ${taskId}
        `;
        log.info({ taskId }, 'dispatcher: task completed');
      } else {
        // failed or cancelled
        const [msg] = await sql<{ content: string | null }[]>`
          SELECT content FROM messages WHERE id = ${assistantId}
        `;
        const summary = (msg?.content ?? 'Inference failed').slice(0, 500);
        await sql`
          UPDATE tasks
          SET state = 'failed', ended_at = clock_timestamp(), output_summary = ${summary}
          WHERE id = ${taskId}
        `;
        log.warn({ taskId, finalStatus }, 'dispatcher: task failed');
      }
    } catch (err) {
      const errMsg = err instanceof Error ? err.message : String(err);
      log.error({ taskId, err: errMsg }, 'dispatcher: task error');
      await sql`
        UPDATE tasks
        SET state = 'failed', ended_at = clock_timestamp(), output_summary = ${errMsg.slice(0, 500)}
        WHERE id = ${taskId}
      `.catch(() => {}); // best-effort
    }
  }

  async function waitForCompletion(assistantId: string): Promise<string> {
    // Poll until the assistant message is no longer streaming
    for (;;) {
      if (stopping) return 'cancelled';

      const [row] = await sql<{ status: string }[]>`
        SELECT status FROM messages WHERE id = ${assistantId}
      `;
      const status = row?.status ?? 'failed';
      if (status !== 'streaming') return status;

      await sleep(COMPLETION_POLL_MS);
    }
  }

  function sleep(ms: number): Promise<void> {
    return new Promise((resolve) => setTimeout(resolve, ms));
  }

  return {
    start() {
      log.info('dispatcher: starting poll loop');
      timer = setInterval(() => {
        poll().catch((err) => {
          log.error({ err }, 'dispatcher: poll error');
        });
      }, POLL_INTERVAL_MS);
    },

    async stop() {
      stopping = true;
      if (timer) {
        clearInterval(timer);
        timer = null;
      }
      if (inflightPromise) {
        log.info('dispatcher: waiting for in-flight task');
        await inflightPromise;
      }
      log.info('dispatcher: stopped');
    },
  };
}