import express, { type Request, type Response } from 'express';
import fs from 'node:fs/promises';
import path from 'node:path';
import type { ControlPlaneState, CreateUserInput } from '../src/shared/contracts';
import {
  buildRuntimePaths,
  createUserRecord,
  deriveDashboardSnapshot,
  render3proxyConfig,
  validateCreateUserInput,
  type RuntimePaths,
} from './lib/config';
import type { RuntimeController } from './lib/runtime';
import { StateStore } from './lib/store';

export interface AppServices {
  store: StateStore;
  runtime: RuntimeController;
  runtimeRootDir: string;
}

export function createApp({ store, runtime, runtimeRootDir }: AppServices) {
  const app = express();
  const runtimePaths = buildRuntimePaths(runtimeRootDir);
  const distDir = path.resolve('dist');

  app.use(express.json());
  app.use(express.static(distDir));

  app.get('/api/health', async (_request, response) => {
    const state = await store.read();
    const previewConfig = render3proxyConfig(state, runtimePaths);
    response.json({
      ok: true,
      runtime: runtime.getSnapshot(),
      users: state.userRecords.length,
      configBytes: Buffer.byteLength(previewConfig),
    });
  });

  app.get('/api/state', async (_request, response, next) => {
    try {
      const payload = await getSnapshot(store, runtime, runtimePaths);
      response.json(payload);
    } catch (error) {
      next(error);
    }
  });

  app.post('/api/runtime/:action', async (request, response, next) => {
    try {
      const state = await store.read();
      const action = request.params.action;
      const controller = action === 'restart' ? runtime.restart.bind(runtime) : runtime.start.bind(runtime);

      if (!['start', 'restart'].includes(action)) {
        response.status(404).json({ error: 'Unknown runtime action.' });
        return;
      }

      const runtimeSnapshot = await controller();
      state.service.lastEvent = action === 'restart' ? 'Runtime restarted from panel' : 'Runtime start requested from panel';
      if (runtimeSnapshot.startedAt) {
        state.service.startedAt = runtimeSnapshot.startedAt;
      }

      await writeConfigAndState(store, state, runtimePaths);
      response.json(await getSnapshot(store, runtime, runtimePaths));
    } catch (error) {
      next(error);
    }
  });

  app.post('/api/users', async (request, response, next) => {
    try {
      const state = await store.read();
      const input = validateCreateUserInput(request.body as Partial<CreateUserInput>, state.system.services);
      const record = createUserRecord(state, input);
      state.userRecords.push(record);
      state.service.lastEvent = `User ${record.username} created from panel`;
      await persistRuntimeMutation(store, runtime, state, runtimePaths);
      response.status(201).json(await getSnapshot(store, runtime, runtimePaths));
    } catch (error) {
      next(error);
    }
  });

  app.post('/api/users/:id/pause', async (request, response, next) => {
    try {
      const state = await store.read();
      const user = state.userRecords.find((entry) => entry.id === request.params.id);

      if (!user) {
        response.status(404).json({ error: 'User not found.' });
        return;
      }

      user.paused = !user.paused;
      state.service.lastEvent = user.paused
        ? `User ${user.username} paused from panel`
        : `User ${user.username} resumed from panel`;

      await persistRuntimeMutation(store, runtime, state, runtimePaths);
      response.json(await getSnapshot(store, runtime, runtimePaths));
    } catch (error) {
      next(error);
    }
  });

  app.delete('/api/users/:id', async (request, response, next) => {
    try {
      const state = await store.read();
      const index = state.userRecords.findIndex((entry) => entry.id === request.params.id);

      if (index === -1) {
        response.status(404).json({ error: 'User not found.' });
        return;
      }

      const [removed] = state.userRecords.splice(index, 1);
      state.service.lastEvent = `User ${removed.username} deleted from panel`;
      await persistRuntimeMutation(store, runtime, state, runtimePaths);
      response.json(await getSnapshot(store, runtime, runtimePaths));
    } catch (error) {
      next(error);
    }
  });

  app.use(async (_request, response) => {
    const distPath = path.join(distDir, 'index.html');

    try {
      const html = await fs.readFile(distPath, 'utf8');
      response.type('html').send(html);
    } catch {
      response.status(404).send('Frontend build not found.');
    }
  });

  app.use((error: unknown, _request: Request, response: Response, _next: express.NextFunction) => {
    response.status(400).json({
      error: error instanceof Error ? error.message : 'Unknown server error.',
    });
  });

  return app;
}

async function getSnapshot(
  store: StateStore,
  runtime: RuntimeController,
  runtimePaths: RuntimePaths,
) {
  const state = await store.read();
  const previewConfig = render3proxyConfig(state, runtimePaths);
  return deriveDashboardSnapshot(state, runtime.getSnapshot(), previewConfig);
}
async function persistRuntimeMutation(
  store: StateStore,
  runtime: RuntimeController,
  state: ControlPlaneState,
  runtimePaths: RuntimePaths,
) {
  await writeConfigAndState(store, state, runtimePaths);
  await runtime.reload();
}

async function writeConfigAndState(
  store: StateStore,
  state: ControlPlaneState,
  runtimePaths: RuntimePaths,
) {
  const config = render3proxyConfig(state, runtimePaths);
  await fs.mkdir(path.dirname(runtimePaths.configPath), { recursive: true });
  await fs.mkdir(path.dirname(runtimePaths.logPath), { recursive: true });
  await fs.mkdir(runtimePaths.reportDir, { recursive: true });
  await fs.writeFile(runtimePaths.configPath, config, 'utf8');
  await store.write(state);
}