import * as http from 'node:http';
import type { IApiError } from '../../interfaces/api.ts';
import type { IClusterNodeHeartbeat } from '../../interfaces/cluster.ts';
import { ClusterCoordinator } from '../../cluster/coordinator.ts';
import { CLUSTER } from '../../constants.ts';

export class ClusterHandler {
  private clusterCoordinator: ClusterCoordinator;

  constructor(clusterCoordinator: ClusterCoordinator) {
    this.clusterCoordinator = clusterCoordinator;
  }

  public async handle(
    req: http.IncomingMessage,
    res: http.ServerResponse,
    path: string,
    url: URL,
  ): Promise<void> {
    if (!this.authenticate(req)) {
      return this.sendError(res, 401, 'Invalid cluster secret', 'authentication_error');
    }

    if (path === '/_cluster/status' && req.method === 'GET') {
      return this.sendJson(res, 200, this.clusterCoordinator.getStatus());
    }

    if (path === '/_cluster/nodes' && req.method === 'GET') {
      return this.sendJson(res, 200, this.clusterCoordinator.getStatus().nodes);
    }

    if (path === '/_cluster/desired' && req.method === 'GET') {
      return this.sendJson(res, 200, this.clusterCoordinator.getDesiredDeployments());
    }

    if (
      (path === '/_cluster/nodes/register' || path === '/_cluster/nodes/heartbeat') &&
      req.method === 'POST'
    ) {
      const body = await this.parseBody(req) as IClusterNodeHeartbeat | null;
      if (!body) {
        return this.sendError(
          res,
          400,
          'Invalid cluster heartbeat payload',
          'invalid_request_error',
        );
      }

      this.clusterCoordinator.acceptHeartbeat(body);
      return this.sendJson(res, 200, { ok: true });
    }

    if (path === '/_cluster/models/resolve' && req.method === 'GET') {
      const model = url.searchParams.get('model');
      if (!model) {
        return this.sendError(res, 400, 'Missing model query parameter', 'invalid_request_error');
      }

      const resolved = await this.clusterCoordinator.resolveModel(model);
      if (!resolved) {
        return this.sendError(res, 404, `Model "${model}" not found in cluster`, 'model_not_found');
      }

      return this.sendJson(res, 200, resolved);
    }

    if (path === '/_cluster/models/ensure' && req.method === 'POST') {
      if (!this.clusterCoordinator.canManageClusterState()) {
        return this.sendError(
          res,
          409,
          'This node is not the control plane',
          'invalid_request_error',
        );
      }

      const body = await this.parseBody(req) as { model?: string } | null;
      if (!body?.model) {
        return this.sendError(res, 400, 'Missing model in request body', 'invalid_request_error');
      }

      const ensured = await this.clusterCoordinator.ensureModel(body.model);
      if (!ensured) {
        return this.sendError(res, 503, `Unable to schedule model "${body.model}"`, 'server_error');
      }

      return this.sendJson(res, 200, ensured);
    }

    if (path === '/_cluster/models/desired' && req.method === 'POST') {
      if (!this.clusterCoordinator.canManageClusterState()) {
        return this.sendError(
          res,
          409,
          'This node is not the control plane',
          'invalid_request_error',
        );
      }

      const body = await this.parseBody(req) as { model?: string; desiredReplicas?: number } | null;
      if (!body?.model || body.desiredReplicas === undefined) {
        return this.sendError(
          res,
          400,
          'Missing model or desiredReplicas in request body',
          'invalid_request_error',
        );
      }

      const desiredDeployment = await this.clusterCoordinator.setDesiredReplicas(
        body.model,
        body.desiredReplicas,
      );
      if (!desiredDeployment) {
        return this.sendError(res, 404, `Model "${body.model}" not found`, 'model_not_found');
      }

      return this.sendJson(res, 200, desiredDeployment);
    }

    if (path === '/_cluster/models/desired/remove' && req.method === 'POST') {
      if (!this.clusterCoordinator.canManageClusterState()) {
        return this.sendError(
          res,
          409,
          'This node is not the control plane',
          'invalid_request_error',
        );
      }

      const body = await this.parseBody(req) as { model?: string } | null;
      if (!body?.model) {
        return this.sendError(res, 400, 'Missing model in request body', 'invalid_request_error');
      }

      const removed = await this.clusterCoordinator.clearDesiredDeployment(body.model);
      return this.sendJson(res, 200, { removed });
    }

    if (path === '/_cluster/deployments' && req.method === 'POST') {
      const body = await this.parseBody(req) as { model?: string; replicaOrdinal?: number } | null;
      if (!body?.model) {
        return this.sendError(res, 400, 'Missing model in request body', 'invalid_request_error');
      }

      const deployed = body.replicaOrdinal !== undefined
        ? await this.clusterCoordinator.deployReplicaLocally(body.model, body.replicaOrdinal)
        : await this.clusterCoordinator.deployModelLocally(body.model);
      if (!deployed) {
        return this.sendError(res, 503, `Unable to deploy model "${body.model}"`, 'server_error');
      }

      return this.sendJson(res, 200, deployed);
    }

    if (path === '/_cluster/nodes/cordon' && req.method === 'POST') {
      if (!this.clusterCoordinator.canManageClusterState()) {
        return this.sendError(
          res,
          409,
          'This node is not the control plane',
          'invalid_request_error',
        );
      }

      const body = await this.parseBody(req) as { nodeName?: string } | null;
      if (!body?.nodeName) {
        return this.sendError(
          res,
          400,
          'Missing nodeName in request body',
          'invalid_request_error',
        );
      }

      const schedulerState = this.clusterCoordinator.setNodeSchedulerState(
        body.nodeName,
        'cordoned',
      );
      return this.sendJson(res, 200, { nodeName: body.nodeName, schedulerState });
    }

    if (path === '/_cluster/nodes/uncordon' && req.method === 'POST') {
      if (!this.clusterCoordinator.canManageClusterState()) {
        return this.sendError(
          res,
          409,
          'This node is not the control plane',
          'invalid_request_error',
        );
      }

      const body = await this.parseBody(req) as { nodeName?: string } | null;
      if (!body?.nodeName) {
        return this.sendError(
          res,
          400,
          'Missing nodeName in request body',
          'invalid_request_error',
        );
      }

      const schedulerState = this.clusterCoordinator.setNodeSchedulerState(body.nodeName, 'active');
      return this.sendJson(res, 200, { nodeName: body.nodeName, schedulerState });
    }

    if (path === '/_cluster/nodes/drain' && req.method === 'POST') {
      if (!this.clusterCoordinator.canManageClusterState()) {
        return this.sendError(
          res,
          409,
          'This node is not the control plane',
          'invalid_request_error',
        );
      }

      const body = await this.parseBody(req) as { nodeName?: string } | null;
      if (!body?.nodeName) {
        return this.sendError(
          res,
          400,
          'Missing nodeName in request body',
          'invalid_request_error',
        );
      }

      const schedulerState = this.clusterCoordinator.setNodeSchedulerState(
        body.nodeName,
        'draining',
      );
      return this.sendJson(res, 200, { nodeName: body.nodeName, schedulerState });
    }

    if (path === '/_cluster/nodes/activate' && req.method === 'POST') {
      if (!this.clusterCoordinator.canManageClusterState()) {
        return this.sendError(
          res,
          409,
          'This node is not the control plane',
          'invalid_request_error',
        );
      }

      const body = await this.parseBody(req) as { nodeName?: string } | null;
      if (!body?.nodeName) {
        return this.sendError(
          res,
          400,
          'Missing nodeName in request body',
          'invalid_request_error',
        );
      }

      const schedulerState = this.clusterCoordinator.setNodeSchedulerState(body.nodeName, 'active');
      return this.sendJson(res, 200, { nodeName: body.nodeName, schedulerState });
    }

    return this.sendError(res, 404, `Unknown cluster endpoint: ${path}`, 'invalid_request_error');
  }

  private authenticate(req: http.IncomingMessage): boolean {
    const sharedSecret = this.clusterCoordinator.getSharedSecret();
    if (!sharedSecret) {
      return true;
    }

    return req.headers[CLUSTER.AUTH_HEADER_NAME] === sharedSecret;
  }

  private async parseBody(req: http.IncomingMessage): Promise<unknown | null> {
    return new Promise((resolve) => {
      let body = '';

      req.on('data', (chunk) => {
        body += chunk.toString();
      });

      req.on('end', () => {
        if (!body) {
          resolve(null);
          return;
        }

        try {
          resolve(JSON.parse(body));
        } catch {
          resolve(null);
        }
      });

      req.on('error', () => resolve(null));
    });
  }

  private sendJson(res: http.ServerResponse, statusCode: number, body: unknown): void {
    res.writeHead(statusCode, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify(body));
  }

  private sendError(
    res: http.ServerResponse,
    statusCode: number,
    message: string,
    type: string,
  ): void {
    const error: IApiError = {
      error: {
        message,
        type,
      },
    };

    this.sendJson(res, statusCode, error);
  }
}