import type { GatewayRequest, OutboundMessage } from '../protocol.js';
import { makeResponse, makeError, ErrorCode } from '../protocol.js';
import type { MetricsSnapshot, EventEntry, ActiveRequestInfo } from '../metrics.js';

/** Per-session token usage report returned by system.tokenUsage. */
export interface TokenUsageEntry {
  sessionId: string;
  primary: { inputTokens: number; outputTokens: number; calls: number };
  delegation: Record<string, { inputTokens: number; outputTokens: number; calls: number }>;
  total: { inputTokens: number; outputTokens: number; calls: number; estimatedCost: number };
}

export interface SystemHandlerDeps {
  startTime: number;
  version: string;
  getSessionCount: () => number;
  getToolCount: () => number;
  getConnectionCount: () => number;
  /** Optional callback to trigger a graceful restart. If not provided, system.restart returns an error. */
  restart?: () => Promise<void>;
  getChannels?: () => Array<{ name: string; status: string }>;
  getUsage?: () => { totalSessions: number; activeConnections: number };
  /** Optional callback to retrieve per-session token usage data. */
  getTokenUsage?: () => TokenUsageEntry[];
  /** Optional callback to retrieve aggregated metrics snapshot. */
  getMetrics?: () => MetricsSnapshot;
  /** Optional callback to retrieve recent events. */
  getEvents?: (opts?: { level?: string; limit?: number }) => EventEntry[];
  /** Optional callback to retrieve active requests. */
  getActiveRequests?: () => ActiveRequestInfo[];
}

export function createSystemHandlers(deps: SystemHandlerDeps) {
  return {
    'system.health': async (request: GatewayRequest): Promise<OutboundMessage> => {
      return makeResponse(request.id, {
        status: 'ok',
        uptime: Math.floor((Date.now() - deps.startTime) / 1000),
        version: deps.version,
        sessions: deps.getSessionCount(),
        tools: deps.getToolCount(),
        connections: deps.getConnectionCount(),
      });
    },

    'system.restart': async (request: GatewayRequest): Promise<OutboundMessage> => {
      if (!deps.restart) {
        return makeError(request.id, ErrorCode.InternalError, 'Restart not available in this environment');
      }

      // Send response before initiating restart (client receives confirmation)
      const response = makeResponse(request.id, { restarting: true });

      // Schedule restart after response is sent (next tick)
      queueMicrotask(() => {
        deps.restart!().catch((err) => {
          console.error('Restart failed:', err);
        });
      });

      return response;
    },

    'system.channels': async (request: GatewayRequest): Promise<OutboundMessage> => {
      if (!deps.getChannels) {
        return makeResponse(request.id, { channels: [] });
      }
      return makeResponse(request.id, { channels: deps.getChannels() });
    },

    'system.usage': async (request: GatewayRequest): Promise<OutboundMessage> => {
      const uptime = Math.floor((Date.now() - deps.startTime) / 1000);
      const usage = deps.getUsage?.() ?? { totalSessions: 0, activeConnections: 0 };
      return makeResponse(request.id, {
        uptime,
        ...usage,
        tools: deps.getToolCount(),
      });
    },

    'system.tokenUsage': async (request: GatewayRequest): Promise<OutboundMessage> => {
      const sessions = deps.getTokenUsage?.() ?? [];
      return makeResponse(request.id, { sessions });
    },

    'system.metrics': async (request: GatewayRequest): Promise<OutboundMessage> => {
      if (!deps.getMetrics) {
        return makeResponse(request.id, {});
      }
      return makeResponse(request.id, deps.getMetrics());
    },

    'system.events': async (request: GatewayRequest): Promise<OutboundMessage> => {
      if (!deps.getEvents) {
        return makeResponse(request.id, { events: [] });
      }
      const params = request.params as { level?: string; limit?: number } | undefined;
      const events = deps.getEvents({ level: params?.level, limit: params?.limit });
      return makeResponse(request.id, { events });
    },

    'system.activeRequests': async (request: GatewayRequest): Promise<OutboundMessage> => {
      if (!deps.getActiveRequests) {
        return makeResponse(request.id, { requests: [] });
      }
      return makeResponse(request.id, { requests: deps.getActiveRequests() });
    },
  };
}