import type { GatewayRequest, GatewayAttachment, OutboundMessage } from '../protocol.js';
import type { SendFn } from '../router.js';
import { makeEvent, makeError, ErrorCode } from '../protocol.js';
import type { SessionBridge } from '../session-bridge.js';
import type { LaneQueue } from '../lane-queue.js';
import type { MetricsCollector } from '../metrics.js';
import type { Attachment } from '../../channels/types.js';
import type { SessionManager } from '../../session/manager.js';
import type { ModelTier } from '../../models/router.js';
import type { CommandRegistry } from '../../commands/index.js';

export interface AgentHandlerDeps {
  sessionBridge: SessionBridge;
  laneQueue: LaneQueue;
  metrics?: MetricsCollector;
  sessionManager?: SessionManager;
  commandRegistry?: CommandRegistry;
}

export function createAgentHandlers(deps: AgentHandlerDeps) {
  return {
    'agent.send': async (request: GatewayRequest, send: SendFn): Promise<OutboundMessage | void> => {
      const params = request.params as { message?: string; connectionId?: string; attachments?: GatewayAttachment[]; metadata?: { isCommand?: boolean; command?: string; commandArgs?: string } } | undefined;
      if (!params?.message && !params?.metadata?.isCommand) {
        return makeError(request.id, ErrorCode.InvalidRequest, 'message is required');
      }

      const connectionId = params.connectionId as string;
      if (!connectionId) {
        return makeError(request.id, ErrorCode.InvalidRequest, 'connectionId is required (set by server)');
      }

      const agent = deps.sessionBridge.getAgent(connectionId);
      if (!agent) {
        return makeError(request.id, ErrorCode.SessionNotFound, 'No agent for this connection');
      }

      // Queue by session ID so multiple connections sharing a session are serialised.
      // Falls back to connectionId if session lookup fails (shouldn't happen).
      const sessionId = deps.sessionBridge.getSessionId(connectionId);
      const laneId = sessionId ?? connectionId;

      // Enqueue the work — if the lane is idle it runs immediately,
      // otherwise it waits for earlier requests on the same session to finish.
      const requestId = request.id.toString();
      deps.metrics?.startRequest(requestId, { sessionId: laneId, channel: 'ws' });

      return deps.laneQueue.enqueue(laneId, async () => {
        deps.sessionBridge.setBusy(connectionId, true);

        const commandInput = params.metadata?.isCommand && typeof params.metadata.command === 'string'
          ? `/${params.metadata.command}${params.metadata.commandArgs ? ` ${params.metadata.commandArgs}` : ''}`
          : params.message;

        if (commandInput && deps.commandRegistry?.isCommand(commandInput)) {
          const sessionId = deps.sessionBridge.getSessionId(connectionId);
          const commandResult = await deps.commandRegistry.execute(commandInput, {
            channel: 'ws',
            senderId: connectionId,
            sessionId: sessionId ?? `ws:${connectionId}`,
            rawInput: commandInput,
            services: {
              getStatus: () => `Gateway session active. Current model tier: ${agent.getModelTier()}`,
              getUsage: () => {
                const usage = agent.getUsage();
                const lines = [
                  '**Token Usage**',
                  '',
                  `Primary: ${usage.primary.inputTokens.toLocaleString()} in / ${usage.primary.outputTokens.toLocaleString()} out (${usage.primary.calls} calls)`,
                ];

                const delegationEntries = Object.entries(usage.delegation);
                if (delegationEntries.length > 0) {
                  lines.push('');
                  lines.push('Delegation:');
                  for (const [tier, stats] of delegationEntries) {
                    lines.push(`  ${tier}: ${stats.inputTokens.toLocaleString()} in / ${stats.outputTokens.toLocaleString()} out (${stats.calls} calls)`);
                  }
                }

                lines.push('');
                lines.push(`**Total:** ${usage.total.inputTokens.toLocaleString()} in / ${usage.total.outputTokens.toLocaleString()} out (${usage.total.calls} calls)`);

                if (usage.total.estimatedCost > 0) {
                  lines.push(`**Estimated cost:** $${usage.total.estimatedCost.toFixed(4)}`);
                }

                return lines.join('\n');
              },
              getModel: () => `Current model tier: ${agent.getModelTier()}`,
              setModel: (tier) => {
                const validTiers: ModelTier[] = ['fast', 'default', 'complex', 'local'];
                const modelTier = tier as ModelTier;
                if (!validTiers.includes(modelTier)) {
                  return `Invalid tier: ${tier}. Available: ${validTiers.join(', ')}`;
                }
                agent.setModelTier(modelTier);
                if (sessionId && deps.sessionManager) {
                  deps.sessionManager.setSessionConfig('ws', sessionId, 'modelTier', modelTier);
                }
                return `Switched to model tier: ${modelTier}`;
              },
              compact: async () => {
                const result = await agent.compact();
                if (result && result.compactedCount > 0) {
                  return `Compacted ${result.compactedCount} messages: ${result.tokensBefore} → ${result.tokensAfter} tokens`;
                }
                return 'Nothing to compact.';
              },
              reset: () => {
                agent.reset();
                if (sessionId && deps.sessionManager) {
                  deps.sessionManager.deleteSessionConfig('ws', sessionId, 'modelTier');
                }
                return 'Session reset.';
              },
            },
          });

          if (commandResult.handled) {
            send(makeEvent(request.id, 'done', { content: commandResult.text }));
            return;
          }
        }

        // Set up tool use callback to emit streaming events
        deps.sessionBridge.setOnToolUse(connectionId, (event) => {
          if (event.type === 'start') {
            send(makeEvent(request.id, 'tool_start', { tool: event.tool, args: event.args }));
          } else if (event.type === 'end') {
            send(makeEvent(request.id, 'tool_end', {
              tool: event.tool,
              result: event.result ? {
                success: event.result.success,
                output: event.result.output,
                error: event.result.error,
              } : undefined,
            }));
            // Record tool failures as error events
            if (event.result && !event.result.success) {
              deps.metrics?.incrementErrors();
              deps.metrics?.recordEvent({
                timestamp: Date.now(),
                level: 'error',
                source: 'tool',
                message: `Tool '${event.tool}' failed: ${event.result.error ?? 'unknown error'}`,
                context: { sessionId: laneId, tool: event.tool },
              });
            }
          }
        });

        try {
          // Convert gateway attachments to channel attachments
          const attachments: Attachment[] | undefined = params.attachments?.map(a => ({
            mimeType: a.mimeType,
            data: a.data,
            url: a.url,
            filename: a.filename,
          }));

          const response = await agent.process(params.message!, attachments);
          deps.metrics?.incrementMessages();
          send(makeEvent(request.id, 'done', { content: response }));
        } catch (err) {
          const message = err instanceof Error ? err.message : 'Unknown error';
          deps.metrics?.incrementErrors();
          deps.metrics?.recordEvent({
            timestamp: Date.now(),
            level: 'error',
            source: 'agent.send',
            message,
            context: { sessionId: laneId },
          });
          send(makeEvent(request.id, 'error', { code: ErrorCode.InternalError, message }));
        } finally {
          deps.sessionBridge.setBusy(connectionId, false);
          deps.sessionBridge.setOnToolUse(connectionId, undefined);
          deps.metrics?.endRequest(requestId);
        }
      });
    },

    'agent.cancel': async (request: GatewayRequest): Promise<OutboundMessage> => {
      // Cancel is a placeholder — proper cancellation requires abort controller support in NativeAgent.
      // For now, just report whether the agent was busy.
      const params = request.params as { connectionId?: string } | undefined;
      const connectionId = params?.connectionId as string;

      if (!connectionId) {
        return makeError(request.id, ErrorCode.InvalidRequest, 'connectionId is required');
      }

      const wasBusy = deps.sessionBridge.isBusy(connectionId);
      // TODO: Wire AbortController into NativeAgent for actual cancellation
      return { id: request.id, result: { cancelled: wasBusy } };
    },
  };
}