// SSE 端点（P5：ai.StreamChat gRPC stream → BFF → 前端 EventSource）
// 路由：GET /ai/chat/stream
// 裁决依据：02-architecture-design.md §10
import { Controller, Get, Query, Res, Req } from "@nestjs/common";
import type { Request, Response } from "express";
import { TeacherService } from "./teacher.service.js";
import type { CallContext } from "../clients/types.js";
import type { ChatMessage } from "../clients/ai/ai.types.js";

@Controller("/ai/chat")
export class AiChatSseController {
  constructor(private readonly teacherService: TeacherService) {}

  /**
   * SSE 流式聊天端点
   * 前端使用 EventSource 连接，BFF 透传 ai.StreamChat gRPC stream
   */
  @Get("stream")
  async streamChat(
    @Req() req: Request,
    @Res() res: Response,
    @Query("prompt") prompt: string,
  ): Promise<void> {
    // 设置 SSE 响应头
    res.setHeader("Content-Type", "text/event-stream");
    res.setHeader("Cache-Control", "no-cache");
    res.setHeader("Connection", "keep-alive");
    res.setHeader("X-Accel-Buffering", "no"); // 禁用 Nginx 缓冲

    // 构造 CallContext（从 req.headers 提取 x-user-id 和 x-request-id）
    const ctx: CallContext = {
      userId: (req.headers["x-user-id"] as string) ?? "dev-user",
      traceId: (req.headers["x-request-id"] as string) ?? "",
    };

    // 构造聊天消息
    const messages: ChatMessage[] = [{ role: "user", content: prompt }];

    try {
      const stream = await this.teacherService.streamChat(ctx, messages);

      for await (const chunk of stream) {
        const data = JSON.stringify({
          content: chunk.content,
          done: chunk.done,
        });
        res.write(`data: ${data}\n\n`);

        if (chunk.done) {
          break;
        }
      }

      res.write("event: done\ndata: {}\n\n");
    } catch (err) {
      const errorData = JSON.stringify({
        error: err instanceof Error ? err.message : "Unknown error",
      });
      res.write(`event: error\ndata: ${errorData}\n\n`);
    } finally {
      res.end();
    }
  }
}