import { generateText } from "ai";
import { type LanguageModel } from "ai";
import { resolveModelForUser, resolveModelAny, toLanguageModel } from "#server/service/llm/model-resolver";
import { updateSession } from "./session";
import type { AgentRow } from "./agent";
import log4js from "logger";

const logger = log4js.getLogger("APP");

const FIRST_LINE_MAX_LENGTH = 50;

export type TitleStrategy = "llm" | "first-line" | "none";

export function truncateFirstLine(text: string): string {
  const firstLine = text.split("\n")[0]?.trim() ?? "";
  if (firstLine.length <= FIRST_LINE_MAX_LENGTH) return firstLine;
  return firstLine.slice(0, FIRST_LINE_MAX_LENGTH) + "…";
}

export async function generateSessionTitle(params: {
  sessionId: string;
  agent: AgentRow;
  firstUserMessage: string;
  firstAssistantMessage: string;
  userId: number | null;
}): Promise<void> {
  const { sessionId, agent, firstUserMessage, firstAssistantMessage, userId } = params;
  const strategy: TitleStrategy = (agent.titleStrategy as TitleStrategy) ?? "llm";

  if (strategy === "none") {
    return;
  }

  if (strategy === "first-line") {
    const title = truncateFirstLine(firstUserMessage);
    if (title) {
      await updateSession(sessionId, { title });
      logger.info("[AGENT-TITLE] first-line sessionId=%s title=%s", sessionId, title);
    }
    return;
  }

  try {
    const titleModelId = agent.titleModelId ?? agent.defaultModelId;
    if (!titleModelId) {
      logger.warn("[AGENT-TITLE] no titleModelId/defaultModelId for agent=%s, fallback to first-line", agent.slug);
      const title = truncateFirstLine(firstUserMessage);
      if (title) await updateSession(sessionId, { title });
      return;
    }

    const resolved = await resolveModelForUser(titleModelId, userId);
    if (!resolved) {
      logger.warn("[AGENT-TITLE] titleModelId=%d not resolvable, fallback to first-line", titleModelId);
      const title = truncateFirstLine(firstUserMessage);
      if (title) await updateSession(sessionId, { title });
      return;
    }

    const languageModel: LanguageModel = toLanguageModel(resolved);

    const prompt = `请根据以下对话生成一个简短的标题（不超过20个字，不要加引号、不要加书名号）：

用户: ${firstUserMessage.slice(0, 500)}
助手: ${firstAssistantMessage.slice(0, 500)}

标题:`;

    const result = await generateText({
      model: languageModel,
      prompt,
      maxOutputTokens: 200,
    });

    const title = result.text.trim().slice(0, 100);

    if (title) {
      await updateSession(sessionId, { title });
      logger.info("[AGENT-TITLE] llm sessionId=%s title=%s", sessionId, title);
    }
  } catch (err) {
    logger.error("[AGENT-TITLE] sessionId=%s error: %s", sessionId, err instanceof Error ? err.message : String(err));
  }
}