import { streamText, type LanguageModel, type ModelMessage } from "ai";
import { resolveModelForUser, resolveModelAny, toLanguageModel } from "#server/service/llm/model-resolver";
import { buildCharacterSystemPrompt } from "./persona";
import {
  getMessagesByCharacterSession,
  getMaxCharacterSortOrder,
  saveCharacterMessage,
  touchCharacterSession,
  countCharacterMessagesByRole,
  updateCharacterSession,
} from "./session";
import { registerCharacterAbort, unregisterCharacterAbort } from "./abort";
import { checkCharacterRateLimit, incrementCharacterRateLimit } from "./rate-limit";
import {
  createCharacterStreamBuffer,
  appendCharacterChunk,
  markCharacterBufferDone,
} from "./stream-buffer";
import type { CharacterCardRow, CharacterSessionRow } from "./types";
import log4js from "logger";

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

export interface CharacterChatEngineParams {
  card: CharacterCardRow;
  session: CharacterSessionRow;
  user: { id: number } | null;
  content: string;
  preferredModelId?: number | null;
  globalDefaultModelId?: number | null;
  ip: string;
  setRateLimitHeaders?: (headers: Record<string, string>) => void;
  requestId?: string;
  onClientClose?: (cb: () => void) => void;
}

export interface CharacterChatEngineResult {
  response: Response;
  userMessageId: string | null;
}

function truncateFirstLine(text: string): string {
  const firstLine = text.split("\n")[0]?.trim() ?? "";
  if (firstLine.length <= 50) return firstLine;
  return firstLine.slice(0, 50) + "…";
}

/**
 * 角色对话引擎（纯文本流式）。
 *
 * 与 agent 的 chat-engine 完全解耦：不支持工具调用、审批、思考模式、
 * 持久记忆注入、多步推理。只做一件事 —— 用组装好的人设上下文
 * （buildCharacterSystemPrompt）做角色扮演式流式回复。
 */
export async function executeCharacterChat(
  params: CharacterChatEngineParams,
): Promise<CharacterChatEngineResult> {
  const { card, session, user, content, ip, requestId = "-" } = params;
  const sessionId = session.id;
  const textContent = content.trim();

  // 0. 访客限流（仅未登录用户生效）
  if (!user) {
    const rateLimit = checkCharacterRateLimit(card.slug, sessionId, ip);
    if (rateLimit.blocked) {
      params.setRateLimitHeaders?.({
        "X-RateLimit-Session-Remaining": String(rateLimit.sessionRemaining),
        "X-RateLimit-Ip-Remaining": String(rateLimit.ipRemaining),
      });
      throw createError({
        statusCode: 429,
        statusMessage:
          rateLimit.sessionRemaining === 0
            ? "当前会话已达回复上限，请登录后继续"
            : "今日回复次数已达上限，请登录或明日再试",
      });
    }
    params.setRateLimitHeaders?.({
      "X-RateLimit-Session-Remaining": String(rateLimit.sessionRemaining),
      "X-RateLimit-Ip-Remaining": String(rateLimit.ipRemaining),
    });
  }

  // 1. 模型解析（复用 llm 原语）：session > 本次请求覆盖 > card > 全局默认
  const targetModelId =
    session.modelId ??
    params.preferredModelId ??
    card.defaultModelId ??
    params.globalDefaultModelId ??
    null;

  if (!targetModelId) {
    throw createError({ statusCode: 400, statusMessage: "未配置模型，请先在设置中选择模型" });
  }

  const resolvedModel = user
    ? await resolveModelForUser(targetModelId, user.id)
    : await resolveModelAny(targetModelId);

  if (!resolvedModel) {
    throw createError({ statusCode: 404, statusMessage: "模型不存在或无权访问" });
  }
  if (!resolvedModel.provider.apiKey) {
    throw createError({ statusCode: 400, statusMessage: "供应商未配置 API Key" });
  }

  const languageModel: LanguageModel = toLanguageModel(resolvedModel);

  // 2. 上下文自主设计：由角色卡组装 system prompt
  const systemPrompt = buildCharacterSystemPrompt(card);

  // 3. 持久化用户消息
  const sortOrder = (await getMaxCharacterSortOrder(sessionId)) + 1;
  const userMessage = await saveCharacterMessage({
    sessionId,
    role: "user",
    content: textContent,
    sortOrder,
  });

  // 首条用户消息 → 用首行作为会话标题（无需额外 LLM 调用）
  const userCount = await countCharacterMessagesByRole(sessionId, "user");
  if (userCount === 1) {
    const title = truncateFirstLine(textContent);
    if (title) {
      await updateCharacterSession(sessionId, { title });
    }
  }

  // 4. 组装历史消息（纯文本 user/assistant）
  const history = await getMessagesByCharacterSession(sessionId, { limit: 100, latest: true });
  const messages: ModelMessage[] = history
    .filter((m) => m.id !== userMessage.id && (m.role === "user" || m.role === "assistant"))
    .map((m) => ({ role: m.role as "user" | "assistant", content: m.content } as ModelMessage));
  messages.push({ role: "user", content: textContent } as ModelMessage);

  // 5. 流式生成
  const controller = new AbortController();
  registerCharacterAbort(sessionId, controller);
  params.onClientClose?.(() => {
    if (!controller.signal.aborted) {
      controller.abort();
    }
  });

  createCharacterStreamBuffer(sessionId, {
    modelId: resolvedModel.dbId,
    userMessageId: userMessage.id,
  });

  let streamedText = "";

  logger.info(
    "[%s] [CHAR-ENGINE] card=%s sessionId=%s model=%d",
    requestId,
    card.slug,
    sessionId,
    resolvedModel.dbId,
  );

  const result = streamText({
    model: languageModel,
    system: systemPrompt,
    messages,
    abortSignal: controller.signal,
    onChunk: ({ chunk }) => {
      if (chunk.type === "text-delta") {
        streamedText += chunk.text;
      }
    },
    onFinish: async ({ text }) => {
      try {
        if (controller.signal.aborted) {
          unregisterCharacterAbort(sessionId);
          markCharacterBufferDone(sessionId);
          return;
        }
        const finalText = text.trim();
        if (finalText) {
          const assistantSortOrder = (await getMaxCharacterSortOrder(sessionId)) + 1;
          await saveCharacterMessage({
            sessionId,
            role: "assistant",
            content: finalText,
            sortOrder: assistantSortOrder,
          });
        }
        await touchCharacterSession(sessionId);
        if (!user) {
          incrementCharacterRateLimit(card.slug, sessionId, ip);
          const rateLimit = checkCharacterRateLimit(card.slug, sessionId, ip);
          params.setRateLimitHeaders?.({
            "X-RateLimit-Session-Remaining": String(rateLimit.sessionRemaining),
            "X-RateLimit-Ip-Remaining": String(rateLimit.ipRemaining),
          });
        }
        unregisterCharacterAbort(sessionId);
        markCharacterBufferDone(sessionId);
      } catch (e) {
        logger.error("[%s] [CHAR-ENGINE] onFinish error: %s", requestId, e instanceof Error ? e.message : String(e));
        unregisterCharacterAbort(sessionId);
        markCharacterBufferDone(sessionId);
      }
    },
    onAbort: async () => {
      try {
        const partial = streamedText.trim();
        if (partial) {
          const assistantSortOrder = (await getMaxCharacterSortOrder(sessionId)) + 1;
          await saveCharacterMessage({
            sessionId,
            role: "assistant",
            content: partial,
            sortOrder: assistantSortOrder,
          });
        }
        await touchCharacterSession(sessionId);
        if (!user) {
          incrementCharacterRateLimit(card.slug, sessionId, ip);
        }
        unregisterCharacterAbort(sessionId);
        markCharacterBufferDone(sessionId);
      } catch (e) {
        logger.error("[%s] [CHAR-ENGINE] onAbort error: %s", requestId, e instanceof Error ? e.message : String(e));
        unregisterCharacterAbort(sessionId);
        markCharacterBufferDone(sessionId);
      }
    },
  });

  const response = result.toUIMessageStreamResponse({
    headers: { "X-User-Message-Id": userMessage.id },
  });

  if (response.body) {
    const bufferedBody = wrapStreamWithBuffer(response.body, sessionId, controller, requestId);
    return {
      response: new Response(bufferedBody, {
        status: response.status,
        statusText: response.statusText,
        headers: response.headers,
      }),
      userMessageId: userMessage.id,
    };
  }

  return { response, userMessageId: userMessage.id };
}

function wrapStreamWithBuffer(
  originalBody: ReadableStream<Uint8Array>,
  sessionId: string,
  serverAbortController: AbortController,
  requestId: string,
): ReadableStream<Uint8Array> {
  return new ReadableStream({
    start(controller) {
      const reader = originalBody.getReader();
      let clientDisconnected = false;
      function pump() {
        reader.read().then(({ done, value }) => {
          if (done) {
            markCharacterBufferDone(sessionId);
            if (!clientDisconnected) {
              try { controller.close(); } catch { /* already closed */ }
            }
            return;
          }
          if (value) {
            appendCharacterChunk(sessionId, value);
            if (!clientDisconnected) {
              try {
                controller.enqueue(value);
              } catch {
                clientDisconnected = true;
              }
            }
          }
          pump();
        }).catch((err) => {
          if (serverAbortController.signal.aborted) {
            logger.info("[%s] [CHAR-ENGINE] stream reader aborted by server abort", requestId);
          } else {
            logger.error("[%s] [CHAR-ENGINE] buffer stream read error: %s", requestId, err instanceof Error ? err.message : String(err));
          }
          markCharacterBufferDone(sessionId);
          if (!clientDisconnected) {
            try { controller.close(); } catch { /* already closed */ }
          }
        });
      }
      pump();
    },
  });
}