import { useState, useRef, useCallback, useEffect } from "react";
import {
  AutoModelForCausalLM,
  AutoTokenizer,
  TextStreamer,
} from "@huggingface/transformers";

const MODEL_ID = "shreyask/Maincoder-1B-ONNX-web";

interface LLMState {
  isLoading: boolean;
  isReady: boolean;
  error: string | null;
  progress: number;
}

interface LLMInstance {
  model: any;
  tokenizer: any;
}

let cachedInstance: LLMInstance | null = null;
let loadingPromise: Promise<LLMInstance> | null = null;

export const useLLM = () => {
  const [state, setState] = useState<LLMState>({
    isLoading: false,
    isReady: false,
    error: null,
    progress: 0,
  });

  const instanceRef = useRef<LLMInstance | null>(null);
  const pastKeyValuesRef = useRef<any>(null);

  const loadModel = useCallback(async () => {
    if (instanceRef.current || cachedInstance) {
      const instance = instanceRef.current || cachedInstance;
      instanceRef.current = instance;
      cachedInstance = instance;
      setState((prev) => ({ ...prev, isReady: true, isLoading: false }));
      return instance;
    }

    if (loadingPromise) {
      const instance = await loadingPromise;
      instanceRef.current = instance;
      cachedInstance = instance;
      setState((prev) => ({ ...prev, isReady: true, isLoading: false }));
      return instance;
    }

    setState((prev) => ({
      ...prev,
      isLoading: true,
      error: null,
      progress: 0,
    }));

    loadingPromise = (async () => {
      try {
        const progress_callback = (progress: any) => {
          if (
            progress.status === "progress" &&
            (progress.file?.endsWith(".onnx") ||
              progress.file?.endsWith(".onnx_data"))
          ) {
            const percentage = Math.round(
              (progress.loaded / progress.total) * 100,
            );
            setState((prev) => ({ ...prev, progress: percentage }));
          }
        };

        const tokenizer = await AutoTokenizer.from_pretrained(MODEL_ID, {
          progress_callback,
        });

        const model = await AutoModelForCausalLM.from_pretrained(MODEL_ID, {
          dtype: "q4",
          device: "webgpu",
          progress_callback,
        });

        const instance = { model, tokenizer };
        instanceRef.current = instance;
        cachedInstance = instance;
        loadingPromise = null;

        setState({
          isLoading: false,
          isReady: true,
          error: null,
          progress: 100,
        });
        return instance;
      } catch (error) {
        loadingPromise = null;
        const message =
          error instanceof Error ? error.message : "Failed to load model";
        setState((prev) => ({
          ...prev,
          isLoading: false,
          error: message,
        }));
        throw error;
      }
    })();

    return loadingPromise;
  }, []);

  const generateResponse = useCallback(
    async (
      messages: Array<{ role: string; content: string }>,
      onToken?: (token: string) => void,
    ): Promise<string> => {
      const instance = instanceRef.current;
      if (!instance) {
        throw new Error("Model not loaded. Call loadModel() first.");
      }

      const { model, tokenizer } = instance;

      const input = tokenizer.apply_chat_template(messages, {
        add_generation_prompt: true,
        return_dict: true,
      });

      const streamer = onToken
        ? new TextStreamer(tokenizer, {
            skip_prompt: true,
            skip_special_tokens: true,
            callback_function: onToken,
          })
        : undefined;

      const { sequences, past_key_values } = await model.generate({
        ...input,
        past_key_values: pastKeyValuesRef.current,
        max_new_tokens: 1024,
        do_sample: false,
        repetition_penalty: 1.2,
        eos_token_id: [151643, 151645], // <|endoftext|> and <|im_end|>
        streamer,
        return_dict_in_generate: true,
      });
      pastKeyValuesRef.current = past_key_values;

      const response = tokenizer
        .batch_decode(sequences.slice(null, [input.input_ids.dims[1], null]), {
          skip_special_tokens: true,
        })[0];

      return response;
    },
    [],
  );

  const clearHistory = useCallback(() => {
    pastKeyValuesRef.current = null;
  }, []);

  useEffect(() => {
    if (cachedInstance) {
      instanceRef.current = cachedInstance;
      setState((prev) => ({ ...prev, isReady: true }));
    }
  }, []);

  return {
    ...state,
    loadModel,
    generateResponse,
    clearHistory,
  };
};