import { useRef, useState, useEffect, useCallback, type ReactNode } from "react";
import {
  pipeline,
  TextStreamer,
  InterruptableStoppingCriteria,
  type TextGenerationPipeline,
} from "@huggingface/transformers";
import { LLMContext, createMessageId, type ChatMessage, type LoadingStatus } from "./LLMContext";

interface LLMProviderProps {
  modelId: string;
  children: ReactNode;
  onReady?: () => void;
}

export function LLMProvider({ modelId, children, onReady }: LLMProviderProps) {
  const generatorRef = useRef<Promise<TextGenerationPipeline> | null>(null);
  const stoppingCriteria = useRef(new InterruptableStoppingCriteria());

  const [status, setStatus] = useState<LoadingStatus>({ state: "idle" });
  const [messages, setMessages] = useState<ChatMessage[]>([]);
  const messagesRef = useRef<ChatMessage[]>([]);
  const [isGenerating, setIsGenerating] = useState(false);
  const isGeneratingRef = useRef(false);
  const [tps, setTps] = useState(0);

  useEffect(() => {
    messagesRef.current = messages;
  }, [messages]);

  useEffect(() => {
    isGeneratingRef.current = isGenerating;
  }, [isGenerating]);

  const onReadyRef = useRef(onReady);
  onReadyRef.current = onReady;

  useEffect(() => {
    if (status.state === "ready") onReadyRef.current?.();
  }, [status.state]);

  useEffect(() => {
    if (generatorRef.current) return;

    generatorRef.current = (async () => {
      setStatus({ state: "loading", message: "Downloading model…" });
      try {
        const gen = await pipeline("text-generation", modelId, {
          dtype: "q4f16",
          device: "webgpu",
          progress_callback: (info) => {
            if (info.status !== "progress_total") return;

            const loaded = Number(info.loaded ?? 0);
            const total = Number(info.total ?? 0);
            const pct = Number(info.progress ?? 0);
            const toGB = (b: number) => (b / 1e9).toFixed(2);

            setStatus({
              state: "loading",
              progress: pct,
              message:
                total > 0 ? `${toGB(loaded)} GB of ${toGB(total)} GB (${Math.round(pct)}%)` : `Downloading model…`,
            });
          },
        });
        setStatus({ state: "ready" });
        return gen;
      } catch (err) {
        const msg = err instanceof Error ? err.message : String(err);
        setStatus({ state: "error", error: msg });
        generatorRef.current = null;
        throw err;
      }
    })();
  }, [modelId]);

  const runGeneration = useCallback(async (chatHistory: ChatMessage[]) => {
    const generator = await generatorRef.current!;
    setIsGenerating(true);
    setTps(0);
    stoppingCriteria.current.reset();

    let tokenCount = 0;
    let firstTokenTime = 0;

    const assistantIdx = chatHistory.length;
    setMessages((prev) => [...prev, { id: createMessageId(), role: "assistant", content: "" }]);

    const streamer = new TextStreamer(generator.tokenizer, {
      skip_prompt: true,
      skip_special_tokens: true,
      callback_function: (output: string) => {
        if (!output) return;

        setMessages((prev) => {
          const updated = [...prev];
          updated[assistantIdx] = {
            ...updated[assistantIdx],
            content: updated[assistantIdx].content + output,
          };
          return updated;
        });
      },
      token_callback_function: () => {
        tokenCount++;
        if (tokenCount === 1) {
          firstTokenTime = performance.now();
        } else {
          const elapsed = (performance.now() - firstTokenTime) / 1000;
          if (elapsed > 0) {
            setTps(Math.round(((tokenCount - 1) / elapsed) * 10) / 10);
          }
        }
      },
    });

    try {
      await generator(
        chatHistory.map((message) => ({
          role: message.role,
          content: message.content,
        })),
        {
          max_new_tokens: 4096,
          do_sample: false,
          streamer,
          stopping_criteria: stoppingCriteria.current,
        },
      );
    } catch (err) {
      console.error("Generation error:", err);
    }

    const finalTps =
      tokenCount > 1 ? Math.round(((tokenCount - 1) / ((performance.now() - firstTokenTime) / 1000)) * 10) / 10 : 0;

    setMessages((prev) => {
      const updated = [...prev];
      updated[assistantIdx] = {
        ...updated[assistantIdx],
        content: updated[assistantIdx].content.trim(),
        tps: finalTps > 0 ? finalTps : undefined,
      };
      return updated;
    });

    setIsGenerating(false);
  }, []);

  const send = useCallback(
    (text: string) => {
      if (!generatorRef.current || isGeneratingRef.current) return;

      const userMsg: ChatMessage = {
        id: createMessageId(),
        role: "user",
        content: text,
      };

      setMessages((prev) => [...prev, userMsg]);
      runGeneration([...messagesRef.current, userMsg]);
    },
    [runGeneration],
  );

  const stop = useCallback(() => {
    stoppingCriteria.current.interrupt();
  }, []);

  const clearChat = useCallback(() => {
    if (isGeneratingRef.current) return;
    setMessages([]);
  }, []);

  const editMessage = useCallback(
    (index: number, newContent: string) => {
      if (isGeneratingRef.current) return;

      const updatedHistory = [
        ...messagesRef.current.slice(0, index),
        { ...messagesRef.current[index], content: newContent },
      ];

      setMessages(updatedHistory);

      if (messagesRef.current[index]?.role === "user") {
        setTimeout(() => runGeneration(updatedHistory), 0);
      }
    },
    [runGeneration],
  );

  const retryMessage = useCallback(
    (index: number) => {
      if (isGeneratingRef.current) return;

      const history = messagesRef.current.slice(0, index);
      setMessages(history);
      setTimeout(() => runGeneration(history), 0);
    },
    [runGeneration],
  );

  return (
    <LLMContext.Provider
      value={{
        status,
        messages,
        isGenerating,
        tps,
        send,
        stop,
        clearChat,
        editMessage,
        retryMessage,
      }}
    >
      {children}
    </LLMContext.Provider>
  );
}