import type { Dispatch } from 'react';
import type { AppAction, AppState, Topic, Task, ProviderConfig } from '@/types';

// Parse the task generation response into a structured Task object
function parseTask(raw: string, topic: Topic): Task {
  const titleMatch = raw.match(/TITLE:\s*(.+)/);
  const descMatch = raw.match(/DESCRIPTION:\s*([\s\S]*?)(?=HINTS:|STARTER_CODE:|$)/);
  const hintsMatch = raw.match(/HINTS:\s*([\s\S]*?)(?=STARTER_CODE:|$)/);
  const codeMatch = raw.match(/STARTER_CODE:\s*```[\w]*\n([\s\S]*?)```/);

  const hints = hintsMatch
    ? hintsMatch[1]
        .trim()
        .split('\n')
        .map((h) => h.replace(/^[-*]\s*/, '').trim())
        .filter(Boolean)
    : [];

  return {
    title: titleMatch ? titleMatch[1].trim() : topic.label,
    description: descMatch ? descMatch[1].trim() : raw,
    hints,
    starterCode: codeMatch ? codeMatch[1] : topic.starterCode,
  };
}

async function streamFromAPI(
  body: Record<string, unknown> & { providerConfig: ProviderConfig },
  onChunk: (chunk: string) => void,
  signal?: AbortSignal
): Promise<string> {
  const res = await fetch('/api/ai', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify(body),
    signal,
  });

  if (!res.ok || !res.body) {
    throw new Error(`AI request failed: ${res.status}`);
  }

  const reader = res.body.getReader();
  const decoder = new TextDecoder();
  let full = '';

  while (true) {
    const { done, value } = await reader.read();
    if (done) break;
    const chunk = decoder.decode(value, { stream: true });
    full += chunk;
    onChunk(chunk);
  }

  return full;
}

export function useAI(dispatch: Dispatch<AppAction>, providerConfig: ProviderConfig) {
  async function generateTask(topic: Topic): Promise<void> {
    dispatch({ type: 'TASK_STREAM_START' });

    try {
      const raw = await streamFromAPI(
        { mode: 'generate_task', topic, code: topic.starterCode, messages: [], providerConfig },
        (chunk) => dispatch({ type: 'TASK_STREAM_CHUNK', payload: chunk })
      );

      const task = parseTask(raw, topic);
      dispatch({ type: 'TASK_STREAM_DONE', payload: task });
    } catch (err) {
      dispatch({
        type: 'SET_ERROR',
        payload: err instanceof Error ? err.message : 'Failed to generate task',
      });
    }
  }

  async function reviewCode(state: AppState): Promise<void> {
    if (!state.topic) return;
    dispatch({ type: 'REVIEW_START' });

    try {
      const raw = await streamFromAPI(
        {
          mode: 'review_code',
          topic: state.topic,
          code: state.code,
          executionResult: state.executionResult ?? undefined,
          messages: state.messages.map((m) => ({ role: m.role, content: m.content })),
          providerConfig,
          responseMode: state.responseMode,
        },
        (chunk) => dispatch({ type: 'STREAM_CHUNK', payload: chunk })
      );

      dispatch({
        type: 'STREAM_DONE',
        payload: {
          id: crypto.randomUUID(),
          role: 'assistant',
          content: raw,
          timestamp: Date.now(),
          type: 'review',
        },
      });
    } catch (err) {
      dispatch({
        type: 'SET_ERROR',
        payload: err instanceof Error ? err.message : 'Failed to review code',
      });
    }
  }

  async function sendMessage(state: AppState, userMessage: string): Promise<void> {
    if (!state.topic) return;
    dispatch({ type: 'SEND_USER_MESSAGE', payload: userMessage });

    const history = [
      ...state.messages.map((m) => ({ role: m.role, content: m.content })),
      { role: 'user' as const, content: userMessage },
    ];

    try {
      const raw = await streamFromAPI(
        {
          mode: 'chat',
          topic: state.topic,
          code: state.code,
          messages: history,
          providerConfig,
          responseMode: state.responseMode,
        },
        (chunk) => dispatch({ type: 'STREAM_CHUNK', payload: chunk })
      );

      dispatch({
        type: 'STREAM_DONE',
        payload: {
          id: crypto.randomUUID(),
          role: 'assistant',
          content: raw,
          timestamp: Date.now(),
          type: 'chat',
        },
      });
    } catch (err) {
      dispatch({
        type: 'SET_ERROR',
        payload: err instanceof Error ? err.message : 'Failed to send message',
      });
    }
  }

  async function generateLesson(topic: Topic): Promise<void> {
    dispatch({ type: 'LESSON_STREAM_START' });

    try {
      const raw = await streamFromAPI(
        { mode: 'generate_lesson', topic, code: '', messages: [], providerConfig },
        (chunk) => dispatch({ type: 'STREAM_CHUNK', payload: chunk })
      );
      dispatch({ type: 'LESSON_STREAM_DONE', payload: raw });
    } catch (err) {
      dispatch({
        type: 'SET_ERROR',
        payload: err instanceof Error ? err.message : 'Failed to generate lesson',
      });
    }
  }

  async function sendClassroomMessage(state: AppState, userMessage: string): Promise<void> {
    if (!state.topic) return;
    dispatch({ type: 'SEND_CLASSROOM_MESSAGE', payload: userMessage });

    const history = [
      ...state.classroomMessages.map((m) => ({ role: m.role, content: m.content })),
      { role: 'user' as const, content: userMessage },
    ];

    try {
      const raw = await streamFromAPI(
        {
          mode: 'classroom_chat',
          topic: state.topic,
          code: '',
          messages: history,
          providerConfig,
        },
        (chunk) => dispatch({ type: 'STREAM_CHUNK', payload: chunk })
      );

      dispatch({
        type: 'CLASSROOM_MESSAGE_DONE',
        payload: {
          id: crypto.randomUUID(),
          role: 'assistant',
          content: raw,
          timestamp: Date.now(),
          type: 'chat',
        },
      });
    } catch (err) {
      dispatch({
        type: 'SET_ERROR',
        payload: err instanceof Error ? err.message : 'Failed to send message',
      });
    }
  }

  return { generateTask, reviewCode, sendMessage, generateLesson, sendClassroomMessage };
}