import { useState, useCallback, useEffect } from "react";
import {
  listTasks,
  getTask,
  createTask,
  updateTask,
  deleteTask,
  VersionConflictError,
  type TaskSummary,
  type TaskWithSubtasks,
  type CreateTaskRequest,
  type UpdateTaskRequest,
} from "../lib/api";

export interface ConflictState {
  hasConflict: boolean;
  expectedVersion: number;
  actualVersion: number;
}

export function useTasks() {
  const [tasks, setTasks] = useState<TaskSummary[]>([]);
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState<string | null>(null);
  const [conflict, setConflict] = useState<ConflictState | null>(null);

  const fetchTasks = useCallback(async () => {
    setLoading(true);
    setError(null);
    try {
      const response = await listTasks();
      setTasks(response.tasks);
    } catch (e) {
      setError(e instanceof Error ? e.message : "Failed to fetch tasks");
    } finally {
      setLoading(false);
    }
  }, []);

  const fetchTask = useCallback(
    async (id: string): Promise<TaskWithSubtasks | null> => {
      setError(null);
      try {
        return await getTask(id);
      } catch (e) {
        setError(e instanceof Error ? e.message : "Failed to fetch task");
        return null;
      }
    },
    []
  );

  const saveTask = useCallback(
    async (data: CreateTaskRequest): Promise<TaskWithSubtasks | null> => {
      setError(null);
      try {
        const task = await createTask(data);
        await fetchTasks(); // Refresh list
        // Return as TaskWithSubtasks
        return { ...task, subtasks: [] };
      } catch (e) {
        setError(e instanceof Error ? e.message : "Failed to save task");
        return null;
      }
    },
    [fetchTasks]
  );

  const editTask = useCallback(
    async (id: string, data: UpdateTaskRequest): Promise<TaskWithSubtasks | null> => {
      setError(null);
      setConflict(null);
      try {
        await updateTask(id, data);
        await fetchTasks(); // Refresh list
        // Re-fetch to get subtasks
        return await getTask(id);
      } catch (e) {
        if (e instanceof VersionConflictError) {
          setConflict({
            hasConflict: true,
            expectedVersion: e.expectedVersion,
            actualVersion: e.actualVersion,
          });
          return null;
        }
        setError(e instanceof Error ? e.message : "Failed to update task");
        return null;
      }
    },
    [fetchTasks]
  );

  const clearConflict = useCallback(() => {
    setConflict(null);
  }, []);

  const removeTask = useCallback(
    async (id: string): Promise<boolean> => {
      setError(null);
      try {
        await deleteTask(id);
        await fetchTasks(); // Refresh list
        return true;
      } catch (e) {
        setError(e instanceof Error ? e.message : "Failed to delete task");
        return false;
      }
    },
    [fetchTasks]
  );

  // Initial fetch
  useEffect(() => {
    fetchTasks();
  }, [fetchTasks]);

  return {
    tasks,
    loading,
    error,
    conflict,
    clearConflict,
    fetchTasks,
    fetchTask,
    saveTask,
    editTask,
    removeTask,
  };
}