import { useState, useEffect } from 'react';
import {
  DndContext,
  DragOverlay,
  PointerSensor,
  useSensor,
  useSensors,
} from '@dnd-kit/core';
import type { DragEndEvent, DragOverEvent, DragStartEvent } from '@dnd-kit/core';
import { Column } from './components/Column';
import { TaskCard } from './components/TaskCard';
import type { Task, Column as ColumnType, ColumnId } from './types';
import './App.css';

const defaultColumns: ColumnType[] = [
  { id: 'backlog', title: '📋 Backlog', tasks: [] },
  { id: 'todo', title: '📝 To Do', tasks: [] },
  { id: 'doing', title: '🔨 Doing', tasks: [] },
  { id: 'done', title: '✅ Done', tasks: [] },
];

function App() {
  const [columns, setColumns] = useState<ColumnType[]>(() => {
    const saved = localStorage.getItem('kanban-data');
    return saved ? JSON.parse(saved) : defaultColumns;
  });
  const [activeTask, setActiveTask] = useState<Task | null>(null);

  const sensors = useSensors(
    useSensor(PointerSensor, { activationConstraint: { distance: 5 } })
  );

  useEffect(() => {
    localStorage.setItem('kanban-data', JSON.stringify(columns));
  }, [columns]);

  const findTask = (id: string): { task: Task; columnId: string } | null => {
    for (const column of columns) {
      const task = column.tasks.find((t) => t.id === id);
      if (task) return { task, columnId: column.id };
    }
    return null;
  };

  const handleDragStart = (event: DragStartEvent) => {
    const found = findTask(event.active.id as string);
    if (found) setActiveTask(found.task);
  };

  const handleDragOver = (event: DragOverEvent) => {
    const { active, over } = event;
    if (!over) return;

    const activeId = active.id as string;
    const overId = over.id as string;

    const activeData = findTask(activeId);
    if (!activeData) return;

    const overColumn = columns.find((c) => c.id === overId);
    const overTask = findTask(overId);

    const targetColumnId = overColumn?.id || overTask?.columnId;
    if (!targetColumnId || targetColumnId === activeData.columnId) return;

    setColumns((cols) => {
      const newCols = cols.map((c) => ({ ...c, tasks: [...c.tasks] }));
      const sourceCol = newCols.find((c) => c.id === activeData.columnId)!;
      const targetCol = newCols.find((c) => c.id === targetColumnId)!;

      const taskIndex = sourceCol.tasks.findIndex((t) => t.id === activeId);
      const [task] = sourceCol.tasks.splice(taskIndex, 1);
      targetCol.tasks.push(task);

      return newCols;
    });
  };

  const handleDragEnd = (_event: DragEndEvent) => {
    setActiveTask(null);
  };

  const addTask = (columnId: ColumnId, title: string) => {
    const newTask: Task = {
      id: crypto.randomUUID(),
      title,
      createdAt: Date.now(),
    };
    setColumns((cols) =>
      cols.map((c) =>
        c.id === columnId ? { ...c, tasks: [...c.tasks, newTask] } : c
      )
    );
  };

  const deleteTask = (taskId: string) => {
    setColumns((cols) =>
      cols.map((c) => ({
        ...c,
        tasks: c.tasks.filter((t) => t.id !== taskId),
      }))
    );
  };

  const updateTask = (taskId: string, updates: Partial<Task>) => {
    setColumns((cols) =>
      cols.map((c) => ({
        ...c,
        tasks: c.tasks.map((t) =>
          t.id === taskId ? { ...t, ...updates } : t
        ),
      }))
    );
  };

  return (
    <div className="app">
      <header>
        <h1>🐾 Clawd's Kanban</h1>
      </header>
      <DndContext
        sensors={sensors}
        onDragStart={handleDragStart}
        onDragOver={handleDragOver}
        onDragEnd={handleDragEnd}
      >
        <div className="board">
          {columns.map((column) => (
            <Column
              key={column.id}
              column={column}
              onAddTask={(title) => addTask(column.id as ColumnId, title)}
              onDeleteTask={deleteTask}
              onUpdateTask={updateTask}
            />
          ))}
        </div>
        <DragOverlay>
          {activeTask && <TaskCard task={activeTask} isDragging />}
        </DragOverlay>
      </DndContext>
    </div>
  );
}

export default App;