Calendar/src/v2/managers/DragDropManager.ts

import { IEventBus } from '../types/CalendarTypes';
import { IGridConfig } from '../core/IGridConfig';
import { CoreEvents } from '../constants/CoreEvents';
import { snapToGrid } from '../utils/PositionUtils';
import {
  IMousePosition,
  IDragStartPayload,
  IDragMovePayload,
  IDragEndPayload,
  IDragCancelPayload
} from '../types/DragTypes';

interface DragState {
  eventId: string;
  element: HTMLElement;
  ghostElement: HTMLElement;
  startY: number;
  mouseOffset: IMousePosition;
  columnElement: HTMLElement;
  targetY: number;
  currentY: number;
  animationId: number;
}

/**
 * DragDropManager - Handles drag-drop for calendar events
 *
 * Strategy: Drag original element, leave ghost-clone in place
 * - mousedown: Store initial state, wait for movement
 * - mousemove (>5px): Create ghost, start dragging original
 * - mouseup: Snap to grid, remove ghost, emit drag:end
 * - cancel: Animate back to startY, remove ghost
 */
export class DragDropManager {
  private dragState: DragState | null = null;
  private mouseDownPosition: IMousePosition | null = null;
  private pendingElement: HTMLElement | null = null;
  private pendingMouseOffset: IMousePosition | null = null;

  private readonly DRAG_THRESHOLD = 5;
  private readonly INTERPOLATION_FACTOR = 0.3;

  constructor(
    private eventBus: IEventBus,
    private gridConfig: IGridConfig
  ) {}

  /**
   * Initialize drag-drop on a container element
   */
  init(container: HTMLElement): void {
    container.addEventListener('pointerdown', this.handlePointerDown);
    document.addEventListener('pointermove', this.handlePointerMove);
    document.addEventListener('pointerup', this.handlePointerUp);
  }

  private handlePointerDown = (e: PointerEvent): void => {
    const target = e.target as HTMLElement;
    const eventElement = target.closest('swp-event') as HTMLElement;

    if (!eventElement) return;

    // Store for potential drag
    this.mouseDownPosition = { x: e.clientX, y: e.clientY };
    this.pendingElement = eventElement;

    // Calculate mouse offset within element
    const rect = eventElement.getBoundingClientRect();
    this.pendingMouseOffset = {
      x: e.clientX - rect.left,
      y: e.clientY - rect.top
    };

    // Capture pointer for reliable tracking
    eventElement.setPointerCapture(e.pointerId);
  };

  private handlePointerMove = (e: PointerEvent): void => {
    // Not in potential drag state
    if (!this.mouseDownPosition || !this.pendingElement) {
      // Already dragging - update target
      if (this.dragState) {
        this.updateDragTarget(e);
      }
      return;
    }

    // Check threshold
    const deltaX = Math.abs(e.clientX - this.mouseDownPosition.x);
    const deltaY = Math.abs(e.clientY - this.mouseDownPosition.y);
    const distance = Math.sqrt(deltaX * deltaX + deltaY * deltaY);

    if (distance < this.DRAG_THRESHOLD) return;

    // Start drag
    this.initializeDrag(this.pendingElement, this.pendingMouseOffset!, e);
    this.mouseDownPosition = null;
    this.pendingElement = null;
    this.pendingMouseOffset = null;
  };

  private handlePointerUp = (_e: PointerEvent): void => {
    // Clear pending state
    this.mouseDownPosition = null;
    this.pendingElement = null;
    this.pendingMouseOffset = null;

    if (!this.dragState) return;

    // Stop animation
    cancelAnimationFrame(this.dragState.animationId);

    // Snap to grid
    const snappedY = snapToGrid(this.dragState.currentY, this.gridConfig);
    this.dragState.element.style.top = `${snappedY}px`;

    // Remove ghost
    this.dragState.ghostElement.remove();

    // Get column data
    const dateKey = this.dragState.columnElement.dataset.date || '';
    const resourceId = this.dragState.columnElement.dataset.resourceId;

    // Emit drag:end
    const payload: IDragEndPayload = {
      eventId: this.dragState.eventId,
      element: this.dragState.element,
      snappedY,
      columnElement: this.dragState.columnElement,
      dateKey,
      resourceId
    };

    this.eventBus.emit(CoreEvents.EVENT_DRAG_END, payload);

    // Cleanup
    this.dragState.element.classList.remove('dragging');
    this.dragState = null;
  };

  private initializeDrag(element: HTMLElement, mouseOffset: IMousePosition, e: PointerEvent): void {
    const eventId = element.dataset.eventId || '';
    const columnElement = element.closest('swp-day-column') as HTMLElement;

    if (!columnElement) return;
    const startY = parseFloat(element.style.top) || 0;

    // Create ghost clone
    const ghostElement = element.cloneNode(true) as HTMLElement;
    ghostElement.classList.add('drag-ghost');
    ghostElement.style.opacity = '0.3';
    ghostElement.style.pointerEvents = 'none';

    // Insert ghost before original
    element.parentNode?.insertBefore(ghostElement, element);

    // Setup element for dragging
    element.classList.add('dragging');

    // Calculate initial target from mouse position
    const columnRect = columnElement.getBoundingClientRect();
    const targetY = e.clientY - columnRect.top - mouseOffset.y;

    // Initialize drag state
    this.dragState = {
      eventId,
      element,
      ghostElement,
      startY,
      mouseOffset,
      columnElement,
      targetY: Math.max(0, targetY),
      currentY: startY,
      animationId: 0
    };

    // Emit drag:start
    const payload: IDragStartPayload = {
      eventId,
      element,
      ghostElement,
      startY,
      mouseOffset,
      columnElement
    };

    this.eventBus.emit(CoreEvents.EVENT_DRAG_START, payload);

    // Start animation loop
    this.animateDrag();
  }

  private updateDragTarget(e: PointerEvent): void {
    if (!this.dragState) return;

    const columnRect = this.dragState.columnElement.getBoundingClientRect();
    const targetY = e.clientY - columnRect.top - this.dragState.mouseOffset.y;

    this.dragState.targetY = Math.max(0, targetY);

    // Start animation if not running
    if (!this.dragState.animationId) {
      this.animateDrag();
    }
  }

  private animateDrag = (): void => {
    if (!this.dragState) return;

    const diff = this.dragState.targetY - this.dragState.currentY;

    // Stop animation when close enough to target
    if (Math.abs(diff) <= 0.5) {
      this.dragState.animationId = 0;
      return;
    }

    // Interpolate towards target
    this.dragState.currentY += diff * this.INTERPOLATION_FACTOR;

    // Update element position
    this.dragState.element.style.top = `${this.dragState.currentY}px`;

    // Emit drag:move
    const payload: IDragMovePayload = {
      eventId: this.dragState.eventId,
      element: this.dragState.element,
      currentY: this.dragState.currentY,
      columnElement: this.dragState.columnElement
    };

    this.eventBus.emit(CoreEvents.EVENT_DRAG_MOVE, payload);

    // Continue animation
    this.dragState.animationId = requestAnimationFrame(this.animateDrag);
  };

  /**
   * Cancel drag and animate back to start position
   */
  cancelDrag(): void {
    if (!this.dragState) return;

    // Stop animation
    cancelAnimationFrame(this.dragState.animationId);

    const { element, ghostElement, startY, eventId } = this.dragState;

    // Animate back to start
    element.style.transition = 'top 200ms ease-out';
    element.style.top = `${startY}px`;

    // Remove ghost after animation
    setTimeout(() => {
      ghostElement.remove();
      element.style.transition = '';
      element.classList.remove('dragging');
    }, 200);

    // Emit drag:cancel
    const payload: IDragCancelPayload = {
      eventId,
      element,
      startY
    };

    this.eventBus.emit(CoreEvents.EVENT_DRAG_CANCEL, payload);

    this.dragState = null;
  }
}