Calendar/src/managers/DragDropManager.ts

/**
 * DragDropManager - Optimized drag and drop with consolidated position calculations
 * Reduces redundant DOM queries and improves performance through caching
 */

import { IEventBus } from '../types/CalendarTypes';
import { calendarConfig } from '../core/CalendarConfig';
import { PositionUtils } from '../utils/PositionUtils';
import { ColumnBounds, ColumnDetectionUtils } from '../utils/ColumnDetectionUtils';
import { SwpEventElement } from '../elements/SwpEventElement';
import {
  DragStartEventPayload,
  DragMoveEventPayload,
  DragEndEventPayload,
  DragMouseEnterHeaderEventPayload,
  DragMouseLeaveHeaderEventPayload,
  DragColumnChangeEventPayload
} from '../types/EventTypes';
import { MousePosition } from '../types/DragDropTypes';

interface CachedElements {
  scrollContainer: HTMLElement | null;
}




export class DragDropManager {
  private eventBus: IEventBus;

  // Mouse tracking with optimized state
  private lastMousePosition: MousePosition = { x: 0, y: 0 };
  private lastLoggedPosition: MousePosition = { x: 0, y: 0 };
  private currentMouseY = 0;
  private mouseOffset: MousePosition = { x: 0, y: 0 };
  private initialMousePosition: MousePosition = { x: 0, y: 0 };
  private lastColumn: ColumnBounds | null = null;

  // Drag state
  private draggedElement!: HTMLElement | null;
  private draggedClone!: HTMLElement | null;
  private currentColumnBounds: ColumnBounds | null = null;
  private isDragStarted = false;

  // Header tracking state
  private isInHeader = false;

  // Movement threshold to distinguish click from drag
  private readonly dragThreshold = 5; // pixels

  private scrollContainer!: HTMLElement | null;
  // Cached DOM elements for performance




  // Auto-scroll properties
  private autoScrollAnimationId: number | null = null;
  private readonly scrollSpeed = 10; // pixels per frame
  private readonly scrollThreshold = 30; // pixels from edge

  // Snap configuration
  private snapIntervalMinutes = 15; // Default 15 minutes
  private hourHeightPx: number; // Will be set from config

  // Event listener references for proper cleanup
  private boundHandlers = {
    mouseMove: this.handleMouseMove.bind(this),
    mouseDown: this.handleMouseDown.bind(this),
    mouseUp: this.handleMouseUp.bind(this)
  };

  private get snapDistancePx(): number {
    return (this.snapIntervalMinutes / 60) * this.hourHeightPx;
  }

  constructor(eventBus: IEventBus) {
    this.eventBus = eventBus;
    // Get config values
    const gridSettings = calendarConfig.getGridSettings();
    this.hourHeightPx = gridSettings.hourHeight;
    this.snapIntervalMinutes = gridSettings.snapInterval;

    this.init();
  }

  /**
   * Configure snap interval
   */
  public setSnapInterval(minutes: number): void {
    this.snapIntervalMinutes = minutes;
  }

  /**
   * Initialize with optimized event listener setup
   */
  private init(): void {
    // Use bound handlers for proper cleanup
    document.body.addEventListener('mousemove', this.boundHandlers.mouseMove);
    document.body.addEventListener('mousedown', this.boundHandlers.mouseDown);
    document.body.addEventListener('mouseup', this.boundHandlers.mouseUp);

    this.scrollContainer = document.querySelector('swp-scrollable-content') as HTMLElement;
    const calendarContainer = document.querySelector('swp-calendar-container');
    if (calendarContainer) {
      calendarContainer.addEventListener('mouseleave', () => {
        if (this.draggedElement && this.isDragStarted) {
          this.cancelDrag();
        }
      });
    }

    // Initialize column bounds cache
    ColumnDetectionUtils.updateColumnBoundsCache();

    // Listen to resize events to update cache
    window.addEventListener('resize', () => {
      ColumnDetectionUtils.updateColumnBoundsCache();
    });

    // Listen to navigation events to update cache
    this.eventBus.on('navigation:completed', () => {
      ColumnDetectionUtils.updateColumnBoundsCache();
    });

  }

  private handleMouseDown(event: MouseEvent): void {

    // Clean up drag state first
    this.cleanupDragState();

    this.lastMousePosition = { x: event.clientX, y: event.clientY };
    this.lastLoggedPosition = { x: event.clientX, y: event.clientY };
    this.initialMousePosition = { x: event.clientX, y: event.clientY };

    // Check if mousedown is on an event
    const target = event.target as HTMLElement;
    let eventElement = target;

    while (eventElement && eventElement.tagName !== 'SWP-EVENTS-LAYER') {
      if (eventElement.tagName === 'SWP-EVENT') {
        break;
      }
      eventElement = eventElement.parentElement as HTMLElement;
      if (!eventElement) return;
    }

    // If we reached SWP-EVENTS-LAYER without finding an event, return
    if (!eventElement || eventElement.tagName === 'SWP-EVENTS-LAYER') {
      return;
    }

    // Found an event - prepare for potential dragging
    if (eventElement) {
      this.draggedElement = eventElement;
      this.lastColumn = ColumnDetectionUtils.getColumnBounds(this.lastMousePosition)
      // Calculate mouse offset within event
      const eventRect = eventElement.getBoundingClientRect();
      this.mouseOffset = {
        x: event.clientX - eventRect.left,
        y: event.clientY - eventRect.top
      };
    }
  }

  /**
   * Optimized mouse move handler with consolidated position calculations
   */
  private handleMouseMove(event: MouseEvent): void {
    this.currentMouseY = event.clientY;
    this.lastMousePosition = { x: event.clientX, y: event.clientY };

    // Check for header enter/leave during drag
    if (this.draggedElement) {
      this.checkHeaderEnterLeave(event);
    }

    if (event.buttons === 1 && this.draggedElement) {
      const currentPosition: MousePosition = { x: event.clientX, y: event.clientY }; //TODO: Is this really needed? why not just use event.clientX + Y directly

      // Check if we need to start drag (movement threshold)
      if (!this.isDragStarted) {
        const deltaX = Math.abs(currentPosition.x - this.initialMousePosition.x);
        const deltaY = Math.abs(currentPosition.y - this.initialMousePosition.y);
        const totalMovement = Math.sqrt(deltaX * deltaX + deltaY * deltaY);

        if (totalMovement >= this.dragThreshold) {
          // Start drag - emit drag:start event
          this.isDragStarted = true;

          // Detect current column
          this.currentColumnBounds = ColumnDetectionUtils.getColumnBounds(currentPosition);

          // Create SwpEventElement from existing DOM element and clone it
          const originalSwpEvent = SwpEventElement.fromExistingElement(this.draggedElement);
          const clonedSwpEvent = originalSwpEvent.createClone();

          // Get the cloned DOM element
          this.draggedClone = clonedSwpEvent.getElement();

          const dragStartPayload: DragStartEventPayload = {
            draggedElement: this.draggedElement,
            draggedClone: this.draggedClone,
            mousePosition: this.initialMousePosition,
            mouseOffset: this.mouseOffset,
            columnBounds: this.currentColumnBounds
          };
          this.eventBus.emit('drag:start', dragStartPayload);
        } else {
          // Not enough movement yet - don't start drag
          return;
        }
      }

      // Continue with normal drag behavior only if drag has started
      if (this.isDragStarted) {
        const deltaY = Math.abs(currentPosition.y - this.lastLoggedPosition.y);

        // Check for snap interval vertical movement (normal drag behavior)
        if (deltaY >= this.snapDistancePx) {
          this.lastLoggedPosition = currentPosition;

          // Consolidated position calculations with snapping for normal drag
          const positionData = this.calculateDragPosition(currentPosition);

          // Emit drag move event with snapped position (normal behavior)
          const dragMovePayload: DragMoveEventPayload = {
            draggedElement: this.draggedElement,
            mousePosition: currentPosition,
            snappedY: positionData.snappedY,
            columnBounds: positionData.column,
            mouseOffset: this.mouseOffset
          };
          this.eventBus.emit('drag:move', dragMovePayload);
        }

        // Check for auto-scroll
        this.checkAutoScroll(currentPosition);

        // Check for column change using cached data
        const newColumn = ColumnDetectionUtils.getColumnBounds(currentPosition);

        if (newColumn && newColumn !== this.currentColumnBounds) {
          const previousColumn = this.currentColumnBounds;
          this.currentColumnBounds = newColumn;

          const dragColumnChangePayload: DragColumnChangeEventPayload = {
            draggedElement: this.draggedElement,
            draggedClone: this.draggedClone,
            previousColumn,
            newColumn,
            mousePosition: currentPosition
          };
          this.eventBus.emit('drag:column-change', dragColumnChangePayload);
        }
      }
    }
  }

  /**
   * Optimized mouse up handler with consolidated cleanup
   */
  private handleMouseUp(event: MouseEvent): void {
    this.stopAutoScroll();

    if (this.draggedElement) {

      // Only emit drag:end if drag was actually started
      if (this.isDragStarted) {
        const mousePosition: MousePosition = { x: event.clientX, y: event.clientY };

        // Use consolidated position calculation
        const positionData = this.calculateDragPosition(mousePosition);

        // Detect drop target (swp-day-column or swp-day-header)
        const dropTarget = this.detectDropTarget(mousePosition);

        console.log('🎯 DragDropManager: Emitting drag:end', {
          draggedElement: this.draggedElement.dataset.eventId,
          finalColumn: positionData.column,
          finalY: positionData.snappedY,
          dropTarget: dropTarget,
          isDragStarted: this.isDragStarted
        });

        const dragEndPayload: DragEndEventPayload = {
          draggedElement: this.draggedElement,
          draggedClone: this.draggedClone,
          mousePosition,
          finalPosition: positionData,
          target: dropTarget
        };
        this.eventBus.emit('drag:end', dragEndPayload);
        
        this.draggedElement.remove(); // TODO: this should be changed into a subscriber which only after a succesful placement is fired, not just mouseup as this can remove elements that are not placed.

      } else {
        // This was just a click - emit click event instead
        this.eventBus.emit('event:click', {
          draggedElement: this.draggedElement,
          mousePosition: { x: event.clientX, y: event.clientY }
        });
      }
    }
  }
  // Add a cleanup method that finds and removes ALL clones
  private cleanupAllClones(): void {
    // Remove clones from all possible locations
    const allClones = document.querySelectorAll('[data-event-id^="clone"]');

    if (allClones.length > 0) {
      console.log(`🧹 DragDropManager: Removing ${allClones.length} clone(s)`);
      allClones.forEach(clone => clone.remove());
    }
  }

  /**
   * Cancel drag operation when mouse leaves grid container
   */
  private cancelDrag(): void {
    if (!this.draggedElement) return;

    console.log('🚫 DragDropManager: Cancelling drag - mouse left grid container');

    const draggedElement = this.draggedElement;

    // 1. Remove all clones
    this.cleanupAllClones();

    // 2. Restore original element
    if (draggedElement) {
      draggedElement.style.opacity = '';
      draggedElement.style.cursor = '';
    }

    // 3. Emit cancellation event
    this.eventBus.emit('drag:cancelled', {
      draggedElement: draggedElement,
      reason: 'mouse-left-grid'
    });

    // 4. Clean up state
    this.cleanupDragState();
    this.stopAutoScroll();
  }

  /**
   * Consolidated position calculation method using PositionUtils
   */
  private calculateDragPosition(mousePosition: MousePosition): { column: ColumnBounds | null; snappedY: number } {
    let column = ColumnDetectionUtils.getColumnBounds(mousePosition);
    let snappedY = 0;
    if (column) {
      snappedY = this.calculateSnapPosition(mousePosition.y, column);
      return { column, snappedY };
    }

    return { column, snappedY };
  }

  /**
   * Optimized snap position calculation using PositionUtils
   */
  private calculateSnapPosition(mouseY: number, column: ColumnBounds): number {
    const snappedY = PositionUtils.getPositionFromCoordinate(mouseY, column);

    return Math.max(0, snappedY);
  }


  /**
   * Optimized auto-scroll check with cached container
   */
  private checkAutoScroll(mousePosition: MousePosition): void {

    if (this.scrollContainer == null)
      return;

    const containerRect = this.scrollContainer.getBoundingClientRect();
    const mouseY = mousePosition.clientY;

    // Calculate distances from edges
    const distanceFromTop = mousePosition.y - containerRect.top;
    const distanceFromBottom = containerRect.bottom - mousePosition.y;

    // Check if we need to scroll
    if (distanceFromTop <= this.scrollThreshold && distanceFromTop > 0) {
      this.startAutoScroll('up', mousePosition);
    } else if (distanceFromBottom <= this.scrollThreshold && distanceFromBottom > 0) {
      this.startAutoScroll('down', mousePosition);
    } else {
      this.stopAutoScroll();
    }
  }

  /**
   * Optimized auto-scroll with cached container reference
   */
  private startAutoScroll(direction: 'up' | 'down', event: MousePosition): void {
    if (this.autoScrollAnimationId !== null) return;

    const scroll = () => {
      if (!this.scrollContainer || !this.draggedElement) {
        this.stopAutoScroll();
        return;
      }

      const scrollAmount = direction === 'up' ? -this.scrollSpeed : this.scrollSpeed;
      this.scrollContainer.scrollTop += scrollAmount;

      // Emit updated position during scroll - adjust for scroll movement
      if (this.draggedElement) {
        // During autoscroll, we need to calculate position relative to the scrolled content
        // The mouse hasn't moved, but the content has scrolled
        const columnElement = ColumnDetectionUtils.getColumnBounds(event);

        if (columnElement) {
          const columnRect = columnElement.boundingClientRect;
          // Calculate free position relative to column, accounting for scroll movement (no snapping during scroll)
          const relativeY = this.currentMouseY - columnRect.top - this.mouseOffset.y;
          const freeY = Math.max(0, relativeY);

          this.eventBus.emit('drag:auto-scroll', {
            draggedElement: this.draggedElement,
            snappedY: freeY, // Actually free position during scroll
            scrollTop: this.scrollContainer.scrollTop
          });
        }
      }

      this.autoScrollAnimationId = requestAnimationFrame(scroll);
    };

    this.autoScrollAnimationId = requestAnimationFrame(scroll);
  }

  /**
   * Stop auto-scroll animation
   */
  private stopAutoScroll(): void {
    if (this.autoScrollAnimationId !== null) {
      cancelAnimationFrame(this.autoScrollAnimationId);
      this.autoScrollAnimationId = null;
    }
  }

  /**
   * Clean up drag state
   */
  private cleanupDragState(): void {
    this.draggedElement = null;
    this.draggedClone = null;
    this.isDragStarted = false;
    this.isInHeader = false;
  }

  /**
   * Detect drop target - whether dropped in swp-day-column or swp-day-header
   */
  private detectDropTarget(position: MousePosition): 'swp-day-column' | 'swp-day-header' | null {

    // Traverse up the DOM tree to find the target container
    let currentElement = this.draggedClone;
    while (currentElement && currentElement !== document.body) {
      if (currentElement.tagName === 'SWP-ALLDAY-CONTAINER') {
        return 'swp-day-header';
      }
      if (currentElement.tagName === 'SWP-DAY-COLUMN') {
        return 'swp-day-column';
      }
      currentElement = currentElement.parentElement as HTMLElement;
    }

    return null;
  }

  /**
   * Check for header enter/leave during drag operations
   */
  private checkHeaderEnterLeave(event: MouseEvent): void {

    let position: MousePosition = { x: event.clientX, y: event.clientY };
    const elementAtPosition = document.elementFromPoint(event.clientX, event.clientY);
    if (!elementAtPosition) return;

    // Check if we're in a header area
    const headerElement = elementAtPosition.closest('swp-day-header, swp-calendar-header');
    const isCurrentlyInHeader = !!headerElement;

    // Detect header enter
    if (!this.isInHeader && isCurrentlyInHeader) {
      this.isInHeader = true;

      // Calculate target date using existing method
      const targetColumn = ColumnDetectionUtils.getColumnBounds(position);

      if (targetColumn) {
        console.log('🎯 DragDropManager: Emitting drag:mouseenter-header', { targetDate: targetColumn });

        // Find clone element (if it exists)
        const eventId = this.draggedElement?.dataset.eventId;
        const cloneElement = document.querySelector(`[data-event-id="clone-${eventId}"]`) as HTMLElement;

        const dragMouseEnterPayload: DragMouseEnterHeaderEventPayload = {
          targetColumn: targetColumn,
          mousePosition: { x: event.clientX, y: event.clientY },
          originalElement: this.draggedElement,
          cloneElement: cloneElement
        };
        this.eventBus.emit('drag:mouseenter-header', dragMouseEnterPayload);
      }
    }

    // Detect header leave
    if (this.isInHeader && !isCurrentlyInHeader) {
      this.isInHeader = false;

      console.log('🚪 DragDropManager: Emitting drag:mouseleave-header');

      // Calculate target date using existing method
      const targetColumn = ColumnDetectionUtils.getColumnBounds(position);
      if (!targetColumn) {
        console.warn("No column detected, unknown reason");
        return;

      }
      // Find clone element (if it exists)
      const eventId = this.draggedElement?.dataset.eventId;
      const cloneElement = document.querySelector(`[data-event-id="clone-${eventId}"]`) as HTMLElement;

      const dragMouseLeavePayload: DragMouseLeaveHeaderEventPayload = {
        targetDate: targetColumn.date,
        mousePosition: { x: event.clientX, y: event.clientY },
        originalElement: this.draggedElement,
        cloneElement: cloneElement
      };
      this.eventBus.emit('drag:mouseleave-header', dragMouseLeavePayload);
    }
  }

  /**
   * Clean up all resources and event listeners
   */
  public destroy(): void {
    this.stopAutoScroll();

    // Remove event listeners using bound references
    document.body.removeEventListener('mousemove', this.boundHandlers.mouseMove);
    document.body.removeEventListener('mousedown', this.boundHandlers.mouseDown);
    document.body.removeEventListener('mouseup', this.boundHandlers.mouseUp);

    // Clean up drag state
    this.cleanupDragState();
  }
}