/**
 * 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, BaseSwpEventElement } 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;

  // Hover state
  private isHoverTrackingActive = false;
  private currentHoveredEvent: HTMLElement | null = null;

  // 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

  // Smooth drag animation
  private dragAnimationId: number | null = null;
  private targetY = 0;
  private currentY = 0;
  private targetColumn: ColumnBounds | null = null;

  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 {
    // Add event listeners
    document.body.addEventListener('mousemove', this.handleMouseMove.bind(this));
    document.body.addEventListener('mousedown', this.handleMouseDown.bind(this));
    document.body.addEventListener('mouseup', this.handleMouseUp.bind(this));

    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();
        }
      });

      // Event delegation for header enter/leave
      calendarContainer.addEventListener('mouseenter', (e) => {
        const target = e.target as HTMLElement;
        if (target.closest('swp-calendar-header')) {
          this.handleHeaderMouseEnter(e as MouseEvent);
        } else if (target.closest('swp-event')) {
          // Entered an event - activate hover tracking and set color
          const eventElement = target.closest<HTMLElement>('swp-event');
          const mouseEvent = e as MouseEvent;

          // Only handle hover if mouse button is up
          if (eventElement && !this.isDragStarted && mouseEvent.buttons === 0) {
            // Clear any previous hover first
            if (this.currentHoveredEvent && this.currentHoveredEvent !== eventElement) {
              this.currentHoveredEvent.classList.remove('hover');
            }

            this.isHoverTrackingActive = true;
            this.currentHoveredEvent = eventElement;
            eventElement.classList.add('hover');
          }
        }
      }, true); // Use capture phase

      calendarContainer.addEventListener('mouseleave', (e) => {
        const target = e.target as HTMLElement;
        if (target.closest('swp-calendar-header')) {
          this.handleHeaderMouseLeave(e as MouseEvent);
        }
        // Don't handle swp-event mouseleave here - let mousemove handle it
      }, true); // Use capture phase
    }

    // 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();
    ColumnDetectionUtils.updateColumnBoundsCache();
    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-GRID-CONTAINER') {
      if (eventElement.tagName === 'SWP-EVENT' || eventElement.tagName === 'SWP-ALLDAY-EVENT') {
        break;
      }
      eventElement = eventElement.parentElement as HTMLElement;
      if (!eventElement) return;
    }


    // Found an event - check if in resize zone first
    if (eventElement) {
      // Check if click is in bottom resize zone
      const rect = eventElement.getBoundingClientRect();
      const mouseY = event.clientY;
      const distanceFromBottom = rect.bottom - mouseY;
      const resizeZoneHeight = 15; // Match ResizeHandleManager

      // If in resize zone, don't handle this - let ResizeHandleManager take over
      if (distanceFromBottom >= 0 && distanceFromBottom <= resizeZoneHeight) {
        return; // Exit early - this is a resize operation
      }

      // Normal drag - prepare for potential dragging
      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 event hover (coordinate-based) - only when mouse button is up
    if (this.isHoverTrackingActive && event.buttons === 0) {
      this.checkEventHover(event);
    }

    if (event.buttons === 1) {
      const currentPosition: MousePosition = { x: event.clientX, y: event.clientY };

      // Check if we need to start drag (movement threshold)
      if (!this.isDragStarted && this.draggedElement) {
        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;

          // Set high z-index on event-group if exists, otherwise on event itself
          const eventGroup = this.draggedElement.closest<HTMLElement>('swp-event-group');
          if (eventGroup) {
            eventGroup.style.zIndex = '9999';
          } else {
            this.draggedElement.style.zIndex = '9999';
          }

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

          // Cast to BaseSwpEventElement and create clone (works for both SwpEventElement and SwpAllDayEventElement)
          const originalElement = this.draggedElement as BaseSwpEventElement;
          this.draggedClone = originalElement.createClone();

          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 && this.draggedElement && this.draggedClone) {
        if (!this.draggedElement.hasAttribute("data-allday")) {
          // Calculate raw position from mouse (no snapping)
          const column = ColumnDetectionUtils.getColumnBounds(currentPosition);

          if (column) {
            // Calculate raw Y position relative to column (accounting for mouse offset)
            const columnRect = column.boundingClientRect;
            const eventTopY = currentPosition.y - columnRect.top - this.mouseOffset.y;
            this.targetY = Math.max(0, eventTopY); // Store raw Y as target (no snapping)
            this.targetColumn = column;

            // Start animation loop if not already running
            if (this.dragAnimationId === null) {
              this.currentY = parseFloat(this.draggedClone.style.top) || 0;
              this.animateDrag();
            }
          }

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

        const newColumn = ColumnDetectionUtils.getColumnBounds(currentPosition);
        if (newColumn == null)
          return;

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

          const dragColumnChangePayload: DragColumnChangeEventPayload = {
            originalElement: 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();
    this.stopDragAnimation();

    if (this.draggedElement) {

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

        // Snap to grid on mouse up (like ResizeHandleManager)
        const column = ColumnDetectionUtils.getColumnBounds(mousePosition);

        if (!column) {
          console.warn('No column detected on mouseUp');
          return;
        }

        // Get current position and snap it to grid
        const currentY = parseFloat(this.draggedClone?.style.top || '0');
        const snappedY = this.calculateSnapPosition(mousePosition.y, column);

        // Update clone to snapped position immediately
        if (this.draggedClone) {
          this.draggedClone.style.top = `${snappedY}px`;
        }

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

        if (!dropTarget)
          throw "dropTarget is null";

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

        const dragEndPayload: DragEndEventPayload = {
          originalElement: this.draggedElement,
          draggedClone: this.draggedClone,
          mousePosition,
          finalPosition: { column, snappedY },
          target: dropTarget
        };
        this.eventBus.emit('drag:end', dragEndPayload);

        this.cleanupDragState();

      } 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();
    this.stopDragAnimation();
  }

  /**
   * 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 {
    // Calculate where the event top would be (accounting for mouse offset)
    const eventTopY = mouseY - this.mouseOffset.y;

    // Snap the event top position, not the mouse position
    const snappedY = PositionUtils.getPositionFromCoordinate(eventTopY, column);

    return Math.max(0, snappedY);
  }

  /**
   * Smooth drag animation using requestAnimationFrame
   */
  private animateDrag(): void {
    if (!this.isDragStarted || !this.draggedClone || !this.targetColumn) {
      this.dragAnimationId = null;
      return;
    }

    // Smooth interpolation towards target
    const diff = this.targetY - this.currentY;
    const step = diff * 0.3; // 30% of distance per frame

    // Update if difference is significant
    if (Math.abs(diff) > 0.5) {
      this.currentY += step;

      // Emit drag move event with interpolated position
      const dragMovePayload: DragMoveEventPayload = {
        draggedElement: this.draggedElement!,
        draggedClone: this.draggedClone,
        mousePosition: this.lastMousePosition,
        snappedY: this.currentY,
        columnBounds: this.targetColumn,
        mouseOffset: this.mouseOffset
      };
      this.eventBus.emit('drag:move', dragMovePayload);

      this.dragAnimationId = requestAnimationFrame(() => this.animateDrag());
    } else {
      // Close enough - snap to target
      this.currentY = this.targetY;

      const dragMovePayload: DragMoveEventPayload = {
        draggedElement: this.draggedElement!,
        draggedClone: this.draggedClone,
        mousePosition: this.lastMousePosition,
        snappedY: this.currentY,
        columnBounds: this.targetColumn,
        mouseOffset: this.mouseOffset
      };
      this.eventBus.emit('drag:move', dragMovePayload);

      this.dragAnimationId = null;
    }
  }


  /**
   * 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;
    }
  }

  /**
   * Stop drag animation
   */
  private stopDragAnimation(): void {
    if (this.dragAnimationId !== null) {
      cancelAnimationFrame(this.dragAnimationId);
      this.dragAnimationId = null;
    }
  }

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

  /**
   * Handle mouse enter on calendar header - simplified using native events
   */
  private handleHeaderMouseEnter(event: MouseEvent): void {
    // Only handle if we're dragging a timed event (not all-day)
    if (!this.isDragStarted || !this.draggedClone) {
      return;
    }

    const position: MousePosition = { x: event.clientX, y: event.clientY };
    const targetColumn = ColumnDetectionUtils.getColumnBounds(position);

    if (targetColumn) {
      console.log('🎯 DragDropManager: Mouse entered header', { targetDate: targetColumn });

      // Extract CalendarEvent from the dragged clone
      const calendarEvent = SwpEventElement.extractCalendarEventFromElement(this.draggedClone);

      const dragMouseEnterPayload: DragMouseEnterHeaderEventPayload = {
        targetColumn: targetColumn,
        mousePosition: position,
        originalElement: this.draggedElement,
        draggedClone: this.draggedClone,
        calendarEvent: calendarEvent,
        // Delegate pattern - allows AllDayManager to replace the clone
        replaceClone: (newClone: HTMLElement) => {
          this.draggedClone = newClone;
        }
      };
      this.eventBus.emit('drag:mouseenter-header', dragMouseEnterPayload);
    }
  }

  /**
   * Handle mouse leave from calendar header - simplified using native events
   */
  private handleHeaderMouseLeave(event: MouseEvent): void {
    // Only handle if we're dragging an all-day event
    if (!this.isDragStarted || !this.draggedClone || !this.draggedClone.hasAttribute("data-allday")) {
      return;
    }

    console.log('🚪 DragDropManager: Mouse left header');

    const position: MousePosition = { x: event.clientX, y: event.clientY };
    const targetColumn = ColumnDetectionUtils.getColumnBounds(position);

    if (!targetColumn) {
      console.warn("No column detected when leaving header");
      return;
    }

    const dragMouseLeavePayload: DragMouseLeaveHeaderEventPayload = {
      targetDate: targetColumn.date,
      mousePosition: position,
      originalElement: this.draggedElement,
      draggedClone: this.draggedClone
    };
    this.eventBus.emit('drag:mouseleave-header', dragMouseLeavePayload);
  }

  private checkEventHover(event: MouseEvent): void {
    // Use currentHoveredEvent to check if mouse is still within bounds
    if (!this.currentHoveredEvent) return;

    const rect = this.currentHoveredEvent.getBoundingClientRect();
    const mouseX = event.clientX;
    const mouseY = event.clientY;

    // Check if mouse is still within the current hovered event
    const isStillInside = mouseX >= rect.left && mouseX <= rect.right &&
                          mouseY >= rect.top && mouseY <= rect.bottom;

    // If mouse left the event
    if (!isStillInside) {
      // Only disable tracking and clear if mouse is NOT pressed (allow resize to work)
      if (event.buttons === 0) {
        this.isHoverTrackingActive = false;
        this.clearEventHover();
      }
    }
  }

  private clearEventHover(): void {
    if (this.currentHoveredEvent) {
      this.currentHoveredEvent.classList.remove('hover');
      this.currentHoveredEvent = null;
    }
  }
}