/**
 * 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 { DateCalculator } from '../utils/DateCalculator';
import { PositionUtils } from '../utils/PositionUtils';

interface CachedElements {
  scrollContainer: HTMLElement | null;
  currentColumn: HTMLElement | null;
  lastColumnDate: string | null;
}

interface Position {
  x: number;
  y: number;
}

export class DragDropManager {
  private eventBus: IEventBus;
  
  // Mouse tracking with optimized state
  private lastMousePosition: Position = { x: 0, y: 0 };
  private lastLoggedPosition: Position = { x: 0, y: 0 };
  private currentMouseY = 0;
  private mouseOffset: Position = { x: 0, y: 0 };
  private initialMousePosition: Position = { x: 0, y: 0 };
  
  // Drag state
  private draggedEventId: string | null = null;
  private originalElement: HTMLElement | null = null;
  private currentColumn: string | null = null;
  private isDragStarted = false;
  
  // Movement threshold to distinguish click from drag
  private readonly dragThreshold = 5; // pixels
  
  // Cached DOM elements for performance
  private cachedElements: CachedElements = {
    scrollContainer: null,
    currentColumn: null,
    lastColumnDate: null
  };
  
  // 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);
    
    // Listen for header mouseover events
    this.eventBus.on('header:mouseover', (event) => {
      const { targetDate, headerRenderer } = (event as CustomEvent).detail;
      
      if (this.draggedEventId && targetDate) {
        // Find dragget element dynamisk
        const draggedElement = document.querySelector(`swp-event[data-event-id="${this.draggedEventId}"]`);
        
        if (draggedElement) {
          // Element findes stadig som day-event, så konverter
          this.eventBus.emit('drag:convert-to-allday', {
            targetDate,
            originalElement: draggedElement,
            headerRenderer
          });
          
          // Hide drag clone completely
          const dragClone = document.querySelector(`swp-event[data-event-id="clone-${this.draggedEventId}"]`);
          if (dragClone) {
            (dragClone as HTMLElement).style.display = 'none';
          }
        }
      }
    });

    // Listen for column mouseover events (for all-day to timed conversion)
    this.eventBus.on('column:mouseover', (event) => {
      const { targetColumn, targetY } = (event as CustomEvent).detail;
      
      if (this.draggedEventId && this.isAllDayEventBeingDragged()) {
        // Emit event to convert to timed
        this.eventBus.emit('drag:convert-to-timed', {
          eventId: this.draggedEventId,
          targetColumn,
          targetY
        });
      }
    });

    // Listen for header mouseleave events (remove all-day event, let clone take over)
    this.eventBus.on('header:mouseleave', (event) => {
      // Check if we're dragging ANY event
      if (this.draggedEventId) {
        // Find and remove all-day event specifically in the container
        const allDayEvent = document.querySelector(`swp-allday-container swp-allday-event[data-event-id="${this.draggedEventId}"]`);
        if (allDayEvent) {
          allDayEvent.remove();
        }
        
        // Show drag clone again
        const dragClone = document.querySelector(`swp-event[data-event-id="clone-${this.draggedEventId}"]`);
        if (dragClone) {
          (dragClone as HTMLElement).style.display = 'block';
        }
      }
    });
  }
  
  private handleMouseDown(event: MouseEvent): void {
    this.isDragStarted = false;
    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.originalElement = eventElement;
      this.draggedEventId = eventElement.dataset.eventId || null;
      
      // Calculate mouse offset within event
      const eventRect = eventElement.getBoundingClientRect();
      this.mouseOffset = {
        x: event.clientX - eventRect.left,
        y: event.clientY - eventRect.top
      };
      
      // Detect current column
      const column = this.detectColumn(event.clientX, event.clientY);
      if (column) {
        this.currentColumn = column;
      }
      
      // Don't emit drag:start yet - wait for movement threshold
    }
  }
  
  /**
   * Optimized mouse move handler with consolidated position calculations
   */
  private handleMouseMove(event: MouseEvent): void {
    this.currentMouseY = event.clientY;
    
    if (event.buttons === 1 && this.draggedEventId) {
      const currentPosition: Position = { x: event.clientX, y: event.clientY };
      
      // 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;
          this.eventBus.emit('drag:start', {
            eventId: this.draggedEventId,
            mousePosition: this.initialMousePosition,
            mouseOffset: this.mouseOffset,
            column: this.currentColumn
          });
        } 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)
          this.eventBus.emit('drag:move', {
            eventId: this.draggedEventId,
            mousePosition: currentPosition,
            snappedY: positionData.snappedY,
            column: positionData.column,
            mouseOffset: this.mouseOffset
          });
        }
        
        // Check for auto-scroll
        this.checkAutoScroll(event);
        
        // Check for column change using cached data
        const newColumn = this.getColumnFromCache(currentPosition);
        if (newColumn && newColumn !== this.currentColumn) {
          const previousColumn = this.currentColumn;
          this.currentColumn = newColumn;
          
          this.eventBus.emit('drag:column-change', {
            eventId: this.draggedEventId,
            previousColumn,
            newColumn,
            mousePosition: currentPosition
          });
        }
      }
    }
  }
  
  /**
   * Optimized mouse up handler with consolidated cleanup
   */
  private handleMouseUp(event: MouseEvent): void {
    this.stopAutoScroll();
    
    if (this.draggedEventId && this.originalElement) {
      // Store variables locally before cleanup
      const eventId = this.draggedEventId;
      const originalElement = this.originalElement;
      const isDragStarted = this.isDragStarted;
      
      // Clean up drag state first
      this.cleanupDragState();
      
      // Only emit drag:end if drag was actually started
      if (isDragStarted) {
        const finalPosition: Position = { x: event.clientX, y: event.clientY };
        
        // Use consolidated position calculation
        const positionData = this.calculateDragPosition(finalPosition);
        
        this.eventBus.emit('drag:end', {
          eventId: eventId,
          finalPosition,
          finalColumn: positionData.column,
          finalY: positionData.snappedY
        });
      } else {
        // This was just a click - emit click event instead
        this.eventBus.emit('event:click', {
          eventId: eventId,
          mousePosition: { x: event.clientX, y: event.clientY }
        });
      }
    }
  }
  
  /**
   * Consolidated position calculation method using PositionUtils
   */
  private calculateDragPosition(mousePosition: Position): { column: string | null; snappedY: number } {
    const column = this.detectColumn(mousePosition.x, mousePosition.y);
    const snappedY = this.calculateSnapPosition(mousePosition.y, column);
    
    return { column, snappedY };
  }

  /**
   * Calculate free position (follows mouse exactly)
   */
  private calculateFreePosition(mouseY: number, column: string | null = null): number {
    const targetColumn = column || this.currentColumn;
    
    // Use cached column element if available
    const columnElement = this.getCachedColumnElement(targetColumn);
    if (!columnElement) return mouseY;
    
    const relativeY = PositionUtils.getPositionFromCoordinate(mouseY, columnElement);
    
    // Return free position (no snapping)
    return Math.max(0, relativeY);
  }

  /**
   * Optimized snap position calculation using PositionUtils
   */
  private calculateSnapPosition(mouseY: number, column: string | null = null): number {
    const targetColumn = column || this.currentColumn;
    
    // Use cached column element if available
    const columnElement = this.getCachedColumnElement(targetColumn);
    if (!columnElement) return mouseY;
    
    // Use PositionUtils for consistent snapping behavior
    const snappedY = PositionUtils.getPositionFromCoordinate(mouseY, columnElement);
    
    return Math.max(0, snappedY);
  }
  
  /**
   * Optimized column detection with caching
   */
  private detectColumn(mouseX: number, mouseY: number): string | null {
    const element = document.elementFromPoint(mouseX, mouseY);
    if (!element) return null;
    
    // Walk up DOM tree to find swp-day-column
    let current = element as HTMLElement;
    while (current && current.tagName !== 'SWP-DAY-COLUMN') {
      current = current.parentElement as HTMLElement;
      if (!current) return null;
    }
    
    const columnDate = current.dataset.date || null;
    
    // Update cache if we found a new column
    if (columnDate && columnDate !== this.cachedElements.lastColumnDate) {
      this.cachedElements.currentColumn = current;
      this.cachedElements.lastColumnDate = columnDate;
    }
    
    return columnDate;
  }

  /**
   * Get column from cache or detect new one
   */
  private getColumnFromCache(mousePosition: Position): string | null {
    // Try to use cached column first
    if (this.cachedElements.currentColumn && this.cachedElements.lastColumnDate) {
      const rect = this.cachedElements.currentColumn.getBoundingClientRect();
      if (mousePosition.x >= rect.left && mousePosition.x <= rect.right) {
        return this.cachedElements.lastColumnDate;
      }
    }
    
    // Cache miss - detect new column
    return this.detectColumn(mousePosition.x, mousePosition.y);
  }

  /**
   * Get cached column element or query for new one
   */
  private getCachedColumnElement(columnDate: string | null): HTMLElement | null {
    if (!columnDate) return null;
    
    // Return cached element if it matches
    if (this.cachedElements.lastColumnDate === columnDate && this.cachedElements.currentColumn) {
      return this.cachedElements.currentColumn;
    }
    
    // Query for new element and cache it
    const element = document.querySelector(`swp-day-column[data-date="${columnDate}"]`) as HTMLElement;
    if (element) {
      this.cachedElements.currentColumn = element;
      this.cachedElements.lastColumnDate = columnDate;
    }
    
    return element;
  }
  
  /**
   * Optimized auto-scroll check with cached container
   */
  private checkAutoScroll(event: MouseEvent): void {
    // Use cached scroll container
    if (!this.cachedElements.scrollContainer) {
      this.cachedElements.scrollContainer = document.querySelector('swp-scrollable-content') as HTMLElement;
      if (!this.cachedElements.scrollContainer) {
        return;
      }
    }
    
    const containerRect = this.cachedElements.scrollContainer.getBoundingClientRect();
    const mouseY = event.clientY;
    
    // Calculate distances from edges
    const distanceFromTop = mouseY - containerRect.top;
    const distanceFromBottom = containerRect.bottom - mouseY;
    
    // Check if we need to scroll
    if (distanceFromTop <= this.scrollThreshold && distanceFromTop > 0) {
      this.startAutoScroll('up');
    } else if (distanceFromBottom <= this.scrollThreshold && distanceFromBottom > 0) {
      this.startAutoScroll('down');
    } else {
      this.stopAutoScroll();
    }
  }
  
  /**
   * Optimized auto-scroll with cached container reference
   */
  private startAutoScroll(direction: 'up' | 'down'): void {
    if (this.autoScrollAnimationId !== null) return;
    
    const scroll = () => {
      if (!this.cachedElements.scrollContainer || !this.draggedEventId) {
        this.stopAutoScroll();
        return;
      }
      
      const scrollAmount = direction === 'up' ? -this.scrollSpeed : this.scrollSpeed;
      this.cachedElements.scrollContainer.scrollTop += scrollAmount;
      
      // Emit updated position during scroll - adjust for scroll movement
      if (this.draggedEventId) {
        // During autoscroll, we need to calculate position relative to the scrolled content
        // The mouse hasn't moved, but the content has scrolled
        const columnElement = this.getCachedColumnElement(this.currentColumn);
        if (columnElement) {
          const columnRect = columnElement.getBoundingClientRect();
          // 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', {
            eventId: this.draggedEventId,
            snappedY: freeY, // Actually free position during scroll
            scrollTop: this.cachedElements.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.draggedEventId = null;
    this.originalElement = null;
    this.currentColumn = null;
    this.isDragStarted = false;
    
    // Clear cached elements
    this.cachedElements.currentColumn = null;
    this.cachedElements.lastColumnDate = null;
  }

  /**
   * Check if an all-day event is currently being dragged
   */
  private isAllDayEventBeingDragged(): boolean {
    if (!this.draggedEventId) return false;
    // Check if element exists as all-day event
    const allDayElement = document.querySelector(`swp-allday-event[data-event-id="${this.draggedEventId}"]`);
    return allDayElement !== null;
  }

  /**
   * 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);
    
    // Clear all cached elements
    this.cachedElements.scrollContainer = null;
    this.cachedElements.currentColumn = null;
    this.cachedElements.lastColumnDate = null;
    
    // Clean up drag state
    this.cleanupDragState();
  }
}