package de.midlane_illaoi.eventflow.event;

import java.util.Comparator;

import de.midlane_illaoi.eventflow.listener.SortableEventListener;

public interface ObserverSortingEvent
{
	
	/**
	 * TODO write library to handle bitflags
	 * refactor this code & AbstractBuff
	public static final int ON_UNCOMPARABLE_LISTENERS_THROW_EXCEPTION	= 1;
	public static final int EXECUTE_UNCOMPARABLE_LISTENERS_FIRST		= 2;
	public static final int EXECUTE_UNCOMPARABLE_LISTENERS_LAST			= 4;
	public static final int COMPARE_UNCAMPARABLE_LISTENERS_BY_HASHCODE	= 8;
	*/
	
	
    enum SortingMode {
        ON_UNCOMPARABLE_LISTENERS_THROW_EXCEPTION, 
        EXECUTE_UNCOMPARABLE_LISTENERS_FIRST,
        EXECUTE_UNCOMPARABLE_LISTENERS_LAST,
    }
    
    
    public Comparator<? extends Object> getObserverComparator();
    
    default public boolean isComparatorUsedForAllEventsOfType() { return true; }

	/**
	 * The comparator compares all objects,
	 * but treats every object that does 
	 * not implement the SortableEventListener interface as equal
	 * */
	default Comparator<? extends Object> createObserverComparator(SortingMode sortingMode){
		return new Comparator<Object>() {
			@Override
			public int compare(Object o1, Object o2) {
				boolean isO1Comparable = o1 instanceof SortableEventListener;
				boolean isO2Comparable = o2 instanceof SortableEventListener;
				
				if( sortingMode == SortingMode.ON_UNCOMPARABLE_LISTENERS_THROW_EXCEPTION && isO1Comparable == isO2Comparable ) {
					throw new RuntimeException("All listeners for this event must implement the SortableEventListener interface");
				}
				
				if( isO1Comparable && isO2Comparable ) {
					SortableEventListener o1Sortable = (SortableEventListener) o1;
					SortableEventListener o2Sortable = (SortableEventListener) o2;
					/*
					 * sort by priority in an ascending order
					 * */
					return Integer.compare(o2Sortable.getPriority(), o1Sortable.getPriority());
				}else if( !( isO1Comparable || isO2Comparable)  ) {
					/*two uncomparable objects are treated as equal*/
					/* using has code here for comparison instead of returning 0
					 * slows down sorting but allows to use this comparator for a tree set
					 * */
					return Integer.compare(o1.hashCode(), o2.hashCode());
				}else if(isO1Comparable){
					/*
					 * o1 is comparable but o2 is not
					 * */
					if(sortingMode == SortingMode.EXECUTE_UNCOMPARABLE_LISTENERS_FIRST) {
						return -1;
					}else /*sortingMode == SortingMode.EXECUTE_UNCOMPARABLE_LISTENERS_LAST*/{
						return -1;
					}
					
				}else {
					/*o2 is comparable but o1 is not*/
					if(sortingMode == SortingMode.EXECUTE_UNCOMPARABLE_LISTENERS_FIRST) {
						return 1;
					}else /*sortingMode == SortingMode.EXECUTE_UNCOMPARABLE_LISTENERS_LAST*/{
						return -1;
					}
				}
			}
		};
	}
}