package org.simantics.scl.runtime.chr;

import java.util.Arrays;

public class FactActivationQueue {
    public static final boolean TRACE = false;
    
    private final PriorityContainer[] containers;
    private PriorityContainer[] activeContainers = new PriorityContainer[8];
    private int activeContainerCount; 

    public FactActivationQueue(int priorityCount) {
        if(TRACE)
            System.out.println("priorityCount = " + priorityCount);
        containers = new PriorityContainer[priorityCount];
        for(int i=0;i<priorityCount;++i)
            containers[i] = new PriorityContainer(i); 
    }
    
    /**
     * Adds a new fact with a given priority
     */
    public void add(int priority, Fact item) {
        if(TRACE)
            System.out.println("FactActivationQueue.add " + priority + "@" + item);
        PriorityContainer container = containers[priority];
        if(container.size == 0)
            activateContainer(container);
        container.push(item);
    }
    
    private void activateContainer(PriorityContainer container) {
        if(TRACE)
            System.out.println("FactActivationQueue.activate priority " + container.priority);
        if(activeContainers.length == activeContainerCount)
            activeContainers = Arrays.copyOf(activeContainers, activeContainerCount*2);
        adjustUpwards(activeContainerCount, container);
        ++activeContainerCount;
    }

    private void deactivateContainer() {
        --activeContainerCount;
        adjustDownwards(0, activeContainers[activeContainerCount]);
        activeContainers[activeContainerCount] = null;
    }

    private void adjustDownwards(int pos, PriorityContainer item) {
        int priority = item.priority;
        while(true) {
            int npos = 2*pos+1;
            if(npos+1 >= activeContainerCount) {
                if(npos >= activeContainerCount)
                    break;
                PriorityContainer item1 = activeContainers[npos];
                if(priority > item1.priority) {
                    activeContainers[pos] = item1;
                    activeContainers[npos] = item;
                    return;
                }
                else
                    break;
            }
            PriorityContainer item1 = activeContainers[npos];
            PriorityContainer item2 = activeContainers[npos+1];
            if(priority < item1.priority) {
                if(priority < item2.priority)
                    break;
            }
            else {
                if(item1.priority < item2.priority) {
                    activeContainers[pos] = item1;
                    pos = npos;
                    continue;
                }
            }
            activeContainers[pos] = item2;
            pos = npos+1;
        }
        activeContainers[pos] = item;
    }

    private void adjustUpwards(int pos, PriorityContainer item) {
        int priority = item.priority;
        while(pos > 0) {
            int npos = (pos-1)/2;
            PriorityContainer item1 = activeContainers[npos];
            if(item1.priority > priority) {
                activeContainers[pos] = item1;
                pos = npos;
            }
            else
                break;
        }
        activeContainers[pos] = item;
    }
    
    /**
     * Activates all facts with priority less than the current priority
     */
    public void activate(Object context, int currentPriority) {
        if(TRACE)
            System.out.println("FactActivationQueue.activate " + currentPriority);
        while(activeContainerCount > 0) {
            PriorityContainer topContainer = activeContainers[0];
            int priority = topContainer.priority;
            if(priority >= currentPriority)
                return;
            
            Fact fact = topContainer.pop();
            if(topContainer.size == 0)
                deactivateContainer();
            
            int newPriority = fact.activate(context, priority);
            if(TRACE)
                System.out.println("    [" + currentPriority + "] " + fact + " oldPriority=" + priority + ", newPriority=" + newPriority);
            if(newPriority >= 0)
                add(newPriority, fact);
        }
    }
}