import java.util.ArrayList;
import java.util.List;

/*
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 * and open the template in the editor.
 */

/**
 *
 * @author Mustafa
 */
public class SecondChance extends PageReplacement {
    ArrayList<PageTableEntry> validPages = new ArrayList<PageTableEntry>(); // store all the pages in memory
    ArrayList<PageTableEntry> inValidPages = new ArrayList<PageTableEntry>(); // store all the not in memory

    public SecondChance(List<PageTableEntry> pageTable, boolean[] memoryFrames) {
        super(pageTable, memoryFrames);

        // add all the valid pages
        for(PageTableEntry pte : super.pageTable) {
            if(pte.isValid()) {
                validPages.add(pte);
            }
        }
        // add all the invalid pages
        for(PageTableEntry pte : super.pageTable) {
            if(!pte.isValid()) {
                inValidPages.add(pte);
            }
        }
    }



    @Override
    public int getTargetPage(int numberNewPTE) {
        PageTableEntry topPage = super.pageTable.get(numberNewPTE);

        if(validPages.size() > 0) { // check if there is pages in memory
            topPage = validPages.get(0); // get the top page of the memeory
            while(topPage.isReferenced()) { // loop until you find a non refrenced

                //take the top page out of memeory
                topPage = validPages.remove(0);

                //change its refrence bit
                topPage.setReferenced(false);

                // now add it to the tail
                validPages.add(topPage);

                topPage = validPages.get(0); // get the top page again for checking.
            }

            // we a got page that is not refrenced Remove it now
            topPage = validPages.remove(0);

            //now add it to the tail of virtual pages
            inValidPages.add(topPage);

            // now add the page number in virtual space to memory tail
            if(inValidPages.size() > 0) {
                validPages.add(inValidPages.remove(0)); // take page on top of virtual memory and add it to tail of memory pages
            }

        }
        return topPage.getPageFrameNumber();
    }

}