// PageTable.cpp        Dave Reed        4/1/05

#include <iostream>
#include <vector>
#include "PageTable.h"
using namespace std;

PageTable::PageTable(int log, int phys)
// constructor
// Assumes: log is the number of pages in the page table
//          phys is the number of frames in physical memory
// Results: creates and initializes the entries in the page table
{
    numStored = 0;
    pageMap.resize(log);

    for (int i = phys-1; i >= 0; i--) {
        freeFrames.push_back(i);
    }
}

bool PageTable::isValid(int pageNum)
// Assumes: 0 <= pageNum < page table size
// Returns: true if valid bit is set for that index, else false
{
    return pageMap[pageNum].valid;
}

void PageTable::accessPage(int pageNum)
// Assumes: 0 <= pageNum < page table size
// Returns: the frame number where pageNum is stored
{
    cout << pageNum << ": page found at frame " << pageMap[pageNum].frameNumber << endl;

}

void PageTable::storePage(int pageNum)
// Assumes: 0 <= pageNum < page table size
// Results: stores pageNum in a free frame, updating the table
{
    int frameNum;
    if (freeFrames.empty()) {
        int swapPage = selectSwapPage();
        pageMap[swapPage].valid = false;
        frameNum = pageMap[swapPage].frameNumber;
        cout << pageNum << ": PAGE FAULT -- swapping page " << pageNum << " into frame " 
             << frameNum << endl << "   ";
    }
    else {
        frameNum = freeFrames.back();
        freeFrames.pop_back();
        cout << pageNum << ": PAGE FAULT -- inserting page " << pageNum << " into frame " 
             << frameNum << endl << "   ";
    }

    pageMap[pageNum].frameNumber = frameNum;
    pageMap[pageNum].timeStamp = numStored;
    pageMap[pageNum].valid = true;

    numStored++;
}

int PageTable::selectSwapPage()
// Assumes: at least one page is stored in the table
// Returns: index of the oldest page in the table
{
    int oldPage, oldTime = numStored;
    for (int i = 0; i < pageMap.size(); i++) {
        if (pageMap[i].valid && pageMap[i].timeStamp < oldTime) {
            oldTime = pageMap[i].timeStamp;
            oldPage = i;
        }
    }
    return oldPage;
}