#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>

#include "kernel.h"
#include "process.h"

#include "config.h"

extern struct RunQ *runq;

extern struct PhysPage *first_free_page;
extern struct PhysPage *first_busy_page;

extern size_t system_time;


struct RunQ *
RunQ(size_t max_procs)
{
	struct RunQ *runq = malloc(sizeof(struct RunQ));
	runq->current_proc = NULL;
	runq->max_procs = max_procs;
	runq->proc_amount = 0;
	runq->next_proc_id = 1;

	return runq;
}

void
RUNQ_add_process(size_t max_page_accesses,
		size_t total_pages_owned)
{
	if (runq->proc_amount >= runq->max_procs)
		return;

	struct Process *new_p = Process(runq->next_proc_id, max_page_accesses, total_pages_owned);

	if (!runq->current_proc) {
		runq->current_proc = new_p;
		new_p->next = new_p;
		new_p->prev = new_p;
	} else {
		new_p->next = runq->current_proc;
		new_p->prev = runq->current_proc->prev;
		new_p->next->prev = new_p;
		new_p->prev->next = new_p;
		runq->current_proc = new_p;
	}

	runq->proc_amount++;
	runq->next_proc_id++;
}


void
KERNEL_page_fault(struct PageTableEntry *pt, size_t page_no)
{
	printf("[kernel:page_fault] Handling %d started\n", page_no);

	if (first_free_page) {
		printf("[kernel:page_fault] Found free page #%d, using it\n", first_free_page->ppn);
		pt[page_no].ppn = first_free_page->ppn;
		pt[page_no].p = 1;

		first_free_page->busy_flag = 1;
		first_free_page->pt = pt;
		first_free_page->pt_index = page_no;

		// ---- free list -> busy list ----
		struct PhysPage *this_page = first_free_page;

		if (first_free_page->next != first_free_page) {
			// reconnect free list items together
			first_free_page->prev->next = first_free_page->next;
			first_free_page->next->prev = first_free_page->prev;
			first_free_page = first_free_page->next;
		} else {
			// clear list if it only had this page
			first_free_page = NULL;
		}

		if (!first_busy_page) {
			// initialize the busy list with this page
			first_busy_page = this_page;
		} else {
			// insert this page at the end of the list
			this_page->next = first_busy_page;
			this_page->prev = first_busy_page->prev;
			this_page->prev->next = this_page;
			this_page->next->prev = this_page;
		}
	} else {
		printf("[kernel:page_fault] No free pages available, trying to swap...\n");

		#if PAGE_REPLACEMENT_ALGORITHM == 1
		printf("[kernel:page_fault:random] Selected physical page #%d for replacement\n", first_busy_page->ppn);

		// clear presence 'bit' from old PTE
		first_busy_page->pt[first_busy_page->pt_index].p = 0;

		// update physical page data
		first_busy_page->pt = pt;
		first_busy_page->pt_index = page_no;

		// update PTE data
		pt[page_no].p = 1;
		pt[page_no].ppn = first_busy_page->ppn;

		// move hand to next physical page
		first_busy_page = first_busy_page->next;

		printf("[kernel:page_fault:random] Auto-advanced the list of busy pages to ppn %d\n", first_busy_page->ppn);
		#elif PAGE_REPLACEMENT_ALGORITHM == 2

		// first pass (no reference flag + out of time window)
		for (size_t i = 0; i < PHYSICAL_PAGE_AMOUNT; i++) {
			if (first_busy_page->pt[first_busy_page->pt_index].r) {
				printf("[kernel:page_fault:wsclock] ppn %d: r = 1, time %d -> %d\n",
						first_busy_page->ppn, first_busy_page->last_accessed, system_time);
				first_busy_page->last_accessed = system_time;
				first_busy_page->pt[first_busy_page->pt_index].r = 0;

				first_busy_page = first_busy_page->next;
			} else if ((system_time - first_busy_page->last_accessed) > WSCLOCK_TIME_WINDOW) {
				printf("[kernel:page_fault:wsclock] ppn %d: r = 0, time_window = %d (> WSCLOCK_TIME_WINDOW), using it\n",
						first_busy_page->ppn, system_time - first_busy_page->last_accessed);
				first_busy_page->pt[first_busy_page->pt_index].p = 0;
				first_busy_page->pt = pt;
				first_busy_page->pt_index = page_no;
				pt[page_no].p = 1;
				pt[page_no].ppn = first_busy_page->ppn;

				first_busy_page = first_busy_page->next;

				goto page_replacement_resolved;
			} else {
				printf("[kernel:page_fault:wsclock] ppn %d: r = 0, time_window = %d (<= WSCLOCK_TIME_WINDOW), still active\n",
						first_busy_page->ppn, system_time - first_busy_page->last_accessed);

				first_busy_page = first_busy_page->next;
			}
		}

		// fallback to random
		printf("[kernel:page_fault:wsclock] Failed to find non-active page, randomly selecting ppn %d\n", first_busy_page->ppn);

		// clear presence 'bit' from old PTE
		first_busy_page->pt[first_busy_page->pt_index].p = 0;

		// update physical page data
		first_busy_page->pt = pt;
		first_busy_page->pt_index = page_no;

		// update PTE data
		pt[page_no].p = 1;
		pt[page_no].ppn = first_busy_page->ppn;

		// move hand to next physical page
		first_busy_page = first_busy_page->next;

		printf("[kernel:page_fault:wsclock] Auto-advanced the list of busy pages to ppn %d\n", first_busy_page->ppn);

page_replacement_resolved:
		#endif
	}
}

void KERNEL_update_job(size_t page_amount)
{
	if (first_busy_page == NULL) {
		printf("[kernel:update_job] No pages to update\n");
		return;
	}

	struct PhysPage *starting_page = first_busy_page;

	for (size_t i = 0; i < page_amount; i++) {
		if (first_busy_page->pt[first_busy_page->pt_index].r) {
			printf("[kernel:update_job] ppn %d updated time %d -> %d\n", first_busy_page->ppn, first_busy_page->last_accessed, system_time);
			first_busy_page->pt[first_busy_page->pt_index].r = 0;
			first_busy_page->last_accessed = system_time;
		} else {
			printf("[kernel:update_job] ppn %d is up-to-date (time = %d)\n", first_busy_page->ppn, first_busy_page->last_accessed);
		}

		first_busy_page = first_busy_page->next;

		if (first_busy_page == starting_page) {
			printf("[kernel:update_job] Looped around the busy page list, exiting after %d iterations\n", i);
			break;
		}
	}
}