#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>

#define CHECK_FERROR(f) { if (ferror(f)) {fprintf(stderr, "IO Error"); exit(1);} }

#include "mmap.h"

MMap* mmap_init(){
    MMap *mmap = malloc(sizeof(MMap));
    mmap->size = 4096*100;
    mmap->memory = malloc(mmap->size);
    mmap->count = 0;
    mmap->support = malloc(sizeof(PageInfo));
    mmap->support->data = malloc(4096);
    mmap->free_list = createLinkedList();
    // insert 100 pages in the free list
    for (int i=0; i < 100; i++) {
        PageInfo *page = malloc(sizeof(PageInfo));
        page->data = mmap->memory + i*4096;
        page->key = i;
        insertFirst(mmap->free_list, i, page);
    }
    mmap->alloc_list = createLinkedList();
    mmap->swap = fopen("/tmp/myswap", "wb+");
    int tmp = -1;
    for (int i=0; i < 100; i++) {
        fwrite(&tmp, sizeof(int), 1, mmap->swap);
    }
    char tmp2 = '\0';
    for (int i=0; i < 100*4096; i++) {
            fwrite(&tmp2, 1, 1, mmap->swap);
    }
    return mmap;
}

void mmap_clean(MMap *mmap) {
    free(mmap->memory);
    fclose(mmap->swap);
    free(mmap);
    remove("/tmp/myswap");
}

PageInfo* page_alloc(MMap *mmap) {
    PageInfo *page = NULL;
    page = page_free(mmap);
    if (page) {
        insertFirst(mmap->alloc_list, page->key, page);
        mmap->count++;
    }
    return page;
}

PageInfo* page_free(MMap *mmap) {
    PageInfo *page = NULL;
    node *node = deleteFirst(mmap->free_list);
    if (node) {
        page = node->data;
    }
    return page;
}

int check_page_free_list(MMap *mmap) {
    return length(mmap->free_list);
}

int check_page_alloc(MMap *mmap) {
    return length(mmap->alloc_list);
}

int move_to_swap(MMap *mmap, PageInfo *page) {
    int key = -1;
    fseek(mmap->swap, 0, SEEK_SET);
    CHECK_FERROR(mmap->swap);

    for (int i=0; i < 100; i++) {
        fread(&key, sizeof(int), 1, mmap->swap);
        CHECK_FERROR(mmap->swap);

        if (key == -1) {
            fseek(mmap->swap, i*sizeof(int), SEEK_SET);
            CHECK_FERROR(mmap->swap);

            fwrite(&page->key, sizeof(int), 1, mmap->swap);
            CHECK_FERROR(mmap->swap);

            fseek(mmap->swap, 100*sizeof(int) + i*4096, SEEK_SET);
            CHECK_FERROR(mmap->swap);

            fwrite(page->data, 4096, 1, mmap->swap);
            CHECK_FERROR(mmap->swap);

            return 0;
        }
    }
    return -1;
}

PageInfo* read_from_swap(MMap* mmap, PageInfo *page) {
    int key = -1;
    fseek(mmap->swap, 0, SEEK_SET);
    CHECK_FERROR(mmap->swap);

    for (int i=0; i < 100; i++) {
        (void)fread(&key, sizeof(int), 1, mmap->swap);
        CHECK_FERROR(mmap->swap);

        if (key != page->key)
            continue;

        fseek(mmap->swap, 100*sizeof(int) + i*4096, SEEK_SET);
        CHECK_FERROR(mmap->swap);

        fread(page->data, 4096, 1, mmap->swap);
        CHECK_FERROR(mmap->swap);

        fseek(mmap->swap, i*sizeof(int), SEEK_SET);
        CHECK_FERROR(mmap->swap);

        int tmp = -1;
        fwrite(&tmp, sizeof(int), 1, mmap->swap);
        CHECK_FERROR(mmap->swap);

        return page;
    }
    return NULL;
}

PageInfo* page_lookup(MMap* mmap, int key) {
    node* data = find(mmap->alloc_list, key);
    if (data) {
        return data->data;
    }

    mmap->support->key = key;
    PageInfo* page = read_from_swap(mmap, mmap->support);
    if (page) { // Move one elem from mem to swap
        PageInfo* swapped_page = deleteFirst(mmap->alloc_list)->data;
        move_to_swap(mmap, swapped_page);

        memcpy(swapped_page->data, mmap->support->data, 4096);
        swapped_page->key = key;
        insertFirst(mmap->alloc_list, key, swapped_page);
        return page;
    }
    return NULL;
}

void page_remove(MMap *mmap, int key) {
    PageInfo* page = page_lookup(mmap, key);
    if (!page)
        return;

    deleteElement(mmap->alloc_list, key);
    mmap->count--;
}

PageInfo *page_create(MMap *mmap, bool *moved_to_swap) {
    if (mmap->count >= 200)
        return NULL;

    PageInfo* page = page_alloc(mmap);
    *moved_to_swap = false;

    if (page)
        return page;

    // Another page has been moved to swap
    *moved_to_swap = true;
    
    page = deleteFirst(mmap->alloc_list)->data;
    move_to_swap(mmap, page);
    // Reuse swapped page for the new one
    page->key = mmap->count;
    mmap->count++;
    insertFirst(mmap->alloc_list, page->key, page);

    return page;
}