#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <stdbool.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <limits.h>

#define PADDR_MASK ((1UL << 54) - 1)
#define INRAM_MASK ((1UL << 63))
#define PAGE_SIZE  getpagesize()

int main(int argc, char**argv){
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <PID>\n", argv[0]);
        return -1;
    }
    pid_t pid = atol(argv[1]);
    if (pid == 0) {
        fprintf(stderr, "Provided PID \"%s\" invalid\n", argv[1]);
        return -1;
    }

    char maps_file[PATH_MAX];
    char pagemap_file[PATH_MAX]; 
    snprintf(maps_file, sizeof(maps_file), "/proc/%d/maps", pid);
    snprintf(pagemap_file, sizeof(maps_file), "/proc/%d/pagemap", pid);

    FILE* maps_fp = fopen(maps_file, "r");
    if (maps_fp == NULL) {
        fprintf(stderr, "Unable to open \"%s\"\n", maps_file);
        return -1;
    }
    FILE* pagemap_fp = fopen(pagemap_file, "r");
    if (pagemap_fp == NULL) {
        fprintf(stderr, "Unable to open \"%s\"\n", pagemap_file);
        return -1;
    }

    while(1) {
        char buf[1024];
        if (fgets(buf, sizeof(buf), maps_fp) == NULL){
            // End of file
            break;
        }

        printf("\n%s", buf);

        unsigned long base;
        unsigned long limit;
        if (sscanf(buf, "%lx-%lx", &base, &limit) != 2) {
            fprintf(stderr, "Failed to parse line in maps file\n");
        } else {
            printf("%18s | %18s | %s\n", "Virtual", "Physical", "Page table entry");
            printf("------------------------------------------------------------\n");
            for (; base < limit; base += PAGE_SIZE) {
                // Read the page table entry
                unsigned long page_number = base / PAGE_SIZE;
                uint64_t pte = 0;
                int err = fseek(pagemap_fp, page_number * sizeof(pte), SEEK_SET);
                if (err == -1) {
                    fprintf(stderr, "Failed to seek to page number %lu in %s: %s\n", page_number, pagemap_file, strerror(errno));
                    continue;
                }
                size_t entries_read = fread(&pte, sizeof(pte), 1, pagemap_fp);
                if (entries_read != 1) {
                    fprintf(stderr, "Failed to read page number %lu in %s: %s\n", page_number, pagemap_file, strerror(errno));
                    continue;
                }
    
                // Decode and report mappings
                printf("0x%016lx | ", base);
                bool in_ram = !!(pte & INRAM_MASK);
                if (in_ram) {
                    uint64_t paddr = (pte & PADDR_MASK) * PAGE_SIZE;
                    if (paddr == 0) {
                        printf("%18s | ", "NULL");
                    } else {
                        printf("0x%016lx | ", paddr);
                    }
                } else {
                    printf("%18s | ", "Not in RAM");
                }
                printf("0x%016lx\n", pte);
            }
        }
    }

    return 0;
}