#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/sysmacros.h>
#include <time.h>
#include <unistd.h>

#define FALSE 0
#define FILE_BUFF 4096
#define TRUE  1

struct NODE {
    char filename[FILE_BUFF];
    int inode;
    long atime;
    struct NODE *next;
};

int makeList(struct NODE **head) {
    /*
     * makeList builds a linked list of nodes representing the filenames
     * given on stdin and their access time.
     */
    char filename[FILE_BUFF];
    int inList = FALSE;
    struct NODE *currentNode = NULL;
    struct NODE *newNode = NULL;
    struct stat statData;

    while (scanf(" %s", filename) == 1) {

        if (stat(filename, &statData) == 0 && S_ISREG(statData.st_mode)) {
            inList = FALSE;

            for (currentNode = *head; currentNode != NULL; currentNode = currentNode->next) {

                if (currentNode->inode == statData.st_ino) {
                    inList = TRUE;
                }

            }

            if (!inList) {
                newNode = (struct NODE *) malloc(sizeof(struct NODE));
                newNode->inode = statData.st_ino;
                strcpy(newNode->filename, filename);
                newNode->atime = (time(NULL) - statData.st_atime) / 86400;
                newNode->next = *head;
                *head = newNode;
            }

        }

    }

    return 0;
}

int main(int argc, char *argv[]) {
    /*
     * accessed takes in filenames from stdin and one command line argument,
     * "num". It then builds a linked list of the unique, regular files and
     * prints out those files not accessed in "num" days (if num is positive)
     * or prints out those files accesssed within "num" days (if num is
     * negative).
     */
    int accessedNum = 0;
    struct NODE *currentNode = NULL;
    struct NODE *list = NULL;

    // Go through args
    if (argc != 2) {
        fprintf(stderr, "accessed: usage: ./accessed [num days]\n");
        exit(1);
    }

    accessedNum = strtol(argv[1], NULL, 10);

    if (errno == EINVAL) {
        fprintf(stderr, "accessed: error: num must be integer type.\n");
        exit(1);
    }
    else if (errno == ERANGE) {
        fprintf(stderr, "accessed: error: num must be of integer size.\n");
        exit(1);
    }
    else if (accessedNum == 0) {
        fprintf(stderr, "accessed: error: num must be nonzero integer.\n");
        exit(1);
    }

    if (makeList(&list) != 0) {
        fprintf(stderr, "accessed: error: could not build linked list.\n");
        exit(1);
    }

    // print out filenames that match requested access time
    for (currentNode = list; currentNode != NULL; currentNode = currentNode->next) {

        if (accessedNum > 0 && currentNode->atime > accessedNum) { // not within num days
            printf("%s\n", currentNode->filename);
        }

        if (accessedNum < 0 && currentNode->atime <= (accessedNum * -1)) { // within num days
            printf("%s\n", currentNode->filename);
        }

    }

    // free list
    while (currentNode != NULL) {
        currentNode = list;
        list = list->next;
        free(currentNode);
    }

    exit(0);
}