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

typedef struct line {
    char* line;
    struct line *prev, *next;
} LINE;

const int LINE_MAX = 80;
char *addlines(LINE** list, unsigned int line_no);
char *pline = NULL;
LINE *list = NULL; // this will serve as the head of a list.
LINE *endList = NULL; // this points to the last element of a list.
int len=0;
int count=0; //serves as the counter for the number of lines.
char mystring[500]; //serves as the new string that will be inserted.

int main() {
    printf("Please enter any number of lines. End with a ^D/^Z:\n");

    char line[LINE_MAX];

    while(fgets(line, LINE_MAX, stdin)){
        len = strlen(line);

        count++;
        line[len-1] = '\0';
        pline = (char *)malloc(sizeof(char) * (len + 1));
        strncpy(pline, line, len);
        pline[len] = '\0';

        LINE *temp;
        // test first if your list is non empty
        if(list != NULL) {
            for(temp = list; temp->next != NULL; temp = temp->next)
            ;
            // at this point, you're at the last element
            temp->next = (LINE*)malloc(sizeof(LINE));
            temp->next->line = pline;
            temp->next->prev = temp;
            temp->next->next = NULL;
            endList = temp->next;


        }

        else {// our list is empty
        // temp at the last element of the list.
            temp = (LINE *)malloc(sizeof(LINE));
            temp->line = pline;
            temp->prev = temp->next = NULL;
            list = temp;
            endList = temp;
        }

    }

    LINE* p;
       int line_no;


        printf("\nEnter the line number where you want to insert a new line:"); //asks the user what line number he wants the string he wants to be printed.
        scanf("%d", &line_no);

    if(line_no > count) {
        printf("\nINVALID.");
    }

    else {
        printf("\nYou want to add a new line on: %d\n\n\n",line_no);
        printf("Please enter the line you want to insert:\n\n");
        fscanf(stdin, "%s", mystring);
        fgets(mystring, 500, stdin);


        addlines (list, line_no);
    }

    return 0;

}

char *addlines (LINE** list, unsigned int line_no) {
    LINE *q, *temp;

    printf("\nYour new lines\n\n");

    for(q = list; q!= NULL; q=q->next) {
        temp = (LINE *)malloc(sizeof(LINE));
            temp->line = pline;
            temp->prev = temp->next = NULL;
            list = temp;
            q->line;



        printf("%s\n", q->line);
    }
}

for(q = list; q!= NULL; q=q->next) {
        temp = (LINE *)malloc(sizeof(LINE));
            temp->line = pline;
            temp->prev = temp->next = NULL;
            list = temp;
            q->line;
}