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

typedef struct _t_line {
    struct _t_line *next;
    size_t offset;
    size_t length;
} t_line;

static t_line *list = NULL;

void read_to_list(char *fname, t_line **list)
{
    if (!list)
        return;

    FILE *f = fopen(fname, "rb");
    if (!f)
        return;

    t_line *cur = *list;
    size_t offset = 0;
    while (!feof(f))
    {
        while (fgetc(f) != '\n')
            if (feof(f))
                break;
        t_line *new_item = malloc(sizeof(t_line));
        if (!new_item)
            return;
        new_item->next = NULL;
        new_item->offset = offset;
        new_item->length = ftell(f) - offset;
        //printf("o: %d l: %d\n", new_item->offset, new_item->length);

        offset = ftell(f);

        if (!cur) {
            *list = new_item;
            cur = new_item;
        }   else {
            cur->next = new_item;
            cur = new_item;
        }
    }

    fclose(f);
}

void print_list(t_line *list)
{
    if (!list)
        return;
    do {
        printf("o: %d l: %d\n", list->offset, list->length);
        list = list->next;
    } while (list);
    return;
}

char *get_line_at(char *fname, t_line *list, size_t idx)
{
    if (!list)
        return NULL;

    for (size_t i = 0; i < idx; i++) {
        list = list->next;
        if (!list)
            return NULL;
    }
    //printf("o: %d l: %d\n", list->offset, list->length);

    FILE *f = fopen(fname, "rb");
    if (!f)
        return NULL;
    fseek(f, list->offset, SEEK_SET);
    char *line = calloc(list->length + 1, 1);
    if (!line) {
        fclose(f);
        return NULL;
    }
    fread(line, sizeof(char), list->length, f);
    fclose(f);
    return line;
}

int main (int argc, char **argv)
{
    read_to_list(__FILE__, &list);
    print_list(list);
    puts(get_line_at(__FILE__, list, 3));
    return 0;
}