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

// Returns pointer to a line read from fp (excluding line-ending), returns NULL
// on error or if EOF is reached.
#define INITIAL_SIZE 1
#define INCREMENT 1 
static char *read_line(FILE *fp)
{
    int c, bufsize = INITIAL_SIZE, len = 0;

    char *buffer = (char *) malloc(sizeof(char) * INITIAL_SIZE);
    
    if (buffer == NULL)
        return NULL;

    while (1) {
    
        c = fgetc(fp);

        if (c == EOF) {

            if (len == 0) {

                // Reached end of line without actually reading anything, return NULL;
                free(buffer);
                return NULL;
            }

            break;

        } else if (c == '\n') {

            break;

        } else if (c == '\r') { // Mac or Win line-ending

            // Attempt to read optional \n (Win line-ending).
            c = fgetc(fp);

            if (c != '\n')
                ungetc(c, fp);

            break;

        } else {

            if (len > bufsize-1) {
                
                // TODO: handle realloc returning NULL properly
                bufsize += INCREMENT;
                buffer = (char *) realloc(buffer, sizeof(char) * bufsize);

                if (buffer == NULL) fprintf(stderr, "oh crap\n");
            }

            buffer[len] = c;
            len++;
        }
    }

    buffer[len] = '\0';
    return buffer;
}

int main(int argc, char **argv)
{
    FILE *file;
    char *line;

    if (argc < 2) {

        printf("Add filename to read as commandline argument\n");
        return 1;
    }

    if ( (file = fopen(argv[1], "rb")) == NULL ) {

        fprintf(stderr, "Failed to open file.\n");
        return 1;
    }

    while ((line = read_line(file)) != NULL) {

        printf("line read: %s\n", line);
        free(line);
    }

    return 0;
}