#define _POSIX_C_SOURCE 200809L
#define BUFFER_SIZE 1024
#define STRING_BUFFER_SIZE 32

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

// Helps to match a string (excludes blanks and special characters)
static int is_char(char c)
{
    return c != '\0' && !isblank(c) && c != ':' && c != '=' && c != '#';
}

// Returns the next word from buf until buf_len,
// and the numbers of read characters in *read_chars
// WARNING allocates the result on the heap
static char *readWord(char *buf, size_t buf_len, size_t *read_chars)
{
    size_t i = 0;
    size_t str_buf_size = STRING_BUFFER_SIZE;
    char *str_buf = malloc(sizeof(char) * str_buf_size);
    while (i < buf_len && is_char(buf[i]))
    {
        // Reallocate more space if necessary
        if (i >= str_buf_size - 1)
        {
            str_buf_size += STRING_BUFFER_SIZE;
            str_buf = realloc(str_buf, str_buf_size);
            if (str_buf == NULL)
                errx(2, "Could not realloc");
        }

        str_buf[i] = buf[i];
        i++;
    }

    str_buf[i] = '\0';
    *read_chars = i;

    return str_buf;
}

int skip_blanks(char *buf, size_t buf_len)
{
    size_t i = 0;
    while (i < buf_len && isblank(buf[i]))
        i++;
    return i;
}

int main(int argc, char **argv)
{
    if (argc < 2)
        errx(2, "Not enough arguments");
    if (argc > 2)
        errx(2, "Not enough arguments");

    // Open file
    FILE *stream = fopen(argv[1], "r");
    if (stream == 0)
        errx(2, "Could not open file");

    // Allocate buffer
    size_t buf_size = BUFFER_SIZE;
    char *buf = malloc(sizeof(char) * buf_size);
    if (buf == NULL)
        errx(2, "Could not allocate more memory");

    // Read
    ssize_t nread;
    while ((nread = getline(&buf, &buf_size, stream)) != -1)
    {
        size_t u_nread = nread;
        size_t i = 0;
        // Skip blanks
        i += skip_blanks(buf + i, nread - i);

        // Read target name
        size_t skipped_chars = 0;
        char *rule_name = readWord(buf + i, nread - i, &skipped_chars);
        if (skipped_chars != 0)
            printf("%s:", rule_name);
        i += skipped_chars;

        // Skip until ':'
        i += skip_blanks(buf + i, nread - i);
        if (buf[i] != ':')
            errx(2, "Unexpected character '%c' after rule declaration '%s'",
                 buf[i], rule_name);
        i++;

        // Read deps
        while (i < u_nread)
        {
            // Skip blanks
            i += skip_blanks(buf + i, nread - i);

            // Read word
            size_t skipped_chars = 0;
            char *dep_name = readWord(buf + i, nread - i, &skipped_chars);
            if (skipped_chars != 0)
                printf(" %s", dep_name);
            free(dep_name);
            i += skipped_chars;

            if (!is_char(buf[i]) && !isblank(buf[i]) && buf[i] != '\0')
                errx(2, "Unexpected character '%c'", buf[i]);
        }

        i++;
        free(rule_name);
    }

    free(buf);
    fclose(stream);
    return 0;
}