#include <errno.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define BUF_SIZE 128

typedef struct creds creds_t;

typedef struct creds {
  char str[BUF_SIZE];
  void (*welcome)(void);
} creds_t;
static creds_t *creds;

/* internal prototypes */
static void cat(const char *s1, uint32_t len1, const char *s2, uint32_t len2);

static void print(void);

static void s3cr3t(void);

/* entry point */
// ./mixed02 dddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd 4294967295 d 10
int main(int argc, char **argv) {
  if (argc < 5) {
    printf("usage: %s <string1> <length1> <string2> <length2>\n", argv[0]);
    return -1;
  }

  char *endptr;
  errno = 0;
  uint32_t len1 = (uint32_t)strtoul(argv[2], &endptr, 10);
  if (errno || *endptr) {
    fprintf(stderr, "Conversion error, non-convertible part: %s\n", endptr);
    exit(EXIT_FAILURE);
  }
  errno = 0;
  uint32_t len2 = (uint32_t)strtoul(argv[4], &endptr, 10);
  if (errno || *endptr) {
    fprintf(stderr, "Conversion error, non-convertible part: %s\n", endptr);
    exit(EXIT_FAILURE);
  }

  creds = (creds_t *)calloc(1, sizeof(creds_t));
  if (!creds) {
    perror("calloc");
    return -1;
  }
  creds->welcome = print;
  cat(argv[1], len1, argv[3], len2);
  creds->welcome();
  free(creds);
  return 0;
}

/* internal function definitions */
static void cat(const char *s1, uint32_t len1, const char *s2, uint32_t len2) {
  if ((len1 + len2) >= BUF_SIZE) {
    fprintf(stderr, "Input strings exceed buffer size\n");
    exit(EXIT_FAILURE);
  }
  snprintf(creds->str, len1 + 1, "%s", s1);
  // TODO: creds->str+len1+1
  snprintf(creds->str + len1, len2 + 1, "%s", s2);
}

static void print(void) { printf("%s!\n", creds->str); }

static void s3cr3t(void) { printf("You've gathered secret material!\n"); }