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

int process_file(FILE* input, const char* input_filename);
int convert(FILE* input, const char* input_filename, FILE* output
  , const char* output_filename);

// procedure main:
int main(int argc, char* argv[]) {
  int error = EXIT_SUCCESS;
  if (argc == 1) {
    process_file(stdin, "stdin");
  } else {
    for (int index = 1; index < argc; ++index) {
      FILE* input = fopen(argv[index], "r");
      if (input) {  // input != NULL
        error = process_file(input, argv[index]);
        fclose(input);
      } else {
        fprintf(stderr, "txt2bin: error: could not open %s\n", argv[index]);
        error = EXIT_FAILURE;
      }
    }
  }
  return error;
}

size_t length_idx(const char* text) {
  size_t index = 0;
  while (text[index]) {  // != '\0'
    ++index;
  }
  return index;
}

size_t length_ptr(const char* text) {
  size_t length = 0;
  while (*text++) {  // *(text + length)
    ++length;
  }
  return length;
}

int process_file(FILE* input, const char* input_filename) {
  int error = EXIT_SUCCESS;
  // const char* output_filename = input_filename + ".bin";
  const char* extension = ".bin";
  const size_t len_output_filename = length_ptr(input_filename)
    + length_ptr(extension);
  const size_t capacity_output_filename = len_output_filename + 1;
  char output_filename[capacity_output_filename];
  sprintf(output_filename, "%s%s", input_filename, extension);
  FILE* output = fopen(output_filename, "wb");
  if (output) {
    convert(input, input_filename, output, output_filename);
    fclose(output);
  } else {
    fprintf(stderr, "txt2bin: error: could not create %s\n", output_filename);
    error = EXIT_FAILURE;
  }
  return error;
}

int convert(FILE* input, const char* input_filename, FILE* output
  , const char* output_filename) {
  int error = EXIT_SUCCESS;
  (void)input_filename;
  double value = 0.0;
  while (fscanf(input, "%lg", &value) == 1) {
    // fprintf(output, "%lg", value);
    // size_t fwrite(const void* ptr, size_t size, size_t count, FILE* stream);
    const size_t written_count = fwrite(&value, sizeof(value), 1, output);
    if (written_count < 1) {
      fprintf(stderr, "txt2bin: error: could not write %s\n", output_filename);
      error = EXIT_FAILURE;
      break;
    }
  }
  // printf("converting from %s to %s\n", input_filename, output_filename);
  return error;
}

#if 0
  for (size_t index = 0; index < length(input_filename); ++index) {
    // 1µs  10^12/10^6 = 10^6
  }

  const size_t len = length(input_filename);
  for (size_t index = 0; index < len; ++index) {
  }
#endif