#include <string.h>
#include <stdio.h>

char line[100000];

int lineno;

/* 0 = other, 1 = if, 2 = else, 3 = endif */
int iftype;

/* 0, 1, 2, ... - preprocessor indentation
   -1 other line
   -2 blank line
 */
int linetype()
{
  int i = 0;
  int hashpos;

  if (line[0] == '\0')
    return -2;
  while (line[i] == ' ' || line[i] == '\t')
    i++;
  if (line[i] != '#')
    return -1;
  i++;
  hashpos = i;
  iftype = 0;
  while (line[i] == ' ' || line[i] == '\t')
    i++;
  if (strncmp (line + i, "if", 2) == 0
      && (line[i+2] == ' ' || line[i+2] == '\t'))
    iftype = 1;
  else if (strncmp (line + i, "ifdef", 5) == 0
           && (line[i+5] == ' ' || line[i+5] == '\t'))
    iftype = 1;
  else if (strncmp (line + i, "ifndef", 6) == 0
           && (line[i+6] == ' ' || line[i+6] == '\t'))
    iftype = 1;
  else if (strncmp (line + i, "else", 4) == 0
           && (line[i+4] == ' ' || line[i+4] == '\t' || line[i+4] == '\0'))
    iftype = 2;
  else if (strncmp (line + i, "elif", 4) == 0
           && (line[i+4] == ' ' || line[i+4] == '\t'))
    iftype = 2;
  else if (strncmp (line + i, "endif", 5) == 0
           && (line[i+5] == ' ' || line[i+5] == '\t' || line[i+5] == '\0'))
    iftype = 3;
  return i - hashpos;
}

int main (int argc, char *argv[])
{
  const char *filename = argv[1];
  int expected_indentation = -1000;
  int block_lineno = 1;
  int block_start_indentation = 0;
  int block_end_expected_indentation = 0;
  int block_directive_count = 0;
  int block_if_directive_count = 0;
  int block_endif_directive_count = 0;
  int block_not_cppi_like_indented = 0;
  int exitcode = 0;

  if (freopen (filename, "r", stdin) == NULL)
    {
      fprintf (stderr, "file not found: %s\n", filename);
      return 1;
    }

  while (!feof (stdin))
    {
      lineno++;
      if (gets (line) == NULL)
        break;
      int type = linetype();
      if (type == -2)
        {
          /* end of block */
          if (block_directive_count > 1
              && (block_if_directive_count > 0 && block_endif_directive_count > 0)
              && block_not_cppi_like_indented
              && (block_end_expected_indentation != block_start_indentation
                  || expected_indentation != block_start_indentation))
            {
              fprintf (stderr, "misindented block at %s:%d\n", filename, block_lineno);
              exitcode = 1;
            }
          expected_indentation = -1000;
          block_lineno = lineno + 1;
          block_start_indentation = 0;
          block_end_expected_indentation = 0;
          block_directive_count = 0;
          block_if_directive_count = 0;
          block_endif_directive_count = 0;
          block_not_cppi_like_indented = 0;
        }
      else if (type >= 0)
        {
          if (block_directive_count == 0)
            {
              block_start_indentation = type;
              block_end_expected_indentation = type;
              expected_indentation = type;
            }
          else
            {
              if (iftype == 2 || iftype == 3)
                expected_indentation--;
              if (type != expected_indentation)
                block_not_cppi_like_indented = 1;
              expected_indentation = type;
            }
          if (iftype == 2 || iftype == 3)
            block_end_expected_indentation--;
          if (iftype == 1 || iftype == 2)
            {
              expected_indentation++;
              block_end_expected_indentation++;
            }
          if (iftype > 0)
            block_directive_count++;
          if (iftype == 1)
            block_if_directive_count++;
          if (iftype == 3)
            block_endif_directive_count++;
        }
    }

  /* end of file */
  if (block_directive_count > 1
      && (block_if_directive_count > 0 && block_endif_directive_count > 0)
      && block_not_cppi_like_indented
      && (block_end_expected_indentation != block_start_indentation
          || expected_indentation != block_start_indentation))
    {
      fprintf (stderr, "misindented block at %s:%d\n", filename, block_lineno);
      exitcode = 1;
    }

  return exitcode;
}