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

int main(int argc, char ** argv) {
  int silent_mode = 0;
  int print_all_diff = 0;
  int keep_printing = 1;
  int files_differ = 0;
  int i, f1num = 1;
  FILE *file1, *file2;
  char c1, c2;
  int line = 1, byte = 1;

  if(argv[1][0] == '-' && argv[1][1] == 's' && argv[1][2] == '\0') {
    silent_mode = 1;
    f1num++;
    if(argv[2][0] == '-' && argv[2][1] == 'l' &&
       argv[2][2] == '\0') {
      f1num++;
    }
  }
  else if(argv[1][0] == '-' && argv[1][1] == 'l' &&
	  argv[1][2] == '\0') {
    print_all_diff = 1;
    f1num++;
    if(argv[2][0] == '-' && argv[2][1] == 's' &&
       argv[2][2] == '\0') {
      f1num++;
    }
  }

  if(strcmp(argv[f1num], "-") == 0 && strcmp(argv[f1num+1], "-") == 0) {
    fprintf(stderr, "%s: Cannot accept stdin for both files\n", argv[0]);
    return 2;
  }
  else if(strcmp(argv[f1num], "-") == 0) {
    file1 = stdin;
    file2 = fopen(argv[f1num+1], "r");
  }
  else if(strcmp(argv[f1num+1], "-") == 0) {
    file1 = fopen(argv[f1num], "r");
    file2 = stdin;
  }
  else {
    file1 = fopen(argv[f1num], "r");
    file2 = fopen(argv[f1num+1], "r");
  }

  if(silent_mode) {
    c1 = fgetc(file1);
    c2 = fgetc(file2);
    for(i = 0; !(c1 == EOF || c2 == EOF); i++) {
      if(c1 != c2) {
	return 1;
      }
      c1 = fgetc(file1);
      c2 = fgetc(file2);
    }
    if(c1 != c2) {
      return 1;
    }
    else {
      return 0;
    }
  }
  else if(print_all_diff) {
    c1 = fgetc(file1);
    c2 = fgetc(file2);
    for(i = 0; !(c1 == EOF || c2 == EOF); i++) {
      if(c1 != c2) {
	printf("%d %o %o\n", byte, c1, c2);
	files_differ = 1;
      }
      c1 = fgetc(file1);
      c2 = fgetc(file2);
      line++;
      byte++;
    }
    if(c1 != c2) {
      fprintf(stderr, "%s: EOF on %s%s\n", argv[0],
	      c1 == EOF ? argv[f1num] : argv[f1num+1], "");
      return 1;
    }
    else if(files_differ) {
      return 1;
    }
    else {
      return 0;
    }
  }
  else {
    c1 = fgetc(file1);
    c2 = fgetc(file2);
    for(i = 0; !(c1 == EOF || c2 == EOF); i++) {
      if(c1 != c2 && keep_printing) {
	keep_printing = 0;
	printf("%s %s differ: char %d, line %d\n", argv[f1num], argv[f1num+1], byte, line);
	files_differ = 1;
      }
      c1 = fgetc(file1);
      c2 = fgetc(file2);
      if(c1 == '\n') line++;
      byte++;
    }
    if(c1 != c2) {
      fprintf(stderr, "%s: EOF on %s%s\n", argv[0],
	      c1 == EOF ? argv[f1num] : argv[f1num+1], "");
      return 1;
    }
    else if(files_differ) {
      return 1;
    }
    else {
      return 0;
    }
  }
}