/* Matt Mahoney, mmahoney@cs.fit.edu

compare.cpp is a program to compare two text files.  To run, specify the
two file names on the command line:

  compare file1 file2

The possible outcomes are:

  Usage: compare file1 file2                (If there are not 2 arguments)

  file1 not found                           (Whether or not file2 exists)

  file2 not found                           (If file1 exists)

  file1 and file2 are identical             (Files match exactly)

  file1 and file2 differ on line N          (Only the first differing line
  file1: contents of line N                  is shown.  N = 1, 2, 3...)
  file2: contents of line N

  file1 continues past end of file2         (If the files are identical up
                                             to the end of the shorter one,
  file2 continues past end of file1          but one file continues on)

For example:

    file1:       file2:        file3:
    this is      this          this
    a test       is a test

  compare
  Usage: compare file1 file2

  compare file1 file2
  file1 and file2 differ on line 1
  file1: this is
  file2: this

  compare file2 file3
  file2 continues past end of file3

  compare file1 file1
  file1 and file1 are identical

  compare foo bar
  foo not found

*/

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main(int argc, char** argv) {

  // Test for 2 arguments: compare file1 file2
  if (argc!=3) {
    cout << "Usage: compare file1 file2\n";
    return 1;
  }

  // Open, test file1
  ifstream f1(argv[1]);
  if (!f1) {
    cout << argv[1] << " not found\n";
    return 1;
  }

  // Open, test file2
  ifstream f2(argv[2]);
  if (!f2) {
    cout << argv[2] << " not found\n";
    return 1;
  }

  // Compare line by line until a mismatch is found or until either file ends
  string s1, s2;  // Lines of file1 and file2
  int lines=0;  // Count
  while (true) {
    getline(f1, s1);
    getline(f2, s2);
    if (!f1 || !f2)
      break;
    ++lines;
    if (s1 != s2) {
      cout << argv[1] << " and " << argv[2] << " differ on line " << lines
           << "\n" << argv[1] << ": " << s1 << "\n"
           << argv[2] << ": " << s2 << "\n";
      return 0;
    }
  }

  // Test for different lengths
  if (f1)
    cout << argv[1] << " continues past end of " << argv[2] << "\n";
  else if (f2)
    cout << argv[2] << " continues past end of " << argv[1] << "\n";
  else
    cout << argv[1] << " and " << argv[2] << " are identical\n";
  return 0;
}