/* Program to illustrate string processing using a global file reference - more modular*/
#include <iostream>
#include <fstream>
#include <string>
using namespace std;

//function prototypes
void change(string &line);
bool getchanges(ifstream &changesfile, string &oldstr, string &newstr);
void change_one_line(string &line, string oldstr, string newstr);

//global declarations
ifstream changesfile;

int main()
{
    string line;

    // open input file
    ifstream infile("c:\\bc\\CISC1110\\pgms\\chapter8\\myinput.txt"); //comment-out for debugging
    //ifstream infile("con");                     //un-comment for debugging

    // open output file
    //ofstream outfile("c:\\bc\\CISC1110\\pgms\\chapter8\\myoutput.txt"); //comment-out for debugging
    ofstream outfile("con");                    //un-comment for debugging

    while (getline(infile, line))
    {
        outfile << line << endl;                //output old line
        change(line);                           //make changes
        outfile << line << endl;                //output revised line
    }

    infile.close();                             //close input file
    outfile.close();                            //close output file

//  system("pause");
    return 0;
}

/* Function change()
 * Input:
 *  line - a reference to the string to be processed
 * Globals:
 *  changesfile - global reference to the file that contains the replacement pairs
 * Process:
 *  repeatedly call getchanges() to get a new set of
 *  replacement strings (oldstr & newstr), until there
 *  are no more sets of changes.
 * Output:
 *  line - the processed string
 */
void change(string &line)
{
    string oldstr, newstr;

    // open changes file
    changesfile.open("c:\\bc\\CISC1110\\pgms\\chapter8\\mychanges.txt"); //comment-out for debugging
    //changesfile.open("con");                    //un-comment for debugging
    changesfile.clear();                        //reset EOF flag

    while (getchanges(changesfile, oldstr, newstr))
    {
        change_one_line(line, oldstr, newstr);
    }
    changesfile.close();
    return;
}

/* Function getchanges():
 * Input:
 *  changesfile - a reference to the file that contains the replacement pairs
 *  oldstr - a reference to the old string to search for
 *  newstr - a reference to the new replacement string
 * Process:
 *  reads in a pair of strings (oldstr & newstr) if they exist
 * Output:
 *  oldstr - the old string to search for
 *  newstr - the new replacement string
 *  if they exist, returns true; else, returns false
 */
bool getchanges(ifstream &changesfile, string &oldstr, string &newstr)
{
    if (getline(changesfile, oldstr))           //read oldstr if it exists
    {
        getline(changesfile, newstr);           //read newstr
        return true;
    }
    return false;                               //reached end-of-file
}

/* Function change_one_line():
 * Input:
 *  line - a reference to the string to be processed
 *  oldstr - the old string to search for
 *  newstr - the new replacement string
 * Process:
 *  searches line for position of oldstr
 *  if oldstr exists, replace oldstr with newstr
 *  returns when all replacements have been made
 * Output:
 *  line - the processed string
 */
void change_one_line(string &line, string oldstr, string newstr)
{
    string::size_type pos;

    pos = line.find(oldstr, 0);                         //search for oldstr
    while (pos != line.npos)                            //if oldstr found
    {
        line.replace(pos, oldstr.length(), newstr);     //replace oldstr with newstr
        pos = line.find(oldstr, pos+newstr.length());   //search for oldstr
    }
    return;
}