#include "stdstuff.h"


const int GRADESIZE = 4,
          NAMESIZE = 40,
          MAXCOURSES = 60;

struct courseItem {
  int number; // of course
  char grade [GRADESIZE]; // "CUR", "ABS", "FND", "F" or one of
                          // "D-", "D", "D+", and so on
};

struct studentItem {
  int number; // of student
  char name[NAMESIZE]; // of student
  int actualCourses; // for this student
  courseItem courses[MAXCOURSES];
};


// Returns true if "grade" is one of "D-", "D", "D+", and so on.
// Returns false otherwise.
bool isPassingGrade (char grade[]) {

  static char table [][GRADESIZE] = { "D-", "D", "D+",
                                      "C-", "C", "C+",
                                      "B-", "B", "B+",
                                      "A-", "A", "A+" };

  for (int i = 0; i < 12; i++) {
    if (stricmp(grade, table[i]) == 0) return true;
  }
  return false;

}


// Returns true if "grade" is "CUR" and false otherwise
bool isCurrent (char grade[]) {

  return (stricmp (grade, "CUR") == 0);

}


// Returns true if grade is valid (one of "CUR", "ABS", "FND", "F", "D-", etc.)
// and false otherwie.
bool isValidGrade (char grade[]) {

  return ( isCurrent (grade) ||
           (stricmp (grade, "ABS") == 0) ||
           (stricmp (grade, "FND") == 0) ||
           (stricmp (grade, "F") == 0) ||
           isPassingGrade (grade) );

}


// Reads student information from a file and stores it into an array of
// "studentItem" structures.  Sets "actualStudents" to the actual number
// of students in the file.  Returns true if entirely successful and
// false otherwise.
bool readInData (studentItem database[], int MAXSTUDENTS, int &actualStudents) {

  const int FILENAMESIZE = 60;
  char filename [FILENAMESIZE];
  ifstream fin;
  int studentNumber, i;

  cout << "Enter filename for data file: ";
  cin >> setw(FILENAMESIZE) >> filename;

  fin.open (filename);
  if (fin.fail()) {
    cout << "Unable to open file <" << filename << ">.\n";
    return false;
  }

  actualStudents = 0; // none so far

  for (;;) {

    fin >> studentNumber;

    if (fin.fail()) {
      if (fin.eof()) {
        return true; // normal end of reads
      } else {
        cout << "Error in reading data file (after data for "
             << actualStudents << " students successfully read.\n";
        return false;
      }
    }

    if (actualStudents == MAXSTUDENTS) {
      cout << "Insufficient space for student data.\n";
      return false;
    }

    database[actualStudents].number = studentNumber;
    fin >> ws; // skip whitespace after number
    fin.getline (database[actualStudents].name, NAMESIZE);

    database[actualStudents].actualCourses = 0;

    while (fin.peek() == '-') {

      i = database[actualStudents].actualCourses++;

      if (i == MAXCOURSES) {
        cout << "Student has too many courses.\n";
        return false;
      }

      fin.get(); // dispose of the '-'

      fin >> database[actualStudents].courses[i].number
          >> setw(GRADESIZE)
          >> database[actualStudents].courses[i].grade;

      if (fin.fail()) {
        cout << "Error in reading data file (after data for "
             << actualStudents << " students successfully read.\n";
        return false;
      }

      fin.ignore (INT_MAX, '\n'); // discard rest of line

      if (!isValidGrade (database[actualStudents].courses[i].grade)) {
        cout << "Invalid grade (" << database[actualStudents].courses[i].grade
             << ") encountered.\n";
        return false;
      }

    }

    actualStudents++;

  }

}


// Returns true if the student is taking the course or has ever taken it.
// Returns false otherwise.  If true is returned, the student's grade in
// the course is "returned" via call by reference parameter "grade".
bool courseSearch (const studentItem &studentData, int course, char grade[]) {

  int i;

  for (i = 0; i < studentData.actualCourses; i++) {
    if (studentData.courses[i].number == course){
      strcpy (grade, studentData.courses[i].grade);
      return true;
    }
  }

  return false;

}


// Returns false if the student is taking course "course" and does
// not have a passing grade in course "requiredCourse".
// Returns true otherwise.
bool prerequisitesOK (const studentItem &studentData,
                      int course, int requiredCourse) {

  char grade[GRADESIZE];

  if (!courseSearch (studentData, course, grade) || !isCurrent (grade)) {
    // student is not currently taking the course
    return true;
  }

  if (!courseSearch (studentData, requiredCourse, grade) ||
      !isPassingGrade (grade) ) {
    // student has not passed the prerequisite course
    return false;
  }

  return true; // student has passed the required course

}


// Lists all students who are taking course "course" without having
// previously passed course "requiredCourse".
void doPrerequisiteCheck (const studentItem database[], int actualStudents,
                          int course, int requiredCourse) {

  int i, count = 0;

  cout << "\n";

  for (i = 0; i < actualStudents; i++) {
    if (!prerequisitesOK (database[i], course, requiredCourse)) {
      cout << database[i].number << " " << database[i].name << "\n";
      count++;
    }
  }

  if (count == 0) {
    cout << "No prerequisite violations found.\n";
  } else {
    cout << count << " prerequisite violations found.\n";
  }

}


int main () {

  const int MAXSTUDENTS = 500;
  studentItem database[MAXSTUDENTS];
  int actualStudents, course, requiredCourse;

  if (!readInData (database, MAXSTUDENTS, actualStudents)) {
    cout << "Unable to read in data.\n";
    pause (); 
    return 0;
  }

  for (;;) {

    cout << "\nEnter numbers for course and required course (0 0 to stop): ";
    cin >> course >> requiredCourse;

    if ((course == 0) && (requiredCourse == 0)) {
      pause();
      return 0;
    }

    doPrerequisiteCheck (database, actualStudents, course, requiredCourse);

  }

}