/* This program demonstrates
 * 1. A dynamic struct variable
 * 2. Dynamic arrays of structs
 * 3. Working with Files
 *
 * C++ programs can interact with files - read data from files instead fo the keyboard
 * and print data to files instead of the terminal/screen
 * To work with files,
 * 1. Create the file variables - > ifstream for input (cin), ofstream for output (cout)
 * 2. open a file with the file variable -> check if ok
 * 3. Use the file, just like cin/cout
 * 4. close them
 *
 */

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

/* We use the Date and student structs we created for the previous example, along with the
 * previously written functions, readDate, printDate, readStudent, and printStudent
 *
 * However, the functions have been edited to read from a file and write to a file
 * Since the file(s) will be opened only once, in main, we have to pass the file
 * object (ifstream or ofstream variables) into the function.
 *
 * Stream variables always pass by reference
 */
struct Date
{
    int month, day, year;
    char dayOfWeek[15];
};

struct Student
{
    string name, major;
    float gpa;
    long empl;
    float grades[3];
    Date dateOfBirth;
};

// If a function uses a structure, it has to be declared after the struct declaration

void printDate(Date d, ofstream &);

Date readDate(ifstream &);

void printStudent(Student s, ofstream &);

void readStudent( Student &s, ifstream &);

double classAverage(Student *arr, int size);

int main()
{
    /* To open an input file, that is, a file that contains data we need to
    * read into our program, a la cin, we need a variable of type ifstream
    * Similarly, to open an output file, that contains data that we are
    * producing in the program, we need a variable of type ofstream.
    */
    ifstream in;
    ofstream out;

    in.open("inputFile.txt");
    out.open("outputFile.txt");
    if(!in)
    {
        cout<<"Unable to open input file"<<endl;
    }
    else if(!out)
    {
        cout<<"Cannot open the output file"<<endl;
    }
    else {
        /* file was opened successfully.
         * We can now use the ifstream variable just like cin, to read from the file
         * We cna use the ofstrema variable just like cout, to print to the output file
         * We don't need any "prompts" here, since the interaction is with a file and
         * not with a human. So, all prompts have been removed.
         */

        int num;
        in >> num;

        /* Here, we create a dynamic array of structs */
        Student *sPtr = new Student[num];

        // Once we have declared it, there is no difference in use between a
        // dynamic array of structs and an in-stack array of structs
        // read student data from the file
        for (int i = 0; i < num; i++) {
            in.ignore();        // Remove the preceding newline
            readStudent(sPtr[i], in);  // use same as previous example
        }

        out<<"Printing student details: "<<endl;
        for(int i=0; i<num; i++)
        {
            printStudent(sPtr[i], out);
        }

        out<<"Class average: "<<classAverage(sPtr, num)<<endl;

        for(int i=0; i<num; i++)
        {
            out<<sPtr[i].name << " is "<< 2022 - sPtr[i].dateOfBirth.year<<" years old"<<endl;
        }

        // delete when array is no longer needed
        delete [] sPtr;
        cout<<"Files successfully processed. Look at outputFile.txt"<<endl;
    }

    // close the files
    in.close();
    out.close();
    return 0;
}

double classAverage(Student *arr, int size)
{
    double sum =0;

    /* Calculating class average for this array */
    for(int i=0; i<size; i++)
    {
        for(int j=0; j<3; j++)
        {
            /* arr[i] will take us to the student variable element of the array
             * arr[i].grades takes us to the grades array data element of the student
             * arr[i].grades[j] takes us to each individual grade of the student
             */
            sum = sum + arr[i].grades[j];
        }

    }
    double avg = sum / size / 3;
    return avg;
}

/* This function takes a Date variable as a parameter and the prints the elements */
void printDate(Date d, ofstream &output)
{
    output<<d.dayOfWeek<<", ";

    switch(d.month)
    {   case 1: output<<"January";
            break;
        case 2: output<<"February";
            break;
        case 3: output<<"March";
            break;
        case 4: output<<"April";
            break;
        case 5: output<<"May";
            break;
        case 6: output<<"June";
            break;
        case 7: output<<"July";
            break;
        case 8: output<<"August";
            break;
        case 9: output<<"September";
            break;
        case 10: output<<"October";
            break;
        case 11: output<<"November";
            break;
        case 12: output<<"December";
            break;
        default: output<<"Invalid Month";
    }
    output<<" "<<d.day<<" "<<d.year<<endl;
}

/* This function creates a Date variable, reads in the values and returns it. */
Date readDate(ifstream & input)
{
    Date var;
    input.getline(var.dayOfWeek, 15, ',');
    char junk;
    input>>var.month>> junk>> var.day>>junk>>var.year;
    return var;
}

/* This function accepts a structure variable and prints out the details in the structure
* We use the dot (.) operator to access individual elements.
*/
void printStudent( Student s, ofstream & output)
{
    output<<s.name <<" ( EMPLID "<< s.empl<<") is a "<< s.major<<" major with a "
        << s.gpa<<" GPA."<<endl<<"3 grades: ";
    for(int i=0; i<3; i++)
        output<<s.grades[i]<<"\t";
    output<<"\nDate if birth: ";
    printDate(s.dateOfBirth, output);
}
/* This function reads the values into a structure variable.
 * Since structure variables usually pass by value, we use a reference variable
 * to read. That way, any changes we make to the individual elements while
 * reading in values from the user will be retained across the function call.
 */
void readStudent (Student &s, ifstream & input)
{
    getline(input, s.name);
    getline(input, s.major);
    input>>s.gpa;
    input>>s.empl;
    for(int i=0; i<3;i++)
        input>>s.grades[i];
    input.getline(s.dateOfBirth.dayOfWeek, 15, ',');
    input>>s.dateOfBirth.month;
    input.ignore();
    input>>s.dateOfBirth.day;
    input.ignore();
    input>>s.dateOfBirth.year;

}