/**
 * This class models a gradebook used to record scores for students in a class.
 * It uses a 2D array to store the scores.  The array has numStudents rows and
 * numAssignments columns.
 * 
 * @author Brad Richards
 */
public class GradeBook
{
    // Declares a 2D array of integers.  We'll think of the first "dimension" as
    // being students and the second as assignments.  Each "cell" in the 2D array
    // of integers is a score.  Note that we don't STORE any student names or
    // assignment names -- just the scores.
    int[][] grades;

    // Unused cells are marked with this.  Don't want to confuse with 0.
    public static final int NO_GRADE = -1;

    /**
     * Constructor creates the 2D array and fills it with NO_GRADE values.
     * 
     * @param numStudents  The number of students in the class
     * @param numAssignments  The number of assignments used
     */
    public GradeBook(int numStudents, int numAssignments) {
        grades = new int[numStudents][numAssignments];  // Create 2D array
        // For loop across rows
        //    For loop down columns

        for(int student=0; student<grades.length; student=student+1) {
            for(int assignment=0; assignment<grades[student].length; assignment=assignment+1) {
                grades[student][assignment] = NO_GRADE;
            }
        }

    }

    /**
     * Records a score for a particular student and assignment.
     * 
     * @param student  The student whose score should be set (zero-based)
     * @param assignNum  Number of the assignment score to set (zero-based)
     * @param score  The score the student got on the assignment
     */
    public void setAssignmentScore(int student, int assignNum, int score) {
        if (student >= 0 && student < grades.length &&
        assignNum >= 0 && assignNum < grades[student].length) 
        {
            grades[student][assignNum] = score;
        }
    }

    /**
     * Calculates a student's average score across assignments. Ignores
     * assignments that haven't been done yet. (Ignores -1)
     * 
     * @param student  The student whose assignments should be averaged
     * @return  Student's average score
     */
    public double getStudentAverage(int student) {
        int sum = 0;
        int numAsmts = 0;
        // Make sure the student number is valid
        if (student >= 0 && student < grades.length) {
            // Step through each assignment, keeping the row (student) fixed.
            for(int asmt=0; asmt<grades[student].length; asmt=asmt+1) {
                if (grades[student][asmt] != NO_GRADE) {
                    sum = sum + grades[student][asmt];
                    numAsmts = numAsmts + 1;
                }
            }
        }
        return sum / (double)numAsmts;
    }

    /**
     * Calculates the average score received on a particular assignment.
     * 
     * @param asmt  The assignment number whose values should be averaged
     * @return Average score received on this assignment
     */
    public double getAssignmentAverage(int asmt) {
        // Need to go down a COLUMN this time, adding up values.
        int sum = 0;
        int numScores = 0;
        // Make sure asmt is a legal assignment number. 
        // Loop through students, keeping assignment # fixed
        if (asmt >= 0 && asmt < grades[0].length) {
            for(int student=0; student<grades.length; student=student+1) {
                if (grades[student][asmt] != NO_GRADE) {
                    sum = sum + grades[student][asmt];
                    numScores = numScores + 1;
                }
            }
        }
        return sum / (double)numScores;
    }

    /**
     * Calculates the average across ALL scores in the gradebook (ignoring 
     * NO_GRADE values). 
     * 
     * @return Average score received on this assignment
     */
    public double getTotalAverage() {
        int sum = 0;
        int numScores = 0;

        // Outer loop specifies which column to look at (which asmt number)
        for(int asmt=0; asmt<grades[0].length; asmt=asmt+1) {
            // Inner loop still goes down a column
            for(int student=0; student<grades.length; student=student+1) {
                int grade = grades[student][asmt];
                if (grade != NO_GRADE) {
                    sum = sum + grade;  // It's a legitimate score
                    numScores = numScores + 1;
                }
            }
        }

        return sum / (double)numScores;
    }

    /**
     * Traverse the entire 2D array and print contents.
     */
    public void printGrades() {
        for(int[] row : grades) {
            for(int score : row) {
                System.out.print(score+"\t");
            }
            System.out.println(); // Go to next line now
        }
    }

}