#!/usr/bin/python3

from MITPerson import *

class Grades(object):
    """ A mapping from students to a list of grades """
    def __init__(self):
        """ Create empty grade book """
        self.students = []      # List of student objects
        self.grades = {}        # maps idNum -> list of grades
        self.isSorted = True    # true if self.students is sorted

    def addStudent(self, student):
        """
            Assumes: student is of type Student
            Add student to the grade book
        """
        if student in self.students:
            raise ValueError('Duplicated student')

        self.students.append(student)
        self.grades[student.getIdNum()] = []    # dict is a ID:List pair
        self.isSorted = False

    def addGrade(self, student, grade):
        """
            Assumes: grade is a float
            Add grade to the list of grades for student
        """
        try:
            self.grades[student.getIdNum()].append(grade)
        except KeyError:
            raise ValueError('Student not in grade book')

    def getGrades(self, student):
        """ Return a list of grades for student """
        try:    # Return a COPY of student's grades
            return self.grades[student.getIdNum()][:]
        except KeyError:
            raise ValueError('Student not in grade book')

    def allStudents(self):
        """ Return a list of the students in the grade book """
        if not self.isSorted:
            self.students.sort()
            self.isSorted = True
        return self.students[:] # Return a COPY of students, so we avoid any
                                # externalmodification to the original list



### TESTS

def gradeReport(course):
    """ Assumes: course is of type grades """

    report = []

    for s in course.allStudents():
        tot = 0.0
        numGrades = 0

        for g in course.getGrades(s):
            tot += g
            numGrades += 1

        try:
            mean = tot/numGrades
            report.append(str(s) + '\'s mean grade is ' + str(mean))
        except ZeroDivisionError:
            report.append(str(s) + ' has no grades')

    return ' \n'.join(report)


six00 = Grades()
ug3 = UG('Drew Houston', 2017)
ug1 = UG('Matt Damon', 2018)
ug2 = UG('Ben Affleck', 2019)
ug4 = UG('Mark Zuckerberg', 2017)
g1 = Grad('Bill Gates')
g2 = Grad('Steve Wozniak')

six00.addStudent(g1)
six00.addStudent(ug2)
six00.addStudent(ug1)
six00.addStudent(g2)
six00.addStudent(ug4)
six00.addStudent(ug3)

six00.addGrade(g1, 90)
six00.addGrade(g2, 45)
six00.addGrade(ug1, 80)
six00.addGrade(ug2, 75)