var studentScores = {
  student1: {
    id: 123456789,
    scores: {
      exams: [90, 95, 100, 80],
      exercises: [20, 15, 10, 19, 15],
    },
  },
  student2: {
    id: 123456799,
    scores: {
      exams: [50, 70, 90, 100],
      exercises: [0, 15, 20, 15, 15],
    },
  },
  student3: {
    id: 123457789,
    scores: {
      exams: [88, 87, 88, 89],
      exercises: [10, 20, 10, 19, 18],
    },
  },
  student4: {
    id: 112233445,
    scores: {
      exams: [100, 100, 100, 100],
      exercises: [10, 15, 10, 10, 15],
    },
  },
  student5: {
    id: 112233446,
    scores: {
      exams: [50, 80, 60, 90],
      exercises: [10, 0, 10, 10, 0],
    },
  },
};

var EXAMWEIGHT = .65;

var EXERCISEWEIGHT = .35;

function generateClassRecordSummary(scores) {
  var studentGrades = Object.keys(scores).map(getStudentGrade);
  var exams = groupExamsByIndex();
  var examSummary = generateExamSummary(exams);

  function getStudentGrade(student) {
    var exams = scores[student].scores.exams;
    var exercises = scores[student].scores.exercises;
    var grade = calculateGrade(exams, exercises);
    return convertGrade(grade);
  }

  function groupExamsByIndex() {
    var exams = Object.keys(scores).map(getExams);
    var examGroup = [];
    var i;
    var length = exams[0].length;

    for (i = 0; i < length; i++) {
      var group = [];
      exams.forEach(function(element) {
	group.push(element[i]);
      });

      examGroup.push(group);
    }

    return examGroup;
  }

  function generateExamSummary(exams) {
    return exams.map(createStudentExamSummary);
  }

  function getExams(student) {
    var exams = scores[student].scores.exams;
    return exams;
  }

  return examSummary;
}

function createStudentExamSummary(exam) {
  return { average: calculateStudentAverageExam(exam), minimum: getMinScore(exam), maximum: getMaxScore(exam) }
}

function calculateGrade(exams, exercises) {
  var examscore = calculateExamScore(exams);
  var exercisescore = calculateExerciseScore(exercises);

  return examscore + exercisescore;
}

function calculateExamScore(exams) {
  return (calculateStudentAverageExam(exams) * EXAMWEIGHT);
}

function calculateStudentAverageExam(array) {
  return array.reduce(add)/array.length;
}

function calculateExerciseScore(exercises) {
  return exercises.reduce(add) * EXERCISEWEIGHT;
}

function add(grade1, grade2) {
  return grade1 + grade2;
}

function getMaxScore(array) {
  return array.reduce(maximumExamGrade);
}

function getMinScore(array) {
  return array.reduce(minimumExamGrade);
}

function minimumExamGrade(result, value) {
  return result <= value ? result : value;
}

function maximumExamGrade(result, value) {
  return result >= value ? result : value;
}

function convertGrade(score) {
  if (gradeIsA(score)) {
    return "" + Math.round(score) + " (A)";
  } else if (gradeIsB(score)) {
    return "" + Math.round(score) + " (B)";
  } else if (gradeIsC(score)) {
    return "" + Math.round(score) + " (C)";
  } else if(gradeIsD(score)) {
    return "" + Math.round(score) + " (D)";
  } else if(gradeIsE(score)) {
    return "" + Math.round(score) + " (E)";
  } else if(gradeIsF(score)) {
    return "" + Math.round(score) + " (F)";
  }
}

function gradeIsA(score) {
  return Math.round(score) > 92 && Math.round(score) <= 100;
}

function gradeIsB(score) {
  return Math.round(score) > 84 && Math.round(score) <= 92;
}

function gradeIsC(score) {
  return Math.round(score) > 76 && Math.round(score) <= 84;
}

function gradeIsD(score) {
  return Math.round(score) > 68 && Math.round(score) <= 76;
}

function gradeIsE(score) {
  return Math.round(score) > 59 && Math.round(score) <= 68;
}

function gradeIsF(score) {
  return Math.round(score) <= 59;
}

generateClassRecordSummary(studentScores);