Service Objects: Implementation

determineStudentPassingStatus.js

var _ = require('underscore');

/**
 * For a given student, determine whether or not they are passing
 * @constructor
 * @param {Object} student - The student that being evaluated.
 */
var DetermineStudentPassingStatus = function(student) {
  this.student = student;
}

DetermineStudentPassingStatus.minimumPassingPercentage = 0.6

DetermineStudentPassingStatus.prototype = _.extend(DetermineStudentPassingStatus.prototype, {

  /**
   * The API method for calculating passing status from
   * a set of assignments that belong to the student
   * @param {Array} assignments - The assignments to be used in calculating passing status.
   */
  fromAssignments: function(assignments) {
    return _.compose(
      this.determinePassingStatus,
      this.averageAssignmentGrade,
      this.extractAssignmentGrades
    ).call(this, assignments);
  },

  // return the 'grade' value objects from each assignment
  extractAssignmentGrades: function(assignments) {
    return _.pluck(assignments, 'grade');
  },

  // take all grades and find the average percentage
  averageAssignmentGrade: function(grades) {
    return grades.reduce(function(memo, grade) {
      return memo + grade.percentage;
    }, 0) / grades.length;
  },

  // compare the averages from all assignments to the minimumPassingPercentage value defined above
  determinePassingStatus: function(averageGrade) {
    return averageGrade >= DetermineStudentPassingStatus.minimumPassingPercentage;
  }

});

module.exports = DetermineStudentPassingStatus;

// new DetermineStudentPassingStatus(student).fromAssignments([assignments]);
// => true/false