more improvement docs changes

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+/**
+ * A simple node driver to interact with mongo database
+ */
+
+/**********************
+ **** COLLECTIONS: ****
+ * ********************
+ *
+ * * * ADMINS - Admins login info
+ *         {
+ *              fname: first name,
+ *              lname: last name,
+ *              username: admin username,
+ *              password: hashed password
+ *         }
+ *
+ * * * COURSES - Course info
+ *         {
+ *              course_code: course code,
+ *              title: course title
+ *         }
+ *
+ *
+ * * * EXAMS - Exams info
+ *         {
+ *              course_code: course code,
+ *              year: course year,
+ *              term: course term,
+ *              type: midterm or final,
+ *              instructors: array of instructor names,
+ *              page_count: the midterm/exam's number of pages,
+ *              questions_count: the midterm/exam's number of questions,
+ *              questions_list: array containing question objects, {q_id: question #, question: question},
+ *              upload_date: date,
+ *              uploaded_by: username
+ *         }
+ *
+ *
+ * * * LOGINS - Users login info
+ *         {
+ *              email: user email,
+ *              user_name: user username,
+ *              password: users hashed password
+ *         }
+ *
+ *
+ * * * MAIL - messaging system base
+ *         {
+ *              sender: the message sender's username,
+ *              receiver: the receiver's username,
+ *              message: message,
+ *              date: date message was sent
+ *         }
+ *
+ *
+ * * * SOLUTIONS - exam solutions
+ *         {
+ *              exam_id: the id of the exam this solution applies to,
+ *              q_id: question id,
+ *              text: users solution,
+ *              votes: votes,
+ *              comments: list of comment objects, {text: comment, date: comment date, by: username}
+ *         }
+ *
+ * * * USERS
+ *         {
+ *              email: user email,
+ *              username: username,
+ *              f_name: first name,
+ *              l_name: last name,
+ *              university: user's university,
+ *              department: user's department,
+ *              answered: number of solutions user posted,
+ *              messages: user's inbox count,
+ *              comments: user comment count,
+ *              phone_num: user phone number,
+ *              followers: the list of exams that the user follows
+ *         }
+ *
+ *
+ * * * VERIFICATIONS - link facebook profile to the user
+ *         {
+ *              username: user username,
+ *              facebookID: facebook profile id,
+ *              facebookToken: facebook token,
+ *         }
+ *
+ *
+ */
+
+
+var exports = module.exports = {};
+
+const debug_mode = false;
+
+Object.assign = require('object-assign');
+var mongodb = require('mongodb');
+var mongoFactory = require('mongo-factory');
+var ObjectId = require('mongodb').ObjectID;
+var assert = require('assert');
+var _ = require('underscore');
+
+// Standard URI format: mongodb://[dbuser:dbpassword@]host:port/dbname
+// var uri = exports.uri =  'mongodb://general:assignment4@ds057862.mlab.com:57862/solutions_repo';
+
+
+// Keep this for testing on local machine, do not remove. - Humair
+var uri = exports.uri = 'mongodb://localhost:27017/db';
+
+
+/*******************************FUNCTIONS************************************************/
+
+
+
+/************************* USERS **********************************/
+
+/**
+ * This function will remove the user given user_name from the users table
+ * and the logins table. So far.
+ * IF there is a sessions table, we need to remove it from there as well.
+ * We can leave it in the mail table (involves another user).
+ * We can leave it in the solutions table (solution may still be valid).
+ *
+ * @param {string}    username: the unique user_name for the user
+ * @param  {function} callback: 2 args: (boolean, <string>),
+ *                              where <boolean> : err ? false : true
+ *                              where <string> : error ? error_mssg : success_mssg
+ */
+exports.remove_user = function (username, callback) {
+
+    mongoFactory.getConnection(uri).then(function(db) {
+
+        // fetch the exams table
+        var users = db.collection('users');
+        var logins = db.collection('logins');
+
+        // look for the specific user
+        users.removeOne( { user_name: username }, function (err, docs) {
+            if (err) throw err;
+            else if (docs.deletedCount == 1) {
+                // now remove it from logins ....
+                logins.removeOne( { user_name: username }, function (err, result) {
+                    if (err) throw err;
+                    else if (result.deletedCount == 1) {
+                        callback(true, "User was removed successfully from both tables");
+
+                    }
+                });
+            }
+            else if (docs.deletedCount == 0) {
+                callback(false, "No such user was found");
+
+            }
+        });
+    }).catch(function(err) {
+        console.error(err);
+    });
+};
+
+/**
+ * This function will search through the users table to look for 'token'.
+ * It will search the user_name, f_name, l_name fields of the table.
+ * Do not worry about case sensitivity. Malicious string is a possibility though.
+ * Returns a [] of user object(s)
+ *
+ * @params {string}   token: search term (hopefully user info)
+ * @params {function} callback: with 2 args: (boolean, <string>),
+ *                              where <boolean> : err ? false : true
+ *                              where <string> can be error message
+ *                              OR on success <[Objs]> RESULT
+ * */
+exports.search_users = function ( token, callback ) {
+
+    mongoFactory.getConnection(uri).then(function (db) {
+        var users = db.collection('users');
+        users.createIndex(          // make the following fields searchable
+            {
+                "user_name":"text",
+                "f_name":"text",
+                "l_name":"text"
+            });
+        users.find(
+            { $text: { $search: token } },
+            { score: { $meta: "textScore" } }
+        ).sort( { score: { $meta:"textScore" } } ).toArray(function (err, docs) {
+            if (err) callback(false, "Error: some error while searching");
+            else {
+                callback(true, docs);
+            }
+        });
+
+
+
+    }).catch(function (err) {
+        console.error(err);
+    });
+};
+
+
+/**
+ * This function will return a list of followers of user i.e. a list of
+ * exam_ids that the user has chosen to follow
+ *
+ * @param {string}   user_name: the unique user name for the user
+ * @param {function} callback: with 2 args: (boolean, <string>),
+ *                             where boolean : err ? false : true
+ *                             where <string> can be error message
+ *                             OR on success <[<strings>]> RESULT
+ **/
+exports.retrieveFollows = function (user_name, callback) {
+
+    mongoFactory.getConnection(uri).then(function (db) {
+
+        // find the solutions table
+        var users = db.collection('users');
+        // insert data into table
+        users.find( {user_name: user_name} ).toArray(function (err, docs) {
+            // if (err) throw err;
+            if (err) callback(false, "Error: followers could not be retrieved for some reason");
+            else {
+                callback(true, docs[0].followers);
+            }
+        });
+
+    }).catch(function (err) {
+        console.error(err);
+    });
+};
+
+/**
+ * This function will retrieve ALL the comments a user has ever made.
+ * It returns an array containing objects of the form: {exam_id, comment, date, ...
+ * course_code, year, term}.
+ * Note: a comment should only exist IF a solution exists.
+ *
+ * @param {string}   username: the unique user name for the user
+ * @param {function} callback: with 2 args: (boolean, <string>),
+ *                             where boolean : err ? false : true
+ *                             where <string> can be error message
+ *                             OR on success <[Objs]> RESULT
+ **/
+exports.retrieve_userComments_history = function (username, callback) {
+
+    // get a connection
+    mongoFactory.getConnection(uri).then(function (db) {
+        var solutions = db.collection('solutions');
+        var exams = db.collection('exams');
+        var mylist = [];
+        solutions.aggregate([
+
+            { $match : {
+                "comments.by": username
+            }},
+            { $unwind : "$comments" },
+            { $match : {
+                "comments.by": username
+            }},
+            {$project: {
+                comment: "$comments.text",
+                date: "$comments.date",
+                exam_id: "$exam_id",
+                _id: 0
+            }}
+        ]).toArray(function (err, res) {
+            if(!res.length){ // Ensure a callback is executed if res is empty
+                callback(true, res);
+            }else{
+                var finised = _.after(res.length, doCall);      // execute "doCall" only after res.length # of attempts
+                res.forEach(function (comment) {
+                    exams.find( { _id: ObjectId(comment.exam_id) } ).toArray(function (err, docs) {// get the exam info
+                        comment.course_code = docs[0].course_code;
+                        comment.year = docs[0].year;
+                        comment.term = docs[0].term;
+                        mylist.push(comment);       // save it to array
+                        finised();
+                    });
+                });
+            }
+        });
+
+        function doCall() {
+            callback(true, mylist);
+        }
+
+
+    }).catch(function (err) {
+        callback(false, "Error: failed to connect to db");
+    })
+};
+
+/** We CAN use this. IF we do, we should remove the comments_count field from a user
+ * IF we dont wanna go that route, need to update these fields whenever they are altered
+ * by the user manually.
+ *
+ * @param {string}   username: the unique user name for the user
+ * @param {function} callback: with 2 args: (boolean, <string>),
+ *                             where boolean : err ? false : true
+ *                             where <string> can be error message
+ *                             OR on success <int> RESULT
+ **/
+exports.retrieve_userComments_count = function (username, callback) {
+
+    exports.retrieve_userComments_history(username, function (bool, results) {
+        if (!bool) callback(false, "Error: error occurred");
+        else {
+            var length = results.length;
+            callback(true, length);
+        }
+    });
+
+};
+
+/**
+ * This function will retrieve ALL the solutions a user has ever provided.
+ * It returns an array containing objects of the solution form.
+ *
+ * @param {string}   username: the unique user name for the user
+ * @param {function} callback: with 2 args: (boolean, <string>),
+ *                             where boolean : err ? false : true
+ *                             where <string> can be error message
+ *                             OR on success <[Objs]> RESULT
+ **/
+exports.retrieve_userSolutions_history = function (username, callback) {
+
+    // get a connection
+    mongoFactory.getConnection(uri).then(function (db) {
+
+        var solutions = db.collection('solutions');
+        solutions.find( { author: username } ).toArray(function (err, result) {
+            if (err) callback(false, "Error: problem while looking for stuff");
+            else {
+                callback(true, result);
+            }
+
+        });
+
+    }).catch(function (err) {
+        // console.err(err);
+        callback(false, "Error: failed to connect to db");
+    })
+};
+
+/** We CAN use this. IF we do, we should remove the solutions_count field from a user
+ * IF we dont wanna go that route, need to update these fields whenever they are altered
+ * by the user manually.
+ *
+ * @param {string}   username: the unique user name for the user
+ * @param {function} callback: with 2 args: (boolean, <string>),
+ *                             where boolean is false if err OR true if no error
+ *                             where <string> can be error message
+ *                             OR on success <int> RESULT
+ **/
+exports.retrieve_userSolutions_count = function (username, callback) {
+
+    exports.retrieve_userSolutions_history(username, function (bool, results) {
+        if (!bool) callback(false, "Error: error occured");
+        else {
+            var length = results.length;
+            callback(true, length);
+        }
+    });
+
+};
+
+/**
+ * This function creates and adds a user to users table.
+ * IFF both the email and the user_name are not in the database already.
+ * If either of them exist, the user is NOT added.
+ *
+ * @param {string[]} fields: [email, user_name, f_name, l_name, uni, department, password, phone_num]
+ * @param {function} callbackUser: of the form (<boolean1>, <boolean2>, <string>)
+ *                                  where, <boolean1> -
+ *                                   <boolean2> -
+ *                                   <string> - error ? error_mssg : success_mssg
+ **/
+exports.add_user = function (fields, callbackUser) {
+    // create a user object
+    var user_data = {
+        email: fields[0],
+        user_name: fields[1],
+        f_name: fields[2],
+        l_name: fields[3],
+        university: fields[4],
+        department: fields[5],
+        answered: 0,
+        messages: 0,
+        comments: 0,
+        phone_num: fields[7],
+        followers: []
+    };
+
+    var login_data = {
+        email: fields[0],
+        user_name: fields[1],
+        password: fields[6]
+    };
+
+    // find out if this user already exists by checking their email
+    exports.find_user( fields[0], function (result) {
+        if  (result == false) {
+
+            // find out if the user_name is taken
+            exports.find_user_name( fields[1], function (docs) {
+                if (docs == false) {        // if not ...
+                    // continue
+
+                    // when both are valid add the user to the users and logins table
+                    mongoFactory.getConnection(uri)
+                        .then(function (db) {
+
+                            var users = db.collection('users');
+                            var logins = db.collection('logins');
+
+                            // Add users, and login through callbacks
+                            users.insertOne( user_data, function (err) {
+                                if (err) {
+                                    callbackUser(false, true, "Error : User has not been added.");
+
+                                }
+
+                                else {// user insert successfull
+                                    logins.insertOne(login_data, function (err) {
+                                        if (err) {
+                                            callbackUser(false, true, "Error : User has not been added.");
+
+                                        }
+
+                                        else {// login insert successfull
+                                            callbackUser(true, false, "User has been added.");
+
+                                        }
+                                    });
+                                }
+                            });
+
+                        })
+                        .catch(function (err) {
+                            callbackUser(false, true,  "Unable to connect.");
+                        })
+                }
+                else {
+                    callbackUser(false, false, "Username is taken.");
+                }
+            });
+        }
+        else {
+            callbackUser(false, false, "User with this email already exists.");
+        }
+    });
+};
+
+
+
+
+/**
+ * This function returns whether the user with the given username has already been signed in before.
+ * This is important because we need to link a unique facebook account with a username. If the user has signed in
+ * before, return the verification object, consisting of facebook profile id.
+ *
+ * @param {string} username
+ * @param {function} callbackUser: of the form (<boolean>, verifications object (See COLLECTION)) -
+ *  callbackUser(error, object)
+ *
+ **/
+
+exports.userVerifiedBefore = function(username, callback) {
+    mongoFactory.getConnection(uri)
+        .then(function (db) {
+            var verif = db.collection('verifications');
+
+            verif.find( { username : username } ).toArray(function(err, result) {
+                if (err) {
+                    callback(true, null);
+                } else {
+                    callback(false, result);
+                }
+
+            });
+        });
+}
+
+
+/**
+ * THis function adds the user's facebook account verification to the database and links it to the user's local in site
+ * account.
+ *
+ * @param {object}  - verifications object
+ * @param {function} callbackUser: of the form (<boolean>) - callback(error)
+ *
+ **/
+exports.addVerification = function(verification, callBack) {
+    mongoFactory.getConnection(uri)
+        .then(function (db) {
+            var verif = db.collection('verifications');
+
+            verif.insertOne(verification, function (err) {
+                if (err) {
+                    callBack(true);
+                } else {
+                    callBack(false);
+                }
+            })
+        });
+}
+
+/**
+ * This (helper) function returns true IFF user_name already exists in the database
+ *
+ * @param {string}   user_name: the user name
+ * @param {function} callback: of the arg (bool)
+ *                              where <bool> : found ? true : false
+ * */
+exports.find_user_name = function (user_name, callback) {
+    // make a connection
+    mongoFactory.getConnection(uri)
+        .then(function (db) {
+
+            var logins = db.collection('logins');
+            var admins = db.collection('admins');
+            logins.find( { user_name: user_name } ).toArray(function (err, result) {
+                if (err) throw err;
+                else if (result.length == 0) {  // nothing was found in users
+                    // check if user_name is taken by admin
+                    admins.find({username : user_name}).toArray(function(err, data) {
+                        if (err) throw err;
+                        else if (data.length == 0) {
+                            callback(false);
+                        }
+                        else {
+                            callback(true);
+                        }
+                    });
+                }
+                else {
+                    callback(true);
+                }
+            });
+        })
+        .catch(function (err) {
+            console.err(err);
+        })
+};
+
+/**
+ * This function retrieves the user object given their user_name
+ *
+ * @param {string}   username: the user name
+ * @param {function} callback: with args (<bool1>,<bool2>,<string1>,<string2>)
+ *                            where, <bool1> : success ? true : false
+ *                            where, <bool2> : error ? true : false
+ *                            where, <string1> : success ? {Obj} : null
+ *                            where, <string2> : success ? success_mssg : err_mssg
+ * */
+exports.retrieveUser = function (username, callback) {
+
+    mongoFactory.getConnection(uri).then(function (db) {
+        var users = db.collection('users');
+
+        users.find({user_name: username}).toArray(function (err, result) {
+            if (err) {
+                // callback(success, error, user, message)
+                callback(false, true,  null, "Error : Could not retrieve user.");
+            }
+
+            else if (result.length) {
+                callback(true, false, result[0], "User retrieved");
+            }
+
+            else {
+                callback(false, false, null, "Username is undefined.");
+            }
+        });
+    });
+}
+
+/**
+ * Returns the hashed password given the username. Assume username exists.
+ * Used for both admins and users.
+ *
+ * @param {string}   username: the user name
+ * @param {function} callback: with args (<bool>,<string>,<string>)
+ *                           where, <bool> : success ? true : false
+ *                           where, <string> : success ? "pwd" : null
+ *                           where, <string> : success ? success_mssg : err_mssg
+ * */
+exports.retrievePassword = function (username, callback) {
+    mongoFactory.getConnection(uri).then(function (db) {
+
+        var collection = db.collection('logins');
+
+        collection.find({user_name: username}).toArray(function(err, result) {
+            if (err) {
+                // callback(success, password, message)
+                callback(false, null, "Error : Could not retrieve password.");
+            }
+
+            else {
+                var pwd = result[0].password; //result is an array
+                callback(true, pwd, "Password retrieved");
+            }
+
+        });
+    });
+}
+
+/**
+ * This (helper) function returns true IFF email already exists in the database
+ *
+ * @param {string}   email: unique email of the user
+ * @param {function} callback: <bool> : found ? true : false
+ * */
+exports.find_user = function (email, callback) {
+    // make a connection
+    mongoFactory.getConnection(uri)
+        .then(function (db) {
+
+            var logins = db.collection('logins');
+            logins.find( { email: email } ).toArray(function (err, result) {
+                if (err) throw err;
+                else if (result.length == 0) {  // nothing was found  so this user is new
+                    callback(false);
+                }
+                else {
+                    callback(true);
+                }
+            });
+        })
+        .catch(function (err) {
+            console.err(err);
+        })
+};
+
+
+/**
+ * This function retrieves the user object from the users collection given the object id.
+ *
+ * @param {string} id
+ * @param {function} callbackUser: of the form (<boolean>, user object (See COLLECTION)) -
+ * callbackUser(error, object)
+ *
+ **/
+exports.findUserByID = function (id, callback) {
+    // make a connection
+    mongoFactory.getConnection(uri)
+        .then(function (db) {
+            var logins = db.collection('logins');
+            logins.find( { _id : id }, function (err, result) {
+                callback(err, result);
+
+            });
+        })
+        .catch(function (err) {
+            console.err(err);
+        })
+};
+
+/************************* COURSES / EXAMS **********************************/
+
+
+/**
+ * Remvove a course from ONLY the courses table IN CASE of accidental
+ * addition.
+ *
+ * @param {string}   course_code: the course code
+ * @param {function} callback: 2 args: (boolean, <string>),
+ *                             where <boolean> : err ? false : true
+ *                             where <string> : error ? error_mssg : success_mssg
+ */
+exports.remove_course = function (course_code, callback) {
+
+    mongoFactory.getConnection(uri).then(function(db) {
+
+        // fetch the exams table
+        var courses = db.collection('courses');
+
+        courses.createIndex(          // make the following fields searchable
+            {
+                "course_code":"text"
+            });
+        // look for the specific course
+        courses.removeOne( { $text: { $search: course_code } }, function (err, docs) {
+            // if (err) throw err;
+            if (err) callback(false, "Error: Failed to remove the course.");
+
+            else if (docs.deletedCount == 1) {
+                callback(true, "Course was removed successfully from JUST courses");
+
+            }
+            else if (docs.deletedCount == 0) {
+                callback(false, "No such user was found");
+
+            }
+        });
+    }).catch(function(err) {
+        console.error(err);
+    });
+};
+
+
+/**
+ * This function will add the given exam_id to the given user's followers list.
+ * It simply appends the exam_id to the list and nothing else.
+ * If the exam_id already exists in the user's followers list,
+ * false will be returned, andnothing will be added.
+ *
+ * Ideally the user shouldnt even be able to attempt to follow an exam twice.
+ *
+ * @param {string}   user_name: the unique user name for the user
+ * @param {string}   exam_id: the _id of the exam TO follow
+ * @param {function} callback: with 2 args: (boolean, <string>),
+ *                             where <boolean> : err ? false : true
+ *                             where <string> : error ? err_messg : success_messg
+ **/
+exports.followExam = function (user_name, exam_id, callback) {
+
+    exports.retrieveFollows(user_name, function (bool, result) {
+        if (!bool) console.log(result);
+        else {      // no err occured so far...
+
+            var found = false;
+            for (var i = 0; i < result.length; i++) {       // search through the list of exams followed
+                if (result[i] == exam_id) {
+                    found = true;
+                }
+            }
+
+            if (found) {    // means exam is already followed by user
+                callback(false, "user is already following this exam");
+            }
+
+            else {      // add it to the user follower list
+                mongoFactory.getConnection(uri).then(function (db) {
+
+                    // find the user table
+                    var users = db.collection('users');
+                    // insert data into table
+                    users.updateOne( {user_name: user_name}, {$push: {followers: exam_id}} , function (err) {
+                        // if (err) throw err;
+                        if (err) callback(false, "Error: some error occurred while following the exam");
+                        else {
+                            callback(true, "Success: user is following this exam");
+                        }
+                    });
+
+
+                }).catch(function (err) {
+                    console.error(err);
+                });
+            }
+        }
+    });
+};
+
+
+
+
+
+/**
+ * This function returns an array where each element contains info for a particular question
+ * such as the question number (_id), number of solutions (count), and number of comments
+ * (comments). [ {_id,count,comments}, {} , ...]
+ *
+ * @param {string}   exam_id: the exam_id of which the info is required
+ * @param {function} callback: with arg (<[Objs]>) - RESULT
+ * */
+exports.get_exam_info_by_ID = function (exam_id, callback) {
+
+    mongoFactory.getConnection(uri)
+        .then(function (db) {
+
+            var solutions = db.collection('solutions');
+
+            solutions.aggregate(
+                [
+
+                    // {$unwind: "$comments"},
+                    { $match: { exam_id: exam_id }},
+                    {
+                        $project:
+                        {
+                            num_comments: { $size: "$comments" },
+                            _id: "$exam_id",
+                            q_id: "$q_id"
+                        }
+                    },
+                    {
+                        $group : {
+                            _id : "$q_id",
+                            count: { $sum: 1 },
+                            comments: {$sum: "$num_comments"}
+                            // num_comments: { $size: "$comments" }
+
+                        }
+                    }
+
+
+                ]).toArray(function (err, result) {
+                callback(result);
+
+            });
+        })
+        .catch(function (err) {
+            console.err(err);
+        })
+
+};
+
+/**
+ * CALLBACK ADDED RECENTLY, BEWARE WHEN CALLING IT
+ * This function will add a comment to the solutions table
+ *
+ * @param {string}   sol_id: id of the solution to which to add the comment
+ * @param {string[]} fields: <[text, by_username]>
+ * @param {function} serverCallback: with args (<bool>,<string>)
+ *                              where <bool> : err ? false : true
+ *                              where <string> : err ? err_mssg : success_mssg
+ * */
+exports.add_comment = function (sol_id, fields, serverCallback) {
+    var date = new Date();
+    var Data = {
+        text: fields[0],
+        date: date.toString().slice(0, 24),
+        by: fields[1]
+    };
+
+    mongoFactory.getConnection(uri)
+        .then(function (db) {
+
+            // find the solutions table
+            var solutions = db.collection('solutions');
+            var users = db.collection('users');
+            // insert data into table
+            solutions.updateOne( {_id: ObjectId(sol_id)}, {$push: {comments: Data}} , function (err, result) {
+                if (err) {
+                    serverCallback(false, "Error: Solution found, but could not update comments.");
+                    throw err;
+                }
+                else {
+                    users.updateOne( { user_name: fields[1] }, { $inc: { comments: 1} }, function (err) {
+                        if (err) serverCallback(false, "Error: Some error occured while updating user info");
+                        else {
+                            serverCallback(true, "Success: comment added successfully");
+                        }
+
+                    });
+                }
+
+            });
+
+        })
+        .catch(function (err) {
+            serverCallback(false, "Error: Could not establish connection with database.");
+            console.error(err);
+        })
+};
+
+/**
+ * This function will get all the solution for a given exam_id and q_num
+ * sorted by highest to lowest votes.
+ *
+ * @param {string}   exam_id: exam_id for which the info is required.
+ * @param {int}      q_num: the question number for which solutions are required.
+ * @param {function} callback: <[Objs]> - RESULT
+ * */
+exports.get_all_solutions = function (exam_id, q_num, callback) {
+
+    // check if the exam id already exists...
+    exports.get_exam_byID(exam_id, function (success, failure, exam) {
+        if (!success && failure) {  // some error occurred while searching
+            callback(false, true, "Error: Some error occurred while searching for exam", null);
+        } else if (!success && !failure) {
+            callback(false, true, "Error: this exam does not exist", null);
+        } else if (success && !failure) {       // this exam exists proceed with task
+            mongoFactory.getConnection(uri).then(function (db) {
+
+                var solutions = db.collection('solutions');
+
+                solutions.find(
+                    {
+                        exam_id: exam_id,
+                        q_id: q_num
+                    }
+                ).sort({ votes: -1}).toArray( function (err, docs) {
+                    if (err) callback(false, true, "Error: Some error occurred while looking for solutions");
+                    else {      // either nothing was found or something was found
+                        callback(true, false, "Solutions", docs);
+                    }
+
+                });
+            }).catch(function () {
+                callback(false, true, "Error: Some error occurred with the db connection", null);
+            })
+        }
+    });
+
+};
+
+/**
+ * CALLBACK ADDED RECENTLY, BEWARE WHEN CALLING IT
+ * This function will add a solution to the solutions table in the database.
+ *
+ * @param {string[]} fields: [exam_id , question_id, solution text, user_name]
+ * @param {function} callback: with args (bool, string)
+ *                       where, <bool>: err ? false : true
+ *                       where, <string>: err ? err_mssg : success_mssg
+ * */
+exports.add_solution = function (fields, callback) {
+    var Data = {
+        exam_id: fields[0],
+        q_id: fields[1],
+        text: fields[2],
+        votes: 0,
+        comments: [],
+        author: fields[3]
+    };
+
+    // establish a connection
+    mongoFactory.getConnection(uri).then(function(db) {
+
+        // find the solutions table
+        var solutions = db.collection('solutions');
+        var users = db.collection('users');
+        // insert data into table
+        solutions.insert(Data, function(err) {
+            if (err) callback(false , "Error: Failed to add the solution");
+            else {
+                users.updateOne( { user_name: fields[3] }, { $inc: { answered: 1} }, function (err) {
+                    if (err) callback(false, "Error: Failed to update the user solution count");
+                    else {
+                        callback(true, "Success: added solution successfully!");
+                    }
+                });
+            }
+        });
+
+
+    }).catch(function(err) {
+        console.error(err);
+    });
+
+};
+
+/**
+ * This function will update the vote count of a solution.
+ *
+ * @param {string}   sol_id: the sol_id of the solution to vote
+ * @param {string}   upORdown: <string> : up_vote ? "up" : "down"
+ * @param {function} callback: with args (bool, string)
+ *                       where, <bool>: err ? false : true
+ *                       where, <string>: err ? err_mssg : success_mssg
+ * */
+exports.vote_solution = function (sol_id, upORdown , callback) {
+    var vote = (upORdown == "up") ? 1 : -1;
+
+    mongoFactory.getConnection(uri).then(function (db) {
+        var solutions = db.collection('solutions');
+        solutions.updateOne(
+            {_id: ObjectId(sol_id) },
+            { $inc: { votes: vote} }, function (err) {
+                // if (err) throw err;
+                if (err) callback(false, "Error: couldnt update the vote count");
+                else {
+                    callback(true, "Success: updated vote count");
+                }
+
+            });
+    }).catch(function (err) {
+        console.log(err);
+    });
+};
+
+/**
+ * This function will retrieve all exams in the database given the course code ...
+ * ... ordered by the year of the exam.
+ *
+ * @param {string}   course_code: the course code to get all the exams for
+ * @param {function} callback: with args (<string>)
+ *                      where on success is <[Objs]>
+ * */
+exports.get_all_exams = function (course_code, callback) {
+
+    // get a connection
+    mongoFactory.getConnection(uri)
+        .then(function(db) {
+
+            // get the exams table
+            var exam_collection = db.collection('exams');
+
+            exam_collection.createIndex(          // make the following fields searchable
+                {
+                    "course_code":"text"
+                });
+            // search exams table with given course code
+            exam_collection.find(
+                { $text: { $search: course_code } }
+            ).sort({ year: -1}).toArray( function (err, docs) {   // order by year
+                if (err) throw err;
+
+                else {    // get the title
+                    exports.find_course(course_code, function (result, data) {
+
+                        if (result == true) {
+                            // append the title from data to each exam object from docs
+                            docs.forEach(function (doc) {
+                                doc.title = data[0].title;
+                            });
+
+                            if (debug_mode == true){
+                                console.log(docs);
+                                console.log(data);
+                            }
+                            /*callback(docs);     // send back the data*/
+                        }
+                        else if (result == false) {    // no such course was found
+                            console.log("This course has not been added to the database.");
+                        }
+                        callback(docs);     // send back the data
+
+                    });
+                }
+            });
+        })
+        .catch(function(err) {
+            console.error(err);
+        });
+
+};
+
+/**
+ * This function will add an exam to the database UNLESS the exams already exists.
+ * If the exams table is empty, this will create one and then add the data.
+ * Note: this assumes that (course_code + year + term + type) together form a unique exam.
+ * i.e there can't be two exams occurring for the same course in the same year in the same term with the same type.
+ *
+ * @param {string[]} fields: an array of format ["course_code", year, "term",
+ *                       ["instructor1",...,"instructor n"], page_count, question_count
+ *                       "upload_date", "user_name"]
+ * @param {string[]} questions_array: a array by format ["q_1", "q_2", ... , "q_question_count"]
+ * @param {function} serverCallback: with args (<bool>, <string>)
+ *                      where <bool> : err ? false : true
+ *                      where <string> : err ? err_mssg : success_mssg
+ *
+ * */
+exports.add_exam = function (fields, questions_array, serverCallback) {
+
+    // construct an exam object
+    var Data =
+    {
+        course_code: fields[0],
+        year: fields[1],
+        term: fields[2],
+        type: fields[3],
+        instructors: fields[4],
+        page_count: fields[5],
+        questions_count: fields[6],
+        questions_list: [],
+        upload_date: fields[7],
+        uploaded_by: fields[8]
+    };
+
+    // create the questions objects
+    for (var i = 1; i <= Data.questions_count; i++) {
+        Data.questions_list.push(
+            {
+                q_id: i,
+                question: questions_array[i - 1]
+            }
+        );
+    }
+
+    // first see if the exam already exists
+    // pass in course_code, year, term and type...
+    exports.find_exam([fields[0], fields[1], fields[2], fields[3]], serverCallback, function(result, serverCallback) {
+
+        if (result == true) {     // meaning that the exam was found
+            serverCallback(false, "This exam already exists in the database.");
+        }
+
+        else {    // add Data to the database
+            // make a connection
+            mongoFactory.getConnection(uri)
+                .then(function(db) {
+
+                    // find the exams table
+                    var exam_collection = db.collection('exams');
+                    // insert data into table
+                    exam_collection.insert(Data, function(err) {
+                        if (err) {
+                            serverCallback(false, "Error: Could not add exam into database.");
+                            throw err;
+                        }
+                        else {
+                            serverCallback(true, "Exam Successfully added.");
+                        }
+                    });
+                })
+                .catch(function(err) {
+                    serverCallback(false, "Error: Could not establish connection with database.");
+                    console.error(err);
+                });
+        }
+    });
+};
+
+/**
+ * This function will return TRUE if the provided exam info already exists in the database
+ * OR FALSE if it does not exist in the database.
+ *
+ * @param {string[]} fields: an array of format ["course_code", year, "term", "type"]
+ * @param {function} serverCallback: ...
+ * @param {function} callback: with args (<bool>, ...)
+ *                      where <bool> : found ? true : false
+ * */
+exports.find_exam = function (fields, serverCallback, callback) {
+
+    var course_code = fields[0];
+    var year = fields[1];
+    var term = fields[2];
+    var type = fields[3];
+
+    // check the data to see if this exam exists...
+
+    // first make a connection
+    mongoFactory.getConnection(uri)
+        .then(function(db) {
+
+            // fetch the exams table
+            var exams = db.collection('exams');
+
+            // look for the exam
+            exams.find(
+                {
+                    course_code: course_code,
+                    year: year,
+                    term: term,
+                    type: type
+                }
+            ).toArray(function (err, docs) {
+                if (err) throw err;
+
+                if (docs.length == 0) { // if this exam doesnt exist.... add it
+                    callback(false, serverCallback);
+                }
+                else {  // exam was found
+                    callback(true, serverCallback);
+                }
+            });
+        })
+        .catch(function(err) {
+            console.error(err);
+        });
+};
+
+/**
+ * This function will add a course to the database UNLESS the course already exists.
+ * If the course table is empty, this will create one and then add the data.
+ * Note: this assumes that (course_codes) are unique.
+ *
+ * @param {string}   course_code: the course code
+ * @param {string}   title: the course description
+ * @param {function} serverCallback: with args (<bool>, <string>)
+ *                          where <bool> : err ? false : true
+ *                          where <string> : err ? err_mssg : success_mssg
+ * */
+exports.add_course = function (course_code, title, serverCallback) {
+
+    var courseData = {
+        course_code: course_code,
+        title: title
+    };
+
+    exports.find_course(course_code, function (result) {
+
+        if (result == true){
+            serverCallback(false, "Course already exists");
+        }
+        else if (result == false) {    // add it
+            mongoFactory.getConnection(uri)
+                .then(function(db) {
+
+                    // find the exams table
+                    var courses = db.collection('courses');
+                    // insert data into table
+                    courses.insert(courseData, function(err) {
+                        if (err) throw err;
+                        else {
+                            serverCallback(true, "Course added successfully.");
+                        }
+                    });
+                })
+                .catch(function(err) {
+                    console.error(err);
+                });
+        }
+    });
+};
+
+/**
+ * This function will return TRUE if the provided course info already exists in the database
+ * OR FALSE if it does not exist in the database.
+ *
+ * @param {string}   course_code: the course code
+ * @param {function} callback: with args (<bool>, <string>)
+ *                          where <bool> : found ? true : false
+ *                          where <string> : found ? null : [{Obj}]
+ * */
+exports.find_course = function (course_code, callback) {
+    // check the data to see if this exam exists...
+
+    // first make a connection
+    mongoFactory.getConnection(uri)
+        .then(function(db) {
+
+            // fetch the courses table
+            var courses = db.collection('courses');
+            courses.createIndex(          // make the following fields searchable
+                {
+                    "course_code":"text"
+                });
+            // look for the courses
+            courses.find(
+                { $text: { $search: course_code } }
+            ).toArray(function (err, docs) {
+                if (err) throw err;
+                // if this course doesnt exist.... add it (via add_course call)
+                if (docs.length == 0) {
+                    callback(false);
+                }
+                else {  // course was found
+                    callback(true, docs);
+                }
+            });
+        })
+        .catch(function(err) {
+            console.error(err);
+        });
+};
+
+/**
+ * This function will remove the exam from the database given the combination
+ * of (course_code+ year +  term + type)
+ *
+ * @param {string[]} fields: an array of format ["course_code", year, "term", "type"]
+ * @param {function} serverCallback: with args (<bool>, <string>)
+ *                              where <bool> : success ? true : false
+ *                              where <string> : success ? success_mssg ? err_mssg
+ *
+ * */
+exports.remove_exam = function (fields, serverCallback) {
+
+    var course_code = fields[0];
+    var year = fields[1];
+    var term = fields[2];
+    var type = fields[3];
+
+    // establish connection
+    mongoFactory.getConnection(uri)
+        .then(function(db) {
+
+            // fetch the exams table
+            var exams = db.collection('exams');
+
+            // look for the specific exam
+            exams.removeOne(
+                {
+                    course_code: course_code,
+                    year: year,
+                    term: term,
+                    type: type
+                }, function (err, docs) {
+                    if (err) throw err;
+                    else {
+                        if (docs.deletedCount == 1) {
+                            serverCallback(true, "Exam was removed successfully");
+                        }
+                        else if (docs.deletedCount == 0) {
+                            serverCallback(false, "No such exam was found");
+                        }
+                    }
+                }
+            );
+        })
+        .catch(function(err) {
+            console.error(err);
+        });
+};
+
+/**
+ * This function will get the specific exam object given its ID.
+ *
+ * @param {string}   id: the exma_id
+ * @param {function} callback: with args (<bool>,<bool>,<string>)
+ *                       where, <bool> : success ? true : false
+ *                       where, <bool> : error ? true : false
+ *                       where, <string> : success ? {Obj}
+ * */
+exports.get_exam_byID = function (id, callback) {
+
+    // establish a connection
+    mongoFactory.getConnection(uri)
+        .then(function(db) {
+
+            // find the solutions table
+            var exams = db.collection('exams');
+            // query
+            exams.find( {_id: ObjectId(id)} ).toArray(function (err, docs) {
+                if  (err) {
+                    callback(false, true,  null);
+                } else if (docs.length == 0) {
+                    callback(false, false, null);
+                }
+                else {
+                    callback(true, false,  docs[0]);
+                }
+            });
+        })
+        .catch(function(err) {
+            callback(false, true, null);
+        });
+};
+
+/******************************  ADMINS *********************************/
+
+/**
+ * This function adds the admin given the admin data admin_data (see ADMINS in COLLECTIONS) into the admins collection.
+ * Does not add and returns a message if the username in admin_data already exists.
+ *
+ * @param {object} admin object (see ADMINS in COLLECTIONS)
+ * @param {function} callbackUser: of the form (<boolean1>, <boolean2>, <string>) -
+ * callback(error, success, message)
+ *
+ **/
+
+exports.addAdmin = function (admin_data, callback) {
+    var logins = db.collection('logins');
+    // Check if the admin username already exists. Also check for user username. If it does, then we don't add the
+    // admin_data and return a message.
+    exports.adminExists( admin_data.username , function (error, exists, data, message) {
+        if (!exists && !error) {
+            logins.find({username: username}).toArray(function (err, result) {
+                if (err){
+                    callback(true, false, "Error: could not retreive logins collection in addAdmin().");
+                } else if (result.length) {
+                    callback(false, false, 'User with given username already exists.');
+                } else {
+                    mongoFactory.getConnection(uri).then(function (db) {
+
+                        var admins = db.collection('admins');
+
+                        admins.insertOne(admin_data, function (err) {
+                            if (err) {
+                                callback(false, true, message);
+                            }
+                            else {
+                                callback(true, false, "Admin added.");
+                            }
+
+                        });
+                    });
+            }
+            }).catch(function (err) {
+                callbackUser(false, true,  "Unable to connect.");
+            })
+        } else {
+            callback(error, exists, message);
+        }
+    });
+
+};
+
+/**
+ * This function checks if the admin username already exists in the ADMINS collection. If it does, then callback
+ * returns success, and the admin object is passed through the callback.
+ *
+ * @param {string} username - admin username
+ * @param {function} callbackUser: of the form (<boolean1>, <boolean2>,<object>, <string>) -
+ * callback(error, success, object,  message)
+ *
+ **/
+exports.adminExists = function (username, callback) {
+    // make a connection
+    mongoFactory.getConnection(uri).then(function (db) {
+
+        var admins = db.collection('admins');
+        admins.find( { username: username } ).toArray(function (err, result) {
+            if (err) {
+                callback(true, false, null, "Error: could not retrieve admin in adminExists().");
+            } else if (result.length) {
+                callback(false, true, result[0], "Admin with given username exists");
+            } else {
+                callback(false, false, null, "Admin with given username does not exist");
+            }
+        });
+    })
+        .catch(function (err) {
+            callback(true, false, "Error: could not connect to the database.");
+        })
+};
+
+/******************************  MAIL *********************************/
+
+/**
+ * This function adds the message object (see MAIL in COLLECTIONS) to the MAIL collection.
+ *
+ * @param {object} mail object
+ * @param {function} callbackUser: of the form (<boolean1>, <boolean2>, <string>) -
+ * callback(error, success, message)
+ *
+ **/
+exports.sendMail = function (mail_data, callback) {
+    exports.find_user_name(mail_data.receiver, function (exist){
+        if (exist) {
+            mongoFactory.getConnection(uri).then(function(db) {
+                var mail = db.collection('mail');
+                mail.insertOne(mail_data, function(err) {
+                    if (err) {
+                        callback(false, true, 'Error: could not send message.');
+                    }
+                    else {
+                        callback(true, false, "Message sent.");
+                    }
+
+                });
+            });
+        } else {
+            callback(false, false, 'The receiver\'s  username is undefined.');
+        }
+    });
+}
+
+/**
+ * This function checks if the user with the given username has mail. If the user does, then sends a list of all
+ * mail through callback.
+ *
+ * @param {object} admin object (see ADMINS in COLLECTIONS)
+ * @param {function} callbackUser: of the form (<boolean1>, <boolean2>, <array of objects>, <string>) -
+ * callback(error, success, mail,  message)
+ *
+ **/
+exports.checkMailbox = function (username, callback) {
+
+    mongoFactory.getConnection(uri).then(function(db) {
+
+        var mail = db.collection('mail');
+
+        mail.find({receiver: username}).toArray(function (err, data) {
+            if (err) {
+                callback(false, true, null, 'Error: could not retrieve inbox messages.');
+            } else if (!data) {
+                callback(false, false, null, 'No inbox.');
+            } else {
+                callback(true, false, data, 'Retrieved inbox');
+            }
+
+        });
+    });
+
+}