Mongodb aggregate function with multiple if else condition

For example: -

we take a collection name as "applicationUsage" which has field(userId,applicationName,duration,startTime,endTime).

we are saving application uses of individual user into applicationUsage collection.

case 1:
Let John used the application A, start From "12th May 2016 ko 11:50 pm" and end at "13th May 2016 12:15 am"
case 2:
Let John used the application B, start From "13th May 2016 3:00 pm" and end at "13th May 2016 5:00 pm" 
case 3:
Let John used the application C, start From "13th May 2016 11:00 pm" and end at "14th May 2016 1:00 am" 

                -------------inserted record in db------------

date will be save as ISO date, only for understanding we are showing date as IST date

userId  startTime                                endTime                              duration       ApplicatonName
John    12th May 2016 11:50pm       13th May 2016 12:15 am    25 minute     application A (case 1)
John    13th May 2016 3:00 pm        13th May 2016 5:00 pm      2 hours         application B    (case 2)
John    13th May 2016 11:00 pm      14th May 2016 1:00 am      2 hours         application C    (case 3)

Now, John wants to know which applicaton i have been used between "13th May 2016 12:00 am" to "13th May 2016 11:59pm".

                        -----------Desired output like---------------
userId  duration                                               ApplicatonName
John    15 minute(not to be 25 minute)          application A(case 1)
John    2 hours                                                application B(case 2)
John    59 minute(not be 2 hours)                  application C(case 3)

Step 1:

var filterDate={from:"2016-05-12T18:30:00.000Z",to:"2016-05-13T18:29:00.000Z"} // converted to ISO date 
 

now , we are writing normal query.

var query=[{ userId: "John"}, { "startTime": { "$gte": new Date(filterDate.from)}},{ "endTime": {"$lte": new Date(filterDate.to) }}];

Now aggregate--> group by Application name, sum of application's duration,

db.applicationusage.aggregate([{ '$match': { $and: query }},

     {$group: {"_id": {"application": "$application"},"count": { "$sum": "$duration" } } },

     {$project: { _id: 0,application: '$_id.application',duration: "$count"}}],function(err,applicationResult){});

output:-
userId  duration    Application
John     2 hours        application B    (case 2)

only second record will be come.

then first of all , we have to get all those record which is lie between "13th May 2016 12:00 am" to "13th May 2016 11:59 pm"

Step 2:

now query ,

var left=[{ "startTime": { "$lt": new Date(filterDate.from) } },{ "endTime": { "$gt": new Date(filterDate.from), "$lte": new Date(filterDate.to) } }] // left Intersection record( case 1)

var middle=[{ "startTime": { "$gte": new Date(filterDate.from)}},{ "endTime": {"$lte": new Date(filterDate.to) }}] //( case 2)

var right=[{ "startTime": { "$gte": new Date(filterDate.from),"$lt": new Date(filterDate.to) } },{ "endTime": { "$gt": new Date(filterDate.to) }}] //Right intersection record (case 3)

var query=[{ userId: "John"}, { $or:[{$and:left},{},{$and:middle},{$and:right}] }];

output:-

userId  duration                                        Applicaton
John    25 minute **(to be 15 minute)     application A (case 1)
John    2 hours                                          application B    (case 2)
John    2 hours **(to be 1 hour)               application C    (case 3)

all record get but did not get desired result, duration is coming wrong.

Step 3:

Now aggregate, group by Application name, sum of duration  with required condition for caluclating right duration,
$cond aggregate variable // for reference https://docs.mongodb.com/manual/reference/operator/aggregation/cond/
$subtract // for reference read https://docs.mongodb.com/manual/reference/operator/aggregation/subtract

$divide // for reference read  https://docs.mongodb.com/v3.0/reference/operator/aggregation/divide

var sumCondition={ "$cond": { 

            "if": {   // (case 1 --> same as left varaible query )

                "$and": [{

                    "$gt": ["$endTime", new Date(filterDate.from)]

                }, {

                    "$lte": ["$endTime", new Date(filterDate.to)]

                }, {

                    "$lt": ["$startTime", new Date(filterDate.from)]

                }]

            },

            "then": {

        

                "$divide": [{

                    "$subtract": ["$endTime", new Date(filterDate.from)]

                }, 1000] // ( case 1 --> duration calculation)

            },

            "else": {

                "$cond": {

                    "if": { // (case 3 --> same as right variable query)

                        "$and": [{

                            "$gte": ["$startTime", new Date(filterDate.from)]

                        }, {

                            "$lt": ["$startTime", new Date(filterDate.to)]

                        }, {

                            "$gt": ["$endTime", new Date(filterDate.to)]

                        }]

                    },

                    "then": {

                        "$divide": [{

                            "$subtract": [new Date(filterDate.to), "$startTime"]

                        }, 1000] //( case 3 --> duration calculation)

                    },

                    "else": "$duration" ( case 2 --> whatever save in duration field)

                }

            }

        }

    };

Now Final aggregate with multiple condition,

Note:- In this step, step 2 query used

final output:-
userId   duration             Applicaton
John     15 minute           application A (case 1)
John      2 hours              application B    (case 2)
John     59 minute           application C    (case 3)

I hope this will be helpful.
Thank You