Azure Data Explorer Kusto: group by with difference in datetime - azure-data-explorer

Question

Is there a way to find datetime difference grouping by a column in Data Explorer Kusto? I would like to find out total time spent by each traveler in Spain.
A traveler is considered to be in a country from the time they arrive in that country till the time they arrive in their next destination. Here are the edge cases:
If TripComplete == 'Yes' and that country is the last visited destination the difference, the trip is ongoing and time spent should be difference between now() and entry time.
If TripComplete == 'No' and that country is the last visited destination it is considered as the end of trip.
Say for Spain, the time spent in Spain should be time spent in Spain in previous trips by the traveler + time since their last entry in that city of Spain (now() - EntryTime).
Here is the expected result.
TravellerId result
1 05:00:00 [Madrid to Barcelona + Barcelona to London]
2 00:00:00 [Trip complete]
3 1.00:00:00 [now() - Malaga EntryTime]
4 05:00:00 [now() - Malaga EntryTime]
5 2:00:00 [Malaga to London]
6 1.16:00:00 [Madrid to Barcelona + (now() - Barcelona EntryTime)]
7 11:00:00 [Madrid to London + Barcelona to Beiging]
Source:
set query_now = datetime(2020-02-04 5:00:00);
datatable(TravellerId:int, Country:string, City:string, TripComplete:string, EntryTime: datetime)
[
1, 'China', 'Beiging', 'Yes', datetime(2020-02-02 12:00:00),
1, 'Spain', 'Madrid', 'Yes',datetime(2020-02-02 13:00:00),
1, 'Spain', 'Barcelona', 'Yes',datetime(2020-02-02 15:00:00),
1, 'UK', 'London', 'Yes', datetime(2020-02-02 18:00:00),
2, 'Spain', 'Malaga', 'Yes', datetime(2020-02-03 5:00:00),
3, 'Spain', 'Malaga', 'No', datetime(2020-02-03 5:00:00),
4, 'China', 'Beiging', 'No', datetime(2020-02-03 5:00:00),
4, 'Spain', 'Malaga', 'No', datetime(2020-02-04 00:00:00),
5, 'China', 'Beiging', 'No', datetime(2020-02-01 5:00:00),
5, 'Spain', 'Malaga', 'No', datetime(2020-02-02 5:00:00),
5, 'UK', 'London', 'No', datetime(2020-02-02 7:00:00),
6, 'China', 'Beiging', 'No', datetime(2020-02-02 12:00:00),
6, 'Spain', 'Madrid', 'No',datetime(2020-02-02 13:00:00),
6, 'Spain', 'Barcelona', 'No',datetime(2020-02-02 14:00:00),
7, 'Spain', 'Madrid', 'Yes',datetime(2020-02-02 13:00:00),
7, 'UK', 'London', 'Yes', datetime(2020-02-02 18:00:00),
7, 'Spain', 'Barcelona', 'Yes',datetime(2020-02-03 15:00:00),
7, 'China', 'Beiging', 'Yes', datetime(2020-02-03 21:00:00),
]
| order by TravellerId asc, TripComplete asc
//Incorrect because next() calculation should be limited to the same traveler.
//Should be something like - if tripComplete = Yes then nextEntry = next(EntryTime, 1, now()) else, nextEntry = next(EntryTime, 1, EntryTime)
| extend nextEntry = next(EntryTime, 1, now())
| extend diffNext = nextEntry - EntryTime
| where Country == "Spain"
| summarize TimeSpentInSpain = sum(diffNext) by TravellerId

Answer 1

you could try something along the following lines:
set query_now = datetime(2020-02-04 5:00:00);
datatable(TravellerId:int, Country:string, City:string, TripComplete:string, EntryTime: datetime)
[
1, 'China', 'Beiging', 'Yes', datetime(2020-02-02 12:00:00),
1, 'Spain', 'Madrid', 'Yes',datetime(2020-02-02 13:00:00),
1, 'Spain', 'Barcelona', 'Yes',datetime(2020-02-02 14:00:00),
1, 'UK', 'London', 'Yes', datetime(2020-02-02 15:00:00),
2, 'Spain', 'Malaga', 'No', datetime(2020-02-03 5:00:00),
]
| order by TravellerId asc, EntryTime asc
| extend diff = EntryTime - prev(EntryTime)
| where Country == "Spain"
| summarize result = sumif(diff, TripComplete == "Yes") + sumif(now() - EntryTime, TripComplete != "Yes") by TravellerId