What is the precise definition of WindowFunnel's “strict” MODE?

[BiteTheDDDDt]

According to my reading of the source code, it seems that strict = true, will return Event INDEX directly.
such as the event sequence is A->B->C->B->D and conditional sequence isA->B->C->D, returns 2 (not 3 or 4) when searching the second B.
But if the conditional sequence isA->B->C, it will return directly to 3 when searching C.
This makes me feel confused to strict.

        for (const auto & pair : data.events_list)
        {
            const T & timestamp = pair.first;
            const auto & event_idx = pair.second - 1;
            if (strict_order && event_idx == -1)
            {
                if (first_event)
                    break;
                else
                    continue;
            }
            else if (event_idx == 0)
            {
                events_timestamp[0] = std::make_pair(timestamp, timestamp);
                first_event = true;
            }
            else if (strict && events_timestamp[event_idx].has_value())
            {
                return event_idx + 1;//example1 return here
            }
            else if (strict_order && first_event && !events_timestamp[event_idx - 1].has_value())
            {
                for (size_t event = 0; event < events_timestamp.size(); ++event)
                {
                    if (!events_timestamp[event].has_value())
                        return event;
                }
            }
            else if (events_timestamp[event_idx - 1].has_value())
            {
                auto first_timestamp = events_timestamp[event_idx - 1]->first;
                bool time_matched = timestamp <= first_timestamp + window;
                if (strict_increase)
                    time_matched = time_matched && events_timestamp[event_idx - 1]->second < timestamp;
                if (time_matched)
                {
                    events_timestamp[event_idx] = std::make_pair(first_timestamp, timestamp);
                    if (event_idx + 1 == events_size)
                        return events_size;//example2 return here
                }
            }
        }

I see a strict design purpose in #6548.
I think the answer in the first example should be 3 instead of 2. Is this a bug?

[tangxueming]

I confused about mode too.

// table schema
CREATE TABLE funnel_test
(
    `code` UInt32 ,
    `user_id` String ,
    `timestamp` UInt64
)
ENGINE = MergeTree()
ORDER BY (user_id, timestamp)
SETTINGS index_granularity = 8192;

// insert data
insert into funnel_test values (1,'id',1),(2,'id',3),(4,'id',4),(1,'id',11),(2,'id',13),(3,'id',15)

// query
// strict_increase mode return 3 rows
select user_id, windowFunnel(20,'strict_increase')(toDateTime(timestamp), code = 1, code = 2, code=3) as level from funnel_test group by user_id 
// strict_order mode return 2 rows
select user_id, windowFunnel(20,'strict_order')(toDateTime(timestamp), code = 1, code = 2, code=3) as level from funnel_test group by user_id
// strict mode return 2 rows
select user_id, windowFunnel(20,'strict')(toDateTime(timestamp), code = 1, code = 2, code=3) as level from funnel_test group by user_id
// without mode return 3 rows
select user_id, windowFunnel(20)(toDateTime(timestamp), code = 1, code = 2, code=3) as level from funnel_test group by user_id

modify first data code from 1 to 6 ,all return 3 rows

truncate table funnel_test
insert into funnel_test values (6,'id',1),(2,'id',3),(4,'id',4),(1,'id',11),(2,'id',13),(3,'id',15)

[alexey-milovidov]

CC @achimbab

[achimbab]

@BiteTheDDDDt
It seems a bug, I will fix it ASAP.
Thank you.