Joining two aggregated streams

[Udhay]

I was trying to join two keyed streams in a particular way and get a combined stream.

For example:

Lets say I call the two streams as X and Y. 

The X stream contains:

(Key,Value)

(A,P)

(A,Q)

(A,R)

(B,P)

(C,P)

(C,Q)

The Y stream contains:

(Key,Value,Flag1,Flag2)

(A,M1,0,0)

(A,M2,0,0)

(A,M3,1,0)

(A,M4,0,0)

(A,M5,1,0)

(A,M6,0,1)

(B,N1,0,0)

(B,N2,1,0)

(B,N3,0,1)

(C,O1,1,0)

(C,O2,0,1)

My objective is to join these two streams and get the combined value as described. I want a keywise aggregated data of "Value" field from the X stream. In the Y stream I want a keywise aggregation of "Value" field based on "Flag1" i.e., the output will be set of aggregated values. I want to join these two streams by maintaining a keyed window and that window gets triggered only when the "Flag2" value of a particular key in the Y stream is "1". These flag values are available only with Y stream and not with the X stream. Thus my end result should look like:

(Key,Data,Value1,Value2,Flag)

(A,(P#Q#R),[(M1#M2#M4#M6),(M3#M5)])

(B,P,[(N1#N3),(N2)])

(C,(P#Q),[(O1),(O2)])

The timings for each of the rows in each stream are such that by the time the Flag2 value is 1 in stream Y (indicates some sort of end of a session), all the rows in stream X are also already available.

I tried to maintains state value inside my join function to get to the output. But I dont know how to query the state value and when to do it. Can anyone please suggest some solution?