Group table into 15 minute intervals

Question

T-SQL, SQL Server 2008 and up

Given a sample table of

 StatusSetDateTime   | UserID | Status    | StatusEndDateTime   | StatusDuration(in seconds)
============================================================================
 2012-01-01 12:00:00 | myID   | Available | 2012-01-01 13:00:00 | 3600

I need to break that down into a view that uses 15 minute intervals for example:

IntervalStart       | UserID | Status | Duration

===========================================

2012-01-01 12:00:00 | myID | Available | 900 

2012-01-01 12:15:00 | myID | Available | 900

2012-01-01 12:30:00 | myID | Available | 900 

2012-01-01 12:45:00 | myID | Available | 900 

2012-01-01 13:00:00 | myID | Available | 0

etc....

Now I've been able to search around and find some queries that will break down I found something similar for MySql Here :

And something for T-SQL Here

But on the second example they are summing the results whereas I need to divide the total duration by the interval time (900 seconds) by user by status.

I was able to adapt the examples in the second link to split everything into intervals but the total duration time is returned and I cannot quite figure out how to get the Interval durations to split (and still sum up to the total original duration).

Thanks in advance for any insight!

edit : First Attempt

 ;with cte as 
    (select MIN(StatusDateTime) as MinDate
          , MAX(StatusDateTime) as MaxDate
          , convert(varchar(14),StatusDateTime, 120) as StartDate
          , DATEPART(minute, StatusDateTime) /15 as GroupID
          , UserID
          , StatusKey
          , avg(StateDuration) as AvgAmount
     from AgentActivityLog
     group by convert(varchar(14),StatusDateTime, 120)
         , DATEPART(minute, StatusDateTime) /15
         , Userid,StatusKey)

  select dateadd(minute, 15*GroupID, CONVERT(datetime,StartDate+'00'))
         as [Start Date]
       , UserID, StatusKey, AvgAmount as [Average Amount]
  from cte

edit : Second Attempt

;With cte As
   (Select DateAdd(minute
                   , 15 * (DateDiff(minute, '20000101', StatusDateTime) / 15)
                   , '20000101') As StatusDateTime
         , userid, statuskey, StateDuration
    From AgentActivityLog)

 Select StatusDateTime, userid,statuskey,Avg(StateDuration)
 From cte
 Group By StatusDateTime,userid,statuskey;

Answer 1

;with cte_max as 
(
   select dateadd(mi, -15, max(StatusEndDateTime)) as EndTime, min(StatusSetDateTime) as StartTime
   from AgentActivityLog
), times as
(
    select StartTime as Time from cte_max
    union all
    select dateadd(mi, 15, c.Time)
    from times as c
        cross join cte_max as cm
    where c.Time <= cm.EndTime
)
select
    t.Time, A.UserID, A.Status,
    case
        when t.Time = A.StatusEndDateTime then 0
        else A.StatusDuration / (count(*) over (partition by A.StatusSetDateTime, A.UserID, A.Status) - 1)
    end as Duration
from AgentActivityLog as A
    left outer join times as t on t.Time >= A.StatusSetDateTime and t.Time <= A.StatusEndDateTime

sql fiddle demo