How to write Navision CALCDATE function in TSQL - sql-server

Question

Here is a definition of Navision CALCDATE function:
NewDate := CALCDATE(DateExpression [, Date])
It takes two parameters:
DateExpression which in Navision has type DateFormula which in SQL is stored as varchar(32)
Date, which in SQL means DateTime. To simplify the problem I'm assuming it's not optional (in Navsion, it is)
I need to access Navision data from SQL and do some calculations based on DateFormulas stored there.
I know how to write such function in SQL CLR, so please don't include this in your answer.
How to write CALCDATE function in TSQL?
[Optional] Is it possible to do it in SQL query only, using some (auxiliary) CTEs (this will allow me to not add function to Navsion database, therefore not modify it)?
Does SQL CLR is my only option?
Main problem I have with this function is that it seems that it must be done in following steps:
Parse DateExpression
Apply parsing result to Date parameter and produce new date.
But how to do the parsing part?
For example DateExpression = '-CW+1W+1D' means that we must do 3 things with our Date parameter in exactly this order:
Find last Monday (current week start) '-CW'
Add 1 week (7 days) '+1W'
Add 1 day '+1D'
It can be written in shorter form '+CW+1D', which means next monday and 1 day.
Generally this varchar(32) can contain 1 or more such expressions and they must be applied in provided order on Date parameter.
How to parse such varchar(32) in SQL?
In C# I would do it in a loop or recursively, but how to do it in SQL (sets)?
How to convert such structured varchar(32) into set of formulas.
Maybe I need to convert it somehow to XML and query it using SQL Server XML functions - but how?
EDIT:
How I want to use it?
I want to use this function as part of larger query.
For example (simplified):
select ...
from [Issued Reminder Header] as reminder
join [Reminder Terms] as terms on ...
join [Reminder Level] as level on ...
cross apply dbo.CalcDate(level.[Grace Period], reminder.[Posting Date]) as calculated
What I mean, is that level.[Grace Period] is in table that can be edited by users and can change any moment. So I cannot take any shortcuts and precalculate few values.

Answer 1

This answer is here primarily as an example in how silly this would be to try and implement in pure SQL (and also because I considered it an interesting challenge).
It is not intended to be used in any kind of production capacity and I am not even sure it properly implements the functionality of calcdate or would work across all the possible scenarios that calcdate allows.
SQL
declare #d date = '19960521';
declare #t table(Expression varchar(32),ExpectedValue date);
insert into #t values
('-CW+1W+1D','19960528')
,('CQ+1M-10D','19960720')
,('+CW+1D','19960528')
,('+CW+1WD','19960528')
,('CM+30D','19960630')
,('-WD2','19960514')
,('WD3','19960522')
,('-D3','19960503')
,('-D27','19960427')
,('D3','19960603')
,('D27','19960527')
,('10D','19960531')
,('1W','19960528')
,('W2','19970106')
,('-W2','19960108')
,('M12','19961201')
,('M2','19970201')
,('-M2','19960201')
,('Q4','19961001')
,('Q2','19970401')
,('-Q2','19960401')
;
with v as
(
select Expression
,ExpectedValue
,stuff(replace(replace(case when left(Expression,1) not in('+','-') then '+' else '' end + Expression
,'+','|+'
)
,'-','|-'
)
,1,1,''
) + '|||' as Fmt
from #t
)
,p as
(
select Expression
,ExpectedValue
,Fmt
,left(v.Fmt,charindex('|',v.Fmt,0)-1) as p1
,substring(v.Fmt
,charindex('|',v.Fmt,0)+1
,(charindex('|',v.Fmt,charindex('|',v.Fmt,0)+1)-1) - (charindex('|',v.Fmt,0))
) as p2
,replace(substring(v.Fmt
,charindex('|',v.Fmt,charindex('|',v.Fmt,0)+1)+1
,999
)
,'|'
,''
) as p3
from v
)
select #d as GivenDate
,p.Expression
,p.ExpectedValue
,cast(v3.retp3 as date) as ReturnedValue
,case when p.ExpectedValue = v3.retp3 then 'Match' else 'No Match' end as ValueCheck
from p
outer apply(values(case when substring(p1,2,1) = 'C' -- <Prefix><Unit>
then case substring(p1,3,2)
when 'D' then #d
when 'WD' then #d
when 'W' then dateadd(week, datediff(week,0,#d) + case when left(p1,1) = '+' then 1 else 0 end, 0)
when 'M' then case when left(p1,1) = '+' then eomonth(#d) else dateadd(day,1,eomonth(#d,-1)) end
when 'Q' then dateadd(day,case when left(p1,1) = '+' then -1 else 0 end,dateadd(quarter, datediff(quarter,0,#d) + case when left(p1,1) = '+' then 1 else 0 end, 0))
when 'Y' then dateadd(year, datediff(year,0,#d) + case when left(p1,1) = '+' then 1 else 0 end, 0)
else ''
end
when isnumeric(substring(p1,2,1)) = 1 -- <Number><Unit>
then case when right(p1,2) = 'WD'
then dateadd(day,cast(replace(p1,'WD','') as int),#d)
else case right(p1,1)
when 'D' then dateadd(day,cast(replace(p1,'D','') as int),#d)
when 'W' then dateadd(week,cast(replace(p1,'W','') as int),#d)
when 'M' then dateadd(month,cast(replace(p1,'M','') as int),#d)
when 'Q' then dateadd(quarter,cast(replace(p1,'Q','') as int),#d)
when 'Y' then dateadd(year,cast(replace(p1,'Y','') as int),#d)
end
end
when isnumeric(substring(p1,2,1)) = 0 -- <Unit><Number>
then case when substring(p1,2,2) = 'WD'
then dateadd(day,right(p1,1)-1,dateadd(week, datediff(week,0,#d) - case when left(p1,1) = '-' then 1 else 0 end, 0))
else case substring(p1,2,1)
when 'D' then dateadd(day,abs(cast(replace(p1,'D','') as int))-1,dateadd(month, datediff(month,0,#d) + case when abs(cast(replace(p1,'D','') as int)) < day(#d) then 1 else 0 end + case when sign(cast(replace(p1,'D','') as int)) = -1 then -1 else 0 end, 0))
when 'W' then dateadd(week,datediff(week,0,dateadd(week,abs(cast(replace(p1,'W','') as int))-1,datefromparts(year(#d) + case when abs(cast(replace(p1,'W','') as int)) <= datepart(week,#d) then 1 else 0 end + case when sign(cast(replace(p1,'W','') as int)) = -1 then -1 else 0 end,1,1))), 0)
when 'M' then datefromparts(year(#d) + case when abs(cast(replace(p1,'M','') as int)) <= month(#d) then 1 else 0 end + case when sign(cast(replace(p1,'M','') as int)) = -1 then -1 else 0 end,abs(cast(replace(p1,'M','') as int)),1)
when 'Q' then datefromparts(year(#d) + case when abs(cast(replace(p1,'Q','') as int)) <= datepart(quarter,#d) then 1 else 0 end + case when sign(cast(replace(p1,'Q','') as int)) = -1 then -1 else 0 end,((abs(cast(replace(p1,'Q','') as int))-1)*3)+1,1)
when 'Y' then datefromparts(abs(cast(replace(p1,'Y','') as int)),1,1)
end
end
else ''
end
)
) as v1(retp1)
outer apply(values(case right(p2,1)
when 'D' then dateadd(day,cast(replace(replace(p2,'W',''),'D','') as int),retp1)
when 'W' then dateadd(day,cast(replace(p2,'W','') as int) * 7,retp1)
when 'M' then dateadd(month,cast(replace(p2,'M','') as int),retp1)
when 'Q' then dateadd(quarter,cast(replace(p2,'Q','') as int),retp1)
when 'Y' then dateadd(year,cast(replace(p2,'Y','') as int),retp1)
else retp1
end
)
) as v2(retp2)
outer apply(values(case right(p3,1)
when 'D' then dateadd(day,cast(replace(replace(p3,'W',''),'D','') as int),retp2)
when 'W' then dateadd(day,cast(replace(p3,'W','') as int) * 7,retp2)
when 'M' then dateadd(month,cast(replace(p3,'M','') as int),retp2)
when 'Q' then dateadd(quarter,cast(replace(p3,'Q','') as int),retp2)
when 'Y' then dateadd(year,cast(replace(p3,'Y','') as int),retp2)
else retp2
end
)
) as v3(retp3);
Output
GivenDate
Expression
ExpectedValue
ReturnedValue
ValueCheck
1996-05-21
-CW+1W+1D
1996-05-28
1996-05-28
Match
1996-05-21
CQ+1M-10D
1996-07-20
1996-07-20
Match
1996-05-21
+CW+1D
1996-05-28
1996-05-28
Match
1996-05-21
+CW+1WD
1996-05-28
1996-05-28
Match
1996-05-21
CM+30D
1996-06-30
1996-06-30
Match
1996-05-21
-WD2
1996-05-14
1996-05-14
Match
1996-05-21
WD3
1996-05-22
1996-05-22
Match
1996-05-21
-D3
1996-05-03
1996-05-03
Match
1996-05-21
-D27
1996-04-27
1996-04-27
Match
1996-05-21
D3
1996-06-03
1996-06-03
Match
1996-05-21
D27
1996-05-27
1996-05-27
Match
1996-05-21
10D
1996-05-31
1996-05-31
Match
1996-05-21
1W
1996-05-28
1996-05-28
Match
1996-05-21
W2
1997-01-06
1997-01-06
Match
1996-05-21
-W2
1996-01-08
1996-01-08
Match
1996-05-21
M12
1996-12-01
1996-12-01
Match
1996-05-21
M2
1997-02-01
1997-02-01
Match
1996-05-21
-M2
1996-02-01
1996-02-01
Match
1996-05-21
Q4
1996-10-01
1996-10-01
Match
1996-05-21
Q2
1997-04-01
1997-04-01
Match
1996-05-21
-Q2
1996-04-01
1996-04-01
Match