SQL Function to add datime to a date , working hours and extra hours and except holidays and lunch time -- 2

I have the function below and it works fine, but now I need to improve it :

1-I need to append the lunch time. ( in lunch time the company don't work)
@StartOfLunch = 12.5,
@EndOfLunch = 13.5,
2- i have a table of DONT WORK (holidays / vacations / ...) ( holiday/vacations the company don't work)
3- i have a table for EXTRA WORK ( in some cases the company make extra-hours and work in days that normally do not work)

Example of table for don't-work and extra-work
name
data_start
data_end
hour_start
hour_end
extra ( 1 - is for work / 0 - for don't work)
....


SIMPLE FUNCTION WITHOUT LUNCH TIME/ HOLIDAYS / EXTRATIME
---------------------------------------------------------------------------


ALTER FUNCTION [dbo].[addhoras] (@Date DATETIME, @DateAdd DATETIME)
RETURNS DATETIME
AS

--Select dbo.addhoras ('2018-01-23 10:00:00.000' , '1900-01-01 02:00:00.000')
--DECLARE @Date DATETIME = '2018-01-23 10:00:00.000';
--DECLARE @DateAdd DATETIME = '1900-01-01 02:00:00.000';

BEGIN
DECLARE @StartOfDay FLOAT = 9.5 ;
DECLARE @EndOfDay FLOAT = 17.5 ;
DECLARE @Datefinal DATETIME


--fix up start date
--before start of day, move to start of day
IF ((CAST(@Date - DATEADD(dd,0, DATEDIFF(dd,0,@Date)) AS FLOAT) * 24) < @StartOfDay)
BEGIN
SET @Date = DATEADD(mi, @StartOfDay * 60, DATEDIFF(dd,0,@Date))
END

--after close of day, move to start of next day
IF ((CAST(@Date - DATEADD(dd,0, DATEDIFF(dd,0,@Date)) AS FLOAT) * 24) > @EndOfDay)
BEGIN
SET @Date = DATEADD(mi, @StartOfDay * 60, DATEDIFF(dd,0,@Date)) + 1
END

--move to monday if on weekend
WHILE DATENAME(dw, @Date) IN ('Saturday','Sunday')
BEGIN
SET @Date = @Date + 1
END

--get the number of hours to add and the total hours per day
DECLARE @HoursPerDay FLOAT
DECLARE @HoursAdd FLOAT
SET @HoursAdd = DATEDIFF(hh, '1900-01-01 00:00:00.000', @DateAdd)
SET @HoursPerDay = @EndOfDay - @StartOfDay

--date the time of geiven day
DECLARE @CurrentHours FLOAT
SET @CurrentHours = CAST(@Date - DATEADD(dd,0, DATEDIFF(dd,0,@Date)) AS FLOAT) * 24

--if we stay in the same day, all is fine
IF (@CurrentHours + @HoursAdd <= @EndOfDay)
BEGIN
SET @Date = @Date + @DateAdd
END
ELSE
BEGIN
--remove part of day
SET @HoursAdd = @HoursAdd - (@EndOfDay - @CurrentHours)
--,ove to next day
SET @Date = DATEADD(dd,0, DATEDIFF(dd,0,@Date)) + 1

--loop day
WHILE @HoursAdd > 0
BEGIN
--add day but keep hours to add same
IF (DATENAME(dw,@Date) IN ('Saturday','Sunday'))
BEGIN
SET @Date = @Date + 1
END
ELSE
BEGIN
--add a day, and reduce hours to add
IF (@HoursAdd > @HoursPerDay)
BEGIN
SET @Date = @Date + 1
SET @HoursAdd = @HoursAdd - @HoursPerDay
END
ELSE
BEGIN
--add the remainder of the day
SET @Date = DATEADD(mi, (@HoursAdd + @StartOfDay) * 60, DATEDIFF(dd,0,@Date))
SET @HoursAdd = 0
END
END
END
END

SET @Datefinal = (SELECT @Date)

Return @Datefinal

END