T-SQL Stored Procedure Question?

Hi all,

I have some problem understanding the following stored procedure. Could you guys explain in detail what the following stored procedure does?


CREATE PROCEDURE Test_StoredProcedure
(
@RecipeID int,            ---- recipe ID
@Quantity decimal,        -----ingredient quantity
@IngredientName varchar(1000), ----- ingredient name
@UnitofMeasurement varchar(1000), ----ingredient unit
@Output varchar(max) output
)
AS
BEGIN

if exists (select 1 from RecipeIngredients where RecipeID = @RecipeID and IngredientName = @IngredientName and
quantity = @Quantity)
 
begin
     return -1
end

else if exists (select 1 from RecipeIngredients where RecipeID = @RecipeID and IngredientName = @IngredientName)

begin
     update RecipeIngredients set quantity = @Quantity where RecipeID = @RecipeID and IngredientName=@IngredientName
     
end

else

begin
      INSERT INTO RecipeIngredients(RecipeID, quantity,IngredientName, UnitofMeasurement)
      VALUES     (@RecipeID, @Quantity, @IngredientName,@UnitofMeasurement)
      
end



select @Output = STUFF( (select CONVERT(VARCHAR,quantity) + ' ' + UnitofMeasurement + ' ' + IngredientName + ''
from RecipeIngredients
where RecipeID = @RecipeID FOR XML PATH ('')) ,1,0, '')

END