How I can replace odd patterns inside a string?

Question

I'm in the process of creating a temporary procedure in SQL because I have a value of a table which is written in markdown, so it appear as rendered HTML in the web browser (markdown to HTML conversion).

String of the column currently look like this:

Questions about **general computing hardware and software** are off-topic for Stack Overflow unless they directly involve tools used primarily for programming. You may be able to get help on [Super User](http://superuser.com/about)

I'm currently working with bold and italic text. This mean (in the case of bold text) I will need to replace odd N times the pattern**with<b>and even times with</b>.
I saw replace() but it perform the replacement on all the patterns of the string.

So How I can replace a sub-string only if it is odd or only it is even?

Update: Some peoples wonder what schemas I'm using so just take a look here.

One more extra if you want: The markdown style hyperlink to html hyperlink doesn't look so simple.

Answer 1

Using theSTUFFfunction and a simpleWHILEloop:

CREATE FUNCTION dbo.fn_OddEvenReplace(@text nvarchar(500), 
                                      @textToReplace nvarchar(10), 
                                      @oddText nvarchar(10), 
                                      @evenText nvarchar(500))
RETURNS varchar(max)
AS
BEGIN
    DECLARE @counter tinyint
    SET @counter = 1

    DECLARE @switchText nvarchar(10)
    WHILE CHARINDEX(@textToReplace, @text, 1) > 0
    BEGIN
        SELECT @text = STUFF(@text, 
                    CHARINDEX(@textToReplace, @text, 1), 
                    LEN(@textToReplace), 
                    IIF(@counter%2=0,@evenText,@oddText)),
                @counter = @counter + 1
    END
    RETURN @text
END

And you can use it like this:

SELECT dbo.fn_OddEvenReplace(column, '**', '<b>', '</b>')
FROM table

UPDATE:

This is re-written as an SP:

CREATE PROC dbo.##sp_OddEvenReplace @text nvarchar(500), 
                                  @textToReplace nvarchar(10), 
                                  @oddText nvarchar(10), 
                                  @evenText nvarchar(10),
                                  @returnText nvarchar(500) output
AS
BEGIN
    DECLARE @counter tinyint
    SET @counter = 1

    DECLARE @switchText nvarchar(10)
    WHILE CHARINDEX(@textToReplace, @text, 1) > 0
    BEGIN
        SELECT @text = STUFF(@text, 
                    CHARINDEX(@textToReplace, @text, 1), 
                    LEN(@textToReplace), 
                    IIF(@counter%2=0,@evenText,@oddText)),
                @counter = @counter + 1
    END
    SET @returnText = @text
END
GO

And to execute:

DECLARE @returnText nvarchar(500)
EXEC dbo.##sp_OddEvenReplace '**a** **b** **c**', '**', '<b>', '</b>', @returnText output

SELECT @returnText