How to convert SCORM 2004 session_time format to a usable datetime format in SQL

So SCORM 2004's session_time format looks like the following

P[yY][mM][dD][T[hH][mM][s[.s]S]]

Where the options in the square brackets are optional, however it must include at least 1 of the options.

An example of the format is PT0H0M47S

Which means 0 hours, 0 minutes and 47 seconds.

The value is stored as varchar in a MSSQL database.

I need to be able to convert this string format into a usable format so that I can add this time onto a Start Date Time to work out the End Date Time.

I am currently moving the SCORM data from an old database to a new 1. I could do this in PHP and format the time easily but I would prefer to write all of the import scripts in SQL.

Any help on this would be greatly appreciated.

EDIT:

If it helps, this is a PHP function I wrote to handle the format for another purpose

private function formatDuration($duration)
{
    $count = preg_match('/P(([0-9]+)Y)?(([0-9]+)M)?(([0-9]+)D)?T?(([0-9]+)H)?(([0-9]+)M)?(([0-9]+)(\.[0-9]+)?S)?/', $duration, $matches);

    if ($count)
    {
        $_years = (int) $matches[2];
        $_months = (int) $matches[4];
        $_days = (int) $matches[6];
        $_hours = (int) $matches[8];
        $_minutes = (int) $matches[10];
        $_seconds = (int) $matches[12];
    }
    else
    {
        if (strstr($duration, ':'))
        {
            list($_hours, $_minutes, $_seconds) = explode(':', $duration);
        }
        else
        {
            $_hours = 0;
            $_minutes = 0;
            $_seconds = 0;
        }
    }

    // I just ignore years, months and days as it is unlikely that a
    // course would take any longer than 1 hour
    return $_seconds + (($_minutes + ($_hours * 60)) * 60);
}

Just worked out a solution for me.

This would need to be put inside a SQL function for me and I would need to finish off the last bit where I decide what format I want.

I am only updating around 900 rows and it is a 1 off update so performance isn't an issue.

DECLARE @session_time varchar(200) = 'P50Y2M3DT4H5M6S'

DECLARE @date varchar(100) = ''
DECLARE @time varchar(100) = ''

DECLARE @year varchar(20) = '0'
DECLARE @month varchar(20) = '0'
DECLARE @day varchar(20) = '0'
DECLARE @hour varchar(20) = '0'
DECLARE @minute varchar(20) = '0'
DECLARE @second varchar(20) = '0'

-- Remove the P
SET @session_time = SUBSTRING(@session_time, 2, LEN(@session_time)-1)

-- If we have a T
IF PATINDEX('%T%',@session_time) > 0
BEGIN
    SET @date = SUBSTRING(@session_time, 0, PATINDEX('%T%',@session_time))

    SET @time = SUBSTRING(@session_time, LEN(@date + 'T') + 1, LEN(@session_time))
END
ELSE
BEGIN
    SET @time = @session_time;
END

-- Get the date parts
IF LEN(@date) > 0
BEGIN
    -- If theres a year
    IF PATINDEX('%Y%',@date) > 0
    BEGIN
        SET @year = SUBSTRING(@date, 0, PATINDEX('%Y%',@date))

        SET @date = SUBSTRING(@date, LEN(@year + 'Y') + 1, LEN(@date))
    END

    -- If theres a month
    IF PATINDEX('%M%',@date) > 0
    BEGIN
        SET @month = SUBSTRING(@date, 0, PATINDEX('%M%',@date))

        SET @date = SUBSTRING(@date, LEN(@month + 'M') + 1, LEN(@date))
    END

    -- If theres a day
    IF PATINDEX('%D%',@date) > 0
    BEGIN
        SET @day = SUBSTRING(@date, 0, PATINDEX('%D%',@date))

        SET @date = SUBSTRING(@date, LEN(@day + 'D') + 1, LEN(@date))
    END
END

-- Get the time parts
IF LEN(@time) > 0
BEGIN
    -- If theres an hour
    IF PATINDEX('%H%',@time) > 0
    BEGIN
        SET @hour = SUBSTRING(@time, 0, PATINDEX('%H%',@time))

        SET @time = SUBSTRING(@time, LEN(@hour + 'H') + 1, LEN(@time))
    END

    -- If theres a minute
    IF PATINDEX('%M%',@time) > 0
    BEGIN
        SET @minute = SUBSTRING(@time, 0, PATINDEX('%M%',@time))

        SET @time = SUBSTRING(@time, LEN(@minute + 'M') + 1, LEN(@time))
    END

    -- If theres a second
    IF PATINDEX('%S%',@time) > 0
    BEGIN
        SET @second = SUBSTRING(@time, 0, PATINDEX('%S%',@time))

        SET @time = SUBSTRING(@time, LEN(@second + 'S') + 1, LEN(@time))
    END
END

PRINT @year + ' years '
PRINT @month + ' months '
PRINT @day + ' days '
PRINT @hour + ' hours '
PRINT @minute + ' minutes '
PRINT @second + ' seconds '