Delphi - User specified string manipulation - regex

Question

I have a problem in Delphi7. My application creates mpg video files according to a set naming convention i.e.
\000_A_Title_YYYY-MM-DD_HH-mm-ss_Index.mpg
In this filename the following rules are enforced:
The 000 is the video sequence. It is incremented whenever the user presses stop.
The A (or B,C,D) specifies the recording camera - so video files are linked with up to four video streams all played simultaneously.
Title is a variable length string. In my application it cannot contain a _.
The YYYY-MM-DD_HH-mm-ss is the starting time of the video sequence (not the single file)
The Index is the zero based ordering index and is incremented within 1 video sequence. That is, video files are a maximum of 15 minutes long, once this is reached a new video file is started with the same sequence number but next index. Using this, we can calculate the actual start time of the file (Filename decoded time + 15*Index)
Using this method my application can extract the starting time that the video file started recording.
Now we have a further requirement to handle arbitrarily named video files. The only thing i know for certain is there will be a YYYY-MM-DD HH-mm-ss somewhere in the filename.
How can i allow the user to specify the filename convention for the files he is importing? Something like Regular expressions? I understand there must be a pattern to the naming scheme.
So if the user inputs ?_(Camera)_*_YYYY-MM-DD_HH-mm-ss_(Index).mpg into a text box, how would i go about getting the start time? Is there a better solution? Or do i just have to handle every single possibility as we come accross them?
(I know this is probably not the best way to handle such a problem, but we cannot change the issue - the new video files are recorded by another company)

Answer 1

I'm not sure if your trying to parse the user input into components '?(Camera)*_YYYY-MM-DD_HH-mm-ss_(Index).mpg` but if your just trying to grab the date and time something like this, the date is in group 1, time in group 2
(\d{4}-\d{2}-\d{2})_(d{2}-\d{2}-\d{2})
Otherwise, not sure what your trying to do.

Answer 2

Possibly you can use the underscores "_" as your positional indicator since you smartly don't allow them in the title.
In your example of a filename convention:
?_(Camera)_*_YYYY-MM-DD_HH-mm-ss_(Index).mpg
you can parse this user-specified string to see that the date YYYY-MM-DD is always between the 3rd and 4th underscore and the time HH-mm-ss is between the 4th and 5th.
Then it becomes a simple matter when getting the actual filenames following this convention, to find the 3rd underscore and know the date and time follow it.

Answer 3

If you want phone-calls 24/7, then you should go for the RegEx-thing and let the user freely enter some cryptography in a TEdit.
If you want happy users and a good night sleep, then be creative and drop the boring RegEx-approach. Create your own filename-decoder by using an Angry bird approach.
Here's the idea:
Create some birds with different string manipulation personalities.
Let the user select and arrange these birds.
Execute the user generated string manipulation.
Sample code:
program AngryBirdFilenameDecoder;
{$APPTYPE CONSOLE}
uses
SysUtils;
procedure PerformEatUntilDash(var aStr: String);
begin
if Pos('-', aStr) > 0 then
Delete(aStr, 1, Pos('-', aStr));
WriteLn(':-{ > ' + aStr);
end;
procedure PerformEatUntilUnderscore(var aStr: String);
begin
if Pos('_', aStr) > 0 then
Delete(aStr, 1, Pos('_', aStr));
WriteLn(':-/ > ' + aStr);
end;
function FetchDate(var aStr: String): String;
begin
Result := Copy(aStr, 1, 10);
Delete(aStr, 1, 10);
WriteLn(':-) > ' + aStr);
end;
var
i: Integer;
FileName: String;
TempFileName: String;
SelectedBirds: String;
MyDate: String;
begin
Write('Enter a filename to decode (eg. ''01-ThisIsAText-Img_01-Date_2011-03-08.png''): ');
ReadLn(FileName);
if FileName = '' then
FileName := '01-ThisIsAText-Img_01-Date_2011-03-08.png';
repeat
TempFileName := FileName;
WriteLn('Now, select some birds:');
WriteLn('Bird No.1 :-{ ==> I''ll eat letters until I find a dash (-)');
WriteLn('Bird No.2 :-/ ==> I''ll eat letters until I find a underscore (_)');
WriteLn('Bird No.3 :-) ==> I''ll remember the date before I eat it');
WriteLn;
Write('Chose your birds: (eg. 112123):');
ReadLn(SelectedBirds);
if SelectedBirds = '' then
SelectedBirds := '112123';
for i := 1 to Length(SelectedBirds) do
case SelectedBirds[i] of
'1': PerformEatUntilDash(TempFileName);
'2': PerformEatUntilUnderscore(TempFileName);
'3': MyDate := FetchDate(TempFileName);
end;
WriteLn('Bird No.3 found this date: ' + MyDate);
WriteLn;
WriteLn;
Write('Check filename with some other birds? (Y/N): ');
ReadLn(SelectedBirds);
until (Length(SelectedBirds)=0) or (Uppercase(SelectedBirds[1])<>'Y');
end.
When you'll do this in Delphi with GUI, you'll add more birds and more checking of course. And find some nice bird glyphs.
Use two list boxes. One one the left with all possible birds, and one on the right with all the selected birds. Drag'n'drop birds from left to right. Rearrange (and remove) birds in the list on the right.
The user should be able to test the setup by entering a filename and see the result of the process. Internally you store the script by using enumerators etc.