Refactor graphImageResponse to use Temporary Files

[a1-su]

Proposed Changes

This PR refactors the graphImageResponse function in Controllers/Graph.hs to use withSystemTempFile temporary files (from the temporary library in Haskell). Previously the files were being manually generated and deleted, so if an error ever occurred during process of saving the graph, the files would be left undeleted.

Note that this modified some other functions, including getActiveGraphImage in Export/GetImages.hs, which was coupled with the exportTimetablePDF function in Controllers/Timetable.hs. I've modified getActiveGraphImage to keep its original functionality and graphImageResponse to use helper function writeActiveGraphImage, but should exportTimetablePDF ever get refactored to also use temporary files and writeActiveGraphImage, getActiveGraphImage can be safely removed.

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[coveralls]

Pull Request Test Coverage Report for Build b17a4f5a-53dd-4f11-807c-7a64c9ccb0cb

Details

• 0 of 22 (0.0%) changed or added relevant lines in 4 files are covered.
• 20 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.2%) to 56.605%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
app/Util/Helpers.hs	0	2	0.0%
app/Svg/Generator.hs	0	4	0.0%
app/Controllers/Graph.hs	0	7	0.0%
app/Export/GetImages.hs	0	9	0.0%

Files with Coverage Reduction	New Missed Lines	%
app/Export/GetImages.hs	20	0.0%

Totals
Change from base Build e318a04a-7db4-4eb7-98e7-21e1ce93c3b7:	0.2%
Covered Lines:	2280
Relevant Lines:	3951

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💛 - Coveralls

[david-yz-liu]

the filenames should still be random (want to avoid possible name collisions if multiple responses are being executed at the same time)

[a1-su]

I could be mistaken, but the withSystemTempFile accounts for this automatically. The "graph.svg" and "graph.png" are file name templates, which have a random number placed after the file name but before the file extension when created, so name collisions are avoided and a random number doesn't need to be added manually.

[david-yz-liu]

Ah yes that's great, thanks for sharing this element of the documentation. 👍

[david-yz-liu]

You should be able to use this handle, passing it down all the way to buildSVGHelper in order to write directly to the file. This is different from the png temp file, since for the latter the file is being created externally to Courseography (by running magick in a subprocess)

[a1-su]

Unfortunately because of how the helper functions were implemented, the way I've decided to make this change included an hClose inside the getGraphImage function in Export/GetImages.hs, which I'm not sure is ideal if it's being called within a helper function inside a withSystemTempFile (or withFile, which was added because the helper functions are coupled with exportTimetablePDFResponse in Controllers/Timetable.hs).

I wasn't sure if I should have since it was outside the scope of the ticket, but if you'd have preferred, I can move createImageFile, which was previously called in getGraphImage, to be imported in Controllers/Graph.hs instead. This way, hClose can be called inside the withSystemTempFile instead of in a helper function inside withSystemTempFile. To keep the original functionality, this would mean the createImageFile would also need to be called in and duplicated in getActiveGraphImage (inside the withFile) instead of just in one place (because of the coupling with the timetable PDF export). I also chose not to do this since getTimetableImage, a very similar function, uses createImageFile as well and I was worried it would be unintuitive to have them behave differently.

If the timetable export also gets refactored, I can modify the code so it's more cohesive and better follows standard practices, and feel free to let me know if this should be changed.

[david-yz-liu]

Hi @a1-su, nice work. Overall this is a bit messy because of the issues you've identified with the existing timetable export. Please go ahead and refactor the timetable exporting functions to use the same approach as well. You're definitely on the right track with this and refactoring both will let you clean the up code, so I'm happy for you to proceed with this.

[david-yz-liu]

Ah yes that's great, thanks for sharing this element of the documentation. 👍