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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Questions and Comments

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[coveralls]

Pull Request Test Coverage Report for Build da278d0c-dde3-470e-b0ed-e13fa305e2f9

Details

• 0 of 23 (0.0%) changed or added relevant lines in 3 files are covered.
• 30 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.1%) to 56.307%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
app/Controllers/Graph.hs	0	6	0.0%
app/Util/Helpers.hs	0	6	0.0%
app/Export/GetImages.hs	0	11	0.0%

Files with Coverage Reduction	New Missed Lines	%
app/Export/GetImages.hs	30	0.0%

Totals
Change from base Build e318a04a-7db4-4eb7-98e7-21e1ce93c3b7:	-0.1%
Covered Lines:	2280
Relevant Lines:	3977

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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)

[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)