Avoid retaking all screenshots on publish unless strictly necessary

[simonw]

Deploy will take half an hour because it's going to need to rebuild all 450 screenshots due to an (invisible) change to the entry HTML.

Originally posted by @simonw in #81 (comment)

[simonw]

Changes to the content of a TIL should generate a new screenshot of that TIL.

But, right now, even the tiniest tweak to the base or entry templates (including changes that wouldn't visibly affect the shots at all) triggers a 450+ screenshot generation process.

[simonw]

Easiest fix: instead of incorporating the hash of the HTML templates themselves, switch to a SCREENSHOT_VERSION constant. I can then manually change that any time I want to trigger a full re-render.

[simonw]

I could set the first version of that to the current hash, to avoid recalculating all 450 existing shots when I deploy this change.

[simonw]

til/generate_screenshots.py

Lines 10 to 13 in b8ab160

	SHOT_HASH_PATHS = [
	(root / "templates" / "pages" / "{topic}" / "{slug}.html"),
	(root / "templates" / "til_base.html"),
	]

til/generate_screenshots.py

Lines 57 to 60 in b8ab160

	shot_html_hash = hashlib.md5()
	for filepath in SHOT_HASH_PATHS:
	shot_html_hash.update(filepath.read_text().encode("utf-8"))
	shot_html_hash = shot_html_hash.hexdigest()

Since those hashes are added in sequence, the constant would need to be a list in order to capture the current state.

[simonw]

If I got this right, the deploy should not recreate any screenshots.

[simonw]

Yes that worked: