feat: The compare feature only accepts two existing products

[g123k]

Hi everyone,

Here are my fixes for the Compare feature on the scanner:

• Ensure to use the correct icons
• Only accept existing products in the Compare feature
• When there is only one product, disable the feature and explain to the user what's the problem
• Improve accessibility for the two buttons

Here are two videos:

• Compare feature with existing products
  Compare.webm

• Compare feature with unknown products
  Compare2.webm

It will fix both #4127 and #4130

[codecov-commenter]

Codecov Report

Merging #4139 (74554db) into develop (55b4894) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop    #4139      +/-   ##
===========================================
- Coverage    10.91%   10.89%   -0.02%     
===========================================
  Files          277      277              
  Lines        13536    13552      +16     
===========================================
  Hits          1477     1477              
- Misses       12059    12075      +16     

Impacted Files	Coverage Δ
...oth_app/lib/data_models/continuous_scan_model.dart	0.00% <0.00%> (ø)
...ges/smooth_app/lib/helpers/collections_helper.dart	13.04% <0.00%> (-0.60%)	⬇️
...pp/lib/pages/product/common/product_list_page.dart	0.00% <0.00%> (ø)
...ackages/smooth_app/lib/pages/scan/scan_header.dart	2.08% <0.00%> (-0.42%)	⬇️

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[monsieurtanuki]

Hi @g123k!
Looks good, but please have a look at my comments.

[monsieurtanuki]

Suggested change

	final int validBarcodes = model.getAvailableBarcodes().length;
	final List<String> barcodes = model.getAvailableBarcodes().toList(growable: false);

Reasons:

• confusion between "available" and "valid" barcodes
• you call again model.getAvailableBarcodes() later in the code
• "validBarcodes" does not sound like a number

If you really want,

final int numberOfBarcodes = barcodes.length;

[g123k]

The problem with your toList() is that it will force to create a new List in memory.
The Iterable is enough here just to count the number of items.

[monsieurtanuki]

Please change RankingFloatingActionButton.rankingIconData instead, for consistency: the same icon for the same action.

[g123k]

The reason I've changed the icon here, is because the RankingFloatingActionButton.rankingIconData is a trophy, and in personal search, this is the right icon to use :/

[g123k]

What would be the best option according to you?
To differentiate the 🏆 and ↔️?

[monsieurtanuki]

I would always use the same icon, as it's the same operation (product list / selected items / ranking page).