Listing problematic attributes for obscure matches

[monsieurtanuki]

Why - Problem description

cf. @teolemon's openfoodfacts/smooth-app#1118
When we try to match a product with the user preferences, sometimes we get an "unknown match".
We just know it's unknown, and we don't list what is missing for a correct yes/no match.

What - Proposed solution

Instead of just saying the match is unknown, we should list which attributes are missing.

[teolemon]

Well, if we could have something pedagogical about the computation as well. I'm unsure whether we'll be at ease showing it to users at first, but it would be interesting to have in Dev mode.

[monsieurtanuki]

@teolemon Understood: I will extend that principle to "may not match" and "does not match".
For the record there are 8 different cases for 6 different match statuses (very good, good, poor, unknown, may not, does not), and in 3 cases we put "unknown" (no attributes at all, at least one mandatory attribute that is unknown, too many unknown attributes).

[monsieurtanuki]

@teolemon @stephanegigandet Btw I think there's a flaw in the score computation, as we loop on the product attributes but not on the preference importances.

That means that a mandatory preference is ignored if the product doesn't have the related attribute at all.

It's OK as long as a product has

• either no attributes at all (probably a corrupted product), as we flag it as "unknown"
• or all the attributes populated.

[stephanegigandet]

@monsieurtanuki The server always compute all attributes so we should be fine.

[stephanegigandet]

I'm not sure if creating a separate list with explanations is the right approach: that kinds of duplicates the information we have on the attribute cards that are displayed on top of the product page.

e.g. on the website we have something like that on top of the product page:

Related to that, is it planned to add the % score on the mobile app, like we have on the website?

Could we also adopt the same translations on the website + app for the strings like "Does not match" etc. e.g. in French on the app we have "Pas de compatibilité" while on the website we have "Ne correspond pas"

[monsieurtanuki]

@stephanegigandet You're right, there's some kind of duplication here, and it may not be necessary.
Maybe I over-interpreted the initial needs.
I needed this step though, to understand the product score/match computations.

Basically there are 3 reasons why the product match is unknown:

1. no attributes at all - let's say it's not the most interesting case
2. unknown mandatory attributes
3. "too many" unknown attributes ("too many" means "sum of factors for unknown attributes >= sum of factors / 2")

It's easy to detect which attributes have an unknown match, and which are mandatory.
But it could be a frustrating experience for the user if you say: "there are unknown mandatory attributes, please 'fix' them to get a correct match". And then to say "oh it's not enough anyway as there are too many non-mandatory attributes" (cases 2 and 3 at the same time).

What can be done is just providing extra data in the "unknown" cases, with 1 bool stating if there are too many unknown attributes.
With that, the developer (e.g. in Smoothie) will be able to detect in which "unknown" cases we are (1, 2, 3, or 2+3), and has enough data to loop the attributes checking which are unknown and which are mandatory.

[monsieurtanuki]

Let's try to code directly in Smoothie first, and then move some code here if relevant.