Add the Eco-Score by country API

[teolemon]

What

• Add the ability to request the Eco-Score by country (ecoscore_grade_fr/be/nl/es/de/it) to support https://github.com/openfoodfacts/openfoodfacts-server/issues/10183

Add this chunk of documentation as a comment

You need to ensure the country your users are in:

- Asking them explicitly at startup, and storing the value
- Geofencing your app to just one country
- Using the phones or the IP address (using eg GeoIP) to infer a country

You need to serve the matching Eco-Score value
You can ask for a country specific Eco-Score
If your users are outside France, you need to clearly display the experimental disclaimer at least once.

Potential block

• [x] #216

[monsieurtanuki]

This is more or less what I've understood:

• on the backend specific ecoscore grades are computed for the following countries: fr/be/nl/es/de/it
• for the moment from flutter we can query ProductField.ECOSCORE_GRADE, ProductField.ECOSCORE_SCORE and ProductField.ECOSCORE_DATA
• in the query we're able to specify an optional country

I guess this issue should be fixed rather on the backend every time there's a query about a ProductField.ECOSCORE_... field:

• if the country is not specified, return null
• if the country is not fr/be/nl/es/de/it, return null
• else return the country related ecoscore data

Am I missing something?

[teolemon]

• I believe returning null server side is problematic, as it will break existing implementations, including the official app.
• There's no proper documentation right now, apart from this, which is not up-to-date https://docs.google.com/document/d/1_5AeofpXbaKY9Rd3eeWmHIrhJE8GiPQ-Mfx1SCvpzME/edit
• The simple way is to use de.openfoodfacts.org as an API endpoint, and I believe we can pass cc=de ? @stephanegigandet

[monsieurtanuki]

@teolemon I still cannot picture the whole thing.

For instance, let's start from https://world.openfoodfacts.org/api/v0/product/8076809572569.json?fields=nutriscore_score,nutriscore_grade,ecoscore_score,ecoscore_grade

1. in this case, whose country are those grades computed for?
2. I got the same result ({"ecoscore_grade":"d","ecoscore_score":39,"nutriscore_grade":"d","nutriscore_score":17}) after replacing world. with fr., es., it., be., de. and nl. - am I just unlucky or is the URL wrong? Btw same result with pt., which is not in the OP country list.
3. If I try to replace the field names like ecoscore_grade_nl, there's not matching output for this particular field

In short, it looks like we have nutriscore and ecoscore fields computed only one way, with no way to specify a country.