Include postal code prefixes for japan zones

[izi-on]

What are you trying to accomplish?

We are trying to implement stricter validation for Japanese postal codes.

...

What approach did you choose and why?

I found a highly credible dataset from GeoPostcodes.
Then, I created a rake task that would read a CSV from this dataset and populate the existing JP.yml with valid zone prefixes.

• 1. Create a hash with zone codes as the key and an array of their postal codes as a value
• 2. Extract the smallest postal code prefix that will uniquely identify some corresponding zone.
• • In order to achieve this 2, I created a trie and populated it with postal codes. When populating, I also marked on the trie node the zone which we are adding the prefix for. Then, I did a simple DFS traversal and stopped when an encountered node has only one single zone associated with it: this means the current prefix uniquely identifies a zone.

3. Populate the JP yaml with this data

The impact of these changes

We can now perform naive postal code validation based off purely the zone.

Testing

For Shopify reviewers, you can compare the results to that of another rake task in country-db:

simply run
rake "postal:codes:import[JP]"
in country-db and compare the modified JP.yml to this

You will notice that this dataset is more complete

Potential question you might ask: why are there so many postal code prefixes for some zones?
That is because the dataset is such, and I believe this is entirely valid. Let's take an example:

Look at the zip prefixes for JP-02:
'03' and '018-550'

'018-550' seems suspicious, let's investigate. If you open the dataset I linked above, search for "018-55" and notice you will get postal codes in zone JP-02 and JP-05 (018-5511 more specifically). Putting these into google maps:

and notice that they are also correspondingly in JP-02 (Aomori Prefecture) and JP-05 (Akita Prefecture):

I would like for reviewers to test it this out themselves, please pick 5 zip prefixes that seem too long, and test it out yourselves following similar steps as me as written above

Validation

1. I got a sample of 10k real Japanese addresses (For Shopifolk, I linked the methodology for this in the issue linked to this PR)

2. Created a jupyter notebook (jp-prefix-validator.ipynb) that will read the CSV, and validate the zip codes against the zip prefixes in JP.yml

3. Compiled results (For Shopifolk, I reported the results of this validation in the issue linked to this PR)

Checklist

• I have added a CHANGELOG entry for this change (or determined that it isn't needed)

[izi-on]

Before I merge this to main, I will conduct tests on actual addresses in Japan and see how they behave with this new prefix validation for japan

EDIT: done

[gabypancu]

I am deleting the flag as we prioritizing other validation work for now. This can be revisited and the flag can be re-created https://experiments.shopify.com/flags/12446