Examine currency before recognizing as an available payment method

[makotom]

By default KOMOJU merchants have multicurrency enabled, with which there can by multiple payment methods with the same type_slug, but with different currency or sets of subtypes (card brands).

This PR makes sure that the plugin disposes only payment methods that don't support the currency configured for the WooCommerce instance.

[Dinwy]

Also, about supporting multi currency, I belive Komoju has currency conversion feature so I am not sure preventing user to pay when the currencies are different.

Below is an example that JPY payment method trying to pay KRW. So, in this case I think we should not filter the payment methods despite WC currency and payment currency is different.

[Dinwy]

This seems wrong to me.
This was checking methods_by_slug is already set, we are skipping the process.
Now it is checking When this slug is already set AND the cureencies are different, then skip
Which means, in the first check when this slug is not set yet, it will always skip this if statement and will set the slug.

Based on the above reason, this should be || or !(A && B)

[makotom]

Good point. Actually I intentionally made this logic in this way.

Given that WC has USD as the default "default currency", it's possible that this part of code is called with the default currency set in non-JPY. Then, if we always reject payment methods with mismatched currency (like isset($methods_by_slug[$slug]) || $pm_currency !== $wc_currency), it can end up with no payment method available, because PMs such as Konbini are available only in JPY.
Therefore I relaxed the condition. With the current logic, it will accept payment methods if 1) the currency matches, OR if 2) there is no alternative one available with the same type_slug. IOW, as negation, it rejects PMs that 1) have alternatives, AND 2) the currency does not match.

Yep indeed I first thought it was a bad idea, and eventually I found out that it would be better, seeing how my first attempt here broke our tests.

That said I think that's not an intuitive logic, I'll add a comment into the code for future reference!

[Dinwy]

Okay, I see. This is not about preventing registering the payment method but changing the priority.
In this case, I recommend to change the logic like below for the better redability.

    // If $slug is not set, register
    if (!isset($methods_by_slug[$slug])) {
        $methods_by_slug[$slug] = $payment_method;
    } else {
        // If $slug is already registered and
        // the payment currency matches the WooCommerce currency then override it
        if ($pm_currency === $wc_currency) {
            $methods_by_slug[$slug] = $payment_method;
        }
    }

[makotom]

Good call, I've pushed another commit! 🙏

[Dinwy]

Thanks! 👍

[makotom]

Also, about supporting multi currency, I belive Komoju has currency conversion feature so I am not sure preventing user to pay when the currencies are different.

Right, this was the decisive fact to employ the logic of accepting PMs that 1) the currency matches, OR if 2) there is no alternative one available with the same type_slug. In this way we just add a preference on PMs with the same currency, but still accepting PMs with different currencies.

[Dinwy]

Also, about supporting multi currency, I belive Komoju has currency conversion feature so I am not sure preventing user to pay when the currencies are different.

Right, this was the decisive fact to employ the logic of accepting PMs that 1) the currency matches, OR if 2) there is no alternative one available with the same type_slug. In this way we just add a preference on PMs with the same currency, but still accepting PMs with different currencies.

Now I understand. It is about the overriding the priority. 😸 No problem. I thought this is about limiting user's payment methods.

[Dinwy]

Thank you for the fix!