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mccy: round to lowest denomination before applying rounding from sett…
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…ings

This is consistent with the results of the discussions in paJDYF-g0K-p2.

Previous behavior as of #9876 is to ceil the price before applying any
rounding options from the settings, but based on the P2 discussions we
identified that using `round` instead of `ceil` is the better approach.
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@reykjalin
reykjalin committed Dec 12, 2024
1 parent 476c528 commit d971558
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Showing 2 changed files with 34 additions and 49 deletions.
68 changes: 26 additions & 42 deletions includes/multi-currency/MultiCurrency.php
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Original file line number Diff line number Diff line change
Expand Up @@ -832,21 +832,23 @@ public function get_price( $price, string $type ): float {
return (float) $price;
}

// We must ceil the converted price here so that we don't introduce rounding errors when
// summing up costs. Consider, e.g. a converted price of 10.003 for a 2-decimal currency.
// A single product would cost 10.00, but 2 of them would cost 20.01, _unless_ we round
// the individual parts correctly.
$converted_price = ( (float) $price ) * $currency->get_rate();
$converted_price = $this->ceil_price_for_currency( $converted_price, $currency );

if ( 'tax' === $type || 'coupon' === $type || 'exchange_rate' === $type ) {
return $converted_price;
// We must make sure the price is rounded properly before returning it, otherwise we
// may end up with inconsistent prices in the cart.
$num_decimals = absint(
$this->localization_service->get_currency_format(
$currency->get_code()
)['num_decimals']
);
return round( $converted_price, $num_decimals );
}

$charm_compatible_types = [ 'product', 'shipping' ];
$apply_charm_pricing = $this->get_apply_charm_only_to_products()
? 'product' === $type
: in_array( $type, $charm_compatible_types, true );
? 'product' === $type
: in_array( $type, $charm_compatible_types, true );

return $this->get_adjusted_price( $converted_price, $apply_charm_pricing, $currency );
}
Expand Down Expand Up @@ -1336,7 +1338,22 @@ public function is_initialized(): bool {
* @return float The adjusted price.
*/
protected function get_adjusted_price( $price, $apply_charm_pricing, $currency ): float {
$price = $this->ceil_price( $price, (float) $currency->get_rounding() );
$rounding = (float) $currency->get_rounding();

// If rounding is configured to be `0.00` we still need to round to the nearest lowest
// currency denomination.
// Otherwise we ceil the price to the configured rounding option.
if ( 0.00 === $rounding ) {
$num_decimals = absint(
$this->localization_service->get_currency_format(
$currency->get_code()
)['num_decimals']
);

$price = round( $price, $num_decimals );
} else {
$price = $this->ceil_price( $price, (float) $currency->get_rounding() );
}

if ( $apply_charm_pricing ) {
$price += (float) $currency->get_charm();
Expand All @@ -1361,39 +1378,6 @@ protected function ceil_price( float $price, float $rounding ): float {
return ceil( $price / $rounding ) * $rounding;
}

/**
* Ceils the price to the precision dictated by the number of decimals in the provided currency.
*
* For example: US$10.0091 -> US$10.01, JPY 1001.01 -> JPY 1002.
*
* @param float $price The price to be ceiled.
* @param Currency $currency The currency used to figure out the ceil precision.
*
* @return float The ceiled price.
*/
protected function ceil_price_for_currency( float $price, Currency $currency ): float {
// phpcs:disable Squiz.PHP.CommentedOutCode.Found, example comments look like code.

// Example to explain the math:
// $price = 10.003.
// expected rounding = 10.01.

// $num_decimals = 2.
// $factor. = 10^2 = 100.
$num_decimals = absint(
$this->localization_service->get_currency_format(
$currency->get_code()
)['num_decimals']
);
$factor = 10 ** $num_decimals; // 10^{$num_decimals}.

// ceil( 10.003 * $factor ) = ceil( 1_000.3 ) = 1_001.
// 1_001 / 100 = 10.01.
return ceil( $price * $factor ) / $factor; // = 10.01.

// phpcs:enable Squiz.PHP.CommentedOutCode.Found
}

/**
* Sets up the available currencies, which are alphabetical by name.
*
Expand Down
15 changes: 8 additions & 7 deletions tests/unit/multi-currency/test-class-multi-currency.php
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Original file line number Diff line number Diff line change
Expand Up @@ -621,26 +621,26 @@ public function test_get_price_returns_converted_coupon_price_without_adjustment
add_filter( 'wcpay_multi_currency_apply_charm_only_to_products', '__return_false' );

// 0.708099 * 10 = 7.08099.
// ceil( 7.08099, 2 ) = 7.09.
$this->assertSame( 7.09, $this->multi_currency->get_price( '10.0', 'coupon' ) );
// round( 7.08099, 2 ) = 7.08.
$this->assertSame( 7.08, $this->multi_currency->get_price( '10.0', 'coupon' ) );
}

public function test_get_price_returns_converted_exchange_rate_without_adjustments() {
WC()->session->set( WCPay\MultiCurrency\MultiCurrency::CURRENCY_SESSION_KEY, 'GBP' );
add_filter( 'wcpay_multi_currency_apply_charm_only_to_products', '__return_false' );

// 0.708099 * 10 = 7.08099.
// ceil( 7.08099, 2 ) = 7.09.
$this->assertSame( 7.09, $this->multi_currency->get_price( '10.0', 'exchange_rate' ) );
// round( 7.08099, 2 ) = 7.08.
$this->assertSame( 7.08, $this->multi_currency->get_price( '10.0', 'exchange_rate' ) );
}

public function test_get_price_returns_converted_tax_price() {
WC()->session->set( WCPay\MultiCurrency\MultiCurrency::CURRENCY_SESSION_KEY, 'GBP' );
add_filter( 'wcpay_multi_currency_apply_charm_only_to_products', '__return_false' );

// 0.708099 * 10 = 7.08099.
// ceil( 7.08099, 2 ) = 7.09.
$this->assertSame( 7.09, $this->multi_currency->get_price( '10.0', 'tax' ) );
// round( 7.08099, 2 ) = 7.08.
$this->assertSame( 7.08, $this->multi_currency->get_price( '10.0', 'tax' ) );
}

/**
Expand Down Expand Up @@ -1017,7 +1017,8 @@ public function test_set_new_customer_currency_meta_does_not_update_user_meta_if

public function get_price_provider() {
return [
[ '5.2499', '0.00', 5.25 ], // Even though the precision is 0.00 we make sure the amount is ceiled to the currency's number of digits.
[ '5.2401', '0.00', 5.24 ], // Even though the precision is 0.00 we make sure the amount is rounded to the currency's number of digits.
[ '5.2499', '0.00', 5.25 ], // Even though the precision is 0.00 we make sure the amount is rounded to the currency's number of digits.
[ '5.2499', '0.25', 5.25 ],
[ '5.2500', '0.25', 5.25 ],
[ '5.2501', '0.25', 5.50 ],
Expand Down

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