Apply Taxes and Discounts to Kasir Object

[risangbaskoro]

Taxes and Discounts is basically just another item. For discounts, the value must subtract the gross_amount from item_details.

Create a discount() method to add discount. This method receives these parameters:

• int $amount - The amount of discount. Automatically converts to a negative value if fixed, positive if percentage.
• string|null $name - The name of applied discount. Defaults to null. If null, 'Discount #<discount_id>' name will be used.
• bool $percent - Determine if the discount in fixed value or in percentage of gross_amount. Default: false.

Create a tax() method to add tax. This method receives these parameters:

• int $amount - The amount of tax. Automatically converts to a negative value if fixed, positive if percentage.
• string|null $name - The name of applied tax. Defaults to null. If null, 'Tax #<tax_id>' name will be used.
• bool $percent - Determine if the tax in fixed value or in percentage of gross_amount. Default: false.

[risangbaskoro]

Example for double discount in percentage:

Given a gross amount of Rp10000

The transaction have two discounts:

• discount #1: 20%
• discount #2: 10%

First, we're doing Rp10000 - 20%, so it would be Rp8000.
Then, the final amount would be Rp8000 - 10%, which is Rp7200.

This also applies with taxes, and multiple discounts and taxes.

[risangbaskoro]

Keeping an index of how many discounts or taxes has been applied would be helpful.

If it's the first index, the discount or tax will be calculated normally from gross amount. If it's not, calculate the discount or tax from the previous result of applied discount or tax.

[risangbaskoro]

Generally, taxes are applied after discounts are applied. By this nature, we can prevent $kasir->tax()->discount() to apply taxes before the discounts is applied.

We can approach this by reversing taxes, do the discount calculation for the gross_amount, and then reapply the taxes.