CS-Cart develop a Prorated Shipping Tax plug-in

Can you write a plug in compatible with CS-cart v4.11.x that will: 1. Add a new tick box option on the admin page under Administration > Shipping & Taxes > Shipping Methods > to select 'Shipping Tax Calculation' as 'Flat Rate' or 'Prorated' . 2. 'Flat Rate' is the default method and makes no changes to current functionality. 3. If the Tax Rate is an Absolute($) amount, selecting 'Prorated' makes no changes to current functionality. 4. If the Tax Rate is a Percent(%), then the 'Prorated' method shall calculate the shipping tax based on the (%)tax rates of the items in the basket and update the order accordingly. 5. Method of calculation of 'Prorated' shipping tax shall be: [Net price of taxable items in basket] * [Tax Rate (%)] / [Net price of all items in basket] 6. Use Standard rounding to 2 decimal places. 7. If working correctly, the following example will be true when pro-rata shipping tax is activated, (assumes a tax rate of 20% has been chosen ): 7.1. A customer buys only items that have zero % tax, then the shipping is also zero % rated for tax 7.2. A customer buys only items that have full 20% tax, then the shipping is also 20% rated for tax 7.3. A customer buys multiple items with combination of tax values eg: $100 taxable at 20% and $50 non-taxable items, the tax that will be applied only to the shipping cost for this order is $100/ $150 * 20% = 13.33% 8. The plug-in code must include appropriate comments that future developers may find useful for debugging or extending or revising. 9. You must agree that we own the intellectual property and rights to use, market or license the plug-in freely or otherwise.