# The Pragmatic Bookshelf has offices in Texas (TX) and North Carolina (NC), so we have to charge sales tax on orders shipped to these states. 
# The rates can be expressed as a keyword list (I wish it were that simple.…):

#    tax_rates = [ NC: 0.075, TX: 0.08 ]
# Here’s a list of orders:

#    orders = [
#        [ id: 123, ship_to: :NC, net_amount: 100.00 ],
#        [ id: 124, ship_to: :OK, net_amount:  35.50 ],
#        [ id: 125, ship_to: :TX, net_amount:  24.00 ],
#        [ id: 126, ship_to: :TX, net_amount:  44.80 ],
#        [ id: 127, ship_to: :NC, net_amount:  25.00 ],
#        [ id: 128, ship_to: :MA, net_amount:  10.00 ],
#        [ id: 129, ship_to: :CA, net_amount: 102.00 ],
#        [ id: 130, ship_to: :NC, net_amount:  50.00 ] ]
# Write a function that takes both lists and returns a copy of the orders, but with an extra field, total_amount, which is the net plus sales tax. 
# If a shipment is not to NC or TX, there’s no tax applied.

tax_rates = [ NC: 0.075, TX: 0.08 ]

orders= [
    [ id: 123, ship_to: :NC, net_amount: 100.00 ],
    [ id: 124, ship_to: :OK, net_amount:  35.50 ],
    [ id: 125, ship_to: :TX, net_amount:  24.00 ],
    [ id: 126, ship_to: :TX, net_amount:  44.80 ],
    [ id: 127, ship_to: :NC, net_amount:  25.00 ],
    [ id: 128, ship_to: :MA, net_amount:  10.00 ],
    [ id: 129, ship_to: :CA, net_amount: 102.00 ],
    [ id: 130, ship_to: :NC, net_amount:  50.00 ]
]

defmodule Calculator do
    
    def process(orders, tax_rates) do
        
        for order <- orders, do: order ++ [ total_amount: total_amount(order, tax_rates) ]

    end

    defp total_amount(order, tax_rates) do
        tax_rate = tax_rates[order[:ship_to]]
        if tax_rate == nil do
            order[:net_amount]
        else
            order[:net_amount] + order[:net_amount] * tax_rate
        end
    end

end

IO.inspect Calculator.process(orders, tax_rates)