# FuelSurcharge

Small, dependency-free Elixir functions for the fuel surcharge line on a
trucking rate: per-mile FSC from a weekly diesel price, the total for a trip,
the share of the linehaul that is really fuel, and the bracket tables shippers
print in their contracts.

## Why

Most contracts don't pay fuel as a flat number. They name a base price (the
peg) and an MPG divisor, then pay the gap between this week's diesel average
and the peg, divided by the MPG, for every loaded mile. It is simple math, but
it is easy to get wrong when the peg and divisor change from customer to
customer.

```elixir
FuelSurcharge.per_mile(3.85, 1.25, 6)
#=> 0.433

FuelSurcharge.for_trip(3.85, 1.25, 6, 812)
#=> 351.6

FuelSurcharge.percent_of_linehaul(3.85, 1.25, 6, 812, 2100)
#=> 16.7
```

Notes:

- Deadhead miles normally earn no surcharge, so pass loaded miles only.
- When diesel drops to or below the peg the surcharge is zero, never negative.
- `bracket_table/5` reproduces the step tables printed in contracts so you can
  check a customer's table against the formula.

If you just need a quick answer without writing code, there is
[an in-browser version of this surcharge math](https://truckleap.com/fuel-surcharge-calculator)
by TruckLeap.

## Installation

```elixir
def deps do
  [{:fuel_surcharge, "~> 0.1"}]
end
```

## License

MIT, by George Green.