#!/usr/bin/python3
"""Example solution of a programming interview question."""


class VolumeRule:
    def __init__(self, steps):
        self.steps = steps

    def compute(self, volume):
        for max_volume, rate in self.steps:
            if volume < max_volume:
                return volume * rate
        raise ValueError("volume too huge", volume, steps)


class PiecewiseLinearContinuousRule:
    def __init__(self, steps):
        self.steps = steps

    def compute(self, quantity):
        total = 0
        prev_max_qty = 0
        for max_qty, rate in self.steps:
            if max_qty is None:
                effective_qty = quantity
            else:
                effective_qty = min(quantity, max_qty)

            total += rate * (effective_qty - prev_max_qty)

            if max_qty is None or quantity < max_qty:
                break
            prev_max_qty = max_qty

        return total


rates = dict(
    crew=PiecewiseLinearContinuousRule([(None, 5)]),
    volume=VolumeRule([(3, 2), (7, 5), (1000, 21)]),
    weight=PiecewiseLinearContinuousRule([(10, 1), (15, 2), (None, 10)]),
)

def freight(shipment, field):
    return rates[field].compute(shipment[field])


if __name__ == '__main__':
    print(freight(dict(weight=4.5, crew=5, volume=37), field='crew'))
    print(freight(dict(weight=4.5, crew=5, volume=37), field='volume'))
    print(freight(dict(weight=20, crew=5, volume=37), field='weight'))
    print(freight(dict(weight=2, crew=5, volume=37), field='weight'))