using System;
using System.Collections.Generic;
using System.Linq;
using BoundaryLab.Domain;
using BoundaryLab.Application;

namespace BoundaryLab.Infrastructure;

public static class ShippingFactory
{
    public static IShippingPolicy Create(string code) => code switch
    {
        "flat" => new FlatShipping(), "unit" => new UnitShipping(),
        _ => throw new ArgumentException("Unknown policy", nameof(code))
    };
}
public sealed class FlatShipping : IShippingPolicy { public int Fee(int units) => 3; }
public sealed class UnitShipping : IShippingPolicy { public int Fee(int units) => checked(units * 2); }