Parsing data from several sources into a common format.

public record ProductDto(
    string ProductId,
    Price Price,
);

public abstract record Price(decimal Value);
public sealed record FixedPrice(decimal Value) : Price(Value);
public sealed record PricePerUnit(decimal Value, string Unit) : Price(Value);

public interface IFieldParser<out T>
{
    T Parse(JsonElement json);
}

public class Source1IdParser : IFieldParser<string>
{
    public string Parse(JsonElement)
    {
        // Here it might be called "id"
        return json.GetProperty("id").GetString() ?? string.Empty;
    }
}

public class Source2IdParser : IFieldParser<string>
{
    public string Parse(JsonElement json)
    {
        // Here it might be called "productCode"
        return json.GetProperty("productCode").GetString() ?? string.Empty;
    }
}

public class Source1PriceParser : IFieldParser<Price>
{
    public Price Parse(JsonElement json)
    {
        var unit = json.GetProperty("unit").GetString() ?? "";
        var amount = json.GetProperty("price").GetString() ?? "";
        return unit == "" 
                    ? new FixedPrice(Convert.ToDecimal(amount))
                    : new PricePerUnit(Convert.ToDecimal(amount), unit);
    }
}