using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var dataRecords = new []

        {

            new Record("foo", "bar", "foobar"),

            new Record("foo", null, "foo"),

            new Record(null, "bar", "bar"),

            new Record(null, null, "DefaultValue"),

        };

        var switchCase = dataRecords

            .Reverse()

            .Select(CreatePattern)

            .Aggregate<Pattern, Func<string, string, string>>(

                (_, _) => null,

                (next, pattern) =>

                    (l, r) => pattern.Predicate(l, r) ? pattern.ReturnValue : next(l, r)

            );

        Console.WriteLine(switchCase("foo", "bar"));

        Console.WriteLine(switchCase("foo", "adfgdafg"));

        Console.WriteLine(switchCase("fadgdsfoo", "bar"));

        Console.WriteLine(switchCase("asdfadfg", "asfhgsd"));

    }

    static Pattern CreatePattern(Record rec)

    {

        return new (

            (l, r) =>

                (l == rec.Input1 || rec.Input1 == null)

                && (r == rec.Input2 || rec.Input2 == null),

            rec.ReturnValue

        );

    }

}

​

public record Pattern(Func<string, string, bool> Predicate, string ReturnValue);

​

public record Record(string Input1, string Input2, string ReturnValue);