//https://stackoverflow.com/questions/39874172/dynamic-string-interpolation

//@nuget: System.Linq.Dynamic.Core

using System;

using System.Linq;

using System.Linq.Dynamic.Core;

​

public static class Program

{

    public static void Main()

    {

        // 1) Just using Substring(start,length)

        Console.Write("1) ");

        var externalKey1 = "xx/ABCDE/2";

        var format1 = "http://example.com?search=`externalKey.Substring(3,5)`";

        var link1 = format1.Interpolate(externalKey1, true);

        Console.WriteLine(link1); // Output: http://example.com?search=ABCDE

        // 2) More complex and dynamic approach:

        // Ternary conditional operator: value ? trueResult : falseResult

        // Dynamic cut detection with IndexOf()

        // Overall treatment (..).ToLower()

        Console.Write("2) ");

        var externalKey2 = "xx/ABCDEFG/1";

        var format2 = @"http://example.com?search=`(externalKey.Count(character => character == '/') > 1 ? externalKey.Substring(0,externalKey.IndexOf('/',externalKey.IndexOf('/')+1)) : externalKey).ToLower()`";

        var link2 = format2.Interpolate(externalKey2, true);

        Console.WriteLine(link2); // Output: http://example.com?search=xx/abcdefg

        // 3) Parsing + formatting of other types. Beware: Currently, database only knows about strings.

        Console.Write("3) ");

        var externalKey3 = "12345678-032C-495B-8AD0-0C6DE720A39D";

        var format3 = @"http://example.com?search=`Guid.Parse(externalKey).ToString(""N"")`";

        var link3 = format3.Interpolate(externalKey3, true);

        Console.WriteLine(link3); // Output: http://example.com?search=12345678032c495b8ad00c6de720a39d

    }

​

    private const char Separator = '`';

    /// <summary>

    ///     Extracts an expression out of a template (e.g. "http://example.com?query=`externalKey.Substring(0,10)`"),

    ///     uses DynamicExpressionParser.ParseLambda() and runs it to replace the expression in the template.

    ///     Set displayErrors to show exception message as result instead of the unmodified externalKey.

    /// </summary>

    /// <remarks>

    ///     Because it's a string method extension, it's private. Therefore, don't rename it without also modifying

    ///     ResponseModelExtensionsTests!

    /// </remarks>

    private static string Interpolate(this string template, string externalKey, bool displayErrors)

    {

        if (!template.Contains(Separator))

            return template;

        var parts = template.Split(Separator);

        foreach (var index in Enumerable.Range(0, parts.Length).Where(index => index % 2 == 1))

        {

            try

            {

                // If the backticks are pairwise only the odd parts must be replaced, see:

                // Sample: http://example.com?q=`externalKey[0..2]`&s=`externalKey[3..]`

                // Index:  0                    `1                `2  `3               `.

                var expression = parts[index];

                var lambda = DynamicExpressionParser.ParseLambda(typeof(string), typeof(string), $"externalKey => {expression}");

                var result = lambda.Compile().DynamicInvoke(externalKey)?.ToString() ?? string.Empty;

                parts[index] = result;

            }

            catch (Exception exception)

            {

                parts[index] = displayErrors ? $"!!!{exception.GetBaseException().Message}!!!" : externalKey;

            }

        }

​

        return string.Join("", parts);

    }

}