cskawari

Program.cs

using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;

namespace ConsoleApp15
{
    class Program
    {
        static void Main(string[] args)
        {
            var dic = new KawariDictionary
            {
                { "day", "Sunday", "Monday", "Tuesday", "Wednesday", "Thirsday", "Friday", "Saturday" },
                { "number", "1", "2", "3", "4", "5", "6" },
                { "sentence", "${number}: Today is ${day}.", "No. ${number}: 今日の曜日は${day}", "${number}, ${number}, ${number}。逆順で言うと${2}, ${1}, ${0}。" }
            };

            for (int i = 0; i < 10; i++)
            {
                Console.WriteLine($"sentence: {dic.Call("sentence")}");
            }
        }
    }

    public class KawariDictionary : Dictionary<string, List<string>>
    {
        private readonly Random _random = new Random();
        private readonly Regex _entryCallRegex = new Regex(@"\$\{([^${}]+)\}", RegexOptions.Compiled);

        public void Add(string entry, params string[] words)
        {
            if (!TryGetValue(entry, out var entryList))
            {
                entryList = new List<string>();

                Add(entry, entryList);
            }

            entryList.AddRange(words);
        }

        public string Call(string entry)
        {
            var history = new List<string>();

            var answer = RawEntryCall(entry, history);

            while (true)
            {
                var result = _entryCallRegex.Match(answer);

                if (!result.Success)
                {
                    break;
                }

                var entryString = RawEntryCall(result.Groups[1].Value, history);

                answer = answer[..result.Index] + entryString + answer[(result.Index + result.Length)..];

                if (!int.TryParse(result.Groups[1].Value, out _))
                {
                    history.Add(entryString);
                }
            }

            return answer;
        }

        private string RawEntryCall(string entry, IReadOnlyList<string> history)
        {
            if (int.TryParse(entry, out var index))
            {
                return index < 0 || index >= history.Count ? "" : history[index];
            }

            if (!TryGetValue(entry, out var entryList))
            {
                return "";
            }

            var wordIndex = _random.Next(entryList.Count);

            return entryList[wordIndex];
        }
    }
}