zedseven/Romanization.NET

using System;
using System.Collections.Generic;
using System.Diagnostics.Contracts;
using System.Linq;
using System.Text;

namespace Romanization.Internal
{
    internal static class CharacterOperations
    {
        [Pure]
        public static string[] SplitIntoSurrogatePairs(this string str)
        {
            List<string> retList = new List<string>(str.Length);
            for (int i = 0; i < str.Length; i++)
            {
                if (!char.IsSurrogatePair(str, i))
                {
                    retList.Add(str[i].ToString());
                    continue;
                }

                retList.Add(str[i].ToString() + str[++i]);
            }

            return retList.ToArray();
        }

        [Pure]
        public static string UnicodeNormalize(this string str)
            => str.Normalize(NormalizationForm.FormD);

        private const string LanguageBoundaryChars = @"a-z";
        private static readonly Lazy<CharSub> LanguageBoundarySubstitution = new Lazy<CharSub>(() =>
            new CharSub(
                $"(?:([{LanguageBoundaryChars}{Constants.Punctuation}])([^ {LanguageBoundaryChars}{Constants.Punctuation}])|([^ {LanguageBoundaryChars}{Constants.Punctuation}])([{LanguageBoundaryChars}]))",
                "${1}${3} ${2}${4}"));

        /// <summary>
        /// Insert spaces at boundaries between Latin and non-Latin characters (ie. <c>ニンテンドーDSiブラウザー</c> -> <c>ニンテンドー DSi ブラウザー</c>).
        /// </summary>
        /// <param name="text">The text to insert spaces in.</param>
        /// <returns>The text with spaces inserted at language boundaries.</returns>
        [Pure]
        internal static string SeparateLanguageBoundaries(this string text)
            => LanguageBoundarySubstitution.Value.Replace(text);

        [Pure]
        internal static TResult? DetermineResultFromString<TResult>(this string text,
            params (TResult res, string[] set)[] possibleKinds)
            where TResult : struct
        {
            foreach ((TResult res, string[] set) possibleKind in possibleKinds)
                if (possibleKind.set.Any(text.Contains))
                    return possibleKind.res;
            return null;
        }
    }
}