StringTokenizer.cs

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Text;
using System.Threading.Tasks;
using Waher.Runtime.Inventory;
 
namespace Waher.Persistence.FullTextSearch.Tokenizers
{
    public class StringTokenizer : ITokenizer
    {
        public StringTokenizer()
        {
        }
 
        public Grade Supports(Type Type)
        {
            if (Type == typeof(string))
                return Grade.Ok;
            else
                return Grade.NotAtAll;
        }
 
        public Task Tokenize(object Value, TokenizationProcess Process)
        {
            if (Value is string s)
                Tokenize(s, Process);
 
            return Task.CompletedTask;
        }
 
        public static void Tokenize(string Text, TokenizationProcess Process)
        {
            if (string.IsNullOrEmpty(Text))
                return;
 
            UnicodeCategory Category;
            StringBuilder sb = new StringBuilder();
            string Token;
            bool First = true;
 
            foreach (char ch in Text.ToLower().Normalize(NormalizationForm.FormD))
            {
                Category = CharUnicodeInfo.GetUnicodeCategory(ch);
                if (Category == UnicodeCategory.NonSpacingMark)
                    continue;
 
                if (char.IsLetterOrDigit(ch))
                {
                    sb.Append(ch);
                    First = false;
                }
                else
                {
                    if (!First)
                    {
                        Token = sb.ToString();
                        sb.Clear();
                        First = true;
 
                        if (!Process.TokenCounts.TryGetValue(Token, out List<uint> DocIndex))
                        {
                            DocIndex = new List<uint>();
                            Process.TokenCounts[Token] = DocIndex;
                        }
 
                        DocIndex.Add(++Process.DocumentIndexOffset);
                    }
                }
            }
 
            if (!First)
            {
                Token = sb.ToString();
                sb.Clear();
 
                if (!Process.TokenCounts.TryGetValue(Token, out List<uint> DocIndex))
                {
                    DocIndex = new List<uint>();
                    Process.TokenCounts[Token] = DocIndex;
                }
 
                DocIndex.Add(++Process.DocumentIndexOffset);
            }
        }
 
    }
}