Move suggestion logic into its own class

Author: reakaleek

src/Elastic.Markdown/Myst/FrontMatter/Products.cs

@@ -2,7 +2,9 @@
 // Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
 // See the LICENSE file in the project root for more information
 
+using System.Collections.Frozen;
 using System.ComponentModel.DataAnnotations;
+using Elastic.Markdown.Suggestions;
 using EnumFastToStringGenerated;
 using YamlDotNet.Core;
 using YamlDotNet.Core.Events;
@@ -255,14 +257,14 @@ public object ReadYaml(IParser parser, Type type, ObjectDeserializer rootDeseria
 public class InvalidProductException(string invalidValue)
 	: Exception(
 		$"Invalid products frontmatter value: \"{invalidValue}\"." +
-		(!string.IsNullOrWhiteSpace(invalidValue) ? $" Did you mean \"{ProductExtensions.Suggestion(invalidValue)}\"?" : "") +
+		(!string.IsNullOrWhiteSpace(invalidValue) ? " " + new Suggestion(ProductExtensions.GetProductIds(), invalidValue).GetSuggestionQuestion() : "") +
 		"\nYou can find the full list at https://docs-v3-preview.elastic.dev/elastic/docs-builder/tree/main/syntax/frontmatter#products.");
 
 public static class ProductExtensions
 {
-	private static IReadOnlyCollection<string> GetProductIds() =>
+	public static IReadOnlySet<string> GetProductIds() =>
 		ProductEnumExtensions.GetValuesFast()
-			.Select(p => p.ToDisplayFast()).ToList();
+			.Select(p => p.ToDisplayFast()).ToFrozenSet();
 
 	public static string Suggestion(string input) =>
 		GetProductIds()

src/Elastic.Markdown/Suggestions/Suggestions.cs

@@ -0,0 +1,65 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+namespace Elastic.Markdown.Suggestions;
+
+public class Suggestion(IReadOnlySet<string> candidates, string input)
+{
+	private IReadOnlyCollection<string> GetSuggestions() =>
+		candidates
+			.Select(source => (source, Distance: LevenshteinDistance(input, source)))
+			.OrderBy(suggestion => suggestion.Distance)
+			.Where(suggestion => suggestion.Distance <= 2)
+			.Select(suggestion => suggestion.source)
+			.Take(3)
+			.ToList();
+
+	public string GetSuggestionQuestion()
+	{
+		var suggestions = GetSuggestions();
+		if (suggestions.Count == 0)
+			return string.Empty;
+
+		return "Did you mean " + string.Join(", ", suggestions.SkipLast(1).Select(s => $"\"{s}\"")) + (suggestions.Count > 1 ? " or " : "") + (suggestions.LastOrDefault() != null ? $"\"{suggestions.LastOrDefault()}\"" : "") + "?";
+	}
+
+	private static int LevenshteinDistance(string source, string target)
+	{
+		if (string.IsNullOrEmpty(target))
+			return int.MaxValue;
+
+		var sourceLength = source.Length;
+		var targetLength = target.Length;
+
+		if (sourceLength == 0)
+			return targetLength;
+
+		if (targetLength == 0)
+			return sourceLength;
+
+		var distance = new int[sourceLength + 1, targetLength + 1];
+
+		for (var i = 0; i <= sourceLength; i++)
+			distance[i, 0] = i;
+
+		for (var j = 0; j <= targetLength; j++)
+			distance[0, j] = j;
+
+		for (var i = 1; i <= sourceLength; i++)
+		{
+			for (var j = 1; j <= targetLength; j++)
+			{
+				var cost = (source[i - 1] == target[j - 1]) ? 0 : 1;
+
+				distance[i, j] = Math.Min(
+					Math.Min(
+						distance[i - 1, j] + 1,
+						distance[i, j - 1] + 1),
+					distance[i - 1, j - 1] + cost);
+			}
+		}
+
+		return distance[sourceLength, targetLength];
+	}
+}