From 43312c336245ac9f3f549aa332b7155148198bd4 Mon Sep 17 00:00:00 2001
From: Tom Pipinic <tom@tompit.net>
Date: Tue, 7 Feb 2023 10:54:27 +0100
Subject: [PATCH] AsUrlFriendly extension added

---
 src/Connected.Services/ServicesExtensions.cs |  10 ++
 src/Connected.Services/UrlGenerator.cs       | 112 +++++++++++++++++++
 2 files changed, 122 insertions(+)
 create mode 100644 src/Connected.Services/UrlGenerator.cs

diff --git a/src/Connected.Services/ServicesExtensions.cs b/src/Connected.Services/ServicesExtensions.cs
index a84f6b9..4941bca 100644
--- a/src/Connected.Services/ServicesExtensions.cs
+++ b/src/Connected.Services/ServicesExtensions.cs
@@ -51,4 +51,14 @@ public static class ServicesExtensions
 		return (f is not null && type.GetInterface(f) is not null)
 			|| (nf is not null && type.GetInterface(nf) is not null);
 	}
+
+	public static string AsUrlFriendly(this string value)
+	{
+		return UrlGenerator.Generate(value);
+	}
+
+	public static string AsUrlFriendly(this string value, IEnumerable<string> existing)
+	{
+		return UrlGenerator.Generate(value, existing);
+	}
 }
\ No newline at end of file
diff --git a/src/Connected.Services/UrlGenerator.cs b/src/Connected.Services/UrlGenerator.cs
new file mode 100644
index 0000000..ce6a527
--- /dev/null
+++ b/src/Connected.Services/UrlGenerator.cs
@@ -0,0 +1,112 @@
+using System.Text;
+
+namespace Connected.Services;
+internal static class UrlGenerator
+{
+	private const string ValidCharacters = "abcdefghijklmnopqrstuvzxyw-";
+	private const string MinusReplacements = "_ .\t\r\n";
+	static UrlGenerator()
+	{
+		Replacements = new(StringComparer.OrdinalIgnoreCase)
+		{
+			{"č", "c"},
+			{"š", "s"},
+			{"ž", "z"},
+			{"đ", "d"},
+			{"ć", "c"}
+		};
+	}
+
+	private static Dictionary<string, string> Replacements { get; }
+
+	public static string Generate(string text)
+	{
+		if (string.IsNullOrEmpty(text))
+			throw new NullReferenceException(nameof(text));
+
+		var result = new StringBuilder();
+		/*
+		 * Analyze each character.
+		 */
+		foreach (var s in text.Trim())
+		{
+			/*
+			 * If it's in a ValidCharacters collection that's fine, we just copy it
+			 * into the result.
+			 */
+			if (ValidCharacters.Contains(s, StringComparison.OrdinalIgnoreCase))
+			{
+				result.Append(s);
+				continue;
+			}
+			/*
+			 * Look if it's in the MinusReplacements collection which means we'll
+			 * replace the character with the minus sign.
+			 */
+			if (MinusReplacements.Contains(s, StringComparison.OrdinalIgnoreCase))
+			{
+				result.Append('-');
+				continue;
+			}
+			/*
+			 * Last chance for the character to be included in the result is to 
+			 * resolve the hardcoded character replacements.
+			 */
+			if (Replacements.TryGetValue(s.ToString(), out var replacement))
+				result.Append(replacement);
+		}
+		/*
+		 * It's possible that no characters are included in the result. If that's
+		 * the case we are going to include an a character just for the sake of
+		 * being a valid string.
+		 */
+		if (result.Length == 0)
+			result.Append('a');
+		/*
+		 * Remove any redundant minus characters and we are done.
+		 */
+		var sb = new StringBuilder();
+		var active = false;
+
+		for (var i = 0; i < result.Length; i++)
+		{
+			if (result[i] == '-')
+			{
+				if (active)
+					continue;
+
+				active = true;
+				sb.Append(result[i]);
+			}
+			else
+			{
+				active = false;
+				sb.Append(result[i]);
+			}
+		}
+		/*
+		 * Remove trailing minus if exists.
+		 */
+		return sb.ToString().Trim().Trim('-').ToLowerInvariant();
+	}
+
+	public static string Generate(string text, IEnumerable<string> existing)
+	{
+		var prepared = Generate(text);
+
+		if (!existing.Any())
+			return prepared;
+
+		var idx = 0;
+
+		while (true)
+		{
+			var key = $"{prepared}-{idx}";
+
+			if (!existing.Contains(key, StringComparer.OrdinalIgnoreCase))
+				return key;
+
+			idx++;
+		}
+	}
+}
\ No newline at end of file