rewrite number whatever to .net and blazor.

Services/SpamDetectionService.cs

@@ -0,0 +1,221 @@
+using System.Text.RegularExpressions;
+
+namespace landing.Services;
+
+public class SpamDetectionService
+{
+    private static readonly string[] SpamPatterns =
+    {
+        "viagra", "cialis", "casino", "lottery", "prize",
+        "click here", "buy now", "limited time",
+        "congratulations", "you have won", "claim your",
+        "bitcoin", "crypto", "forex", "trading bot",
+        "free money", "make money fast", "work from home",
+        "nigerian", "inheritance", "transfer funds",
+        "<!--", "javascript:", "onclick=", "<script",
+        "sveiki", "ciao", "hola", "\u043f\u0440\u0438\u0432\u0435\u0442",
+        "harga", "karna", "anda", "dari",
+        "toughalia", "comfythings",
+        "robertgok"
+    };
+
+    private static readonly string[] EnglishWords =
+    {
+        "the", "and", "is", "to", "of", "for", "that", "with", "this", "have",
+        "from", "be", "are", "was", "were", "been", "i", "you", "he", "she",
+        "we", "they", "my", "your", "his", "her", "it", "what", "which", "who",
+        "when", "where", "why", "how", "can", "will", "would", "should", "could",
+        "do", "does", "did", "get", "got", "go", "going", "make", "made", "know",
+        "think", "want", "need", "like", "help", "work", "use", "ask", "say", "tell",
+        "give", "find", "tell", "become", "leave", "feel", "try", "ask", "need",
+        "meet", "include", "continue", "set", "learn", "change", "lead", "understand"
+    };
+
+    private static readonly HashSet<string> CommonPairs = new()
+    {
+        "th", "he", "in", "er", "an",
+        "ed", "nd", "to", "en", "ti",
+        "es", "or", "te", "ar", "ou",
+        "it", "ha", "is", "co", "me",
+        "we", "be", "se", "as", "de",
+        "so", "re", "st", "up", "at",
+        "ai", "al", "il", "le", "li"
+    };
+
+    private static readonly HashSet<string> ValidSubjects = new()
+    {
+        "general", "support", "partnership", "feedback", "other"
+    };
+
+    private static readonly Regex UrlRegex = new(@"https?://", RegexOptions.Compiled);
+    private static readonly Regex EmailRegex = new(@"[a-zA-Z0-9._%+\-]+@[a-zA-Z0-9.\-]+\.[a-zA-Z]{2,}", RegexOptions.Compiled);
+    private static readonly Regex PhoneRegex = new(@"\+?[0-9]{7,}", RegexOptions.Compiled);
+
+    public bool IsValidName(string name)
+    {
+        if (name.Length < 2 || name.Length > 100)
+            return false;
+
+        int numberCount = name.Count(char.IsDigit);
+        if (numberCount > 0 && (double)numberCount / name.Length > 0.33)
+            return false;
+
+        if (name.Contains("http") || name.Contains("://"))
+            return false;
+
+        return true;
+    }
+
+    public bool IsValidEmail(string email)
+    {
+        if (!email.Contains('@') || !email.Contains('.'))
+            return false;
+
+        var parts = email.Split('@');
+        if (parts.Length != 2)
+            return false;
+
+        if (parts[0].Length < 1 || parts[0].Length > 64)
+            return false;
+
+        if (parts[1].Length < 3 || parts[1].Length > 255)
+            return false;
+
+        var domainParts = parts[1].Split('.');
+        if (domainParts.Length < 2)
+            return false;
+
+        foreach (var label in domainParts)
+        {
+            if (label.Length < 1 || label.Length > 63)
+                return false;
+        }
+
+        return true;
+    }
+
+    public bool IsValidSubject(string subject) => ValidSubjects.Contains(subject);
+
+    public bool IsEnglishText(string text)
+    {
+        if (string.IsNullOrEmpty(text))
+            return true;
+
+        var lowerText = text.ToLowerInvariant();
+        var words = lowerText.Split(
+            new[] { ' ', '\t', '\n', '\r', '.', ',', '!', '?', ';', ':', '-', '(', ')', '[', ']', '{', '}', '"', '\'' },
+            StringSplitOptions.RemoveEmptyEntries
+        );
+
+        int englishWordCount = 0;
+        int totalWords = 0;
+
+        foreach (var word in words)
+        {
+            if (word.Length == 0) continue;
+            totalWords++;
+
+            if (EnglishWords.Contains(word))
+                englishWordCount++;
+        }
+
+        if (text.Length < 50)
+            return englishWordCount >= 1;
+
+        if (text.Length < 200)
+            return englishWordCount >= 2;
+
+        if (totalWords > 0)
+            return (double)englishWordCount / totalWords >= 0.1;
+
+        return true;
+    }
+
+    public bool IsSpamMessage(string message)
+    {
+        var lowerMsg = message.ToLowerInvariant();
+
+        // Check spam keywords
+        foreach (var pattern in SpamPatterns)
+        {
+            if (lowerMsg.Contains(pattern))
+                return true;
+        }
+
+        // Check for excessive URLs
+        if (UrlRegex.Matches(lowerMsg).Count > 1)
+            return true;
+
+        // Check for email addresses in message
+        if (EmailRegex.IsMatch(lowerMsg))
+            return true;
+
+        // Check for phone numbers
+        if (PhoneRegex.IsMatch(lowerMsg))
+            return true;
+
+        // Check for excessive exclamation marks
+        if (lowerMsg.Count(c => c == '!') > 2)
+            return true;
+
+        // Check for repeated characters
+        if (lowerMsg.Contains("!!!") || lowerMsg.Contains("???") || lowerMsg.Contains("..."))
+            return true;
+
+        // Check for all caps
+        if (lowerMsg.Length > 20)
+        {
+            int letterCount = 0;
+            int capsCount = 0;
+            foreach (var c in message)
+            {
+                if (char.IsLetter(c))
+                {
+                    letterCount++;
+                    if (char.IsUpper(c))
+                        capsCount++;
+                }
+            }
+            if (letterCount > 0 && (double)capsCount / letterCount > 0.6)
+                return true;
+        }
+
+        // Check for repeated words
+        var words = lowerMsg.Split(' ', StringSplitOptions.RemoveEmptyEntries);
+        if (words.Length > 5)
+        {
+            var wordCount = new Dictionary<string, int>();
+            foreach (var word in words)
+            {
+                wordCount.TryGetValue(word, out int count);
+                wordCount[word] = count + 1;
+            }
+            if (wordCount.Values.Any(c => c > 3))
+                return true;
+        }
+
+        // Check message length - very short messages are often spam
+        if (message.Length < 15)
+            return true;
+
+        // Check for gibberish - high ratio of uncommon character transitions
+        int uncommonCount = 0;
+        for (int i = 0; i < lowerMsg.Length - 1; i++)
+        {
+            char c = lowerMsg[i];
+            char next = lowerMsg[i + 1];
+
+            if (c >= 'a' && c <= 'z' && next >= 'a' && next <= 'z')
+            {
+                var pair = new string(new[] { c, next });
+                if (!CommonPairs.Contains(pair) && c != next)
+                    uncommonCount++;
+            }
+        }
+
+        if (lowerMsg.Length > 30 && uncommonCount > lowerMsg.Length / 3)
+            return true;
+
+        return false;
+    }
+}