add TotpParameters class

src/KeyKeeper/PasswordStore/TotpParameters.cs

@@ -0,0 +1,68 @@
+using System;
+using System.Web;
+
+namespace KeyKeeper.PasswordStore;
+
+public enum TotpAlgorithm { SHA1, SHA256, SHA512 }
+
+public class TotpParameters
+{
+    public string Secret { get; set; }
+    public TotpAlgorithm Algorithm { get; set; }
+    public int Digits { get; set; }
+    public int Period { get; set; }
+    public string? Issuer { get; set; }
+    public string? AccountName { get; set; }
+
+    public TotpParameters(string secret, TotpAlgorithm algorithm = TotpAlgorithm.SHA1,
+                          int digits = 6, int period = 30,
+                          string? issuer = null, string? accountName = null)
+    {
+        Secret = secret;
+        Algorithm = algorithm;
+        Digits = digits;
+        Period = period;
+        Issuer = issuer;
+        AccountName = accountName;
+    }
+
+    public static TotpParameters FromUri(string uri)
+    {
+        if (!uri.StartsWith("otpauth://totp/", StringComparison.OrdinalIgnoreCase))
+            throw new ArgumentException("URI must start with otpauth://totp/", nameof(uri));
+
+        Uri parsed = new(uri);
+
+        string label = Uri.UnescapeDataString(parsed.AbsolutePath.TrimStart('/'));
+        string? issuer = null;
+        int colon = label.IndexOf(':');
+        string? accountName;
+        if (colon >= 0)
+        {
+            issuer = label[..colon];
+            accountName = label[(colon + 1)..];
+        }
+        else
+        {
+            accountName = label;
+        }
+
+        var query = HttpUtility.ParseQueryString(parsed.Query);
+
+        string secret = query["secret"] ?? throw new ArgumentException("URI is missing required 'secret' parameter", nameof(uri));
+
+        issuer = query["issuer"] ?? issuer;
+
+        TotpAlgorithm algorithm = (query["algorithm"] ?? "SHA1").ToUpperInvariant() switch
+        {
+            "SHA256" => TotpAlgorithm.SHA256,
+            "SHA512" => TotpAlgorithm.SHA512,
+            _ => TotpAlgorithm.SHA1,
+        };
+
+        int digits = int.TryParse(query["digits"], out int d) ? d : 6;
+        int period = int.TryParse(query["period"], out int p) ? p : 30;
+
+        return new TotpParameters(secret, algorithm, digits, period, issuer, accountName);
+    }
+}