Don't show both realname and username if they are the same

Changelog-Changed: Don't show both realname and username if they are the same

damus/Util/DisplayName.swift

@@ -0,0 +1,66 @@
+//
+//  DisplayName.swift
+//  damus
+//
+//  Created by William Casarin on 2023-03-14.
+//
+
+import Foundation
+
+
+struct BothNames {
+    let username: String
+    let display_name: String
+}
+
+enum DisplayName {
+    case both(BothNames)
+    case one(String)
+    
+    var display_name: String {
+        switch self {
+        case .one(let one):
+            return one
+        case .both(let b):
+            return b.display_name
+        }
+    }
+    
+    var username: String {
+        switch self {
+        case .one(let one):
+            return one
+        case .both(let b):
+            return b.username
+        }
+    }
+}
+
+
+func parse_display_name(profile: Profile?, pubkey: String) -> DisplayName {
+    if pubkey == "anon" {
+        return .one("Anonymous")
+    }
+    
+    guard let profile else {
+        return .one(abbrev_bech32_pubkey(pubkey: pubkey))
+    }
+    
+    let name = profile.name?.isEmpty == false ? profile.name : nil
+    let disp_name = profile.display_name?.isEmpty == false ? profile.display_name : nil
+    
+    if let name, let disp_name, name != disp_name {
+        return .both(BothNames(username: name, display_name: disp_name))
+    }
+    
+    if let one = name ?? disp_name {
+        return .one(one)
+    }
+    
+    return .one(abbrev_bech32_pubkey(pubkey: pubkey))
+}
+
+func abbrev_bech32_pubkey(pubkey: String) -> String {
+    let pk = bech32_nopre_pubkey(pubkey) ?? pubkey
+    return abbrev_pubkey(pk)
+}