initial mention parsing

Signed-off-by: William Casarin <jb55@jb55.com>

damus/Views/NoteContentView.swift

@@ -0,0 +1,57 @@
+//
+//  NoteContentView.swift
+//  damus
+//
+//  Created by William Casarin on 2022-05-04.
+//
+
+import SwiftUI
+
+func NoteContentView(_ ev: NostrEvent) -> some View {
+    let txt = parse_mentions(content: ev.content, tags: ev.tags)
+        .reduce("") { str, block in
+            switch block {
+            case .mention(let m):
+                return str + mention_str(m)
+            case .text(let txt):
+                return str + txt
+            }
+        }
+    
+    let md_opts: AttributedString.MarkdownParsingOptions =
+        .init(interpretedSyntax: .inlineOnlyPreservingWhitespace)
+    
+    guard let txt = try? AttributedString(markdown: txt, options: md_opts) else {
+        return Text(ev.content)
+    }
+    
+    return Text(txt)
+}
+
+func mention_str(_ m: Mention) -> String {
+    switch m.type {
+    case .pubkey:
+        let pk = m.ref.ref_id
+        return "[@\(abbrev_pubkey(pk))](nostr:\(encode_pubkey(m.ref)))"
+    case .event:
+        let evid = m.ref.ref_id
+        return "[*\(abbrev_pubkey(evid))](nostr:\(encode_event_id(m.ref)))"
+    }
+}
+
+// TODO: bech32 and relay hints
+func encode_event_id(_ ref: ReferencedId) -> String {
+    return "e_" + ref.ref_id
+}
+
+func encode_pubkey(_ ref: ReferencedId) -> String {
+    return "p_" + ref.ref_id
+}
+
+/*
+struct NoteContentView_Previews: PreviewProvider {
+    static var previews: some View {
+        NoteContentView()
+    }
+}
+ */