User tagging and autocompletion

Co-authored-by: William Casarin <jb55@jb55.com>
Changelog-Added: User tagging and autocompletion in posts
Closes: #347
Fixes: #411, #63

damus/Views/Posting/UserSearch.swift

@@ -0,0 +1,87 @@
+//
+//  UserAutocompletion.swift
+//  damus
+//
+//  Created by William Casarin on 2023-01-28.
+//
+
+import SwiftUI
+
+struct SearchedUser: Identifiable {
+    let petname: String?
+    let profile: Profile?
+    let pubkey: String
+    
+    var id: String {
+        return pubkey
+    }
+}
+
+struct UserSearch: View {
+    let damus_state: DamusState
+    let search: String
+    @Binding var post: String
+    
+    var users: [SearchedUser] {
+        guard let contacts = damus_state.contacts.event else {
+            return []
+        }
+        
+        return search_users(profiles: damus_state.profiles, tags: contacts.tags, search: search)
+    }
+    
+    var body: some View {
+        ScrollView {
+            LazyVStack {
+                ForEach(users) { user in
+                    UserView(damus_state: damus_state, pubkey: user.pubkey)
+                        .onTapGesture {
+                            guard let pk = bech32_pubkey(user.pubkey) else {
+                                return
+                            }
+                            post = post.replacingOccurrences(of: "@"+search, with: "@"+pk)
+                        }
+                }
+            }
+        }
+    }
+}
+
+struct UserSearch_Previews: PreviewProvider {
+    static let search: String = "jb55"
+    @State static var post: String = "some @jb55"
+    
+    static var previews: some View {
+        UserSearch(damus_state: test_damus_state(), search: search, post: $post)
+    }
+}
+
+
+func search_users(profiles: Profiles, tags: [[String]], search: String) -> [SearchedUser] {
+    var seen_user = Set<String>()
+    return tags.reduce(into: Array<SearchedUser>()) { arr, tag in
+        guard tag.count >= 2 && tag[0] == "p" else {
+            return
+        }
+        
+        let pubkey = tag[1]
+        guard !seen_user.contains(pubkey) else {
+            return
+        }
+        seen_user.insert(pubkey)
+        
+        var petname: String? = nil
+        if tag.count >= 4 {
+            petname = tag[3]
+        }
+        
+        let profile = profiles.lookup(id: pubkey)
+        
+        guard ((petname?.hasPrefix(search) ?? false) || (profile?.name?.hasPrefix(search) ?? false)) else {
+            return
+        }
+        
+        let searched_user = SearchedUser(petname: petname, profile: profile, pubkey: pubkey)
+        arr.append(searched_user)
+    }
+}