compose_box: Replace compose box with a banner when cannot post in a channel

lib/api/model/initial_snapshot.dart

@@ -64,6 +64,14 @@ class InitialSnapshot {
 
   final List<UserTopicItem>? userTopics; // TODO(server-6)
 
+  /// The number of days until a user's account is treated as a full member.
+  ///
+  /// Search for "realm_waiting_period_threshold" in https://zulip.com/api/register-queue.
+  ///
+  /// For how to determine if a user is a full member, see:
+  ///   https://zulip.com/api/roles-and-permissions#determining-if-a-user-is-a-full-member
+  final int realmWaitingPeriodThreshold;
+
   final Map<String, RealmDefaultExternalAccount> realmDefaultExternalAccounts;
 
   final int maxFileUploadSizeMib;
@@ -115,6 +123,7 @@ class InitialSnapshot {
     required this.streams,
     required this.userSettings,
     required this.userTopics,
+    required this.realmWaitingPeriodThreshold,
     required this.realmDefaultExternalAccounts,
     required this.maxFileUploadSizeMib,
     required this.realmUsers,

lib/api/model/model.dart

@@ -263,6 +263,18 @@ class User {
   factory User.fromJson(Map<String, dynamic> json) => _$UserFromJson(json);
 
   Map<String, dynamic> toJson() => _$UserToJson(this);
+
+  /// Whether the user has passed the realm's waiting period to be a full member.
+  ///
+  /// See:
+  ///   https://zulip.com/api/roles-and-permissions#determining-if-a-user-is-a-full-member
+  ///
+  /// To determine if a user is a full member, callers must also check that the
+  /// user's role is at least Role.Member.
+  bool hasPassedWaitingPeriod(DateTime byDate, int realmWaitingPeriodThreshold) {
+    final dateJoined = DateTime.parse(this.dateJoined);
+    return byDate.difference(dateJoined).inDays >= realmWaitingPeriodThreshold;
+  }
 }
 
 /// As in [User.profileData].
@@ -303,6 +315,11 @@ enum UserRole{
   final int? apiValue;
 
   int? toJson() => apiValue;
+
+  bool isAtLeast(UserRole threshold) {
+    // Roles with more privilege have lower [apiValue].
+    return (apiValue ?? 0) <= (threshold.apiValue ?? 0);
+  }
 }
 
 /// As in `streams` in the initial snapshot.
@@ -370,6 +387,19 @@ class ZulipStream {
     _$ZulipStreamFromJson(json);
 
   Map<String, dynamic> toJson() => _$ZulipStreamToJson(this);
+
+  bool hasPostingPermission(User user, {required DateTime byDate, required int realmWaitingPeriodThreshold}) {
+    final role = user.role;
+    return switch (channelPostPolicy) {
+      ChannelPostPolicy.any            => true,
+      ChannelPostPolicy.fullMembers    => role.isAtLeast(UserRole.member) && (role == UserRole.member
+                                            ? user.hasPassedWaitingPeriod(byDate, realmWaitingPeriodThreshold)
+                                            : true),
+      ChannelPostPolicy.moderators     => role.isAtLeast(UserRole.moderator),
+      ChannelPostPolicy.administrators => role.isAtLeast(UserRole.administrator),
+      ChannelPostPolicy.unknown        => true,
+    };
+  }
 }
 
 /// The name of a property of [ZulipStream] that gets updated

lib/model/store.dart

@@ -235,6 +235,7 @@ class PerAccountStore extends ChangeNotifier with EmojiStore, ChannelStore, Mess
       connection: connection,
       realmUrl: realmUrl,
       maxFileUploadSizeMib: initialSnapshot.maxFileUploadSizeMib,
+      realmWaitingPeriodThreshold: initialSnapshot.realmWaitingPeriodThreshold,
       realmDefaultExternalAccounts: initialSnapshot.realmDefaultExternalAccounts,
       customProfileFields: _sortCustomProfileFields(initialSnapshot.customProfileFields),
       emailAddressVisibility: initialSnapshot.emailAddressVisibility,
@@ -270,6 +271,7 @@ class PerAccountStore extends ChangeNotifier with EmojiStore, ChannelStore, Mess
     required this.connection,
     required this.realmUrl,
     required this.maxFileUploadSizeMib,
+    required this.realmWaitingPeriodThreshold,
     required this.realmDefaultExternalAccounts,
     required this.customProfileFields,
     required this.emailAddressVisibility,
@@ -324,6 +326,8 @@ class PerAccountStore extends ChangeNotifier with EmojiStore, ChannelStore, Mess
 
   String get zulipVersion => account.zulipVersion;
   final int maxFileUploadSizeMib; // No event for this.
+  /// For docs, please see [InitialSnapshot.realmWaitingPeriodThreshold].
+  final int realmWaitingPeriodThreshold;  // TODO(#668): update this realm setting
   final Map<String, RealmDefaultExternalAccount> realmDefaultExternalAccounts;
   List<CustomProfileField> customProfileFields;
   /// For docs, please see [InitialSnapshot.emailAddressVisibility].

test/example_data.dart

@@ -789,6 +789,7 @@ InitialSnapshot initialSnapshot({
   List<ZulipStream>? streams,
   UserSettings? userSettings,
   List<UserTopicItem>? userTopics,
+  int? realmWaitingPeriodThreshold,
   Map<String, RealmDefaultExternalAccount>? realmDefaultExternalAccounts,
   int? maxFileUploadSizeMib,
   List<User>? realmUsers,
@@ -821,6 +822,7 @@ InitialSnapshot initialSnapshot({
       emojiset: Emojiset.google,
     ),
     userTopics: userTopics,
+    realmWaitingPeriodThreshold: realmWaitingPeriodThreshold ?? 0,
     realmDefaultExternalAccounts: realmDefaultExternalAccounts ?? {},
     maxFileUploadSizeMib: maxFileUploadSizeMib ?? 25,
     realmUsers: realmUsers ?? [],