model: Add hasPostingPermission helper method to PerAccountStore

Author: sm-sayedi

lib/model/store.dart

@@ -474,6 +474,30 @@ class PerAccountStore extends ChangeNotifier with EmojiStore, ChannelStore, Mess
 
   final ChannelStoreImpl _channels;
 
+  bool hasPostingPermission({
+    required ZulipStream inChannel,
+    required User user,
+    required DateTime byDate,
+  }) {
+    final role = user.role;
+    // We let the users with [unknown] role to send the message, then the server
+    // will decide to accept it or not based on its actual role.
+    if (role == UserRole.unknown) return true;
+
+    switch (inChannel.channelPostPolicy) {
+      case ChannelPostPolicy.any:             return true;
+      case ChannelPostPolicy.fullMembers:     {
+        if (!role.isAtLeast(UserRole.member)) return false;
+        return role == UserRole.member
+          ? hasPassedWaitingPeriod(user, byDate: byDate)
+          : true;
+      }
+      case ChannelPostPolicy.moderators:      return role.isAtLeast(UserRole.moderator);
+      case ChannelPostPolicy.administrators:  return role.isAtLeast(UserRole.administrator);
+      case ChannelPostPolicy.unknown:         return true;
+    }
+  }
+
   ////////////////////////////////
   // Messages, and summaries of messages.
 

test/model/store_test.dart

@@ -269,6 +269,82 @@ void main() {
     }
   });
 
+  group('PerAccountStore.hasPostingPermission', () {
+    final testCases = [
+      (ChannelPostPolicy.unknown,        UserRole.unknown,       true),
+      (ChannelPostPolicy.unknown,        UserRole.guest,         true),
+      (ChannelPostPolicy.unknown,        UserRole.member,        true),
+      (ChannelPostPolicy.unknown,        UserRole.moderator,     true),
+      (ChannelPostPolicy.unknown,        UserRole.administrator, true),
+      (ChannelPostPolicy.unknown,        UserRole.owner,         true),
+      (ChannelPostPolicy.any,            UserRole.unknown,       true),
+      (ChannelPostPolicy.any,            UserRole.guest,         true),
+      (ChannelPostPolicy.any,            UserRole.member,        true),
+      (ChannelPostPolicy.any,            UserRole.moderator,     true),
+      (ChannelPostPolicy.any,            UserRole.administrator, true),
+      (ChannelPostPolicy.any,            UserRole.owner,         true),
+      (ChannelPostPolicy.fullMembers,    UserRole.unknown,       true),
+      (ChannelPostPolicy.fullMembers,    UserRole.guest,         false),
+      // The fullMembers/member case gets its own tests further below.
+      // (ChannelPostPolicy.fullMembers,    UserRole.member,        /* complicated */),
+      (ChannelPostPolicy.fullMembers,    UserRole.moderator,     true),
+      (ChannelPostPolicy.fullMembers,    UserRole.administrator, true),
+      (ChannelPostPolicy.fullMembers,    UserRole.owner,         true),
+      (ChannelPostPolicy.moderators,     UserRole.unknown,       true),
+      (ChannelPostPolicy.moderators,     UserRole.guest,         false),
+      (ChannelPostPolicy.moderators,     UserRole.member,        false),
+      (ChannelPostPolicy.moderators,     UserRole.moderator,     true),
+      (ChannelPostPolicy.moderators,     UserRole.administrator, true),
+      (ChannelPostPolicy.moderators,     UserRole.owner,         true),
+      (ChannelPostPolicy.administrators, UserRole.unknown,       true),
+      (ChannelPostPolicy.administrators, UserRole.guest,         false),
+      (ChannelPostPolicy.administrators, UserRole.member,        false),
+      (ChannelPostPolicy.administrators, UserRole.moderator,     false),
+      (ChannelPostPolicy.administrators, UserRole.administrator, true),
+      (ChannelPostPolicy.administrators, UserRole.owner,         true),
+    ];
+
+    for (final (ChannelPostPolicy policy, UserRole role, bool canPost) in testCases) {
+      test('"${role.name}" user ${canPost ? 'can' : "can't"} post in channel '
+          'with "${policy.name}" policy', () {
+        final store = eg.store();
+        final actual = store.hasPostingPermission(
+          inChannel: eg.stream(channelPostPolicy: policy), user: eg.user(role: role),
+          // [byDate] is not actually relevant for these test cases; for the
+          // ones which it is, they're practiced below.
+          byDate: DateTime.now());
+        check(actual).equals(canPost);
+      });
+    }
+
+    group('"member" user posting in a channel with "fullMembers" policy', () {
+      PerAccountStore localStore({required int realmWaitingPeriodThreshold}) =>
+        eg.store(initialSnapshot: eg.initialSnapshot(
+          realmWaitingPeriodThreshold: realmWaitingPeriodThreshold));
+
+      User memberUser({required String dateJoined}) => eg.user(
+        role: UserRole.member, dateJoined: dateJoined);
+
+      test('a "full" member -> can post in the channel', () {
+        final store = localStore(realmWaitingPeriodThreshold: 3);
+        final hasPermission = store.hasPostingPermission(
+          inChannel: eg.stream(channelPostPolicy: ChannelPostPolicy.fullMembers),
+          user: memberUser(dateJoined: '2024-11-25T10:00+00:00'),
+          byDate: DateTime.utc(2024, 11, 28, 10, 00));
+        check(hasPermission).isTrue();
+      });
+
+      test('not a "full" member -> cannot post in the channel', () {
+        final store = localStore(realmWaitingPeriodThreshold: 3);
+        final actual = store.hasPostingPermission(
+          inChannel: eg.stream(channelPostPolicy: ChannelPostPolicy.fullMembers),
+          user: memberUser(dateJoined: '2024-11-25T10:00+00:00'),
+          byDate: DateTime.utc(2024, 11, 28, 09, 59));
+        check(actual).isFalse();
+      });
+    });
+  });
+
   group('PerAccountStore.handleEvent', () {
     // Mostly this method just dispatches to ChannelStore and MessageStore etc.,
     // and so most of the tests live in the test files for those