internal_link [nfc]: Add generic support for is operands.

This also helps us with having more thorough test coverage for different
`is` operands.

Signed-off-by: Zixuan James Li <[email protected]>

Author: PIG208

lib/model/internal_link.dart

@@ -152,7 +152,7 @@ Narrow? _interpretNarrowSegments(List<String> segments, PerAccountStore store) {
   ApiNarrowStream? streamElement;
   ApiNarrowTopic? topicElement;
   ApiNarrowDm? dmElement;
-  ApiNarrowIs? isMentionedElement;
+  Set<IsOperand> isElementOperands = {};
 
   for (var i = 0; i < segments.length; i += 2) {
     final (operator, negated) = _parseOperator(segments[i]);
@@ -181,9 +181,9 @@ Narrow? _interpretNarrowSegments(List<String> segments, PerAccountStore store) {
         dmElement = ApiNarrowDm(dmIds, negated: negated);
 
       case _NarrowOperator.is_:
-        if (isMentionedElement != null) return null;
-        if (operand == 'mentioned') isMentionedElement = ApiNarrowIs(IsOperand.mentioned);
-        return null;
+        final isElementOperand = IsOperand.fromRawString(operand);
+        if (isElementOperands.contains(isElementOperand)) return null;
+        isElementOperands.add(isElementOperand);
 
       case _NarrowOperator.near: // TODO(#82): support for near
       case _NarrowOperator.with_: // TODO(#683): support for with
@@ -194,9 +194,22 @@ Narrow? _interpretNarrowSegments(List<String> segments, PerAccountStore store) {
     }
   }
 
-  if (isMentionedElement != null) {
+  if (isElementOperands.isNotEmpty) {
     if (streamElement != null || topicElement != null || dmElement != null) return null;
-    return const MentionsNarrow();
+    switch (isElementOperands.singleOrNull) {
+      case IsOperand.mentioned:
+        return const MentionsNarrow();
+      case null:
+      case IsOperand.dm:
+      case IsOperand.private:
+      case IsOperand.alerted:
+      case IsOperand.starred:
+      case IsOperand.followed:
+      case IsOperand.resolved:
+      case IsOperand.unread:
+      case IsOperand.unknown:
+        return null;
+    }
   } else if (dmElement != null) {
     if (streamElement != null || topicElement != null) return null;
     return DmNarrow.withUsers(dmElement.operand, selfUserId: store.selfUserId);

test/model/internal_link_test.dart

@@ -221,25 +221,44 @@ void main() {
       testExpectedNarrows(testCases, streams: streams);
     });
 
-    group('"/#narrow/is/mentioned returns expected MentionsNarrow', () {
-      final testCases = [
-        ('/#narrow/is/mentioned',                                     const MentionsNarrow()),
-        ('/#narrow/is/mentioned/near/1',                              const MentionsNarrow()),
-        ('/#narrow/is/mentioned/with/2',                              const MentionsNarrow()),
-        ('/#narrow/channel/7-test-here/is/mentioned',                 null),
-        ('/#narrow/channel/check/topic/test/is/mentioned',            null),
-        ('/#narrow/topic/test/is/mentioned',                          null),
-        ('/#narrow/dm/17327-Chris-Bobbe-(Test-Account)/is/mentioned', null),
-        ('/#narrow/-is/mentioned',                                    null),
-      ];
-      testExpectedNarrows(testCases, streams: streams);
+    group('/#narrow/is/<...> returns corresponding narrow', () {
+      // For these tests, we are more interested in the internal links
+      // containing a single effective `is` operator.
+      // Internal links with multiple operators should be tested separately.
+      for (final operand in IsOperand.values) {
+        List<(String, Narrow?)> sharedCases(Narrow? narrow) => [
+            ('/#narrow/is/$operand',                                     narrow),
+            ('/#narrow/is/$operand/near/1',                              narrow),
+            ('/#narrow/is/$operand/with/2',                              narrow),
+            ('/#narrow/channel/7-test-here/is/$operand',                 null),
+            ('/#narrow/channel/check/topic/test/is/$operand',            null),
+            ('/#narrow/topic/test/is/$operand',                          null),
+            ('/#narrow/dm/17327-Chris-Bobbe-(Test-Account)/is/$operand', null),
+            ('/#narrow/-is/$operand',                                    null),
+          ];
+        final List<(String, Narrow?)> testCases;
+        switch (operand) {
+          case IsOperand.mentioned:
+            testCases = sharedCases(const MentionsNarrow());
+          case IsOperand.dm:
+          case IsOperand.private:
+          case IsOperand.alerted:
+          case IsOperand.starred:
+          case IsOperand.followed:
+          case IsOperand.resolved:
+          case IsOperand.unread:
+          case IsOperand.unknown:
+            // Unsupported operands should not return any narrow.
+            testCases = sharedCases(null);
+        }
+        testExpectedNarrows(testCases, streams: streams);
+      }
     });
 
     group('unexpected link shapes are rejected', () {
       final testCases = [
         ('/#narrow/stream/name/topic/',           null), // missing operand
         ('/#narrow/stream/name/unknown/operand/', null), // unknown operator
-        ('/#narrow/is/starred',                   null), // unknown `is` operand
       ];
       testExpectedNarrows(testCases, streams: streams);
     });