add multimonitor

src/test.zig

@@ -244,6 +244,78 @@ test "bits above the tag range do not affect the slot" {
     try testing.expectEqual(act.tag_count, act.tagSlot(@as(u32, 1) << (act.tag_count - 1)));
 }
 
+// ─── splitting the tag set across screens ────────────────────────────────────
+
+test "a lone screen owns every tag" {
+    try testing.expectEqual(act.all_tags, act.tagsForOutput(0, 1));
+    // No screens at all is not a case callers should have to think about.
+    try testing.expectEqual(act.all_tags, act.tagsForOutput(0, 0));
+}
+
+test "two screens split the tags into contiguous halves" {
+    // Nine tags do not halve evenly; the left screen takes the extra one.
+    try testing.expectEqual(@as(u32, 0b000011111), act.tagsForOutput(0, 2));
+    try testing.expectEqual(@as(u32, 0b111100000), act.tagsForOutput(1, 2));
+}
+
+test "three screens split the tags into thirds" {
+    try testing.expectEqual(@as(u32, 0b000000111), act.tagsForOutput(0, 3));
+    try testing.expectEqual(@as(u32, 0b000111000), act.tagsForOutput(1, 3));
+    try testing.expectEqual(@as(u32, 0b111000000), act.tagsForOutput(2, 3));
+}
+
+test "every tag lands on exactly one screen" {
+    // The whole point of the split: no tag is shared and none goes missing,
+    // whatever the screen count.
+    for (1..act.tag_count + 1) |count| {
+        var seen: u32 = 0;
+        for (0..count) |i| {
+            const mask = act.tagsForOutput(i, count);
+            try testing.expect(mask != 0);
+            try testing.expectEqual(@as(u32, 0), seen & mask);
+            seen |= mask;
+        }
+        try testing.expectEqual(act.all_tags, seen);
+    }
+}
+
+test "ranges are contiguous and in screen order" {
+    for (1..act.tag_count + 1) |count| {
+        var next: u32 = 0;
+        for (0..count) |i| {
+            const mask = act.tagsForOutput(i, count);
+            // Contiguous: a run of ones, starting where the last range ended.
+            const lowest = @ctz(mask);
+            const past_highest = 32 - @clz(mask);
+            try testing.expectEqual(next, lowest);
+            try testing.expectEqual(past_highest - lowest, @popCount(mask));
+            next = past_highest;
+        }
+    }
+}
+
+test "more screens than tags leaves no screen without one" {
+    // Twelve monitors and nine tags: the ones past the end share the last tag
+    // rather than being handed an empty mask, which could show nothing at all.
+    const count = act.tag_count + 3;
+    for (0..count) |i| {
+        try testing.expect(act.tagsForOutput(i, count) != 0);
+    }
+    try testing.expectEqual(act.tagsForOutput(act.tag_count - 1, count), act.tagsForOutput(count - 1, count));
+}
+
+test "a screen index past the end owns everything rather than nothing" {
+    try testing.expectEqual(act.all_tags, act.tagsForOutput(2, 2));
+}
+
+test "the lowest tag is what a stranded view falls back to" {
+    try testing.expectEqual(@as(u32, 0b100000), act.lowestTag(0b111100000));
+    try testing.expectEqual(@as(u32, 1), act.lowestTag(act.all_tags));
+    try testing.expectEqual(@as(u32, 0), act.lowestTag(0));
+    // Junk above the tag range is not a tag to fall back to.
+    try testing.expectEqual(@as(u32, 0), act.lowestTag(~act.all_tags));
+}
+
 // ─── command parsing ─────────────────────────────────────────────────────────
 
 fn parseOk(argv: []const []const u8) act.Action {