Undo reported "nothing left to undo" after a successful undo (#72)

Co-authored-by: Steve Dudenhoeffer <[email protected]>

internal/service/revisions_test.go

@@ -704,3 +704,104 @@ func TestClearObjectOnlyClearsWhatItSnapshotted(t *testing.T) {
 		t.Errorf("cleared %d of %d with %d revisions — all three should match", n, len(before), len(revs))
 	}
 }
+
+// TestRevertResultCarriesItsCounts — found by using the thing.
+//
+// commitScope returns the freshly inserted row, which carries no tally. A caller
+// receiving a change set with empty Counts cannot tell "nothing was reverted"
+// from "the tally wasn't loaded", and the chat panel read that ambiguity the
+// wrong way: a successful undo reported "nothing left to undo", which is the
+// worst possible thing to say about an action that just worked.
+//
+// It also pins the cross-layer contract that fix created. countRevisions tallies
+// in Go what ListChangeSets tallies in SQL, and nothing but this test stops the
+// two drifting — so it compares the FULL per-(entity, op) breakdown, not just
+// the totals, which would agree even if the groupings had diverged.
+func TestRevertResultCarriesItsCounts(t *testing.T) {
+	s := newTestService(t, openConfig())
+	owner := seedUser(t, s, "[email protected]")
+	g := seedGarden(t, s, owner)
+	bed := seedBed(t, s, owner, g.ID)
+	plant := seedOwnPlant(t, s, owner, 15)
+	ctx := context.Background()
+
+	if _, err := s.FillNamedRegion(ctx, owner, bed.ID, "all", plant.ID, nil); err != nil {
+		t.Fatalf("fill: %v", err)
+	}
+	// A second, different kind of change, so the breakdown has more than one row
+	// to get wrong.
+	if _, err := s.UpdateObject(ctx, owner, bed.ID, ObjectPatch{Name: strPtr("North Bed")}, bed.Version); err != nil {
+		t.Fatalf("rename: %v", err)
+	}
+	sets := history(t, s, owner, g.ID)
+	rename, fill := sets[0], sets[1]
+
+	undoRename, conflicts, err := s.RevertChangeSet(ctx, owner, rename.ID, domain.SourceUI)
+	if err != nil || len(conflicts) != 0 {
+		t.Fatalf("revert rename: err=%v conflicts=%+v", err, conflicts)
+	}
+	undoFill, conflicts, err := s.RevertChangeSet(ctx, owner, fill.ID, domain.SourceUI)
+	if err != nil || len(conflicts) != 0 {
+		t.Fatalf("revert fill: err=%v conflicts=%+v", err, conflicts)
+	}
+
+	for _, undo := range []*domain.ChangeSet{undoRename, undoFill} {
+		if undo == nil {
+			t.Fatal("a revert that did work returned no change set")
+		}
+		if len(undo.Counts) == 0 {
+			t.Fatalf("change set %d came back with no tally — an empty tally reads as 'nothing happened'", undo.ID)
+		}
+	}
+	// Undoing a fill deletes every plop it created, so the tallies must match.
+	if got, want := countsTotal(undoFill.Counts), countsTotal(fill.Counts); got != want {
+		t.Errorf("undo of the fill reports %d changes, want %d", got, want)
+	}
+
+	// The SQL tally and the Go tally must agree, row for row.
+	listed := history(t, s, owner, g.ID)
+	byID := map[int64][]domain.ChangeCount{}
+	for _, cs := range listed {
+		byID[cs.ID] = cs.Counts
+	}
+	for _, undo := range []*domain.ChangeSet{undoRename, undoFill} {
+		fromSQL, ok := byID[undo.ID]
+		if !ok {
+			t.Fatalf("revert %d is missing from the history list", undo.ID)
+		}
+		if !sameCounts(undo.Counts, fromSQL) {
+			t.Errorf("change set %d: revert returned %+v, the list read says %+v — countRevisions and the SQL grouping have drifted",
+				undo.ID, undo.Counts, fromSQL)
+		}
+	}
+}
+
+// sameCounts compares two tallies regardless of order.
+func sameCounts(a, b []domain.ChangeCount) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	index := func(cs []domain.ChangeCount) map[string]int {
+		m := map[string]int{}
+		for _, c := range cs {
+			m[c.EntityType+"/"+c.Op] = c.N
+		}
+		return m
+	}
+	ia, ib := index(a), index(b)
+	for k, v := range ia {
+		if ib[k] != v {
+			return false
+		}
+	}
+	return true
+}
+
+// countsTotal sums a tally — the server-side twin of the client's totalChanges.
+func countsTotal(counts []domain.ChangeCount) int {
+	n := 0
+	for _, c := range counts {
+		n += c.N
+	}
+	return n
+}