plan 9: an interrupted or failed undo can be finished

1 files changed, 17 insertions, 2 deletions

diff --git a/internal/engine/apply.go b/internal/engine/apply.go
index 94d65e4..e109aaf 100644
--- a/internal/engine/apply.go
+++ b/internal/engine/apply.go
@@ -343,6 +343,14 @@ func (e *Engine) PlanUndo(runID string) (*UndoPlan, error) {
 		return nil, fmt.Errorf("engine: plan undo: run %s is itself an undo and cannot be undone", runID)
 	}
 
+	// Reversals an earlier undo of this same run already completed are not
+	// offered again (review M10): an undo that stopped part way can be
+	// finished by undoing the run once more.
+	reversed, err := journal.ReversedSteps(e.Config.LogFile(), runID)
+	if err != nil {
+		return nil, fmt.Errorf("engine: plan undo: %w", err)
+	}
+
 	// Entries are grouped by directory and file together (review M7): one run
 	// spans every directory, and two directories can each hold a file of the
 	// same name.
@@ -362,7 +370,7 @@ func (e *Engine) PlanUndo(runID string) (*UndoPlan, error) {
 
 	up := &UndoPlan{Run: runID}
 	for _, k := range order {
-		uf := planUndoFile(k.dir, k.file, byFile[k])
+		uf := planUndoFile(k.dir, k.file, byFile[k], reversed)
 		// Critical finding, Task 8's review: a file every one of whose
 		// entries has Status != "ok" (declined by the ORIGINAL run's own
 		// review, or skipped, or failed before anything happened) yields
@@ -464,7 +472,7 @@ func isFileAffecting(action string) bool {
 // two steps of one file that touch the same path, and every un-contended
 // check keeps behaving exactly as before, since the projection only ever
 // overrides a real occupant that this same chain is itself about to clear.
-func planUndoFile(dir, file string, ents []journal.Entry) UndoFile {
+func planUndoFile(dir, file string, ents []journal.Entry, reversed map[journal.ReversedKey]int) UndoFile {
 	uf := UndoFile{File: file, Dir: dir}
 	proj := newUndoProjection()
 	for i := len(ents) - 1; i >= 0; i-- {
@@ -483,6 +491,13 @@ func planUndoFile(dir, file string, ents []journal.Entry) UndoFile {
 			break
 		}
 		step := reverseStep(en)
+		if k := (journal.ReversedKey{Dir: dir, File: file, Action: step.Action, Src: step.Src}); reversed[k] > 0 {
+			// An earlier undo of this run already reversed this step: the
+			// disk already shows it, and it is not offered again.
+			reversed[k]--
+			proj.record(step)
+			continue
+		}
 		if (en.Action == "move" || en.Action == "rename") && proj.occupied[en.Dst] {
 			// A reversal already queued for this same file puts it back at
 			// en.Dst before this one runs, and that reversal was checked