Navigate to snapshots from the transcript

internal/server/changes.go

@@ -29,6 +29,20 @@ func (s *Server) GetTaskChanges(w http.ResponseWriter, r *http.Request, taskID s
 		return
 	}
 
+	step := params.Step != nil && *params.Step
+	if params.Snapshot != nil {
+		if params.Since != nil {
+			writeError(w, http.StatusBadRequest, errors.New("since and snapshot can't be used together"))
+			return
+		}
+		s.snapshotChanges(w, r, t, p, *params.Snapshot, step)
+		return
+	}
+	if step {
+		writeError(w, http.StatusBadRequest, errors.New("step needs snapshot"))
+		return
+	}
+
 	since := ""
 	if params.Since != nil {
 		since = *params.Since
@@ -46,6 +60,41 @@ func (s *Server) GetTaskChanges(w http.ResponseWriter, r *http.Request, taskID s
 	writeJSON(w, http.StatusOK, changes)
 }
 
+func (s *Server) snapshotChanges(w http.ResponseWriter, r *http.Request, t api.Task, p api.Project, n int, step bool) {
+	snap, err := s.store.GetSnapshot(r.Context(), t.Id, n)
+	if err != nil {
+		writeStoreError(w, err)
+		return
+	}
+
+	since := ""
+	if step {
+		since, err = s.stepBase(r, t, snap)
+		if err != nil {
+			writeStoreError(w, err)
+			return
+		}
+	}
+
+	changes, err := git.Compare(t.WorktreePath, p.DefaultBranch, snap.CommitSha, snap.TreeSha, since)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, err)
+		return
+	}
+	writeJSON(w, http.StatusOK, changes)
+}
+
+func (s *Server) stepBase(r *http.Request, t api.Task, snap api.Snapshot) (string, error) {
+	if snap.N == 1 {
+		return git.Parent(t.WorktreePath, snap.CommitSha)
+	}
+	prev, err := s.store.GetSnapshot(r.Context(), t.Id, snap.N-1)
+	if err != nil {
+		return "", err
+	}
+	return prev.TreeSha, nil
+}
+
 func (s *Server) GetTaskDiff(w http.ResponseWriter, r *http.Request, taskID string, params api.GetTaskDiffParams) {
 	t, err := s.store.GetTask(r.Context(), taskID)
 	if err != nil {