Seed provenance + inventory: source links and seed lots (#50) (#64)

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

internal/service/revisions.go

@@ -417,6 +417,9 @@ type revertOps[T any] struct {
 	// remove undoes a creation. It returns the changes it made, because deleting
 	// an object also deletes the plantings hanging off it.
 	remove func(ctx context.Context, row *T) ([]change, error)
+	// beforeRestore fixes up a snapshot whose references may have gone stale
+	// while it sat in history.
+	beforeRestore func(ctx context.Context, row *T) error
 	// blockRemoval optionally refuses a removal, e.g. an object that has gained
 	// plantings since. Returns a conflict reason, or "" to allow it.
 	blockRemoval func(ctx context.Context, row *T) (string, error)
@@ -445,6 +448,11 @@ func revertEntity[T any](
 		if err := unsnapshot(r.Before, &target); err != nil {
 			return nil, nil, err
 		}
+		if ops.beforeRestore != nil {
+			if err := ops.beforeRestore(ctx, &target); err != nil {
+				return nil, nil, err
+			}
+		}
 		restored, err := ops.restore(ctx, &target)
 		if err != nil {
 			// The id may have been taken between the check above and this insert.
@@ -547,6 +555,22 @@ func plantingRevertOps(s *Service) revertOps[domain.Planting] {
 		get:        s.store.GetPlanting,
 		update:     s.store.UpdatePlanting,
 		restore:    s.store.RestorePlanting,
+		// A snapshot can name a seed lot that has since been deleted. The live
+		// rows got their link nulled by ON DELETE SET NULL, but the snapshot
+		// still holds the old id, and restoring it would violate the foreign key
+		// and abort the whole revert. Drop the dangling link instead: the plant
+		// really was in the ground, which is the part worth restoring.
+		beforeRestore: func(ctx context.Context, p *domain.Planting) error {
+			if p.SeedLotID == nil {
+				return nil
+			}
+			if _, err := s.store.GetSeedLot(ctx, *p.SeedLotID); errors.Is(err, domain.ErrNotFound) {
+				p.SeedLotID = nil
+			} else if err != nil {
+				return err
+			}
+			return nil
+		},
 		remove: func(ctx context.Context, p *domain.Planting) ([]change, error) {
 			if err := s.store.DeletePlanting(ctx, p.ID); err != nil {
 				return nil, err