Function Diff

db/commits/patch.go:151–188

(parent, child *Patch)

}

func Diff(parent, child *Patch) (*Patch, error) {
	var dirty bool
	p := NewPatch(parent)
	deletedObjects := make(map[ksuid.KSUID]struct{})
	for _, id := range child.deletedObjects {
		deletedObjects[id] = struct{}{}
	}
	// For each object in the child patch that isn't in the parent, create an add,
	// unless the parent deletes it, then return an error.
	for _, o := range child.SelectAll() {
		if !Exists(parent, o.ID) {
			if _, ok := deletedObjects[o.ID]; ok {
				return nil, fmt.Errorf("parent branch deletes object that child branch adds: %d", o.ID)
			}
			if err := p.AddDataObject(o); err != nil {
				return nil, err
			}
			dirty = true
		}
	}
	// For each delete in the child patch, create a delete.
	// If the object doesn't exist in the parent, then we have a
	// delete conflict.
	for _, id := range child.deletedObjects {
		if Exists(parent, id) {
			if err := p.DeleteObject(id); err != nil {
				return nil, err
			}
			dirty = true
		} else {
			return nil, fmt.Errorf("delete conflict: %s", id)
		}
	}
	if !dirty {
		return nil, errors.New("difference is empty")
	}
	return p, nil
}