# Storage layer for Notesmachine

This library implements the core functionality of Notesmachine and
describes that functionality to a storage layer.  There's a bit of
intermingling in here which can't be helped, although it may make sense
in the future to separate the decomposition of the note content into a
higher layer.

Notesmachine storage notes consist of two items: Zettle and Kasten,
which are German for "Note" and "Box".  Here are the basic rules:

- Boxes have titles (and date metadata)
- Notes have content and a type (and date metadata)
- Notes are stored in boxes
  - Notes are positioned with respect to other notes.
  - There are two positions:
    - Siblings, creating lists
	- Children, creating trees like this one
- Notes may have references (pointers) to other boxes
- Notes may be moved around
- Notes may be deleted
- Boxes may be deleted
- When a box is renamed, every reference to that box is auto-edited to
  reflect the change. If a box is renamed to match an existing box, the
  notes in both boxes are merged.
  
Note-to-note relationships form trees, and are kept in a SQL database of
(`parent_id`, `child_id`, `position`, `relationship_type`). The
`position` is a monotonic index on the parent (that is, every pair
(`parent_id`, `position`) must be unique).  The `relationship_type` is
an enum and can specify that the relationship is *original*,
*embedding*, or *referencing*.  An embedded or referenced note may be
read/write or read-only with respect to the original, but there is only
one original note at any time.

Note-to-box relationships form a graph, and are kept in the SQL database
as a collection of *edges* from the note to the box (and naturally
vice-versa).

- Decision: When an original note is deleted, do all references and
  embeddings also get deleted, or is the oldest one elevated to be a new
  "original"?  Or is that something the user may choose?

- Decision: Should the merging issue be handled at this layer, or would
  it make sense to move this to a higher layer, and only provide the
  hooks for it here?