# `Kotoba.Collab.Store`
[🔗](https://github.com/hattoriai/kotoba/blob/v0.8.0/lib/kotoba/collab/store.ex#L1)

Atomic persistence for collaboration state and its rendered content.

`save/5` must compare the stored `{epoch, revision}` with `expected`
and commit state and content together. `nil` means the document has no
collaboration state yet. A stale owner must receive `{:error, :conflict}`.
The document's authority (Issho's) acknowledges edits only after this
callback succeeds.

The state is a map of JSON values with `"epoch"` and `"revision"` keys:
keep it as it is, in a map or JSON column. A state saved by Kotoba
before Issho loads as it is too, and is saved in Issho's form with its
next change.

The context is supplied by the application, for example a repository
module or an options map. The guide includes an Ecto implementation.

# `load`

```elixir
@callback load(context :: term(), document_id :: String.t()) ::
  {:ok, %{state: map() | nil, content: Kotoba.Content.t() | nil}}
  | {:error, term()}
```

# `save`

```elixir
@callback save(
  context :: term(),
  document_id :: String.t(),
  expected :: {String.t(), non_neg_integer()} | nil,
  state :: map(),
  content :: Kotoba.Content.t()
) :: :ok | {:error, term()}
```

---

*Consult [api-reference.md](api-reference.md) for complete listing*