# `Hakushi.Issho`
[🔗](https://github.com/hattoriai/hakushi/blob/v0.1.0/lib/hakushi/issho.ex#L2)

A shared canvas on [Issho](https://hex.pm/packages/issho): the canvas's
graph is a document of an Issho room, the canvas's LiveView is one of
the room's sessions, and Issho is the room's people and their cursors.

    <.canvas id="schema" graph={@graph} live={{MyApp.Issho, "schema:42"}} user={@current_user} />

The first canvas to open the room's document gives it its graph, its
rules and its `on_change`; the others get the document as it is. Each
change goes to the document's authority, which checks the rules,
applies it, asks `on_change` (once, whoever made it), and only then
sends it to every canvas of the room. The document lasts as long as a
canvas has it open: your app's tables, which `on_change` writes, are
the truth, and the next canvas starts from the graph you give it.

`change/3` makes your app's own change, from anywhere (a job, another
LiveView), on a canvas someone has open.

# `change`

```elixir
@spec change(atom(), String.t(), Hakushi.Change.t()) :: :ok | {:error, term()}
```

Makes your app's own change on a shared canvas: the way of a person's
(the rules, `on_change`), to everyone in the room, and not a person's to
undo (`by` is `nil`). Gives `:ok`, `{:error, reason}`, or
`{:error, :not_running}` when no canvas has the room open (then change
your own copy, in your database).

# `graph`

```elixir
@spec graph(atom(), String.t()) :: Hakushi.Graph.t() | nil
```

The graph of a shared canvas as its room has it, or `nil` when no canvas has it open.

---

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