Bidirectional communication for Kaleidoscope. With this plugin enabled, plugins that implement the `onFocusEvent` hook will start responding to Focus commands sent via `Serial`, allowing bidirectional communication between firmware and host.
This plugin is an upgrade of the former [Kaleidoscope-Focus][kaleidoscope:focus] plugin. See the [UPGRADING.md][upgrading] document for information about how to transition to the new system.
This plugin is **not** meant to be used by the end-user (apart from setting it up to use plugin-provided hooks), but by plugin authors instead. As an end user, you just need to use Focus-enabled plugins like you normally would, and once `FocusSerial` is enabled, their commands will be available too.
Nevertheless, a very simple example is shown below:
The plugin provides the `Focus` object, with a couple of helper methods aimed at developers. Terminating the response with a dot on its own line is handled implicitly by `FocusSerial`, one does not need to do that explicitly.
### `.send(...)`
### `.sendRaw(...)`
Sends a list of variables over the wire. The difference between `.send()` and `.sendRaw()` is that the former puts a space between each variable, the latter does not. If one just wants to send a list of things, use the former. If one needs more control over the formatting, use the latter. In most cases, `.send()` is the recommended method to use.
Both of them take a variable number of arguments, of almost any type: all built-in types can be sent, `cRGB`, `Key` and `bool` too in addition. For colors, `.send()` will write them as an `R G B` sequence; `Key` objects will be sent as the raw 16-bit keycode; and `bool` will be sent as either the string `true`, or `false`.
### `.read(variable)`
Depending on the type of the variable passed by reference, reads a 8 or 16-bit unsigned integer, a `Key`, or a `cRGB` color from the wire, into the variable passed as the argument.
### `.peek()`
Returns the next character on the wire, without reading it. Subsequent reads will include the peeked-at byte too.
### `.isEOL()`
Returns whether we're at the end of the request line.
### `.COMMENT`
When sending something to the host that is not a response to a request, prefix the response lines with this.
### `.SEPARATOR`
To be used when using `.sendRaw`, when one needs complete control over where separators are inserted into the response.
`Focus` uses a simple, textual, request-response-based wire protocol.
Each request has to be on one line, anything before the first space is the command part (if there is no space, just a newline, then the whole line will be considered a command), everything after are arguments. The plugin itself only parses until the end of the command part, argument parsing is left to the various hooks. If there is anything left on the line after hooks are done processing, it will be ignored.
Responses can be multi-line, but most aren't. Their content is also up to the hooks, `Focus` does not enforce anything, except a trailing dot and a newline. Responses should end with a dot on its own line.
Apart from these, there are no restrictions on what can go over the wire, but to make the experience consistent, find a few guidelines below:
* Commands should be namespaced, so that the plugin name, or functionality comes first, then the sub-command or property. Such as `led.theme`, or `led.setAll`.
* One should not use setters and getters, but a single property command instead. One, which when called without arguments, will act as a getter, and as a setter otherwise.
* Namespaces should be lowercase, while the commands within them camel-case.
* Do as little work in the hooks as possible. While the protocol is human readable, the expectation is that tools will be used to interact with the keyboard.
* As such, keep formatting to the bare minimum. No fancy table-like responses.
* In general, the output of a getter should be copy-pasteable to a setter.
