feat(display.go): Add display brightness settings (#17)

* feat(display.go): impl setDisplayBrightness()

Implements setDisplayBrightness(brightness int) which allows setting the
backlight brightness on JetKVM's hardware.

Needs to be implemented into the RPC, config and frontend.

* feat(config): add backlight control settings

* feat(display): add automatic dimming & switch off to display

WIP, dims the display to 50% of the BacklightMaxBrightness after
BacklightDimAfterMS expires. Turns the display off after
BacklightOffAfterMS

* feat(rpc): add methods to get and set BacklightSettings

* WIP: feat(settings): add Max backlight setting

* chore: use constant for backlight control file

* fix: only attempt to wake the display if it's off

* feat(display): wake on touch

* fix: re-use buffer between reads

* fix: wakeDisplay() on start to fix warm start issue

If the application had turned off the display before exiting, it
wouldn't be brought on when the application restarted without a device
reboot.

* chore: various comment & string updates

* fix: newline on set brightness log

Noticed by @eric
https://github.com/jetkvm/kvm/pull/17#discussion_r1903338705

* fix: set default value for display

Set the DisplayMaxBrightness to the default brightness used
out-of-the-box by JetKVM. Also sets the dim/timeout to 2 minutes and 30
mintes respectively.

* feat(display.go): use tickers to countdown to dim/off

As suggested by tutman in https://github.com/jetkvm/kvm/pull/17, use
tickers set to the duration of dim/off to avoid a loop running every
second. The tickers are reset to the dim/off times whenever
wakeDisplay() is called.

* chore: update config

Changed Dim & Off values to seconds instead of milliseconds, there's no
need for it to be that precise.

* feat(display.go): wakeDisplay() force

Adds the force boolean to wakedisplay() which allows skipping the
backlightState == 0 check, this means you can force a ticker reset, even
if the display is currently in the "full bright" state

* feat(display.go): move tickers into their own method

This allows them to only be started if necessary. If the user has chosen
to keep the display on and not-dimmed all the time, the tickers can't
start as their tick value must be a positive integer.

* feat(display.go): stop tickers when auto-dim/auto-off is disabled

* feat(rpc): implement display backlight control methods

* feat(ui): implement display backlight control

* chore: update variable names

As part of @joshuasing's review on #17, updated variables & constants to
match the Go best practices.

Signed-off-by: Cameron Fleming <cameron@nevexo.space>

* fix(display): move backlightTicker setup into screen setup goroutine

Signed-off-by: Cameron Fleming <cameron@nevexo.space>

* chore: fix some start-up timing issues

* fix(display): Don't attempt to start the tickers if the display is disabled

If max_brightness is zero, then there's no point in trying to dim it (or
turn it off...)

* fix: wakeDisplay() doesn't need to stop the tickers

The tickers only need to be reset, if they're disabled, they won't have
been started.

* fix: Don't wake up the display if it's turned off

---------

Signed-off-by: Cameron Fleming <cameron@nevexo.space>

jsonrpc.go

@@ -34,6 +34,12 @@ type JSONRPCEvent struct {
 	Params  interface{} `json:"params,omitempty"`
 }
 
+type BacklightSettings struct {
+	MaxBrightness int `json:"max_brightness"`
+	DimAfter      int `json:"dim_after"`
+	OffAfter      int `json:"off_after"`
+}
+
 func writeJSONRPCResponse(response JSONRPCResponse, session *Session) {
 	responseBytes, err := json.Marshal(response)
 	if err != nil {
@@ -225,6 +231,56 @@ func rpcTryUpdate() error {
 	return nil
 }
 
+func rpcSetBacklightSettings(params BacklightSettings) error {
+	LoadConfig()
+
+	blConfig := params
+
+	// NOTE: by default, the frontend limits the brightness to 64, as that's what the device originally shipped with.
+	if blConfig.MaxBrightness > 255 || blConfig.MaxBrightness < 0 {
+		return fmt.Errorf("maxBrightness must be between 0 and 255")
+	}
+
+	if blConfig.DimAfter < 0 {
+		return fmt.Errorf("dimAfter must be a positive integer")
+	}
+
+	if blConfig.OffAfter < 0 {
+		return fmt.Errorf("offAfter must be a positive integer")
+	}
+
+	config.DisplayMaxBrightness = blConfig.MaxBrightness
+	config.DisplayDimAfterSec = blConfig.DimAfter
+	config.DisplayOffAfterSec = blConfig.OffAfter
+
+	if err := SaveConfig(); err != nil {
+		return fmt.Errorf("failed to save config: %w", err)
+	}
+
+	log.Printf("rpc: display: settings applied, max_brightness: %d, dim after: %ds, off after: %ds", config.DisplayMaxBrightness, config.DisplayDimAfterSec, config.DisplayOffAfterSec)
+
+	// If the device started up with auto-dim and/or auto-off set to zero, the display init
+	// method will not have started the tickers. So in case that has changed, attempt to start the tickers now.
+	startBacklightTickers()
+
+	// Wake the display after the settings are altered, this ensures the tickers
+	// are reset to the new settings, and will bring the display up to maxBrightness.
+	// Calling with force set to true, to ignore the current state of the display, and force
+	// it to reset the tickers.
+	wakeDisplay(true)
+	return nil
+}
+
+func rpcGetBacklightSettings() (*BacklightSettings, error) {
+	LoadConfig()
+
+	return &BacklightSettings{
+		MaxBrightness: config.DisplayMaxBrightness,
+		DimAfter:      int(config.DisplayDimAfterSec),
+		OffAfter:      int(config.DisplayOffAfterSec),
+	}, nil
+}
+
 const (
 	devModeFile = "/userdata/jetkvm/devmode.enable"
 	sshKeyDir   = "/userdata/dropbear/.ssh"
@@ -385,7 +441,7 @@ func callRPCHandler(handler RPCHandler, params map[string]interface{}) (interfac
 				}
 				args[i] = reflect.ValueOf(newStruct).Elem()
 			} else {
-				return nil, fmt.Errorf("invalid parameter type for: %s", paramName)
+				return nil, fmt.Errorf("invalid parameter type for: %s, type: %s", paramName, paramType.Kind())
 			}
 		} else {
 			args[i] = convertedValue.Convert(paramType)
@@ -560,4 +616,6 @@ var rpcHandlers = map[string]RPCHandler{
 	"getWakeOnLanDevices":    {Func: rpcGetWakeOnLanDevices},
 	"setWakeOnLanDevices":    {Func: rpcSetWakeOnLanDevices, Params: []string{"params"}},
 	"resetConfig":            {Func: rpcResetConfig},
+	"setBacklightSettings":   {Func: rpcSetBacklightSettings, Params: []string{"params"}},
+	"getBacklightSettings":   {Func: rpcGetBacklightSettings},
 }