PowerD: Unbreak frontlight toggle notifications outside of Kobo (#10597)

Fix #10588
Regression since #10305

While we're there, rejig the FL toggle callback shenanigans so that implementation details don't leak through to *other* implementations.
(i.e., leave the Kobo mess in Kobo land, with only a minimal impact on the public API and its implementation).

frontend/device/android/powerd.lua

@@ -1,6 +1,4 @@
 local BasePowerD = require("device/generic/powerd")
-local Event = require("ui/event")
-local UIManager
 local _, android = pcall(require, "android")
 
 local AndroidPowerD = BasePowerD:new{
@@ -8,13 +6,6 @@ local AndroidPowerD = BasePowerD:new{
     fl_max = 100,
 }
 
--- Let the footer know of the change
-local function broadcastLightChanges()
-    if UIManager then
-        UIManager:broadcastEvent(Event:new("FrontlightStateChanged"))
-    end
-end
-
 function AndroidPowerD:frontlightIntensityHW()
     return math.floor(android.getScreenBrightness() / self.bright_diff * self.fl_max)
 end
@@ -66,8 +57,6 @@ function AndroidPowerD:turnOffFrontlightHW()
         return
     end
     android.setScreenBrightness(self.fl_min)
-    self.is_fl_on = false
-    broadcastLightChanges()
 end
 
 function AndroidPowerD:turnOnFrontlightHW()
@@ -78,13 +67,6 @@ function AndroidPowerD:turnOnFrontlightHW()
     android.enableFrontlightSwitch()
 
     android.setScreenBrightness(math.floor(self.fl_intensity * self.bright_diff / self.fl_max))
-
-    self.is_fl_on = true
-    broadcastLightChanges()
-end
-
-function AndroidPowerD:UIManagerReadyHW(uimgr)
-    UIManager = uimgr
 end
 
 return AndroidPowerD

frontend/device/generic/powerd.lua

@@ -59,8 +59,21 @@ function BasePowerD:isAuxChargingHW() return false end
 function BasePowerD:isAuxChargedHW() return false end
 function BasePowerD:frontlightIntensityHW() return 0 end
 function BasePowerD:isFrontlightOnHW() return self.fl_intensity > self.fl_min end
-function BasePowerD:turnOffFrontlightHW(done_callback) self:setIntensityHW(self.fl_min) end
+--- @note: done_callback is used to display Notifications,
-function BasePowerD:turnOnFrontlightHW(done_callback) self:setIntensityHW(self.fl_intensity) end --- @fixme: what if fl_intensity == fl_min (c.f., kindle)?
+---        some implementations *may* need to handle it themselves because of timing constraints,
+---        in which case they should return *true* here, so that the public API knows not to consume the callback early.
+function BasePowerD:turnOffFrontlightHW(done_callback)
+    self:setIntensityHW(self.fl_min)
+
+    -- Nothing fancy required, so we leave done_callback handling to the public API
+    return false
+end
+function BasePowerD:turnOnFrontlightHW(done_callback)
+    --- @fixme: what if fl_intensity == fl_min (c.f., kindle)?
+    self:setIntensityHW(self.fl_intensity)
+
+    return false
+end
 function BasePowerD:frontlightWarmthHW() return 0 end
 -- Anything that needs to be done before doing a real hardware suspend.
 -- (Such as turning the front light off).
@@ -121,9 +134,12 @@ end
 function BasePowerD:turnOffFrontlight(done_callback)
     if not self.device:hasFrontlight() then return end
     if self:isFrontlightOff() then return false end
-    self:turnOffFrontlightHW(done_callback)
+    local cb_handled = self:turnOffFrontlightHW(done_callback)
     self.is_fl_on = false
     self:stateChanged()
+    if not cb_handled and done_callback then
+        done_callback()
+    end
     return true
 end
 
@@ -131,9 +147,12 @@ function BasePowerD:turnOnFrontlight(done_callback)
     if not self.device:hasFrontlight() then return end
     if self:isFrontlightOn() then return false end
     if self.fl_intensity == self.fl_min then return false end  --- @fixme what the hell?
-    self:turnOnFrontlightHW(done_callback)
+    local cb_handled = self:turnOnFrontlightHW(done_callback)
     self.is_fl_on = true
     self:stateChanged()
+    if not cb_handled and done_callback then
+        done_callback()
+    end
     return true
 end
 

frontend/device/kobo/powerd.lua

@@ -364,6 +364,9 @@ function KoboPowerD:turnOffFrontlightHW(done_callback)
         -- If UIManager is not initialized yet, just turn it off immediately
         self:setIntensityHW(self.fl_min)
     end
+
+    -- We consume done_callback ourselves, make sure Generic's PowerD gets the memo
+    return true
 end
 
 -- Similar functionality as `Kobo:turnOnFrontlightHW`, but the other way around ;).
@@ -410,6 +413,9 @@ function KoboPowerD:turnOnFrontlightHW(done_callback)
         -- If UIManager is not initialized yet, just turn it on immediately
         self:setIntensityHW(self.fl_intensity)
     end
+
+    -- We consume done_callback ourselves, make sure Generic's PowerD gets the memo
+    return true
 end
 
 -- Turn off front light before suspend.