Kindle: Fix a smattering of frontlight bugs

* afterResume had *two* different implementations, so the historical one
  that handled frontlight fixups no longer ran
  (regression since #10426)
* isFrontlightOn was completely broken, for a couple of reasons:
  * There was no is isFrontlightOnHW implementation, so when it ran, it
    mostly always thought the frontlight was on, because
    self.fl_intensity doesn't change on toggle off.
  * _decideFrontlightState was never called on Kindle,
    so isFrontlightOnHW was never really called, making isFrontlightOn
    completely useless. Call it in setIntensityHW's coda, as it ought to
    be. And properly document that.

Generic *was* calling _decideFrontlightState is setIntensity, but
*before* actually setting the frontlight, which makes no goddamn sense,
so get rid of that, too.

* Also fix frontlight toggle notifications (regression since #10305)

TL;DR: The PowerD API being a mess strikes again.

frontend/device/android/powerd.lua

@@ -60,7 +60,7 @@ function AndroidPowerD:turnOffFrontlightHW()
     android.setScreenBrightness(self.fl_min)
 end
 
-function AndroidPowerD:turnOnFrontlightHW()
+function AndroidPowerD:turnOnFrontlightHW(done_callback)
     if self:isFrontlightOn() and self:isFrontlightOnHW() then
         return
     end
@@ -68,6 +68,8 @@ function AndroidPowerD:turnOnFrontlightHW()
     android.enableFrontlightSwitch()
 
     android.setScreenBrightness(math.floor(self.fl_intensity * self.bright_diff / self.fl_max))
+
+    return false
 end
 
 return AndroidPowerD

frontend/device/devicelistener.lua

@@ -187,7 +187,7 @@ if Device:hasFrontlight() then
     function DeviceListener:onToggleFrontlight()
         local powerd = Device:getPowerDevice()
         local new_text
-        if powerd.is_fl_on then
+        if powerd:isFrontlightOn() then
             new_text = _("Frontlight disabled.")
         else
             new_text = _("Frontlight enabled.")

frontend/device/generic/powerd.lua

@@ -43,7 +43,10 @@ function BasePowerD:new(o)
 end
 
 function BasePowerD:init() end
-function BasePowerD:setIntensityHW(intensity) end
+--- @note: This should *always* call self:_decideFrontlightState() in its coda (unless you have a custom isFrontlightOn implementation)!
+function BasePowerD:setIntensityHW(intensity)
+    self:_decideFrontlightState()
+end
 --- @note: Unlike the "public" setWarmth, this one takes a value in the *native* scale!
 function BasePowerD:setWarmthHW(warmth) end
 function BasePowerD:getCapacityHW() return 0 end
@@ -207,7 +210,6 @@ function BasePowerD:setIntensity(intensity)
     if not self.device:hasFrontlight() then return false end
     if intensity == self:frontlightIntensity() then return false end
     self.fl_intensity = self:normalizeIntensity(intensity)
-    self:_decideFrontlightState()
     logger.dbg("set light intensity", self.fl_intensity)
     self:setIntensityHW(self.fl_intensity)
     self:stateChanged()

frontend/device/kindle/powerd.lua

@@ -29,17 +29,22 @@ end
 
 -- If we start with the light off (fl_intensity is fl_min), ensure a toggle will set it to the lowest "on" step,
 -- and that we update fl_intensity (by using setIntensity and not setIntensityHW).
-function KindlePowerD:turnOnFrontlightHW()
+function KindlePowerD:turnOnFrontlightHW(done_callback)
     self:setIntensity(self.fl_intensity == self.fl_min and self.fl_min + 1 or self.fl_intensity)
+
+    return false
 end
 -- Which means we need to get rid of the insane fl_intensity == fl_min shortcut in turnOnFrontlight, too...
 -- That dates back to #2941, and I have no idea what it's supposed to help with.
-function BasePowerD:turnOnFrontlight()
+function KindlePowerD:turnOnFrontlight(done_callback)
     if not self.device:hasFrontlight() then return end
     if self:isFrontlightOn() then return false end
-    self:turnOnFrontlightHW()
+    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
 
@@ -79,6 +84,14 @@ function KindlePowerD:frontlightIntensityHW()
     end
 end
 
+-- Make sure isFrontlightOn reflects the actual HW state,
+-- as self.fl_intensity is kept as-is when toggling the light off,
+-- in order to be able to toggle it back on at the right intensity.
+function KindlePowerD:isFrontlightOnHW()
+    local hw_intensity = self:frontlightIntensityHW()
+    return hw_intensity > self.fl_min
+end
+
 function KindlePowerD:setIntensityHW(intensity)
     -- Handle the synthetic step switcheroo on ! canTurnFrontlightOff devices...
     local turn_it_off = false
@@ -108,6 +121,9 @@ function KindlePowerD:setIntensityHW(intensity)
             ffiUtil.writeToSysfs(intensity, self.warmth_intensity_file)
         end
     end
+
+    -- The state might have changed, make sure we don't break isFrontlightOn
+    self:_decideFrontlightState()
 end
 
 function KindlePowerD:frontlightWarmthHW()
@@ -182,22 +198,6 @@ function KindlePowerD:_readFLIntensity()
     return self:read_int_file(self.fl_intensity_file)
 end
 
-function KindlePowerD:afterResume()
-    if not self.device:hasFrontlight() then
-        return
-    end
-    if self:isFrontlightOn() then
-        -- The Kindle framework should turn the front light back on automatically.
-        -- The following statement ensures consistency of intensity, but should basically always be redundant,
-        -- since we set intensity via lipc and not sysfs ;).
-        -- NOTE: This is race-y, and we want to *lose* the race, hence the use of the scheduler (c.f., #4392)
-        UIManager:tickAfterNext(function() self:turnOnFrontlightHW() end)
-    else
-        -- But in the off case, we *do* use sysfs, so this one actually matters.
-        UIManager:tickAfterNext(function() self:turnOffFrontlightHW() end)
-    end
-end
-
 function KindlePowerD:toggleSuspend()
     if self.lipc_handle then
         self.lipc_handle:set_int_property("com.lab126.powerd", "powerButton", 1)
@@ -293,6 +293,20 @@ function KindlePowerD:afterResume()
 
     -- Restore user input and emit the Resume event.
     self.device:_afterResume()
+
+    if not self.device:hasFrontlight() then
+        return
+    end
+    if self:isFrontlightOn() then
+        -- The Kindle framework should turn the front light back on automatically.
+        -- The following statement ensures consistency of intensity, but should basically always be redundant,
+        -- since we set intensity via lipc and not sysfs ;).
+        -- NOTE: This is race-y, and we want to *lose* the race, hence the use of the scheduler (c.f., #4392)
+        UIManager:tickAfterNext(function() self:turnOnFrontlightHW() end)
+    else
+        -- But in the off case, we *do* use sysfs, so this one actually matters.
+        UIManager:tickAfterNext(function() self:turnOffFrontlightHW() end)
+    end
 end
 
 function KindlePowerD:UIManagerReadyHW(uimgr)

frontend/device/pocketbook/powerd.lua

@@ -41,6 +41,9 @@ function PocketBookPowerD:setIntensityHW(intensity)
     else
         inkview.SetFrontlightState(intensity)
     end
+
+    -- We have a custom isFrontlightOn implementation, so this is redundant
+    self:_decideFrontlightState()
 end
 
 function PocketBookPowerD:isFrontlightOn()

frontend/device/sdl/powerd.lua

@@ -18,6 +18,7 @@ end
 function SDLPowerD:setIntensityHW(intensity)
     require("logger").info("set brightness to", intensity)
     self.hw_intensity = intensity or self.hw_intensity
+    self:_decideFrontlightState()
 end
 
 function SDLPowerD:frontlightWarmthHW()

spec/unit/frontlight_spec.lua

@@ -23,6 +23,7 @@ describe("Frontlight function in PowerD", function()
         end
         PowerD.setIntensityHW = function(self, intensity)
             self.frontlight = intensity
+            self:_decideFrontlightState()
         end
     end)