New options -a, -A for low battery notifications

3 files changed, 33 insertions, 2 deletions

diff --git a/changelog.md b/changelog.md
index fd1316d..2ca5d3f 100644
--- a/changelog.md
+++ b/changelog.md
@@ -6,6 +6,9 @@ _New features_
     bytes rather than speeds (see [issue #390].
   - `WeatherX`: An extension to the `Weather` monitor allowing the
     spefication of custom strings or icons for sky conditions.
+  - The battery monitors accept the new arguments `-a` and `-A` to
+    specify a system command executed if battery left goes beyond a
+    given threshold.
 
 [issue #390]: https://github.com/jaor/xmobar/issues/390
 
diff --git a/readme.md b/readme.md
index 2214bda..c8a75e6 100644
--- a/readme.md
+++ b/readme.md
@@ -898,6 +898,12 @@ specification, such as `("clear", "<icon=weather-clear.xbm/>")`.
   - `-p`: color to display positive power (battery charging)
   - `-f`: file in `/sys/class/power_supply` with AC info (default:
     "AC/online")
+  - `-A`: a number between 0 and 100, threshold below which the action
+    given by `-a`, if any, is performed (default: 5)
+  - `-a`: a string with a system command that is run when the
+    percentage left in the battery is less or equal than the threshold
+    given by the `-A` option.  If not present, no action is
+    undertaken.
   - `--on-icon-pattern`: dynamic string for current battery charge
     when AC is "on" in `leftipat`.
   - `--off-icon-pattern`: dynamic string for current battery charge
@@ -916,14 +922,18 @@ specification, such as `("clear", "<icon=weather-clear.xbm/>")`.
                        "-L", "10", "-H", "80", "-p", "3",
                        "--", "-O", "<fc=green>On</fc> - ", "-i", "",
                        "-L", "-15", "-H", "-5",
-                       "-l", "red", "-m", "blue", "-h", "green"]
+                       "-l", "red", "-m", "blue", "-h", "green"
+                       "-a", "notify-send -u critical 'Battery running out!!'",
+                       "-A", "3"]
                       600
 
   In the above example, the thresholds before the "--" separator
   affect only the `<left>` and `<leftbar>` fields, while those after
   the separator affect how `<watts>` is displayed. For this monitor,
   neither the generic nor the specific options have any effect on
-  `<timeleft>`.
+  `<timeleft>`.  We are also telling the monitor to execute the unix
+  command `notify-send` when the percentage left in the battery
+  reaches 6%.
 
   It is also possible to specify template variables in the `-O` and
   `-o` switches, as in the following example:
diff --git a/src/Xmobar/Plugins/Monitors/Batt.hs b/src/Xmobar/Plugins/Monitors/Batt.hs
index 9f74835..bebbf1c 100644
--- a/src/Xmobar/Plugins/Monitors/Batt.hs
+++ b/src/Xmobar/Plugins/Monitors/Batt.hs
@@ -15,6 +15,8 @@
 
 module Xmobar.Plugins.Monitors.Batt ( battConfig, runBatt, runBatt' ) where
 
+import System.Process (system)
+import Control.Monad (void)
 import Control.Exception (SomeException, handle)
 import Xmobar.Plugins.Monitors.Common
 import System.FilePath ((</>))
@@ -36,6 +38,8 @@ data BattOpts = BattOpts
   , highWColor :: Maybe String
   , lowThreshold :: Float
   , highThreshold :: Float
+  , onLowAction :: Maybe String
+  , actionThreshold :: Float
   , onlineFile :: FilePath
   , scale :: Float
   , onIconPattern :: Maybe IconPattern
@@ -52,6 +56,8 @@ defaultOpts = BattOpts
   , lowWColor = Nothing
   , mediumWColor = Nothing
   , highWColor = Nothing
+  , onLowAction = Nothing
+  , actionThreshold = 6
   , lowThreshold = 10
   , highThreshold = 12
   , onlineFile = "AC/online"
@@ -74,6 +80,9 @@ options =
   , Option "H" ["hight"] (ReqArg (\x o -> o { highThreshold = read x }) "") ""
   , Option "f" ["online"] (ReqArg (\x o -> o { onlineFile = x }) "") ""
   , Option "s" ["scale"] (ReqArg (\x o -> o {scale = read x}) "") ""
+  , Option "a" ["action"] (ReqArg (\x o -> o { onLowAction = Just x }) "") ""
+  , Option "A" ["action-threshold"]
+               (ReqArg (\x o -> o { actionThreshold = read x }) "") ""
   , Option "" ["on-icon-pattern"] (ReqArg (\x o ->
      o { onIconPattern = Just $ parseIconPattern x }) "") ""
   , Option "" ["off-icon-pattern"] (ReqArg (\x o ->
@@ -172,6 +181,14 @@ sortOn f =
 mostCommonDef :: Eq a => a -> [a] -> a
 mostCommonDef x xs = head $ last $ [x] : sortOn length (group xs)
 
+maybeAlert :: BattOpts -> Float -> IO ()
+maybeAlert opts left =
+  case onLowAction opts of
+    Nothing -> do return ()
+    Just x -> if not (isNaN left) && actionThreshold opts >= (100 * left)
+              then void $ system x
+              else return ()
+
 readBatteries :: BattOpts -> [Files] -> IO Result
 readBatteries opts bfs =
     do let bfs' = filter (/= NoFiles) bfs
@@ -192,6 +209,7 @@ readBatteries opts bfs =
                  | time == 0 = Idle
                  | ac = Charging
                  | otherwise = Discharging
+       maybeAlert opts left
        return $ if isNaN left then NA else Result left watts time racst
 
 runBatt :: [String] -> Monitor String