InputSourceSwitch: add application watcher support for input source switching

Some apps like kitty-quick-access cannot be captured by window filters.
This adds an alternative watcher mode using hs.application.watcher that
triggers on app activation events instead.

Config format now supports both string (uses window filter) and table
with source and watcher type specification.

Fixes #351

Author: kang8

Source/InputSourceSwitch.spoon/init.lua

@@ -8,7 +8,9 @@
 ---
 --- spoon.InputSourceSwitch:setApplications({
 ---     ["WeChat"] = "Pinyin - Simplified",
----     ["Mail"] = "ABC"
+---     ["Mail"] = "ABC",
+---     -- Use application watcher for apps that window filter can't capture
+---     ["kitty-quick-access"] = { source = "ABC", watcher = "application" }
 --- })
 ---
 --- spoon.InputSourceSwitch:start()
@@ -21,7 +23,7 @@ obj.__index = obj
 
 -- Metadata
 obj.name = "InputSourceSwitch"
-obj.version = "1.0"
+obj.version = "1.1"
 obj.author = "eks5115 <[email protected]>"
 obj.homepage = "https://github.com/Hammerspoon/Spoons"
 obj.license = "MIT - https://opensource.org/licenses/MIT"
@@ -52,43 +54,64 @@ local function isMethod(methodName)
     return false
 end
 
-local function setAppInputSource(appName, sourceName, event)
+local function switchInputSource(sourceName, appName)
+    local r = true
+
+    if (isLayout(sourceName)) then
+        r = hs.keycodes.setLayout(sourceName)
+    elseif isMethod(sourceName) then
+        r = hs.keycodes.setMethod(sourceName)
+    else
+        hs.alert.show(string.format('sourceName: %s is not layout or method', sourceName))
+    end
+
+    if (not r) then
+        hs.alert.show(string.format('set %s to %s failure', appName, sourceName))
+    end
+end
+
+local function setAppInputSourceWithWindowFilter(appName, sourceName, event)
     event = event or hs.window.filter.windowFocused
 
     hs.window.filter.new(appName):subscribe(event, function()
-        local r = true
-
-        if (isLayout(sourceName)) then
-            r = hs.keycodes.setLayout(sourceName)
-        elseif isMethod(sourceName) then
-            r = hs.keycodes.setMethod(sourceName)
-        else
-            hs.alert.show(string.format('sourceName: %s is not layout or method', sourceName))
-        end
+        switchInputSource(sourceName, appName)
+    end)
+end
 
-        if (not r) then
-            hs.alert.show(string.format('set %s to %s failure', appName, sourceName))
+local function setAppInputSourceWithAppWatcher(appName, sourceName)
+    local watcher = hs.application.watcher.new(function(name, eventType, appObj)
+        if eventType == hs.application.watcher.activated and name == appName then
+            switchInputSource(sourceName, appName)
         end
-        end)
+    end)
+    watcher:start()
+    return watcher
 end
 
 --- InputSourceSwitch.applicationMap
 --- Variable
 --- Mapping the application name to the input source
 obj.applicationsMap = {}
 
+-- Store application watchers to prevent garbage collection
+obj.appWatchers = {}
+
 --- InputSourceSwitch:setApplications()
 --- Method
 --- Set that mapping the application name to the input source
 ---
 --- Parameters:
 ---  * applications - A table containing that mapping the application name to the input source
----     key is the application name and value is the input source name
+---     key is the application name
+---     value can be:
+---       - a string: the input source name (uses window filter, default)
+---       - a table: { source = "input source name", watcher = "window" | "application" }
 ---     example:
 --- ```
 --- {
 ---     ["WeChat"] = "Pinyin - Simplified",
----     ["Mail"] = "ABC"
+---     ["Mail"] = "ABC",
+---     ["kitty-quick-access"] = { source = "ABC", watcher = "application" }
 --- }
 --- ```
 function obj:setApplications(applications)
@@ -104,8 +127,22 @@ end
 --- Parameters:
 ---  * None
 function obj:start()
-    for k,v in pairs(self.applicationsMap) do
-        setAppInputSource(k, v)
+    for appName, config in pairs(self.applicationsMap) do
+        local sourceName, watcherType
+
+        if type(config) == "string" then
+            sourceName = config
+            watcherType = "window"
+        else
+            sourceName = config.source
+            watcherType = config.watcher or "window"
+        end
+
+        if watcherType == "application" then
+            self.appWatchers[appName] = setAppInputSourceWithAppWatcher(appName, sourceName)
+        else
+            setAppInputSourceWithWindowFilter(appName, sourceName)
+        end
     end
     return self
 end