Move kobo auto-suspension logic out of UIManager (#2933)

frontend/ui/hook_container.lua

@@ -0,0 +1,101 @@
+--[[--
+HookContainer allows listeners to register and unregister a hook for speakers to execute.
+
+It's an experimental feature: use with cautions, it can easily pin an object in memory and unblock
+GC from recycling the memory.
+]]
+
+local HookContainer = {}
+
+function HookContainer:new(o)
+    o = o or {}
+    setmetatable(o, self)
+    self.__index = self
+    return o
+end
+
+function HookContainer:_assertIsValidName(name)
+    assert(self ~= nil)
+    assert(type(name) == "string")
+    assert(string.len(name) > 0)
+end
+
+function HookContainer:_assertIsValidFunction(func)
+    assert(self ~= nil)
+    assert(type(func) == "function" or type(func) == "table")
+end
+
+function HookContainer:_assertIsValidFunctionOrNil(func)
+    assert(self ~= nil)
+    if func == nil then return end
+    self:_assertIsValidFunction(func)
+end
+
+--- Register a function to name. Must be called with self.
+-- @tparam string name The name of the hook. Can only be an non-empty string.
+-- @tparam function func The function to handle the hook. Can only be a function.
+function HookContainer:register(name, func)
+    self:_assertIsValidName(name)
+    self:_assertIsValidFunction(func)
+    if self[name] == nil then
+        self[name] = {}
+    end
+    table.insert(self[name], func)
+end
+
+--- Register a widget to name. Must be called with self.
+-- @tparam string name The name of the hook. Can only be an non-empty string.
+-- @tparam table widget The widget to handle the hook. Can only be a table with required functions.
+function HookContainer:registerWidget(name, widget)
+    self:_assertIsValidName(name)
+    assert(type(widget) == "table")
+    self:register(name, function(args)
+        local f = widget["on" .. name]
+        self:_assertIsValidFunction(f)
+        f(widget, args)
+    end)
+    local original_close_widget = widget.onCloseWidget
+    self:_assertIsValidFunctionOrNil(original_close_widget)
+    widget.onCloseWidget = function()
+        if original_close_widget then original_close_widget(widget) end
+        self:unregister(name, widget["on" .. name])
+    end
+end
+
+--- Unregister a function from name. Must be called with self.
+-- @tparam string name The name of the hook. Can only be an non-empty string.
+-- @tparam function func The function to handle the hook. Can only be a function.
+-- @treturn boolean Return true if the function is found and removed, otherwise false.
+function HookContainer:unregister(name, func)
+    self:_assertIsValidName(name)
+    self:_assertIsValidFunction(func)
+    if self[name] == nil then
+        return false
+    end
+
+    for i, f in ipairs(self[name]) do
+        if f == func then
+            table.remove(self[name], i)
+            return true
+        end
+    end
+    return false
+end
+
+--- Execute all registered functions of name. Must be called with self.
+-- @tparam string name The name of the hook. Can only be an non-empty string.
+-- @param args Any kind of arguments sending to the functions.
+-- @treturn number The number of functions have been executed.
+function HookContainer:execute(name, args)
+    self:_assertIsValidName(name)
+    if self[name] == nil or #self[name] == 0 then
+        return 0
+    end
+
+    for _, f in ipairs(self[name]) do
+        f(args)
+    end
+    return #self[name]
+end
+
+return HookContainer