Some work to make hotkeys a 'real thing' on the lua side

luprex/lua/hotkeys.lua

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+----------------------------------------------------------------
+--
+-- To add hotkeys to an object (such as a Brick Oven), you will
+-- be adding a function 'lookhotkeys' to the appropriate class,
+-- like this:
+--
+-- function brickoven.lookhotkeys(keys)
+--    keys:add("X", "Light Oven", function () ... end)
+--    keys:add("A", "Add Fuel", function () ... end)
+-- end
+--
+-- This function will get called twice: once in a 'probe' when
+-- Unreal wants to know what hotkeys exist, and a second time in
+-- an 'invoke' to find the right closure.
+--
+-- When the probe happens, we construct a "hotkeylist" to hold
+-- the complete list of hotkeys.  We populate this hotkeylist as
+-- follows:
+--
+--    local keys = hotkeylist.create()
+--    brickoven.lookhotkeys(keys)
+-- 
+-- At this point, if you were to pprint(keys), the output would
+-- look like this:
+--
+--    { "hotkeys", "X", "Light Oven", "A", "Add Fuel" }
+--
+-- The first array element is always the word "hotkeys".  Notice
+-- also that a hotkeylist doesn't store the closures, they are
+-- silently ignored.  The resulting array is in a format that can
+-- be returned directly to Unreal.
+--
+-- Later, when the user presses a key, such as the "Light Oven" key,
+-- we will construct a "hotkeypress" object whose job is to record
+-- the name of the hotkey that was pressed, and the closure that
+-- goes with it.  We populate this object as follows:
+--
+--    local keys = hotkeypress.create("Light Oven")
+--    brickoven.lookhotkeys(keys)
+--
+-- So as you can see, we're using the same 'brickoven.lookhotkeys'
+-- function, but this time, we've passed in a parameter of class
+-- hotkeypress instead of a parameter of class hotkeylist.  This
+-- changes the behavior of the 'add' method: the add function of
+-- a hotkeylist stores all the hotkeys into the list.  But the 'add'
+-- function of a hotkeypress only stores the one closure that
+-- we are interested in.  If you were to pprint(keys), the result
+-- would look like this:
+--
+--    { pressed="Light Oven", closure=<function> }
+--
+-- So the only data stored by a 'hotkeypress' object is the name
+-- of the pressed hotkey, and the closure that goes with it.
+--
+----------------------------------------------------------------
+
+makeclass("hotkeylist")
+makeclass("hotkeypress")
+
+function hotkeylist.create()
+    local result = { "hotkeys" }
+    setmetatable(result, hotkeylist)
+    return result
+end
+
+function hotkeylist.add(self, key, action, closure)
+    table.insert(self, key)
+    table.insert(self, action)
+end
+
+function hotkeypress.create(key)
+    local result = { pressed=key }
+    setmetatable(result, hotkeypress)
+    return result
+end
+
+function hotkeypress.add(self, key, action, closure)
+    if action == self.pressed then
+        self.closure = closure
+    end
+end
+