Experimental new hook registration system based on on_event()

data/lua/core.lua

@@ -372,6 +372,56 @@ if wesnoth.kernel_type() == "Game Lua Kernel" then
 			wml.array_access.set(key, value)
 		end
 	})
+
+	-- Facility to register hooks without interfering with other hooks
+	-- Based on on_event()
+	local hooks = {}
+	local hooks_mt = {
+		__metatable = "Wesnoth hooks registry",
+		__newindex = function(_, k, v)
+			wesnoth.hooks.register(k, v)
+		end,
+		__index = function(_, k)
+			-- Return a COPY of the hooks list
+			local matching = {}
+			for i = 1, #hooks[k] do
+				table.insert(matching, hooks[k][i])
+			end
+			return matching
+		end
+	}
+
+	wesnoth.hooks = setmetatable({}, hooks_mt)
+
+	function wesnoth.hooks.register(name, arg1, arg2)
+		local priority = 0
+		local handler
+		if type(arg1) == "function" then
+			handler = arg1
+		else
+			priority = arg1
+			handler = arg2
+		end
+		if hooks[name] == nil then
+			-- Register the handler in the old way
+			hooks[name] = {}
+			local old_hook = wesnoth.game_events[name] or function(...) end
+			wesnoth.game_events[name] = function(...)
+				local ret = old_hook(...)
+				for k,v in pairs(hooks[name] or {}) do
+					v.h(...)
+				end
+			end
+		end
+		local hl = hooks[name]
+		table.insert(hooks[hl], {h = handler, p = priority})
+		-- sort it.
+		for i = #hl - 1, 1, -1 do
+			if hl[i].p < hl[i + 1].p then
+				hl[i], hl[i + 1] = hl[i + 1], hl[i]
+			end
+		end
+	end
 end
 
 -- Some C++ functions are deprecated; apply the messages here.