Experimental AI: add a simple move to enemy CA

Set up to run if nothing else is available.
In a separate file for use as a stand-alone CA in an AI

data/ai/lua/generic_rush_engine.lua

@@ -1,7 +1,9 @@
 return {
     init = function(ai)
 
-        local generic_rush = {}
+        -- Grab a useful separate CA as a starting point
+        local generic_rush = wesnoth.require("ai/lua/move_to_any_target.lua").init(ai)
+
         -- More generic grunt rush (and can, in fact, be used with other unit types as well)
 
         local H = wesnoth.require "lua/helper.lua"

data/ai/lua/move_to_any_target.lua

@@ -0,0 +1,52 @@
+return {
+    init = function(ai)
+        local AH = wesnoth.require "~/add-ons/AI-demos/lua/ai_helper.lua"
+
+        local move_to_any_target = {}
+
+        function move_to_any_target:move_to_enemy_eval()
+            local units = wesnoth.get_units {
+                side = wesnoth.current.side,
+                canrecruit = 'no',
+                formula = '$this_unit.moves > 0'
+            }
+
+            if (not units[1]) then
+                -- No units with moves left
+                return 0
+            end
+
+            local unit, destination
+            -- Find a unit that has a path to an space close to an enemy
+            for i,u in ipairs(units) do
+                local distance, target = AH.get_closest_enemy({u.x, u.y})
+                if target.x then
+                    unit = u
+
+                    local x, y = wesnoth.find_vacant_tile(target.x, target.y)
+                    destination = AH.next_hop(unit, x, y)
+
+                    if destination then
+                        break
+                    end
+                end
+            end
+
+            if (not destination) then
+                -- No path was found
+                return 0
+            end
+
+            self.data.destination = destination
+            self.data.unit = unit
+
+            return 1
+        end
+
+        function move_to_any_target:move_to_enemy_exec()
+            ai.move(self.data.unit, self.data.destination[1], self.data.destination[2])
+        end
+
+        return move_to_any_target
+    end
+}

data/core/macros/ai.cfg

@@ -571,5 +571,12 @@
             evaluation="return (...):place_healers_eval()"
             execution="(...):place_healers_exec()"
         [/candidate_action]
+        [candidate_action]
+            engine=lua
+            name=move_to_enemy
+            max_score=1
+            evaluation="return (...):move_to_enemy_eval()"
+            execution="(...):move_to_enemy_exec()"
+        [/candidate_action]
     [/stage]
 #enddef