feat(scheduler): add energy-based turn scheduler

src/scheduler.lua

@@ -0,0 +1,52 @@
+-- Energy-based turn scheduler. Every actor accrues its effective speed each
+-- round; an actor may act once its energy reaches the cost threshold, and acting
+-- spends that much. Faster actors therefore act more often. Ordering among ready
+-- actors is fully deterministic: highest energy first, ties broken by ascending
+-- id, so the same seed always yields the same interleaving.
+
+local Scheduler = {}
+
+Scheduler.COST = 100
+
+local function actorList(game)
+  local actors = { game.player }
+  for _, monster in ipairs(game:currentEntities()) do
+    if monster:isAlive() then actors[#actors + 1] = monster end
+  end
+  return actors
+end
+
+local function ready(actor)
+  return actor:isAlive() and actor.energy >= Scheduler.COST
+end
+
+-- Picks the next actor eligible to act, granting energy in id order whenever no
+-- one is ready yet. Returns nil only if there are no living actors at all.
+function Scheduler.next(game)
+  for _ = 1, 10000 do
+    local actors = actorList(game)
+    if #actors == 0 then return nil end
+    local chosen
+    for _, actor in ipairs(actors) do
+      if ready(actor) then
+        if chosen == nil
+          or actor.energy > chosen.energy
+          or (actor.energy == chosen.energy and actor.id < chosen.id) then
+          chosen = actor
+        end
+      end
+    end
+    if chosen then return chosen end
+    table.sort(actors, function(a, b) return a.id < b.id end)
+    for _, actor in ipairs(actors) do
+      actor.energy = actor.energy + actor:effectiveSpeed()
+    end
+  end
+  return nil
+end
+
+function Scheduler.spend(actor)
+  actor.energy = actor.energy - Scheduler.COST
+end
+
+return Scheduler