feat: add chebyshev, novaTargets and Polymorph.pool

src/polymorph.lua

@@ -0,0 +1,63 @@
+-- Rewrites an entity's very body into a different bestiary species mid-run.
+-- Unlike affixes.lua or runewords.lua, which layer bonuses on top of a fixed
+-- body, a polymorph replaces the body outright: name, glyph, ai behaviour,
+-- attack, defense, speed, resistances, faction and any ability tag all come
+-- from the new species wholesale, the same fields Monsters.create stamps
+-- onto a fresh spawn. Only the current hp fraction survives the swap, so a
+-- polymorph is never a cheap full heal and never an outright kill either.
+-- Mutation happens in place on the entity table already held everywhere
+-- else (the turn scheduler, level.entities, a live nemesis reference), so
+-- nothing needs to re-look-up or re-insert anything after a transform.
+
+local Monsters = require("monsters")
+
+local Polymorph = {}
+
+-- Species a polymorph may land on at `depth`, in Monsters.species order so a
+-- given rng draw is deterministic. Excludes the shopkeeper outright: its
+-- "vend" behaviour idles forever once out of the shop context a polymorphed
+-- body would never occupy, leaving it neither hostile nor useful to anyone.
+function Polymorph.pool(depth)
+  local eligible = {}
+  for _, spec in ipairs(Monsters.species) do
+    if spec.key ~= "shopkeeper" and spec.minDepth <= depth then
+      eligible[#eligible + 1] = spec
+    end
+  end
+  return eligible
+end
+
+-- Transforms `entity` in place into a random species drawn from `pool`,
+-- excluding whatever species it already is so a polymorph always changes
+-- something. Returns the species table it became, or nil (entity untouched)
+-- if `pool` has nothing left to offer once the current species is excluded.
+function Polymorph.transform(entity, rng, pool)
+  local choices = {}
+  for _, spec in ipairs(pool) do
+    if spec.key ~= entity.species then choices[#choices + 1] = spec end
+  end
+  if #choices == 0 then return nil end
+  local spec = choices[rng:range(1, #choices)]
+  local fraction = entity.maxHp > 0 and (entity.hp / entity.maxHp) or 1
+  entity.glyph = spec.glyph
+  entity.name = spec.name
+  entity.species = spec.key
+  entity.ai = spec.ai
+  entity.maxHp = spec.hp
+  entity.hp = math.max(1, math.floor(spec.hp * fraction + 0.5))
+  entity.attack = spec.attack
+  entity.defense = spec.defense
+  entity.speed = spec.speed
+  entity.range = spec.range or 0
+  entity.regen = spec.regen
+  entity.onDeath = spec.onDeath
+  entity.breath = spec.breath
+  entity.ability = spec.ability
+  entity.summonSpecies = spec.summonSpecies
+  entity.cooldown = 0
+  entity.resist = spec.resist
+  entity.faction = spec.faction
+  return spec
+end
+
+return Polymorph