feat(effects): add potion and scroll effect resolution

src/effects.lua

@@ -0,0 +1,82 @@
+-- Resolves potion and scroll effect keys against the world. Self-contained buffs
+-- act on the drinker; teleport, mapping, identify and fireball reach into the
+-- game and its current level. Every effect returns log lines in emission order.
+
+local Status = require("status")
+local Identify = require("identify")
+
+local Effects = {}
+
+local handlers = {}
+
+handlers.heal = function(game, target, item)
+  local before = target.hp
+  target.hp = math.min(target.maxHp, target.hp + item.power)
+  return { string.format("%s heals %d", target.name, target.hp - before) }
+end
+
+handlers.poison = function(game, target, item)
+  Status.apply(target, Status.POISON, 6, item.power)
+  return { string.format("%s is poisoned", target.name) }
+end
+
+handlers.strength = function(game, target, _)
+  Status.apply(target, Status.STRENGTH, 30, 3)
+  return { string.format("%s feels mightier", target.name) }
+end
+
+handlers.haste = function(game, target, _)
+  Status.apply(target, Status.HASTE, 20, 1)
+  return { string.format("%s speeds up", target.name) }
+end
+
+handlers.teleport = function(game, target, _)
+  local x, y = game:randomFloorCell()
+  if x then
+    target.x, target.y = x, y
+    return { target.name .. " blinks away" }
+  end
+  return { "the teleport fizzles" }
+end
+
+handlers.mapping = function(game, _, _)
+  game:revealWholeLevel()
+  return { "the level is revealed" }
+end
+
+handlers.identify = function(game, target, _)
+  local revealed = Identify.revealFirstUnknown(game.identify, target.inventory)
+  if revealed then
+    return { "it is " .. revealed.name }
+  end
+  return { "nothing left to identify" }
+end
+
+handlers.fireball = function(game, target, _)
+  local radius = 3
+  local burned = 0
+  for _, monster in ipairs(game:currentEntities()) do
+    if monster:isAlive() then
+      local dist = math.max(math.abs(monster.x - target.x), math.abs(monster.y - target.y))
+      if dist <= radius then
+        monster.hp = monster.hp - 8
+        Status.apply(monster, Status.BURNING, 3, 2)
+        burned = burned + 1
+      end
+    end
+  end
+  game:cleanupDead()
+  return { string.format("fire engulfs %d foes", burned) }
+end
+
+function Effects.apply(effectKey, game, target, item)
+  local handler = handlers[effectKey]
+  if not handler then return {} end
+  return handler(game, target, item)
+end
+
+function Effects.has(effectKey)
+  return handlers[effectKey] ~= nil
+end
+
+return Effects