feat: add Abilities.regenTick and Abilities.onDeath

src/abilities.lua

@@ -0,0 +1,153 @@
+-- Species-level passive and death-triggered abilities layered on top of the
+-- generic AI behaviours in ai.lua. Declared per species in Monsters.species
+-- so a bestiary entry fully describes what a creature does, not just how
+-- hard it hits or how it moves.
+
+local Status = require("status")
+local Items = require("items")
+local Los = require("los")
+local Combat = require("combat")
+local Durability = require("durability")
+local Momentum = require("momentum")
+
+local Abilities = {}
+
+-- Regeneration: heals `monster.regen` hp at the start of its turn, unless it
+-- is actively burning - fire cauterizes the wound faster than it closes.
+-- Runs after Status.tick so a fresh burn this same turn still suppresses it.
+function Abilities.regenTick(monster)
+  local amount = monster.regen
+  if not amount or not monster:isAlive() then return nil end
+  if Status.has(monster, Status.BURNING) then return nil end
+  local before = monster.hp
+  monster.hp = math.min(monster.maxHp, monster.hp + amount)
+  if monster.hp == before then return nil end
+  return string.format("%s knits its wounds for %d", monster.name, monster.hp - before)
+end
+
+-- On-death bursts: some species release a parting effect on whatever is
+-- adjacent to their corpse - including the player - the instant they die.
+-- Keyed by the `onDeath` tag on the species, run from Game:awardKill so the
+-- burst fires no matter what finished the monster off (melee, spell, thrown
+-- weapon, or a status effect ticking it down).
+local bursts = {
+  spores = function(game, monster)
+    local hit = {}
+    local targets = { game.player }
+    for _, other in ipairs(game:currentEntities()) do targets[#targets + 1] = other end
+    for _, victim in ipairs(targets) do
+      if victim ~= monster and victim:isAlive()
+        and math.abs(victim.x - monster.x) <= 1 and math.abs(victim.y - monster.y) <= 1 then
+        Status.apply(victim, Status.POISON, 4, 2)
+        hit[#hit + 1] = victim.name
+      end
+    end
+    if #hit == 0 then return nil end
+    return string.format("a burst of spores poisons %s", table.concat(hit, ", "))
+  end,
+}
+
+function Abilities.onDeath(game, monster)
+  local burst = monster.onDeath and bursts[monster.onDeath]
+  if not burst then return nil end
+  return burst(game, monster)
+end
+
+-- Turn-start special abilities, keyed by the `ability` tag on the species
+-- (Monsters.species) and stamped onto the entity at creation. Abilities.tryAct
+-- runs from Game:takeMonsterTurn BEFORE the plain ai.lua behaviour: when it
+-- fires it consumes the whole turn and the caller must skip Ai.act; when it
+-- returns false the monster falls through to its ordinary ai tag unchanged.
+-- Range/cooldown constants live here, not on the species, mirroring how
+-- `bursts` above centralises onDeath behaviour by tag rather than by species.
+
+local RANGE = { summon = 6, curse = 5, heal = 5, shriek = 5 }
+local COOLDOWN = { summon = 6, curse = 4, heal = 5, rally = 8, shriek = 6 }
+local MAX_SUMMONED = 2
+
+local EIGHT_DIRS = {
+  { 1, 0 }, { -1, 0 }, { 0, 1 }, { 0, -1 },
+  { 1, 1 }, { 1, -1 }, { -1, 1 }, { -1, -1 },
+}
+
+-- The first free, unoccupied, walkable cell next to (x, y), scanning a fixed
+-- direction order so results are deterministic for a given map state.
+local function freeAdjacent(game, x, y)
+  for _, dir in ipairs(EIGHT_DIRS) do
+    local nx, ny = x + dir[1], y + dir[2]
+    if game.level.map:isWalkable(nx, ny) and not game.level:entityAt(nx, ny)
+      and not (nx == game.player.x and ny == game.player.y) then
+      return nx, ny
+    end
+  end
+  return nil
+end
+
+function Abilities.tickCooldown(monster)
+  if monster.cooldown and monster.cooldown > 0 then
+    monster.cooldown = monster.cooldown - 1
+  end
+end
+
+-- Necromancer-style ability: raises a fresh minion of `summonSpecies` beside
+-- itself, tagged `summonedBy` so the population cap only counts its own brood.
+local function trySummon(game, monster)
+  if not game:canSeePlayer(monster, RANGE.summon) then return false end
+  local count = 0
+  for _, other in ipairs(game.level.entities) do
+    if other:isAlive() and other.summonedBy == monster.id then count = count + 1 end
+  end
+  if count >= MAX_SUMMONED then return false end
+  local x, y = freeAdjacent(game, monster.x, monster.y)
+  if not x then return false end
+  local minion = game:spawnMinion(monster.summonSpecies, x, y)
+  minion.summonedBy = monster.id
+  monster.cooldown = COOLDOWN.summon
+  return true, string.format("%s calls forth a %s", monster.name, minion.name)
+end
+
+-- Shaman-style ability: a ranged bolt that both hurts and weakens the player,
+-- withheld at point-blank range so the caster's ai (flee) kites instead. The
+-- hurt half runs through the exact same Combat.damage the melee/shoot paths
+-- use - mitigated by the player's defense and resistances, breaking Momentum
+-- (see momentum.lua's own "claw, breath or ambush" wording - a curse bolt is
+-- none of those by name but is that in shape) and wearing armor exactly like
+-- monsterShoot's breath already does - rather than a flat, unmitigated
+-- subtraction none of that pipeline ever saw.
+local function tryCurse(game, monster)
+  if game:playerAdjacent(monster) then return false end
+  if not game:canSeePlayer(monster, RANGE.curse) or not game:hasClearShot(monster) then
+    return false
+  end
+  local dealt = Combat.damage(monster, game.player, 1)
+  game.player.hp = game.player.hp - dealt
+  Momentum.onDamaged(game.player)
+  local broke = Durability.wearArmor(game.player)
+  if broke then game.log:add(broke) end
+  Status.apply(game.player, Status.WEAKEN, 6, 3)
+  monster.cooldown = COOLDOWN.curse
+  return true, string.format("%s curses you for %d", monster.name, dealt)
+end
+
+-- Banshee-style ability: a ranged wail that blinds instead of hurting,
+-- withheld point-blank exactly like tryCurse so the caster's own "flee" ai
+-- keeps it at kiting distance rather than trading blows. Status.BLIND
+-- (game.lua's Game:effectiveRadius) was previously only ever inflicted BY
+-- the player - a thrown potion, the blind spell, or a shared trap effect -
+-- never the other way around; this is the first hostile source of it, the
+-- same gap tryShriek's sibling "curse" would leave for WEAKEN if a monster
+-- could apply it but nothing here ever did. Duration outlasts the cooldown
+-- by one turn on purpose (5 vs 6) so a banshee left free to keep casting
+-- keeps you blind almost the whole encounter but not with zero window - the
+-- one turn of clear sight between wails is a player's chance to reposition
+-- or close the distance before the next howl lands.
+local function tryShriek(game, monster)
+  if game:playerAdjacent(monster) then return false end
+  if not game:canSeePlayer(monster, RANGE.shriek) or not game:hasClearShot(monster) then
+    return false
+  end
+  Status.apply(game.player, Status.BLIND, 5, 1)
+  monster.cooldown = COOLDOWN.shriek
+  return true, string.format("%s's wail blinds you", monster.name)
+end
+