feat: add Hazards.at and Hazards.spawn

src/hazards.lua

@@ -0,0 +1,114 @@
+-- Timed area hazards that live on the map itself rather than on an entity:
+-- fire and caustic gas. Both linger on their cell, hurt and afflict whoever
+-- ends a turn standing there, and can spread into open neighbouring floor
+-- before burning or blowing themselves out. Fire is doused outright by water.
+-- Hazards are plain data on level.hazards so they serialize like floor items
+-- and traps do, with no special save-format handling.
+
+local Tiles = require("tiles")
+local Status = require("status")
+local Resistances = require("resistances")
+local Conductivity = require("conductivity")
+
+local Hazards = {}
+
+Hazards.FIRE = "fire"
+Hazards.GAS = "gas"
+
+local DIRS = { { 1, 0 }, { -1, 0 }, { 0, 1 }, { 0, -1 } }
+
+-- First hazard occupying (x, y), optionally filtered to a specific kind so
+-- fire and gas can coexist on the same cell without merging into each other.
+function Hazards.at(level, x, y, kind)
+  for _, hz in ipairs(level.hazards) do
+    if hz.x == x and hz.y == y and (not kind or hz.kind == kind) then return hz end
+  end
+  return nil
+end
+
+-- Drops a hazard on (x, y), or refreshes one already there of the same kind
+-- to whichever of the two durations and potencies is stronger. Walls never
+-- catch fire or hold gas.
+function Hazards.spawn(level, x, y, kind, duration, potency)
+  if not level.map:inBounds(x, y) then return nil end
+  if level.map:get(x, y) == Tiles.WALL then return nil end
+  local existing = Hazards.at(level, x, y, kind)
+  if existing then
+    existing.duration = math.max(existing.duration, duration)
+    existing.potency = math.max(existing.potency, potency)
+    return existing
+  end
+  local hz = { x = x, y = y, kind = kind, duration = duration, potency = potency }
+  level.hazards[#level.hazards + 1] = hz
+  return hz
+end
+
+function Hazards.ignite(level, x, y, duration, potency)
+  return Hazards.spawn(level, x, y, Hazards.FIRE, duration or 3, potency or 2)
+end
+
+function Hazards.spawnGas(level, x, y, duration, potency)
+  return Hazards.spawn(level, x, y, Hazards.GAS, duration or 4, potency or 2)
+end
+
+-- Applies whichever hazard occupies entity's current cell, mirroring how
+-- Status.tick afflicts the same actor once per turn. Fire and gas both deal
+-- their potency in direct damage and lay down a fading status effect on top,
+-- so stepping out of the hazard still leaves a lingering burn or sickness.
+function Hazards.afflict(level, entity)
+  local hz = Hazards.at(level, entity.x, entity.y)
+  if not hz then return nil end
+  if hz.kind == Hazards.FIRE then
+    local dealt = Conductivity.applyFire(entity, hz.potency)
+    entity.hp = entity.hp - dealt
+    Status.apply(entity, Status.BURNING, 2, math.max(1, hz.potency // 2))
+    if Conductivity.isWet(entity) then
+      return string.format("flames hiss against %s's soaked skin for %d", entity.name, dealt)
+    end
+    return string.format("flames engulf %s for %d", entity.name, dealt)
+  end
+  local dealt = Resistances.apply(entity, hz.potency, Resistances.POISON)
+  entity.hp = entity.hp - dealt
+  Status.apply(entity, Status.POISON, 2, math.max(1, hz.potency // 2))
+  return string.format("choking fumes sicken %s for %d", entity.name, dealt)
+end
+
+local function canSpreadInto(level, x, y)
+  if not level.map:inBounds(x, y) then return false end
+  local tile = level.map:get(x, y)
+  return Tiles.isWalkable(tile) and tile ~= Tiles.WATER
+end
+
+-- Advances every hazard one environmental step: each has an even chance to
+-- bloom into an open neighbouring cell that isn't already burning or gassed
+-- the same way, water douses fire outright, and every hazard's clock counts
+-- down until it burns or blows itself out. Called once per world round (not
+-- per actor) so a seeded run always spreads identically regardless of how
+-- many actors acted that round.
+function Hazards.step(level, rng)
+  local spawns = {}
+  for _, hz in ipairs(level.hazards) do
+    for _, dir in ipairs(DIRS) do
+      local nx, ny = hz.x + dir[1], hz.y + dir[2]
+      if canSpreadInto(level, nx, ny) and not Hazards.at(level, nx, ny, hz.kind)
+        and rng:chance(1, 2) then
+        spawns[#spawns + 1] = { nx, ny, hz.kind, hz.duration, hz.potency }
+      end
+    end
+  end
+  for _, s in ipairs(spawns) do
+    Hazards.spawn(level, s[1], s[2], s[3], s[4], s[5])
+  end
+
+  local kept = {}
+  for _, hz in ipairs(level.hazards) do
+    local doused = hz.kind == Hazards.FIRE and level.map:get(hz.x, hz.y) == Tiles.WATER
+    hz.duration = hz.duration - 1
+    if hz.duration > 0 and not doused then
+      kept[#kept + 1] = hz
+    end
+  end
+  level.hazards = kept
+end
+
+return Hazards