feat: add canSee and isAlly

src/infighting.lua

@@ -0,0 +1,110 @@
+-- Monsters that share no faction bond will occasionally fight each other
+-- outright instead of always beelining for the player. Two rival factions
+-- (see Factions.RIVALRIES) throw down on sight, and any monster carrying
+-- Status.DISCORD - landed by the discord spell, see spells.lua - is
+-- compelled to strike whatever creature stands nearest it, friend or foe,
+-- for the effect's duration. Either way the fight runs through combat.lua
+-- exactly like a player's own attack - same damage formula, same
+-- resistances, same Game:applyEliteOnHit hooks (an elite attacker's
+-- lifesteal or on-hit status rider fires here too, not just against the
+-- player) and the same disease.lua bite chance (a plague-carrier's bite can
+-- infect a rival monster or the player's own companion/hireling/thrall,
+-- not just the player Game:monsterMelee already covers) - so a discorded
+-- troll among goblins is a real threat to both sides, not a scripted
+-- distraction. A plain monster felled this way
+-- still leaves a corpse (scavenging/reanimation can use it) but pays out no
+-- xp, essence, faction standing, or compendium credit - the player didn't
+-- land the blow. A companion, hireling, or thrall killed this way (only
+-- reachable through discord, since none of them carry a faction) dies
+-- exactly as it would to any other monster.
+
+local Combat = require("combat")
+local Status = require("status")
+local Factions = require("factions")
+local Los = require("los")
+local Corpses = require("corpses")
+local Noise = require("noise")
+local Disease = require("disease")
+
+local Infighting = {}
+
+Infighting.SIGHT_RANGE = 8
+
+local function canSee(game, a, b)
+  local cheb = math.max(math.abs(a.x - b.x), math.abs(a.y - b.y))
+  if cheb > Infighting.SIGHT_RANGE then return false end
+  return Los.clear(game.level.map, a.x, a.y, b.x, b.y)
+end
+
+local function isAlly(actor)
+  return actor.kind == "companion" or actor.kind == "hireling" or actor.kind == "thrall"
+end
+
+-- The other living, non-player creature `monster` should be fighting this
+-- turn instead of following its usual Ai.act behaviour, or nil if none
+-- qualifies. A rival-faction monster always qualifies once seen; under
+-- Status.DISCORD, the nearest visible creature of any kind - including the
+-- player's own companion, hireling, or thrall - qualifies too, since
+-- discord scrambles a mind's sense of friend and foe entirely. Ties break
+-- toward the lower entity id, matching Game:nearestAlly's own tie rule.
+function Infighting.target(game, monster)
+  local discorded = Status.has(monster, Status.DISCORD)
+  local best, bestDist = nil, math.huge
+  for _, other in ipairs(game.level.entities) do
+    if other ~= monster and other:isAlive() then
+      local qualifies = discorded or Factions.areRivals(monster.faction, other.faction)
+      if qualifies and canSee(game, monster, other) then
+        local dist = math.max(math.abs(other.x - monster.x), math.abs(other.y - monster.y))
+        if dist < bestDist or (dist == bestDist and other.id < best.id) then
+          best, bestDist = other, dist
+        end
+      end
+    end
+  end
+  return best
+end
+
+-- Resolves one monster-vs-monster hit through the same damage formula any
+-- other attack uses. A defender that falls is swept immediately: a
+-- companion/hireling/thrall dies exactly as game.lua already reports that,
+-- while a plain hostile monster just drops - Corpses.spawn still leaves
+-- remains behind, but no awardKill means no xp/essence/faction/compendium
+-- credit for a kill the player never made.
+function Infighting.strike(game, attacker, defender)
+  local outcome = Combat.attack(attacker, defender)
+  game.log:add(string.format("%s hits %s for %d", attacker.name, defender.name, outcome.damage))
+  game:applyEliteOnHit(attacker, outcome.damage, defender)
+  if attacker.biteDisease and defender:isAlive() and game.rng:chance(1, 4) then
+    if Disease.infect(defender, attacker.biteDisease) then
+      game.log:add(string.format("%s's bite leaves %s feeling ill", attacker.name, defender.name))
+    end
+  end
+  game:emitNoise(attacker.x, attacker.y, Noise.MELEE)
+  if not defender:isAlive() then
+    if isAlly(defender) then
+      game:onActorDeath(defender)
+    else
+      game.log:add(defender.name .. " dies")
+      Corpses.spawn(game.level, defender)
+    end
+  end
+  return outcome
+end
+
+-- Entry point mirroring Abilities.tryAct's contract: returns true when
+-- infighting consumed the monster's turn (attacked an adjacent target or
+-- stepped toward a farther one), false to let the caller fall through to
+-- Ai.act.
+function Infighting.tryAct(game, monster)
+  local target = Infighting.target(game, monster)
+  if not target then return false end
+  local dist = math.max(math.abs(target.x - monster.x), math.abs(target.y - monster.y))
+  if dist <= 1 then
+    Infighting.strike(game, monster, target)
+  else
+    game:stepMonsterToward(monster, target.x, target.y)
+  end
+  return true
+end
+
+return Infighting