ludic/packages/ludic.gameplay/combat.ludic

# combat.ludic — the shared damage pipeline (#57 foundation).
#
# One place every family routes hits through, so buffs/armor/crits/lifesteal are
# written once as event listeners rather than re-invented per genre. The pipeline
# is the honest no-closure realisation of lever 4 (events) + lever 6 (a mutable
# hook):
#
#   1. mitigate the raw amount by the target's effective defence (Stats.total);
#   2. publish the pending amount and emit `cancellable DamageAboutToApply` —
#      a listener may veto the hit (cancel) or *rewrite the number* by calling
#      Combat.set_amount(n) (the mutable channel, since `emit` only returns the
#      cancelled flag);
#   3. apply the final amount to Stats.hp, emit `Damaged`, and emit `Died` when hp
#      reaches zero.
#
# Determinism: integer arithmetic, fixed listener order, no wall-clock — a hit
# replays identically. Combat never moves or despawns bodies itself; the game
# reacts to `Died` (respawn, ragdoll, loot) so the policy stays with the game.

event cancellable DamageAboutToApply { target: int = 0, src: int = 0, amount: int = 0 }
event Damaged { target: int = 0, src: int = 0, amount: int = 0 }
event Died { e: int = 0, src: int = 0 }
event Healed { e: int = 0, amount: int = 0 }
event Crit { target: int = 0, src: int = 0 }     # the attacker's crit_pct fired

var combat_reflecting: bool = false              # thorns never reflect thorns

# the mutable channel for lever 6: listeners rewrite the pending damage here.
var combat_pending: int = 0

@Namespace(Combat) function combat_amount() -> int { return combat_pending }
@Namespace(Combat) function combat_set_amount(n: int) -> void { combat_pending = n }

# Combat.mitigate(target, raw) — raw minus effective defence, floored at 1 so any
# landed hit chips at least a point (a common, tunable default). A game that wants
# a different formula overrides via the DamageAboutToApply hook.
@Namespace(Combat) function combat_mitigate(target: int, raw: int) -> int {
  let d = stats_total(target, 2)          # stat 2 = def
  var v = raw - d
  if v < 1 { v = 1 }
  return v
}

# Combat.damage(target, src, amount) — the full pipeline. Returns the damage
# actually applied (0 when vetoed or the target has no Stats/hp).
@Namespace(Combat) function combat_damage(target: int, src: int, amount: int) -> int {
  let P = World.prop_id("Stats")
  if P < 0 { return 0 }
  if World.has(target, P) == 0 { return 0 }
  let fhp = World.field_id(P, "hp")
  if fhp < 0 { return 0 }

  # the attacker's build: damage_pct, then a crit_pct chance to double
  var raw = amount * stats_field(src, "damage_pct", 100) / 100
  let crit = stats_field(src, "crit_pct", 0)
  if (crit > 0) and Random.chance(percent: crit) { raw = raw * 2;  emit Crit(target: target, src: src) }
  combat_pending = combat_mitigate(target, raw)
  if emit DamageAboutToApply(target: target, src: src, amount: combat_pending) != 0 { return 0 }
  var dmg = combat_pending
  if dmg < 0 { dmg = 0 }

  var hp = World.get(target, P, fhp) - dmg
  if hp < 0 { hp = 0 }
  World.set(target, P, fhp, hp)
  emit Damaged(target: target, src: src, amount: dmg)
  if hp <= 0 { emit Died(e: target, src: src) }
  # the attacker's leech, and the defender's thorns (never reflected back again)
  if dmg > 0 {
    let leech = stats_field(src, "leech_pct", 0)
    if (leech > 0) and Random.chance(percent: leech) { combat_heal(src, stats_field(src, "leech_hp", 1)) }
    let thorns = stats_field(target, "thorns", 0)
    if (thorns > 0) and (src != target) and (not combat_reflecting) and (World.has(src, P) != 0) {
      combat_reflecting = true
      combat_damage(src, target, thorns)
      combat_reflecting = false
    }
  }
  return dmg
}

# Combat.heal(e, amount) — restore hp, clamped to max_hp (effective, so a +max_hp
# buff raises the ceiling), and emit `Healed`.
@Namespace(Combat) function combat_heal(e: int, amount: int) -> void {
  let P = World.prop_id("Stats")
  if P < 0 { return }
  if World.has(e, P) == 0 { return }
  let fhp = World.field_id(P, "hp")
  if fhp < 0 { return }
  let cap = stats_total(e, 0)             # stat 0 = max_hp
  var hp = World.get(e, P, fhp) + amount
  if (cap > 0) and (hp > cap) { hp = cap }
  World.set(e, P, fhp, hp)
  emit Healed(e: e, amount: amount)
}