gogobee/internal/plugin/dnd_passives.go

package plugin

// Phase 3 — class passives applied via CombatModifiers.
//
// Phase 3 keeps abilities passive-only: they auto-trigger via the existing
// CombatModifiers machinery rather than being player-activated mid-fight
// (the combat engine is one-shot, no turn-based UI). Active/reactive
// abilities arrive once we have a model for them — likely tied to !arena
// pre-arming or to a turn-based PvP variant.
//
// Comment convention: `// internal note (not user-facing)` marks block
// comments that document tuning history (Phase 2/3 balance notes, scaling
// rationale, etc.). Anything inside such a block is engineering context,
// NOT a candidate for codegen to lift into a Description string.

// ── Class passive definitions ────────────────────────────────────────────────

// DnDClassAbility is the lore/UI representation of a class's signature
// passive. Used by !abilities and !sheet for display; mechanics live in
// applyClassPassives below.
type DnDClassAbility struct {
	Name        string
	Description string
}

var dndClassAbilities = map[DnDClass]DnDClassAbility{
	ClassFighter: {
		Name:        "Battle Trained",
		Description: "Years of weapon drill make every swing hit a little harder than it has any right to.",
	},
	ClassRogue: {
		Name:        "Sneak Attack",
		Description: "Your opening strike each fight finds a seam and crits — and the same trained precision keeps every follow-up sharper than it looks.",
	},
	ClassMage: {
		Name:        "Arcane Focus",
		Description: "Practiced channeling steadies your aim and lets a faint arcane crackle leak into every blow you land.",
	},
	ClassCleric: {
		Name:        "Divine Favor",
		Description: "When the fight turns against you, a sliver of divine grace patches you up. Once per combat.",
	},
	ClassRanger: {
		Name:        "Hunter's Mark",
		Description: "You read your prey's tells — openings come easier, and the hits land where it hurts.",
	},
	ClassDruid: {
		Name:        "Wild Resilience",
		Description: "The wild lends you its hide — blows land softer — and the moment you engage, a thorn surge lashes back at whatever picked the fight.",
	},
	ClassBard: {
		Name:        "Bardic Inspiration",
		Description: "Wit and timing put you a beat ahead of the fight: you move first, swing truer, and turn the opening line into a small, mean encore.",
	},
	ClassSorcerer: {
		Name:        "Innate Sorcery",
		Description: "Raw magic boils over the moment the fight starts, scorching whatever's nearest — and every swing rides the leftover heat.",
	},
	ClassWarlock: {
		Name:        "Agonizing Blast",
		Description: "Your pact whispers in the back of your skull; the favor it returns lands on your enemies, harder and surer than ought to be allowed.",
	},
	ClassPaladin: {
		Name:        "Divine Smite",
		Description: "On engagement you channel a burst of radiant power — a sworn promise, paid in light — that hits harder as your oath deepens.",
	},
}

// clampNonNeg returns max(0, x). Used by Phase-2 class passives to keep
// ability-mod-scaled FlatDmgStart additions from going negative when a
// caster's casting stat happens to be below 10 (or when tests construct
// a DnDCharacter with zero-value stats).
func clampNonNeg(x int) int {
	if x < 0 {
		return 0
	}
	return x
}

// applyRacePassives sets the combat-impacting flags from the player's race.
// Elf "trance" (resilience flavor), Half-Elf "adaptable" (cross-cultural know-
// how), and the Human floating +1 are non-combat or stat-only and have no
// engine hook here.
func applyRacePassives(stats *CombatStats, mods *CombatModifiers, c *DnDCharacter) {
	switch c.Race {
	case RaceHalfling:
		mods.LuckyReroll = true
	case RaceOrc:
		mods.RageReady = true
	case RaceDwarf:
		mods.PoisonResist = true
	case RaceTiefling:
		// Fiendish heritage: incoming fire damage is halved by the combat
		// engine (enemy attack path + aoe_fire ability) and by the trap
		// resolver (fire-tagged traps).
		mods.FireResist = true
	}
}

// applyClassPassives mutates a player's CombatModifiers to apply their
// class passive. Called after applyDnDPlayerLayer + DerivePlayerStats but
// BEFORE consumable application (so consumables can stack on top).
//
// Some passives ride on existing CombatModifiers fields:
//   Rogue's Sneak Attack reuses AutoCritFirst (the consumable Crystal Berry
//   field) — the engine already implements first-hit-auto-crit semantics.
//   Cleric's Divine Favor reuses HealItem, the under-50%-HP heal trigger.
//
// This means:
//   - A Rogue carrying a Crystal Berry doesn't get *two* auto-crits;
//     AutoCritFirst is already a one-shot bool.
//   - A Cleric carrying a healing potion stacks: passive 5 + potion 8 = 13.
//     The passive heal triggers first since both use the same threshold.
func applyClassPassives(stats *CombatStats, mods *CombatModifiers, c *DnDCharacter) {
	switch c.Class {
	case ClassFighter:
		mods.DamageBonus += 0.05
		// Class-identity audit (2026-05-16) — Extra Attack. 5e Fighter is
		// defined by attack-action economy: L5 +1 swing/round, L11 +2,
		// L20 +3. Prior to this the Fighter had only +5% Battle Trained
		// at every level, which left the L5 "now I'm a real fighter"
		// power-spike completely invisible. The +5% rider stays as the
		// L1-4 floor; Extra Attack is what carries the chassis from L5.
		// Other martials that 5e gives Extra Attack to (Paladin/Ranger/
		// Barbarian) keep their existing DamageBonus proxies for now —
		// re-tune in a follow-up if their win curves drift after this.
		switch {
		case c.Level >= 20:
			mods.ExtraAttacks += 3
		case c.Level >= 11:
			mods.ExtraAttacks += 2
		case c.Level >= 5:
			mods.ExtraAttacks += 1
		}
	case ClassRogue:
		mods.AutoCritFirst = true
		// Phase 2 class-balance: rogue's once-per-fight auto-crit goes stale
		// at high tiers (T5 mean trails leaders by ~10pp pre-tune). Add a
		// modest steady-DPS rider so post-opener rounds aren't pure attrition.
		mods.DamageBonus += 0.05
		// Class-identity audit (2026-05-16) — actual Sneak Attack as Nd6
		// per hit, scaling with level per 5e (1d6 L1-2 ... 10d6 L19-20).
		// AutoCritFirst + DamageBonus alone left the rogue's defining
		// mechanic invisible at the table: monte-carlo win rates looked
		// fine but a player hitting once per round saw weapon-only damage
		// every swing after the opener. Engine path uses the same "every
		// hit" treatment as Divine Strike (rogues swing 1×/round so this
		// matches the 5e once-per-turn cadence in practice).
		sneakDice := (c.Level + 1) / 2
		if sneakDice > 10 {
			sneakDice = 10
		}
		mods.SneakAttackDie += sneakDice
	case ClassMage:
		stats.AttackBonus++
		// Phase 2 class-balance: +1 attack alone left Mage mid-pack on damage
		// per round. A modest damage rider lifts weapon hits (DamageBonus does
		// not multiply queued SpellPreDamage — that path is its own field).
		mods.DamageBonus += 0.05
		// Phase 2 class-balance: Arcane focus also produces a small pre-combat
		// arcane burst, scaling with level and INT. Helps the L1-4 chassis,
		// which would otherwise rely on a single weak L1 spell + quarterstaff
		// against T2-T3 monsters. Saturates harmlessly at L10+ where every
		// class wins anyway.
		mods.FlatDmgStart += c.Level + clampNonNeg(abilityModifier(c.INT))
	case ClassCleric:
		// Passive heal at <50% HP. Stacks additively with consumable HealItem.
		mods.HealItem += 5
	case ClassRanger:
		// Class-identity audit (2026-05-16) — Hunter's Mark as actual
		// per-hit Nd6, plus L5 Extra Attack from the martial chassis. The
		// previous +5% damage + +1 to-hit was a Phase-2 compensation
		// rider for both being missing; +1 to-hit stays as the "read the
		// prey's tells" half (it's not Hunter's Mark, that's the d6).
		// HuntersMarkDie scales 1/5/10/15 per the 5e upcast progression
		// (1d6 at L1, 2d6 L5+, 3d6 L11+, 4d6 L17+ as a soft proxy).
		stats.AttackBonus++
		switch {
		case c.Level >= 17:
			mods.HuntersMarkDie += 4
		case c.Level >= 11:
			mods.HuntersMarkDie += 3
		case c.Level >= 5:
			mods.HuntersMarkDie += 2
		default:
			mods.HuntersMarkDie += 1
		}
		if c.Level >= 5 {
			mods.ExtraAttacks += 1
		}
	case ClassDruid:
		// Wild Resilience — multiplicative, so it stacks cleanly with the
		// subclass DamageReduct riders. DamageReduct is initialized to 1.0
		// by DerivePlayerStats before passives run.
		mods.DamageReduct *= 0.95
		// Phase 3 class-balance: druid was the only caster chassis with a
		// purely defensive passive, and the off-tier numbers showed it —
		// L1/T2 mean 0.04 vs Mage 0.27. Mirror the other caster bursts so
		// the L1-4 druid can chip a T2 monster: WIS-scaled FlatDmgStart on
		// engage. No DamageBonus rider; the chassis keeps its defensive
		// identity, and the burst alone (plus the existing DR) lifts the
		// off-tier cells without pushing in-tier wins past 1.0.
		mods.FlatDmgStart += c.Level + clampNonNeg(abilityModifier(c.WIS))
		// Class-identity audit (2026-05-16) — thorn lash, the offensive
		// half of Wild Resilience the tooltip already promises ("a thorn
		// surge lashes back at whatever picked the fight"). Per-hit flat
		// counter when the enemy lands on the player. Scales modestly so
		// it's a steady tick, not a damage-race winner — the chassis
		// stays defensive-first.
		mods.ThornLashDmg += 2 + c.Level/4
	case ClassBard:
		// Phase 2 class-balance: bare +1 initiative left Bard the weakest
		// class chassis (T5 mean 0.48 pre-tune). Add a Ranger-tier rider
		// (+1 attack, +5% damage) so the chassis pulls weight before subclass
		// kicks in at L5, plus a CHA-scaled opening flourish (FlatDmgStart) so
		// the L1-4 chassis isn't dead at T3.
		mods.InitiativeBias += 1
		stats.AttackBonus++
		mods.DamageBonus += 0.05
		mods.FlatDmgStart += c.Level + clampNonNeg(abilityModifier(c.CHA))
	case ClassSorcerer:
		// Innate Sorcery — pre-combat burst, CHA-scaled like the Sorcerer's
		// spellcasting stat. Floors at the flat base for low-CHA builds.
		// Phase 2 class-balance: pure FlatDmgStart faded at higher tiers as
		// monster HP grew. Adding a 5% damage rider plus level scaling on the
		// burst keeps the chassis relevant past L1.
		// Phase 3 class-balance: sorcerer was the second-worst off-tier caster
		// (L1/T2 0.10 pre-tune), trailing mage by ~17pp despite a comparable
		// stat line. Bump the burst base 3→5 to lift the L1-4 chassis without
		// touching the +0.05 rider that already saturates at high tier.
		mods.FlatDmgStart += 5 + c.Level + clampNonNeg(abilityModifier(c.CHA))
		mods.DamageBonus += 0.05
	case ClassWarlock:
		// Phase 2 class-balance: bumped from 10% to 12% damage + 1 attack —
		// the Warlock chassis read mid-pack at T5 (0.52) pre-tune. Eldritch
		// blast as an opener (FlatDmgStart, level + CHA-scaled) covers the
		// caster's L1-4 quarterstaff weakness, same shape as the other three
		// arcane chassis.
		mods.DamageBonus += 0.12
		stats.AttackBonus++
		mods.FlatDmgStart += c.Level + clampNonNeg(abilityModifier(c.CHA))
	case ClassPaladin:
		// Class-identity audit (2026-05-16) — Divine Smite as actual
		// per-hit radiant bonus + L5 Extra Attack. 5e: smite consumes a
		// spell slot for Nd8 radiant on a hit. Our engine has no slot
		// tracker for ad-hoc smites; we collapse "paladin has plenty of
		// slots over an adventuring day" to a flat per-hit rider, scaled
		// down so an extra-attack paladin doesn't trivialize every fight.
		// Rides DivineStrikePerHit (already in the weapon-hit damage path).
		// Previous FlatDmgStart opener felt like Lay on Hands, not Smite.
		smite := 3 + c.Level/3
		mods.DivineStrikePerHit += smite
		if c.Level >= 5 {
			mods.ExtraAttacks += 1
		}
	}
}