waving-hands/src/lib/game/resolve.ts

// Simultaneous turn resolution, following the precedence rules in
// docs/waving-hands-rules.txt: dispel magic first, then counter-spells and
// mirrors, banking and permanency, storm and elemental interplay, summons,
// enchantments, damage, monster attacks and stabs, and finally deaths and
// surrenders. A time stop resolves as a turn in which one wizard acts alone.

import { cellsOverlap, completedSpells, handSequence, progressToward, usedCells, type Completion, type HandTurn } from './gestures';
import {
	BLANKET_SPELLS,
	CONTROL_SPELLS,
	GESTURES,
	GESTURE_NAMES,
	HANDS,
	MAGIC_GESTURES,
	MONSTER_STATS,
	SPELLS,
	SPELL_BY_ID,
	SUMMON_KIND,
	isElemental,
	permanencyEligible,
	type Gesture,
	type Hand,
	type MonsterKind,
	type Spell,
	type SpellId
} from './spells';
import {
	MAX_HP,
	NOWHERE,
	beingName,
	controllerOf,
	enemyOf,
	findMonster,
	inDuel,
	isWizardId,
	nextRandom,
	type CastChoice,
	type Constraints,
	type GameState,
	type HistoryEntry,
	type LogKind,
	type Monster,
	type Phase,
	type TargetId,
	type TurnInput,
	type TurnSummary,
	type WizardId,
	type WizardState
} from './state';

interface ActiveCast {
	caster: WizardId;
	hand: Hand;
	spell: Spell;
	target: TargetId;
	choice: CastChoice;
	completion?: Completion;
	/** History index of the completing gesture; -1 for a released banked spell. */
	index: number;
	released?: boolean;
	permanent?: boolean;
	/** Why the spell did nothing, once decided. */
	nullified?: string;
}

const REST: TurnInput = { left: '-', right: '-', casts: [] };

export function paralysedForm(g: Gesture): Gesture {
	if (g === 'C') return 'F';
	if (g === 'S') return 'D';
	if (g === 'W') return 'P';
	return g;
}

export const FEAR_BANNED: Gesture[] = ['C', 'D', 'F', 'S'];

/** A counter-spell cannot touch these. */
const UNCOUNTERABLE: SpellId[] = ['finger_of_death', 'counter_spell', 'magic_mirror'];

function roman(n: number): string {
	const numerals: [number, string][] = [
		[10, 'X'],
		[9, 'IX'],
		[5, 'V'],
		[4, 'IV'],
		[1, 'I']
	];
	let out = '';
	for (const [v, s] of numerals) {
		while (n >= v) {
			out += s;
			n -= v;
		}
	}
	return out;
}

function clearEnchantments(w: WizardState): void {
	w.resistHeat = false;
	w.resistCold = false;
	w.protectionTurns = 0;
	w.blindTurns = 0;
	w.invisibleTurns = 0;
	w.diseaseTurns = null;
	w.poisonTurns = null;
	w.hasteTurns = 0;
	w.delayedTurns = 0;
	w.permanencyTurns = 0;
	w.pending = {};
	w.permanent = {};
}

function clearMonsterEnchantments(m: Monster): void {
	m.resistHeat = false;
	m.resistCold = false;
	m.protectionTurns = 0;
	m.pending = {};
}

/**
 * Last turn's gestures as [first pair, second pair]: a wizard who was hastened
 * repeats both pairs under amnesia, and each hand stays paralysed in its
 * most recent position.
 */
export function previousPairs(w: WizardState): [HistoryEntry | undefined, HistoryEntry | undefined] {
	const last = w.history[w.history.length - 1];
	if (!last) return [undefined, undefined];
	if (last.phase === 'haste') return [w.history[w.history.length - 2], last];
	return [last, last];
}

/** The longest run toward any spell the hand has going. */
function longestRun(seq: HandTurn[], start: number): number {
	let best = 0;
	for (const spell of SPELLS) for (const tokens of spell.tokens) best = Math.max(best, progressToward(tokens, seq, start));
	return best;
}

function tick(n: number): number {
	return n === Infinity ? n : Math.max(0, n - 1);
}

export function resolveTurn(previous: GameState, inputs: Record<WizardId, TurnInput>): GameState {
	const state = structuredClone(previous);
	if (state.over) return state;
	const W = state.wizards;
	const seats = state.seats;
	/** A seat that is out of the duel makes no gestures; its input, if any, is ignored. */
	const input = (id: WizardId): TurnInput => inputs[id] ?? REST;
	const actor = state.timeStops.shift() ?? null;
	const phase: Phase = actor ? 'timestop' : 'main';
	const acting: WizardId[] = actor ? [actor] : seats.filter((id) => inDuel(W[id]));
	/** Time-stop entries and log lines belong to the turn just played. */
	const turn = actor ? state.turn - 1 : state.turn;
	const events: string[] = [];
	const log = (text: string, kind: LogKind = 'info', surface = kind !== 'gesture' && kind !== 'damage', hiddenFrom?: WizardId[]) => {
		state.log.push(hiddenFrom?.length ? { turn, kind, text, hiddenFrom } : { turn, kind, text });
		if (surface) events.push(text);
	};
	const rng = () => nextRandom(state);
	const pick = <T>(items: T[]): T => items[Math.floor(rng() * items.length)];

	const frozen = (id: WizardId) => !acting.includes(id);
	const frozenBeing = (id: TargetId): boolean => {
		const c = controllerOf(state, id);
		return c !== undefined && frozen(c);
	};
	const isWizard = (id: TargetId | undefined): id is WizardId => isWizardId(state, id);
	const isBeing = (id: TargetId | undefined): id is TargetId =>
		id !== undefined && id !== NOWHERE && (isWizard(id) ? W[id].alive : !!findMonster(state, id));
	const monsterOf = (id: TargetId) => findMonster(state, id);
	/** Under time stop, those who cannot move have no resistance to anything. */
	const resists = (id: TargetId, type: 'heat' | 'cold'): boolean => {
		if (frozenBeing(id)) return false;
		const b = isWizard(id) ? W[id] : monsterOf(id);
		if (!b) return false;
		return type === 'heat' ? b.resistHeat : b.resistCold;
	};

	const summary: TurnSummary = {
		turn,
		phase,
		wizards: Object.fromEntries(seats.map((id) => [id, { before: W[id].hp, after: W[id].hp, effects: [] }])),
		events,
		lessons: []
	};
	const tidy = (why: string) => {
		const stripped = why.replace(/^(a|an|the) /, '');
		return stripped.charAt(0).toUpperCase() + stripped.slice(1);
	};
	const note = (id: TargetId, label: string, delta: number) => {
		if (isWizard(id)) summary.wizards[id].effects.push({ label, delta });
	};
	if (actor) log(`Time stands still. ${W[actor].name} alone can move.`, 'spell');
	/** Facts gathered along the way, turned into explanations at the end. */
	const facts = {
		shieldBlocked: new Set<TargetId>(),
		throughShield: [] as { target: TargetId; spell: string }[],
		counterSmothered: 0,
		fingerThroughCounter: false,
		loneClap: [] as string[],
		overlaps: [] as { name: string; spell: string; earlier: string }[],
		broken: [] as { name: string; hand: Hand }[],
		curedAndHurt: [] as { name: string; hurt: number; healed: number }[],
		newMonsterAttacked: '',
		/** A counter-spell aimed at the other wizard, who is then protected by it. */
		counterAimedAway: '' as string
	};

	// ---- 1. Gestures, after last turn's enchantments have their say ----
	const shape = (w: WizardState, c: Constraints, left: Gesture, right: Gesture, prev: HistoryEntry | undefined): [Gesture, Gesture] => {
		if (c.amnesia && prev) {
			log(`${w.name}, struck by amnesia, repeats the last gestures.`);
			return [prev.left, prev.right];
		}
		if (c.charmed) {
			const charmer = input(c.charmed.by);
			const g = c.charmedGesture ?? charmer.charmGestures?.[w.id] ?? charmer.charmGesture ?? '-';
			if (w.permanent.charmed && !w.permanent.charmedGesture) w.permanent.charmedGesture = g;
			if (c.charmed.hand === 'left') left = g;
			else right = g;
			log(`${W[c.charmed.by].name} charms ${w.name}'s ${c.charmed.hand} hand into a ${GESTURE_NAMES[g]}.`);
		}
		if (c.paralysedHand && prev) {
			const g = paralysedForm(w.history[w.history.length - 1][c.paralysedHand]);
			if (c.paralysedHand === 'left') left = g;
			else right = g;
			log(`${w.name}'s ${c.paralysedHand} hand is paralysed into a ${GESTURE_NAMES[g]}.`);
		}
		if (c.fear) {
			if (FEAR_BANNED.includes(left)) left = '-';
			if (FEAR_BANNED.includes(right)) right = '-';
			log(`${w.name} is too afraid to snap, point, clap or wriggle.`);
		}
		if (c.confusion) {
			const slip = c.confusionFixed ?? { hand: rng() < 0.5 ? 'left' : 'right', gesture: pick(MAGIC_GESTURES) };
			if (w.permanent.confusion && !w.permanent.confusionFixed) w.permanent.confusionFixed = slip;
			if (slip.hand === 'left') left = slip.gesture;
			else right = slip.gesture;
			log(`Confused, ${w.name}'s ${slip.hand} hand makes a ${GESTURE_NAMES[slip.gesture]} instead.`);
		}
		if (left === '>' && right === '>') right = '-';
		return [left, right];
	};
	const lone = (g: Gesture, o: Gesture) => (g === 'C' && o !== 'C' ? 'clap with one hand (nothing)' : GESTURE_NAMES[g]);
	const record = (w: WizardState, left: Gesture, right: Gesture, entryPhase: Phase) => {
		const hiddenFrom = seats.filter(
			(other) => other !== w.id && (w.invisibleTurns > 0 || W[other].blindTurns > 0 || phase === 'timestop')
		);
		if ((left === 'C') !== (right === 'C')) facts.loneClap.push(w.name);
		for (const hand of HANDS) {
			const g = hand === 'left' ? left : right;
			if (g !== '>' && g !== '-') continue;
			const seq = handSequence(w.history, hand);
			if (longestRun(seq, w.sequenceStart) >= 2) facts.broken.push({ name: w.name, hand });
		}
		w.history.push({ left, right, turn, phase: entryPhase, hiddenFrom });
		if (left === 'P' && right === 'P') w.surrendered = true;
		const prefix = entryPhase === 'haste' ? `${w.name}, hastened, adds` : `${w.name}:`;
		log(`${prefix} left ${lone(left, right)}, right ${lone(right, left)}.`, 'gesture', false, hiddenFrom);
	};
	/** History indexes of the entries each acting wizard made this turn. */
	const entries: Record<WizardId, number[]> = Object.fromEntries(seats.map((id) => [id, []]));
	for (const id of acting) {
		const w = W[id];
		const inp = input(id);
		w.surrendered = false;
		const c = phase === 'main' ? w.constraints : {};
		const [prevMain, prevHaste] = previousPairs(w);
		const [l, r] = shape(w, c, inp.left, inp.right, prevMain);
		record(w, l, r, phase);
		entries[id].push(w.history.length - 1);
		if (phase === 'main' && w.hasteTurns > 0) {
			const second = inp.second ?? { left: '-', right: '-', casts: [] };
			const [l2, r2] = shape(w, c, second.left, second.right, prevHaste);
			record(w, l2, r2, 'haste');
			entries[id].push(w.history.length - 1);
		}
		if (w.surrendered) log(`${w.name} offers both palms in surrender.`, 'death');
	}

	// ---- 2. Which completed spells are actually loosed ----
	const casts: ActiveCast[] = [];
	/** Who is shielded this turn, and by what, so a blocked blow can name it. */
	const shielded = new Map<TargetId, string>();
	for (const id of acting) {
		const w = W[id];
		const accepted: ActiveCast[] = [];
		entries[id].forEach((index, half) => {
			const upto = w.history.slice(0, index + 1);
			const completions: Record<Hand, Completion[]> = {
				left: completedSpells(handSequence(upto, 'left'), w.sequenceStart),
				right: completedSpells(handSequence(upto, 'right'), w.sequenceStart)
			};
			const choices = half === 0 ? input(id).casts : (input(id).second?.casts ?? []);
			for (const choice of choices) {
				if (accepted.some((a) => a.index === index && a.hand === choice.hand)) continue;
				const options = completions[choice.hand].filter((c) => c.spell.id === choice.spellId);
				const completion =
					options.find((c) => choice.seqIndex === undefined || c.seqIndex === choice.seqIndex) ?? options[0];
				if (!completion) continue;
				if (completion.spell.id === 'lightning_bolt_quick' && w.usedQuickLightning) {
					log(`${w.name}'s quick lightning bolt sputters: it has already been used this duel.`, 'fizzle');
					continue;
				}
				const cells = usedCells(completion, choice.hand, index + 1);
				const clash = accepted.some((a) => !!a.completion && cellsOverlap(cells, usedCells(a.completion, a.hand, a.index + 1)));
				if (clash) {
					log(`${w.name} cannot use the same gesture for two spells; ${completion.spell.name} is dropped.`, 'fizzle');
					continue;
				}
				let target = choice.target ?? (completion.spell.usualTarget === 'self' ? id : enemyOf(state, id));
				if (completion.spell.id === 'summon_elemental' && target === NOWHERE) target = id;
				const earlier = w.casts.find(
					(c) => c.hand === choice.hand && c.index >= 0 && c.index < index && c.index >= index - completion.length + 1
				);
				if (earlier) facts.overlaps.push({ name: w.name, spell: completion.spell.name, earlier: SPELL_BY_ID[earlier.spellId].name });
				accepted.push({ caster: id, hand: choice.hand, spell: completion.spell, target, choice, completion, index });
				w.casts.push({ turn, index, hand: choice.hand, spellId: completion.spell.id, target });
				const at = BLANKET_SPELLS.includes(completion.spell.id) || target === id ? '' : ` at ${beingName(state, target)}`;
				log(`${w.name} casts ${completion.spell.name}${at} (${completion.spell.sequences[completion.seqIndex]}, ${choice.hand} hand).`, 'spell', false);
				if (completion.spell.id === 'lightning_bolt_quick') {
					w.usedQuickLightning = true;
					log(`${w.name}'s quick lightning bolt is spent for this duel.`);
				}
			}
		});
		const release = input(id).release;
		if (release && w.banked) {
			const spell = SPELL_BY_ID[w.banked.spellId];
			const target = release.target ?? (spell.usualTarget === 'self' ? id : enemyOf(state, id));
			accepted.push({
				caster: id,
				hand: 'left',
				spell,
				target,
				choice: { hand: 'left', spellId: spell.id, target, elemental: w.banked.elemental, chosenHand: w.banked.chosenHand, monsterTarget: release.monsterTarget },
				index: -1,
				released: true
			});
			w.casts.push({ turn, index: -1, hand: 'left', spellId: spell.id, target });
			w.banked = null;
			const at = BLANKET_SPELLS.includes(spell.id) || target === id ? '' : ` at ${beingName(state, target)}`;
			log(`${w.name} releases the banked ${spell.name}${at}.`, 'spell');
		}
		casts.push(...accepted);
	}

	for (const c of casts) {
		if (!BLANKET_SPELLS.includes(c.spell.id) && c.target === NOWHERE) {
			c.nullified = 'released harmlessly';
			log(`${W[c.caster].name} lets the ${c.spell.name} dissipate harmlessly.`, 'fizzle');
		} else if (!BLANKET_SPELLS.includes(c.spell.id) && !isBeing(c.target)) {
			c.nullified = 'target gone';
			log(`${W[c.caster].name}'s ${c.spell.name} finds no target.`, 'fizzle');
		}
	}
	const live = () => casts.filter((c) => !c.nullified);

	const destroyedBeforeAttack = new Set<string>();
	const destroyedAfterAttack = new Set<string>();
	const orders = new Map<string, TargetId>();
	for (const m of state.monsters) {
		orders.set(m.id, input(m.owner).monsterOrders?.[m.id] ?? m.constraints.forcedTarget ?? enemyOf(state, m.owner));
	}

	// ---- 3. Dispel magic overrides everything ----
	const countered = new Set<TargetId>();
	const dispels = live().filter((c) => c.spell.id === 'dispel_magic');
	if (dispels.length > 0) {
		log('Dispel magic sweeps the field: every other spell fails, all enchantments end, and every monster will fall after this turn.', 'spell');
		for (const c of casts) if (!c.nullified && c.spell.id !== 'dispel_magic') c.nullified = 'dispelled';
		for (const d of dispels) shielded.set(d.target, 'dispel magic');
		for (const id of seats) clearEnchantments(W[id]);
		for (const m of state.monsters) {
			clearMonsterEnchantments(m);
			destroyedAfterAttack.add(m.id);
		}
	} else {
		// ---- 4. Counter-spells and magic mirrors ----
		for (const c of live()) if (c.spell.id === 'counter_spell') countered.add(c.target);
		for (const c of live()) {
			if (c.spell.id === 'magic_mirror' && countered.has(c.target)) {
				c.nullified = 'countered';
				log(`The magic mirror on ${beingName(state, c.target)} is shattered by a counter-spell.`, 'fizzle');
			}
		}
		const mirrored = new Set(live().filter((c) => c.spell.id === 'magic_mirror').map((c) => c.target));
		for (const c of live()) {
			if (c.spell.id === 'magic_mirror' || c.spell.id === 'counter_spell') continue;
			if (BLANKET_SPELLS.includes(c.spell.id)) continue;
			if (!mirrored.has(c.target)) continue;
			const owner = controllerOf(state, c.target);
			if (owner === c.caster || owner === undefined) continue;
			const original = c.caster;
			c.target = original;
			c.caster = owner;
			log(`${W[owner].name}'s magic mirror turns the ${c.spell.name} back on ${W[original].name}.`, 'spell');
		}
		for (const c of live()) {
			if (UNCOUNTERABLE.includes(c.spell.id)) continue;
			if (BLANKET_SPELLS.includes(c.spell.id)) continue;
			if (countered.has(c.target)) {
				c.nullified = 'countered';
				facts.counterSmothered += 1;
				const subject = beingName(state, c.target);
				const own = c.caster === c.target;
				log(
					c.spell.id === 'shield'
						? `A counter-spell on ${subject} smothers the Shield, and shields ${subject} itself.`
						: `A counter-spell on ${subject} smothers ${own ? 'their own ' : 'the '}${c.spell.name}.`,
					'fizzle'
				);
			}
		}
		if (live().some((c) => c.spell.id === 'finger_of_death' && countered.has(c.target))) facts.fingerThroughCounter = true;
	}

	// ---- 5. Delayed effect banks a spell; permanency extends one ----
	const bankedNow = new Set<WizardId>();
	const extendedNow = new Set<WizardId>();
	for (const id of acting) {
		const w = W[id];
		const own = () => live().filter((c) => c.caster === id && !c.released);
		const delayed = w.delayedTurns > 0 || live().some((c) => c.spell.id === 'delayed_effect' && c.target === id);
		if (delayed && !w.banked) {
			const candidates = own().filter((c) => c.spell.id !== 'delayed_effect');
			const chosen = candidates.find((c) => c.choice.bank) ?? candidates[0];
			if (chosen) {
				chosen.nullified = 'banked';
				w.banked = { spellId: chosen.spell.id, elemental: chosen.choice.elemental, chosenHand: chosen.choice.chosenHand };
				bankedNow.add(id);
				log(`${w.name} banks the ${chosen.spell.name} to release later.`, 'spell');
			}
		}
		const extending = w.permanencyTurns > 0 || live().some((c) => c.spell.id === 'permanency' && c.target === id);
		if (extending) {
			const candidates = own().filter((c) => permanencyEligible(c.spell));
			const chosen = candidates.find((c) => c.choice.permanent) ?? candidates[0];
			if (chosen) {
				chosen.permanent = true;
				extendedNow.add(id);
				log(`${w.name}'s ${chosen.spell.name} is made permanent.`, 'spell');
			}
		}
	}

	// ---- 6. Who is shielded this turn ----
	for (const c of live()) {
		if (c.spell.id === 'shield') shielded.set(c.target, 'shield');
		if (c.spell.id === 'counter_spell') shielded.set(c.target, 'counter-spell');
		if (c.spell.id === 'protection_from_evil') shielded.set(c.target, 'protection from evil');
		if (c.spell.id === 'counter_spell' && isWizard(c.target) && c.target !== c.caster) {
			facts.counterAimedAway = `${W[c.caster].name}'s counter-spell on ${W[c.target].name}`;
		}
	}
	for (const id of seats) if (W[id].protectionTurns > 0 && !shielded.has(id)) shielded.set(id, 'protection from evil');
	for (const m of state.monsters) if (m.protectionTurns > 0 && !shielded.has(m.id)) shielded.set(m.id, 'protection from evil');
	const isShielded = (id: TargetId) => shielded.has(id) && !frozenBeing(id);
	const guard = (id: TargetId) => `${beingName(state, id)}'s ${shielded.get(id) ?? 'shield'}`;

	// ---- 7. Summons, then storms and elementals ----
	for (const c of live()) {
		const kind: MonsterKind | undefined =
			c.spell.id === 'summon_elemental'
				? c.choice.elemental === 'ice'
					? 'ice_elemental'
					: 'fire_elemental'
				: SUMMON_KIND[c.spell.id];
		if (!kind) continue;
		const targetMonster = monsterOf(c.target);
		if (targetMonster && isElemental(targetMonster.kind)) {
			c.nullified = 'cast at an elemental';
			log(`Nothing can be summoned for an elemental; ${W[c.caster].name}'s ${c.spell.name} fails.`, 'fizzle');
			continue;
		}
		const controller = controllerOf(state, c.target);
		if (!controller) continue;
		const stats = MONSTER_STATS[kind];
		const n = (state.summonCounts[kind] ?? 0) + 1;
		state.summonCounts[kind] = n;
		const m: Monster = {
			id: `m${state.nextMonsterId++}`,
			kind,
			name: n === 1 ? stats.name : `${stats.name} ${roman(n)}`,
			hp: stats.hp,
			maxHp: stats.hp,
			attack: stats.attack,
			owner: controller,
			resistHeat: kind === 'fire_elemental',
			resistCold: kind === 'ice_elemental',
			protectionTurns: 0,
			constraints: {},
			pending: {},
			createdTurn: turn
		};
		state.monsters.push(m);
		orders.set(m.id, c.choice.monsterTarget ?? enemyOf(state, controller));
		const creature = stats.name.toLowerCase();
		log(`${/^[aeiou]/.test(creature) ? 'An' : 'A'} ${creature} answers ${W[controller].name}'s summons.`, 'spell');
	}

	let fireStorm = live().some((c) => c.spell.id === 'fire_storm');
	let iceStorm = live().some((c) => c.spell.id === 'ice_storm');
	const elementals = (kind: MonsterKind) => state.monsters.filter((m) => m.kind === kind && !destroyedBeforeAttack.has(m.id));
	const destroyBefore = (m: Monster, why: string) => {
		destroyedBeforeAttack.add(m.id);
		log(`${m.name} is ${why} before it can attack.`, 'death');
	};
	if (fireStorm && iceStorm) {
		fireStorm = iceStorm = false;
		log('The fire storm and the ice storm cancel each other; nothing is harmed.', 'fizzle');
	}
	if (fireStorm && elementals('ice_elemental').length > 0) {
		fireStorm = false;
		for (const m of elementals('ice_elemental')) destroyBefore(m, 'melted by the fire storm, which it quenches');
	}
	if (iceStorm && elementals('fire_elemental').length > 0) {
		iceStorm = false;
		for (const m of elementals('fire_elemental')) destroyBefore(m, 'snuffed by the ice storm, which it dissipates');
	}
	if (fireStorm) for (const m of elementals('fire_elemental')) destroyBefore(m, 'engulfed by the fire storm');
	if (iceStorm) for (const m of elementals('ice_elemental')) destroyBefore(m, 'engulfed by the ice storm');
	const exemptFromIceStorm = new Set<TargetId>();
	for (const c of live()) {
		const tm = monsterOf(c.target);
		if (c.spell.id === 'fireball') {
			if (iceStorm) {
				c.nullified = 'quenched by the ice storm';
				exemptFromIceStorm.add(c.target);
				log(`The fireball and the ice storm cancel around ${beingName(state, c.target)}, who is unharmed by either.`, 'fizzle');
			} else if (tm?.kind === 'ice_elemental') {
				c.nullified = 'spent on the elemental';
				destroyBefore(tm, 'melted by the fireball');
			} else if (tm?.kind === 'fire_elemental') {
				c.nullified = 'no effect on a fire elemental';
				log('The fireball washes harmlessly over the fire elemental.', 'fizzle');
			}
		}
		if (c.spell.id === 'resist_heat' && tm?.kind === 'fire_elemental') {
			c.nullified = 'spent on the elemental';
			destroyBefore(tm, 'unmade by resist heat');
		}
		if (c.spell.id === 'resist_cold' && tm?.kind === 'ice_elemental') {
			c.nullified = 'spent on the elemental';
			destroyBefore(tm, 'unmade by resist cold');
		}
	}
	{
		const fire = elementals('fire_elemental');
		const ice = elementals('ice_elemental');
		if (fire.length > 0 && ice.length > 0) {
			for (const m of [...fire, ...ice]) destroyBefore(m, 'destroyed by its opposite');
		}
		for (const kind of ['fire_elemental', 'ice_elemental'] as MonsterKind[]) {
			const same = elementals(kind);
			for (const extra of same.slice(1)) {
				destroyedBeforeAttack.add(extra.id);
				same[0].hp = same[0].maxHp;
				log(`Two ${MONSTER_STATS[kind].name.toLowerCase()}s merge into one.`, 'info');
			}
		}
	}

	// ---- 8. Enchantments ----
	const controlByTarget = new Map<TargetId, Set<string>>();
	for (const c of live()) {
		if (!CONTROL_SPELLS.includes(c.spell.id)) continue;
		if (!controlByTarget.has(c.target)) controlByTarget.set(c.target, new Set());
		controlByTarget.get(c.target)!.add(c.spell.id);
	}
	for (const [target, ids] of controlByTarget) {
		if (ids.size < 2) continue;
		for (const c of live()) if (c.target === target && ids.has(c.spell.id)) c.nullified = 'contradictory enchantments';
		log(`Contradictory enchantments on ${beingName(state, target)} cancel each other out.`, 'fizzle');
	}
	for (const c of live()) {
		const wiz = isWizard(c.target) ? W[c.target] : undefined;
		const mon = monsterOf(c.target);
		const target = beingName(state, c.target);
		const forever = c.permanent ? ' for the rest of the duel' : '';
		const duration = (n: number) => (c.permanent ? Infinity : n);
		switch (c.spell.id) {
			case 'amnesia':
				if (wiz) {
					wiz.pending.amnesia = true;
					if (c.permanent) wiz.permanent.amnesia = true;
				} else if (mon) mon.pending.forcedTarget = orders.get(mon.id);
				break;
			case 'confusion':
				if (wiz) {
					wiz.pending.confusion = true;
					if (c.permanent) wiz.permanent.confusion = true;
				} else if (mon) {
					const candidates = [...seats.filter((id) => W[id].alive), ...state.monsters.filter((o) => o.id !== mon.id).map((o) => o.id)];
					const t = pick(candidates as TargetId[]);
					orders.set(mon.id, t);
					log(`${mon.name} is confused and lunges at ${beingName(state, t)}.`);
				}
				break;
			case 'charm_person':
				if (wiz) {
					const hand = c.choice.chosenHand ?? pick(HANDS);
					wiz.pending.charmed = { hand, by: c.caster };
					if (c.permanent) wiz.permanent.charmed = { hand, by: c.caster };
					log(`${wiz.name}'s ${hand} hand will obey ${W[c.caster].name}${c.permanent ? ' from now on' : ' next turn'}.`);
				} else {
					c.nullified = 'monsters cannot be charmed as people';
					log(`Charm person has no hold on ${target}.`, 'fizzle');
				}
				break;
			case 'charm_monster':
				if (mon && !isElemental(mon.kind)) {
					mon.owner = c.caster;
					orders.set(mon.id, input(c.caster).monsterOrders?.[mon.id] ?? enemyOf(state, c.caster));
					log(`${mon.name} now serves ${W[c.caster].name}.`);
				} else {
					c.nullified = 'not a charmable monster';
					log(`Charm monster has no hold on ${target}.`, 'fizzle');
				}
				break;
			case 'paralysis':
				if (wiz) {
					const hand = wiz.constraints.paralysedHand ?? c.choice.chosenHand ?? 'left';
					wiz.pending.paralysedHand = hand;
					if (c.permanent) wiz.permanent.paralysedHand = hand;
					log(`${wiz.name}'s ${hand} hand will be paralysed${c.permanent ? ' from now on' : ' next turn'}.`);
				} else if (mon && !isElemental(mon.kind)) {
					mon.pending.skipAttack = true;
					log(`${mon.name} will stand paralysed next turn.`);
				} else {
					c.nullified = 'elementals cannot be paralysed';
				}
				break;
			case 'fear':
				if (wiz) {
					wiz.pending.fear = true;
					if (c.permanent) wiz.permanent.fear = true;
					log(`${wiz.name} will be too afraid to snap, point, clap or wriggle${c.permanent ? ' from now on' : ' next turn'}.`);
				} else c.nullified = 'monsters know no fear';
				break;
			case 'anti_spell':
				if (wiz) {
					wiz.sequenceStart = wiz.history.length;
					log(`${wiz.name}'s gestures so far are wiped from the weave; every spell must start afresh.`);
				}
				break;
			case 'protection_from_evil':
				if (wiz) wiz.protectionTurns = duration(4);
				else if (mon) mon.protectionTurns = duration(4);
				log(`${target} is protected from evil${c.permanent ? forever : ' for this turn and the next three'}.`);
				break;
			case 'resist_heat':
				if (wiz) wiz.resistHeat = true;
				else if (mon) mon.resistHeat = true;
				log(`${target} now resists heat.`);
				break;
			case 'resist_cold':
				if (wiz) wiz.resistCold = true;
				else if (mon) mon.resistCold = true;
				log(`${target} now resists cold.`);
				break;
			case 'disease':
				if (wiz) {
					wiz.diseaseTurns = 6;
					log(`${wiz.name} sickens with a deadly disease: six turns to find a cure.`);
				} else c.nullified = 'monsters do not sicken';
				break;
			case 'poison':
				if (wiz) {
					wiz.poisonTurns = 6;
					log(`${wiz.name} is poisoned: six turns to find a cure.`);
				} else c.nullified = 'monsters do not sicken';
				break;
			case 'blindness':
				if (wiz) {
					wiz.blindTurns = duration(4);
					log(`${wiz.name} is struck blind${c.permanent ? forever : ' for three turns'}.`);
				} else if (mon) destroyBefore(mon, 'blinded and unmade');
				break;
			case 'invisibility':
				if (wiz) {
					wiz.invisibleTurns = duration(4);
					log(`${wiz.name} fades from sight${c.permanent ? forever : ' for three turns'}.`);
				} else if (mon) destroyBefore(mon, 'made invisible and unmade');
				break;
			case 'haste':
				if (wiz) {
					wiz.hasteTurns = duration(4);
					log(`${wiz.name} is hastened${c.permanent ? forever : ' for the next three turns'}: two pairs of gestures a turn.`);
				} else c.nullified = 'monsters cannot be hastened';
				break;
			case 'time_stop':
				if (wiz) {
					state.timeStops.push(wiz.id);
					log(`${wiz.name} will act alone in a stopped moment.`);
				} else c.nullified = 'only wizards can stop time';
				break;
			case 'delayed_effect':
				if (wiz) {
					wiz.delayedTurns = bankedNow.has(wiz.id) ? 0 : duration(4);
					if (!bankedNow.has(wiz.id)) log(`${wiz.name}'s next spell will be banked.`);
				} else c.nullified = 'only wizards can delay a spell';
				break;
			case 'permanency':
				if (wiz) {
					wiz.permanencyTurns = extendedNow.has(wiz.id) ? 0 : 4;
					if (!extendedNow.has(wiz.id)) log(`${wiz.name}'s next enchantment will be permanent.`);
				} else c.nullified = 'only a wizard can hold a permanency';
				break;
		}
	}
	for (const id of bankedNow) W[id].delayedTurns = 0;
	for (const id of extendedNow) W[id].permanencyTurns = 0;
	for (const c of live()) {
		if (c.spell.id !== 'remove_enchantment' && c.spell.id !== 'raise_dead') continue;
		const wiz = isWizard(c.target) ? W[c.target] : undefined;
		const mon = monsterOf(c.target);
		if (wiz) {
			clearEnchantments(wiz);
			log(`Every enchantment on ${wiz.name} is lifted.`);
		} else if (mon && c.spell.id === 'remove_enchantment') {
			destroyedAfterAttack.add(mon.id);
			log(`${mon.name} will be unmade once it has attacked.`);
		}
	}

	// ---- 9. Damage and healing ----
	const damage = new Map<TargetId, number>();
	const healing = new Map<TargetId, number>();
	const slain = new Set<TargetId>();
	const hurt = (id: TargetId, n: number, why: string, by?: WizardId) => {
		damage.set(id, (damage.get(id) ?? 0) + n);
		if (isWizard(id) && by && by !== id) W[id].lastHurtBy = by;
		note(id, tidy(why), -n);
		log(`${beingName(state, id)} takes ${n} from ${why}.`, 'damage');
	};
	const heal = (id: TargetId, n: number, label: string) => {
		healing.set(id, (healing.get(id) ?? 0) + n);
		note(id, label, n);
	};
	for (const c of live()) {
		const t = c.target;
		switch (c.spell.id) {
			case 'missile':
				if (isShielded(t)) {
					facts.shieldBlocked.add(t);
					log(`${guard(t)} turns the missile aside.`, 'fizzle');
				} else hurt(t, 1, 'a missile', c.caster);
				break;
			case 'finger_of_death':
				slain.add(t);
				if (isWizard(t)) W[t].lastHurtBy = c.caster;
				note(t, 'Finger of death', -(isWizard(t) ? W[t].hp : 0));
				log(`The finger of death touches ${beingName(state, t)}.`, 'death');
				break;
			case 'lightning_bolt':
			case 'lightning_bolt_quick':
				if (isShielded(t)) facts.throughShield.push({ target: t, spell: 'a lightning bolt' });
				hurt(t, 5, 'a lightning bolt', c.caster);
				break;
			case 'cause_light_wounds':
				if (isShielded(t)) facts.throughShield.push({ target: t, spell: 'cause light wounds' });
				hurt(t, 2, 'cause light wounds', c.caster);
				break;
			case 'cause_heavy_wounds':
				if (isShielded(t)) facts.throughShield.push({ target: t, spell: 'cause heavy wounds' });
				hurt(t, 3, 'cause heavy wounds', c.caster);
				break;
			case 'fireball':
				if (resists(t, 'heat')) log(`${beingName(state, t)} shrugs off the fireball.`, 'fizzle');
				else {
					if (isShielded(t)) facts.throughShield.push({ target: t, spell: 'a fireball' });
					hurt(t, 5, 'a fireball', c.caster);
				}
				break;
			case 'cure_light_wounds':
				heal(t, 1, 'Cure light wounds');
				break;
			case 'cure_heavy_wounds':
				heal(t, 2, 'Cure heavy wounds');
				if (isWizard(t) && W[t].diseaseTurns !== null) {
					W[t].diseaseTurns = null;
					log(`${W[t].name}'s disease is cured.`);
				}
				break;
			case 'raise_dead':
				heal(t, 5, 'Raise dead');
				break;
		}
	}
	const everyone = (): TargetId[] => [
		...seats.filter((id) => W[id].alive),
		...state.monsters.filter((m) => !destroyedBeforeAttack.has(m.id)).map((m) => m.id)
	];
	if (fireStorm) {
		log('A fire storm rages across the field.', 'spell');
		for (const id of everyone()) {
			if (resists(id, 'heat')) continue;
			if (countered.has(id)) continue;
			hurt(id, 5, 'the fire storm');
		}
	}
	if (iceStorm) {
		log('An ice storm howls across the field.', 'spell');
		for (const id of everyone()) {
			if (resists(id, 'cold')) continue;
			if (countered.has(id) || exemptFromIceStorm.has(id)) continue;
			hurt(id, 5, 'the ice storm');
		}
	}

	// ---- 10. Monsters attack, including those slain this very turn ----
	for (const m of state.monsters) {
		if (destroyedBeforeAttack.has(m.id)) continue;
		if (frozen(m.owner)) continue;
		if (m.constraints.skipAttack && phase === 'main') {
			log(`${m.name} stands paralysed.`);
			continue;
		}
		if (isElemental(m.kind)) {
			const type = m.kind === 'fire_elemental' ? 'heat' : 'cold';
			for (const id of everyone()) {
				if (id === m.id) continue;
				const other = monsterOf(id);
				if (other && isElemental(other.kind)) continue;
				if (phase === 'main') {
					if (resists(id, type)) continue;
					if (isShielded(id)) continue;
					if (isWizard(id) && W[id].invisibleTurns > 0) continue;
				}
				hurt(id, m.attack, `the ${m.name.toLowerCase()}`, m.owner);
			}
			continue;
		}
		const target = orders.get(m.id);
		m.lastTarget = target;
		if (!isBeing(target)) {
			log(`${m.name} has nothing to attack.`);
			continue;
		}
		if (isShielded(target)) {
			facts.shieldBlocked.add(target);
			log(`${m.name}'s blows glance off ${guard(target)}.`, 'fizzle');
		} else if (isWizard(target) && W[target].invisibleTurns > 0 && !frozen(target)) {
			log(`${m.name} flails at the air where ${W[target].name} used to be.`, 'fizzle');
		} else {
			if (m.createdTurn === turn && phase === 'main') facts.newMonsterAttacked = m.name;
			hurt(target, m.attack, `the ${m.name.toLowerCase()}`, m.owner);
		}
	}

	// ---- 11. Stabs ----
	for (const id of acting) {
		const w = W[id];
		entries[id].forEach((index, half) => {
			const g = w.history[index];
			if (g.left !== '>' && g.right !== '>') return;
			const target = (half === 0 ? input(id).stabTarget : input(id).second?.stabTarget) ?? enemyOf(state, id);
			if (target === id || !isBeing(target)) {
				log(`${w.name} stabs at nothing.`, 'fizzle');
			} else if (isShielded(target)) {
				facts.shieldBlocked.add(target);
				log(`${w.name}'s knife skids off ${guard(target)}.`, 'fizzle');
			} else {
				hurt(target, 1, `${w.name}'s knife`, id);
			}
		});
	}

	// ---- 12. Apply the ledger ----
	for (const id of seats) {
		const w = W[id];
		if (!w.alive) continue;
		const net = (healing.get(id) ?? 0) - (damage.get(id) ?? 0);
		if ((healing.get(id) ?? 0) > 0 && (damage.get(id) ?? 0) > 0) {
			facts.curedAndHurt.push({ name: w.name, hurt: damage.get(id) ?? 0, healed: healing.get(id) ?? 0 });
		}
		w.hp = Math.min(MAX_HP, w.hp + net);
		if (slain.has(id)) w.hp = 0;
		if (w.hp <= 0) {
			w.hp = 0;
			w.alive = false;
			log(`${w.name} falls dead.`, 'death');
		}
	}
	state.monsters = state.monsters.filter((m) => {
		m.hp = Math.min(m.maxHp, m.hp + (healing.get(m.id) ?? 0) - (damage.get(m.id) ?? 0));
		if (slain.has(m.id)) m.hp = 0;
		if (destroyedBeforeAttack.has(m.id)) return false;
		if (destroyedAfterAttack.has(m.id)) {
			log(`${m.name} is unmade.`, 'death');
			return false;
		}
		if (m.hp <= 0) {
			log(`${m.name} is destroyed.`, 'death');
			return false;
		}
		return true;
	});

	// ---- 13. The turn ends ----
	if (phase === 'main') {
		for (const id of seats) {
			const w = W[id];
			w.constraints = { ...w.pending, ...w.permanent };
			w.pending = {};
			w.protectionTurns = tick(w.protectionTurns);
			w.blindTurns = tick(w.blindTurns);
			w.invisibleTurns = tick(w.invisibleTurns);
			w.hasteTurns = tick(w.hasteTurns);
			w.delayedTurns = tick(w.delayedTurns);
			w.permanencyTurns = tick(w.permanencyTurns);
			if (w.alive && w.diseaseTurns !== null) {
				w.diseaseTurns -= 1;
				if (w.diseaseTurns <= 0) {
					note(id, 'Disease', -w.hp);
					w.alive = false;
					w.hp = 0;
					log(`${w.name} succumbs to the disease.`, 'death');
				}
			}
			if (w.alive && w.poisonTurns !== null) {
				w.poisonTurns -= 1;
				if (w.poisonTurns <= 0) {
					note(id, 'Poison', -w.hp);
					w.alive = false;
					w.hp = 0;
					log(`${w.name} succumbs to the poison.`, 'death');
				}
			}
		}
		for (const m of state.monsters) {
			m.constraints = m.pending;
			m.pending = {};
			m.protectionTurns = tick(m.protectionTurns);
		}
	} else {
		// A stopped moment: nothing runs down, but what was set in it carries into the next turn.
		for (const id of seats) {
			const w = W[id];
			w.constraints = { ...w.constraints, ...w.pending, ...w.permanent };
			w.pending = {};
		}
		for (const m of state.monsters) {
			m.constraints = { ...m.constraints, ...m.pending };
			m.pending = {};
		}
	}

	// A wizard who is out takes their creatures with them: nobody is left to command them.
	state.monsters = state.monsters.filter((m) => inDuel(W[m.owner]));
	const standing = seats.filter((id) => inDuel(W[id]));
	const fell = (id: WizardId) => (W[id].alive ? `${W[id].name} surrenders` : `${W[id].name} is dead`);
	const wonBy = (winner: WizardId) => {
		// Name those who went out this turn; the rest were already gone.
		const gone = seats.filter((id) => id !== winner && !inDuel(W[id]));
		const thisTurn = gone.filter((id) => inDuel(previous.wizards[id]));
		return { winner, reason: `${(thisTurn.length ? thisTurn : gone).map(fell).join('; ')}. ${W[winner].name} wins the duel.` };
	};
	if (standing.length === 0) {
		// A wizard who surrenders as the last opponent dies is not the loser: the rules let the killing spells count.
		const survivors = seats.filter((id) => W[id].alive);
		if (survivors.length === 1) state.over = wonBy(survivors[0]);
		else if (survivors.length === 0) state.over = { winner: null, reason: 'Every wizard falls together. A posthumous draw.' };
		else state.over = { winner: null, reason: 'Every wizard yields at once. A draw.' };
	} else if (standing.length === 1 && seats.length > 1) {
		state.over = wonBy(standing[0]);
	}
	if (state.over) {
		log(state.over.reason, 'death');
		state.timeStops = [];
	}

	for (const id of seats) summary.wizards[id].after = W[id].hp;
	const lessons: { key: string; text: string }[] = [];
	const through = facts.throughShield.find((h) => facts.shieldBlocked.has(h.target));
	if (through) {
		lessons.push({
			key: 'shield-scope',
			text: `A shield stops creatures, missiles and stabs. It does not stop ${through.spell}, which is why ${beingName(state, through.target)} was hit anyway.`
		});
	} else if (facts.throughShield.length > 0) {
		lessons.push({
			key: 'shield-scope',
			text: `A shield stops only creatures, missiles and stabs, so it did nothing against ${facts.throughShield[0].spell}. Counter-spell is the defence against other spells.`
		});
	}
	if (facts.counterAimedAway) {
		lessons.push({
			key: 'counter-aim',
			text: `A counter-spell protects its subject, not its caster: ${facts.counterAimedAway} cancelled spells aimed at them and shielded them from creatures, missiles and stabs. To stop what the other wizard casts at you, cast the counter-spell on yourself.`
		});
	}
	if (facts.fingerThroughCounter) {
		lessons.push({ key: 'counter-finger', text: 'A counter-spell cannot stop finger of death. Only dispel magic can, or an anti-spell before the eight gestures are finished.' });
	} else if (facts.counterSmothered > 0) {
		lessons.push({ key: 'counter-scope', text: 'A counter-spell stops every other spell cast at its subject that turn, even the subject\'s own, and shields them as well. It cannot stop finger of death or dispel magic.' });
	}
	if (facts.loneClap.length > 0) {
		lessons.push({ key: 'lone-clap', text: `A clap needs both hands at once. ${facts.loneClap[0]}'s single-handed clap counts as nothing, and that hand's spells start from scratch.` });
	}
	if (facts.overlaps.length > 0) {
		const o = facts.overlaps[0];
		lessons.push({ key: 'overlap', text: `A gesture can serve more than one spell as long as each run is unbroken: ${o.name}'s ${o.spell} reused gestures from the earlier ${o.earlier}.` });
	}
	if (facts.broken.length > 0) {
		const b = facts.broken[0];
		lessons.push({ key: 'broken', text: `A stab or a rest belongs to no spell, so ${b.name}'s ${b.hand} hand has thrown away the run it had going and starts again.` });
	}
	if (facts.curedAndHurt.length > 0) {
		const c = facts.curedAndHurt[0];
		lessons.push({ key: 'cure-timing', text: `Cures land in the same turn as the damage: ${c.name} lost ${c.hurt} and regained ${c.healed} at once.` });
	}
	if (facts.newMonsterAttacked) {
		lessons.push({ key: 'monster-same-turn', text: `A creature attacks on the very turn it is summoned: ${facts.newMonsterAttacked} struck at once. A shield that turn is the only defence.` });
	}
	for (const l of lessons) {
		if (state.lessonsShown.includes(l.key) || summary.lessons.length >= 2) continue;
		state.lessonsShown.push(l.key);
		summary.lessons.push(l.text);
	}
	state.lastTurn = summary;
	if (phase === 'main') state.turn += 1;
	return state;
}

/** Gestures a hand may choose this turn, given last turn's enchantments. */
export function allowedGestures(w: WizardState, hand: Hand): Gesture[] {
	if (w.constraints.amnesia) return [];
	if (w.constraints.paralysedHand === hand) return [];
	if (w.constraints.charmed?.hand === hand) return [];
	if (w.constraints.fear) return GESTURES.filter((g) => !FEAR_BANNED.includes(g));
	return GESTURES;
}

/** The gesture a hand is forced to make this turn, if any is known in advance. */
export function forcedGesture(w: WizardState, hand: Hand, second = false): Gesture | undefined {
	const [prevMain, prevHaste] = previousPairs(w);
	const prev = second ? prevHaste : prevMain;
	if (!prev) return undefined;
	if (w.constraints.amnesia) return prev[hand];
	if (w.constraints.paralysedHand === hand) return paralysedForm(prev[hand]);
	return undefined;
}