initiative/packages/domain/src/persistent-damage.ts

import type { DomainEvent } from "./events.js";
import {
	PERSISTENT_DAMAGE_DEFINITIONS,
	type PersistentDamageEntry,
	type PersistentDamageType,
	VALID_PERSISTENT_DAMAGE_TYPES,
} from "./persistent-damage-types.js";
import {
	type CombatantId,
	type DomainError,
	type Encounter,
	findCombatant,
	isDomainError,
} from "./types.js";

export {
	PERSISTENT_DAMAGE_DEFINITIONS,
	PERSISTENT_DAMAGE_TYPES,
	type PersistentDamageDefinition,
	type PersistentDamageEntry,
	type PersistentDamageType,
	VALID_PERSISTENT_DAMAGE_TYPES,
} from "./persistent-damage-types.js";

export interface PersistentDamageSuccess {
	readonly encounter: Encounter;
	readonly events: DomainEvent[];
}

function applyPersistentDamage(
	encounter: Encounter,
	combatantId: CombatantId,
	newEntries: readonly PersistentDamageEntry[] | undefined,
): Encounter {
	return {
		combatants: encounter.combatants.map((c) =>
			c.id === combatantId ? { ...c, persistentDamage: newEntries } : c,
		),
		activeIndex: encounter.activeIndex,
		roundNumber: encounter.roundNumber,
	};
}

export function addPersistentDamage(
	encounter: Encounter,
	combatantId: CombatantId,
	damageType: PersistentDamageType,
	formula: string,
): PersistentDamageSuccess | DomainError {
	if (!VALID_PERSISTENT_DAMAGE_TYPES.has(damageType)) {
		return {
			kind: "domain-error",
			code: "unknown-damage-type",
			message: `Unknown persistent damage type "${damageType}"`,
		};
	}
	if (formula.trim().length === 0) {
		return {
			kind: "domain-error",
			code: "empty-formula",
			message: "Persistent damage formula must not be empty",
		};
	}

	const found = findCombatant(encounter, combatantId);
	if (isDomainError(found)) return found;
	const { combatant: target } = found;
	const current = target.persistentDamage ?? [];

	// Replace existing entry of same type, or append
	const filtered = current.filter((e) => e.type !== damageType);
	const newEntries = [
		...filtered,
		{ type: damageType, formula: formula.trim() },
	];

	// Sort by definition order
	const order = PERSISTENT_DAMAGE_DEFINITIONS.map((d) => d.type);
	newEntries.sort((a, b) => order.indexOf(a.type) - order.indexOf(b.type));

	return {
		encounter: applyPersistentDamage(encounter, combatantId, newEntries),
		events: [
			{
				type: "PersistentDamageAdded",
				combatantId,
				damageType,
				formula: formula.trim(),
			},
		],
	};
}

export function removePersistentDamage(
	encounter: Encounter,
	combatantId: CombatantId,
	damageType: PersistentDamageType,
): PersistentDamageSuccess | DomainError {
	const found = findCombatant(encounter, combatantId);
	if (isDomainError(found)) return found;
	const { combatant: target } = found;
	const current = target.persistentDamage ?? [];

	if (!current.some((e) => e.type === damageType)) {
		return {
			kind: "domain-error",
			code: "persistent-damage-not-active",
			message: `Persistent ${damageType} damage is not active`,
		};
	}

	const filtered = current.filter((e) => e.type !== damageType);
	return {
		encounter: applyPersistentDamage(
			encounter,
			combatantId,
			filtered.length > 0 ? filtered : undefined,
		),
		events: [{ type: "PersistentDamageRemoved", combatantId, damageType }],
	};
}