initiative/packages/domain/src/toggle-condition.ts

import type { ConditionId } from "./conditions.js";
import { CONDITION_DEFINITIONS, VALID_CONDITION_IDS } from "./conditions.js";
import type { DomainEvent } from "./events.js";
import {
	type CombatantId,
	type DomainError,
	type Encounter,
	findCombatant,
	isDomainError,
} from "./types.js";

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

export function toggleCondition(
	encounter: Encounter,
	combatantId: CombatantId,
	conditionId: ConditionId,
): ToggleConditionSuccess | DomainError {
	if (!VALID_CONDITION_IDS.has(conditionId)) {
		return {
			kind: "domain-error",
			code: "unknown-condition",
			message: `Unknown condition "${conditionId}"`,
		};
	}

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

	let newConditions: readonly ConditionId[] | undefined;
	let event: DomainEvent;

	if (isActive) {
		const filtered = current.filter((c) => c !== conditionId);
		newConditions = filtered.length > 0 ? filtered : undefined;
		event = { type: "ConditionRemoved", combatantId, condition: conditionId };
	} else {
		const added = [...current, conditionId];
		const order = CONDITION_DEFINITIONS.map((d) => d.id);
		added.sort((a, b) => order.indexOf(a) - order.indexOf(b));
		newConditions = added;
		event = { type: "ConditionAdded", combatantId, condition: conditionId };
	}

	const updatedCombatants = encounter.combatants.map((c) =>
		c.id === combatantId ? { ...c, conditions: newConditions } : c,
	);

	return {
		encounter: {
			combatants: updatedCombatants,
			activeIndex: encounter.activeIndex,
			roundNumber: encounter.roundNumber,
		},
		events: [event],
	};
}