import type { DomainEvent } from "./events.js";
import type { CombatantId, DomainError, Encounter } from "./types.js";

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

export function toggleConcentration(
	encounter: Encounter,
	combatantId: CombatantId,
): ToggleConcentrationSuccess | DomainError {
	const targetIdx = encounter.combatants.findIndex((c) => c.id === combatantId);

	if (targetIdx === -1) {
		return {
			kind: "domain-error",
			code: "combatant-not-found",
			message: `No combatant found with ID "${combatantId}"`,
		};
	}

	const target = encounter.combatants[targetIdx];
	const wasConcentrating = target.isConcentrating === true;

	const event: DomainEvent = wasConcentrating
		? { type: "ConcentrationEnded", combatantId }
		: { type: "ConcentrationStarted", combatantId };

	const updatedCombatants = encounter.combatants.map((c) =>
		c.id === combatantId
			? { ...c, isConcentrating: wasConcentrating ? undefined : true }
			: c,
	);

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