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

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

/**
 * Pure function that renames a combatant in an encounter by ID.
 *
 * FR-001: Accepts Encounter, CombatantId, and newName; returns next state + events.
 * FR-002: Emits a CombatantUpdated event with combatantId, oldName, newName.
 * FR-004: Rejects empty/whitespace-only names with DomainError.
 * FR-005: Preserves activeIndex and roundNumber.
 * FR-006: Preserves combatant list order.
 */
export function editCombatant(
	encounter: Encounter,
	id: CombatantId,
	newName: string,
): EditCombatantSuccess | DomainError {
	const trimmed = newName.trim();

	if (trimmed === "") {
		return {
			kind: "domain-error",
			code: "invalid-name",
			message: "Combatant name must not be empty",
		};
	}

	const index = encounter.combatants.findIndex((c) => c.id === id);

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

	const oldName = encounter.combatants[index].name;

	return {
		encounter: {
			combatants: encounter.combatants.map((c) =>
				c.id === id ? { ...c, name: trimmed } : c,
			),
			activeIndex: encounter.activeIndex,
			roundNumber: encounter.roundNumber,
		},
		events: [
			{
				type: "CombatantUpdated",
				combatantId: id,
				oldName,
				newName: trimmed,
			},
		],
	};
}