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

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

export function setAc(
	encounter: Encounter,
	combatantId: CombatantId,
	value: number | undefined,
): SetAcSuccess | 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}"`,
		};
	}

	if (value !== undefined) {
		if (!Number.isInteger(value) || value < 0) {
			return {
				kind: "domain-error",
				code: "invalid-ac",
				message: `AC must be a non-negative integer, got ${value}`,
			};
		}
	}

	const target = encounter.combatants[targetIdx];
	const previousAc = target.ac;

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

	return {
		encounter: {
			combatants: updatedCombatants,
			activeIndex: encounter.activeIndex,
			roundNumber: encounter.roundNumber,
		},
		events: [
			{
				type: "AcSet",
				combatantId,
				previousAc,
				newAc: value,
			},
		],
	};
}