import type { DomainEvent } from "./events.js";
import { type HpRange, type HpVariant, hpForVariant } from "./hp-range.js";
import {
	type CombatantId,
	type DomainError,
	type Encounter,
	findCombatant,
	isDomainError,
} from "./types.js";

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

/**
 * Switches a combatant's max HP between the minimum, average and maximum roll
 * of its Hit Dice.
 *
 * The shift is applied as a delta so manual HP edits and damage already taken
 * survive the switch: a creature missing 5 HP still misses 5 HP afterwards.
 */
export function setHpVariant(
	encounter: Encounter,
	combatantId: CombatantId,
	variant: HpVariant | undefined,
	range: HpRange,
): SetHpVariantSuccess | DomainError {
	const found = findCombatant(encounter, combatantId);
	if (isDomainError(found)) return found;

	const { combatant } = found;
	if (combatant.hpVariant === variant) {
		return { encounter, events: [] };
	}

	const delta =
		hpForVariant(range, variant) - hpForVariant(range, combatant.hpVariant);

	const newMaxHp =
		combatant.maxHp === undefined
			? undefined
			: Math.max(1, combatant.maxHp + delta);
	const newCurrentHp =
		combatant.currentHp === undefined || newMaxHp === undefined
			? combatant.currentHp
			: Math.max(0, Math.min(combatant.currentHp + delta, newMaxHp));

	return {
		encounter: {
			...encounter,
			combatants: encounter.combatants.map((c) =>
				c.id === combatantId
					? {
							...c,
							maxHp: newMaxHp,
							currentHp: newCurrentHp,
							hpVariant: variant,
						}
					: c,
			),
		},
		events: [
			{
				type: "HpVariantSet",
				combatantId,
				variant,
				previousMaxHp: combatant.maxHp,
				newMaxHp,
			},
		],
	};
}