/**
 * 선택한 객체들을 하나의 닫힌 경계(점렬)로 잇는다.
 * HATCH·BOUNDARY·REGION·WIPEOUT이 공유한다.
 */
import type { Point } from '@flatten-js/core';
import type { Entity } from '../../entities/Entity';
import { dedupeConsecutive, sampleEntityPoints } from './sample-entity';

const DEFAULT_TOLERANCE = 1e-3;

const near = (a: Point, b: Point, tolerance: number): boolean =>
	Math.abs(a.x - b.x) <= tolerance && Math.abs(a.y - b.y) <= tolerance;

/**
 * 끝점이 맞닿는 순서대로 이어 붙여 경계를 만든다.
 * 이미 닫힌 객체(원·사각형) 하나만 골랐다면 그 점렬을 그대로 돌려준다.
 */
export function entitiesToLoop(entities: Entity[], tolerance = DEFAULT_TOLERANCE): Point[] {
	const chains = entities
		.map((entity) => sampleEntityPoints(entity))
		.filter((points) => points.length >= 2);
	if (!chains.length) return [];
	if (chains.length === 1) return closeLoop(chains[0], tolerance);

	const remaining = [...chains];
	let loop = remaining.shift() as Point[];

	while (remaining.length) {
		const tail = loop[loop.length - 1];
		const index = remaining.findIndex(
			(chain) => near(chain[0], tail, tolerance) || near(chain[chain.length - 1], tail, tolerance)
		);
		if (index === -1) break; // 끊긴 경계 — 여기까지만 잇는다
		const [chain] = remaining.splice(index, 1);
		const ordered = near(chain[0], tail, tolerance) ? chain : [...chain].reverse();
		loop = dedupeConsecutive([...loop, ...ordered]);
	}

	return closeLoop(loop, tolerance);
}

/** 시작점과 끝점이 떨어져 있으면 닫는다 */
export function closeLoop(points: Point[], tolerance = DEFAULT_TOLERANCE): Point[] {
	const cleaned = dedupeConsecutive(points);
	if (cleaned.length < 3) return cleaned;
	const first = cleaned[0];
	const last = cleaned[cleaned.length - 1];
	return near(first, last, tolerance) ? cleaned : [...cleaned, first.clone()];
}