/**
 * Guides d'alignement affiches pendant un deplacement.
 *
 * Volontairement simple : on compare les bords et les centres du noeud deplace
 * a ceux des autres noeuds visibles, et on ne garde que la meilleure
 * correspondance sur chaque axe. Aucun etat global, aucune entree d'historique.
 */

export interface GuideBox {
  id: string;
  x: number;
  y: number;
  width: number;
  height: number;
}

export interface AlignmentGuide {
  orientation: 'vertical' | 'horizontal';
  /** Coordonnee de la ligne (x pour verticale, y pour horizontale). */
  position: number;
  /** Etendue de la ligne, pour ne pas traverser tout le canvas. */
  start: number;
  end: number;
}

export const GUIDE_THRESHOLD = 6;

type Candidate = { value: number; span: [number, number] };

function verticalCandidates(box: GuideBox): Candidate[] {
  const span: [number, number] = [box.y, box.y + box.height];
  return [
    { value: box.x, span },
    { value: box.x + box.width / 2, span },
    { value: box.x + box.width, span },
  ];
}

function horizontalCandidates(box: GuideBox): Candidate[] {
  const span: [number, number] = [box.x, box.x + box.width];
  return [
    { value: box.y, span },
    { value: box.y + box.height / 2, span },
    { value: box.y + box.height, span },
  ];
}

function bestMatch(
  moving: Candidate[],
  others: GuideBox[],
  extract: (box: GuideBox) => Candidate[],
  threshold: number,
): { position: number; span: [number, number] } | null {
  let best: { position: number; span: [number, number]; distance: number } | null = null;

  for (const other of others) {
    for (const candidate of extract(other)) {
      for (const source of moving) {
        const distance = Math.abs(source.value - candidate.value);
        if (distance > threshold) continue;
        if (best && distance >= best.distance) continue;
        best = {
          position: candidate.value,
          span: [
            Math.min(source.span[0], candidate.span[0]),
            Math.max(source.span[1], candidate.span[1]),
          ],
          distance,
        };
      }
    }
  }

  return best ? { position: best.position, span: best.span } : null;
}

/** Au plus un guide vertical et un guide horizontal. */
export function computeAlignmentGuides(
  moving: GuideBox,
  others: GuideBox[],
  threshold: number = GUIDE_THRESHOLD,
): AlignmentGuide[] {
  const candidates = others.filter((box) => box.id !== moving.id);
  if (candidates.length === 0) return [];

  const guides: AlignmentGuide[] = [];

  const vertical = bestMatch(
    verticalCandidates(moving),
    candidates,
    verticalCandidates,
    threshold,
  );
  if (vertical) {
    guides.push({
      orientation: 'vertical',
      position: vertical.position,
      start: vertical.span[0],
      end: vertical.span[1],
    });
  }

  const horizontal = bestMatch(
    horizontalCandidates(moving),
    candidates,
    horizontalCandidates,
    threshold,
  );
  if (horizontal) {
    guides.push({
      orientation: 'horizontal',
      position: horizontal.position,
      start: horizontal.span[0],
      end: horizontal.span[1],
    });
  }

  return guides;
}