import type * as THREE from 'three';

/**
 * Return a texture flipped left/right so it reads correctly when viewed from
 * behind (the back face). The back cap maps with the same planar UVs as the
 * front, so without a flip the back appears mirrored.
 *
 * The source texture is cloned so the transform doesn't leak into other meshes
 * that share the same texture (drei caches textures globally by URL).
 */
export function flipTexture(texture: THREE.Texture): THREE.Texture {
  const tex = texture.clone();
  // Negate repeat.x and shift offset.x by one full repeat so the visible
  // region stays in the same place while mirrored. After negation
  // `repeat.x` is `-rx`, so subtracting it adds `rx` to the offset.
  tex.repeat.x = -tex.repeat.x;
  tex.offset.x -= tex.repeat.x;
  return tex;
}