const POSITION_GAP = 1000

export function computeReorderPositions<
  T extends { identifier: string; position: number },
>(
  items: T[],
  activeIdentifier: string,
  overIdentifier: string
): { itemIdentifiers: string[]; newPositions: number[] } | null {
  const oldIndex = items.findIndex((item) => item.identifier === activeIdentifier)
  const newIndex = items.findIndex((item) => item.identifier === overIdentifier)

  if (oldIndex === -1 || newIndex === -1 || oldIndex === newIndex) return null

  const reordered = [...items]
  const [moved] = reordered.splice(oldIndex, 1)
  reordered.splice(newIndex, 0, moved)

  const itemIdentifiers: string[] = []
  const newPositions: number[] = []

  for (let index = 0; index < reordered.length; index++) {
    const newPosition = (index + 1) * POSITION_GAP

    if (reordered[index].position !== newPosition) {
      itemIdentifiers.push(reordered[index].identifier)
      newPositions.push(newPosition)
    }
  }

  if (itemIdentifiers.length === 0) return null

  return { itemIdentifiers, newPositions }
}