const STORAGE_KEY = 'sg-map-layout-v1'

const EMPTY = { positions: {}, scale: 1, view: null }

let memoryByMapId = null

function readAll() {
  if (memoryByMapId) return memoryByMapId
  try {
    const raw = sessionStorage.getItem(STORAGE_KEY)
    memoryByMapId = raw ? JSON.parse(raw) : {}
  } catch {
    memoryByMapId = {}
  }
  return memoryByMapId
}

export function readMapLayoutCache(mapId) {
  if (!mapId) return { ...EMPTY }
  const all = readAll()
  const entry = all[String(mapId)]
  return entry ? { ...EMPTY, ...entry } : { ...EMPTY }
}

export function writeMapLayoutCache(mapId, { positions, scale, view }) {
  if (!mapId) return
  const key = String(mapId)
  const all = readAll()
  const prev = all[key] || { ...EMPTY }
  all[key] = {
    positions: positions ?? prev.positions,
    scale: scale ?? prev.scale,
    view: view ?? prev.view,
  }
  memoryByMapId = all
  try {
    sessionStorage.setItem(STORAGE_KEY, JSON.stringify(all))
  } catch {
    /* sessionStorage quota */
  }
}

export function clearMapLayoutCache(mapId) {
  if (!mapId) return
  const all = readAll()
  delete all[String(mapId)]
  memoryByMapId = all
  try {
    sessionStorage.setItem(STORAGE_KEY, JSON.stringify(all))
  } catch {
    /* ignore */
  }
}