import { useEffect, useState } from 'react'

// Multi-select over a photo list. Selection lives here (not in the gallery)
// so it survives lightbox open/close, and is pruned automatically when
// photos disappear from the list (deletes, polling refreshes).
export default function useSelection(photos) {
  const [selected, setSelected] = useState(() => new Set())

  useEffect(() => {
    setSelected((prev) => {
      if (prev.size === 0) return prev
      const valid = new Set(photos.map((p) => p.id))
      const next = new Set([...prev].filter((id) => valid.has(id)))
      return next.size === prev.size ? prev : next
    })
  }, [photos])

  const toggle = (photoId) =>
    setSelected((prev) => {
      const next = new Set(prev)
      if (next.has(photoId)) next.delete(photoId)
      else next.add(photoId)
      return next
    })

  // Adds `list` (the caller's currently visible photos) to the selection —
  // additive, so selecting all of one filtered view keeps picks from another.
  const selectAll = (list) =>
    setSelected((prev) => new Set([...prev, ...list.map((p) => p.id)]))
  const clear = () => setSelected(new Set())
  const selectedBytes = photos.reduce((sum, p) => sum + (selected.has(p.id) ? p.size_bytes : 0), 0)
  const totalBytes = photos.reduce((sum, p) => sum + p.size_bytes, 0)

  return { selected, toggle, selectAll, clear, selectedBytes, totalBytes }
}