import { boxBlur, morphDilate } from '@/utils/maskOps'

export type MapU8 = { data: Uint8Array; width: number; height: number }

/**
 * Builds a soft shadow map from the occluder mask:
 * shadow = blur(dilate(occluder))
 * Output is 0..255, masked to tilesMask if provided.
 */
export function buildShadowMap(opts: {
  occluderMask: Uint8Array // 0/255
  tilesMask?: Uint8Array | null // 0/255
  width: number
  height: number
  dilatePx?: number
  blurRadiusPx?: number
  strength?: number // 0..1 (applied as scalar to output)
}): MapU8 {
  const width = Math.max(1, Math.round(opts.width))
  const height = Math.max(1, Math.round(opts.height))
  const dilatePx = Math.max(0, Math.round(opts.dilatePx ?? 6))
  const blurRadiusPx = Math.max(0, Math.round(opts.blurRadiusPx ?? 14))
  const strength = Math.max(0, Math.min(1, opts.strength ?? 0.35))

  const tilesMask = opts.tilesMask ?? null
  const base = dilatePx ? morphDilate(opts.occluderMask, width, height, dilatePx) : opts.occluderMask
  const blurred = blurRadiusPx ? boxBlur(base, width, height, blurRadiusPx) : null

  const out = new Uint8Array(width * height)
  for (let i = 0; i < out.length; i++) {
    if (tilesMask && !tilesMask[i]) {
      out[i] = 0
      continue
    }
    const v = blurred ? blurred[i] : base[i]
    const vv = Number.isFinite(v) ? v : 0
    out[i] = Math.max(0, Math.min(255, Math.round(vv * strength)))
  }
  return { data: out, width, height }
}