export type CompositeParams = {
  groutOpacity?: number // 0..1
  groutColor?: [number, number, number]
  specStrength?: number // 0..1
}

function clampByte(v: number): number {
  if (!Number.isFinite(v)) return 0
  if (v < 0) return 0
  if (v > 255) return 255
  return v | 0
}

/**
 * Applies light/shadow/spec maps to a tile overlay ImageData in-place.
 * Only affects pixels where overlay alpha > 0.
 */
export function shadeTileOverlayInPlace(opts: {
  overlay: ImageData
  lightMap?: Uint8Array | null // 0..255
  shadowMap?: Uint8Array | null // 0..255 (already strength-scaled)
  specMap?: Uint8Array | null // 0..255
  params?: CompositeParams
}) {
  const { overlay, lightMap, shadowMap, specMap } = opts
  const data = overlay.data
  const groutOpacity = Math.max(0, Math.min(1, opts.params?.groutOpacity ?? 0.9))
  const specStrength = Math.max(0, Math.min(1, opts.params?.specStrength ?? 0.25))
  void groutOpacity

  for (let i = 0, p = 0; i < data.length; i += 4, p++) {
    const a = data[i + 3]
    if (a === 0) continue

    const lm = lightMap ? lightMap[p] / 255 : 0.5 // 0..1
    const sm = shadowMap ? shadowMap[p] / 255 : 0 // 0..1, already strength scaled upstream
    const sp = specMap ? specMap[p] / 255 : 0 // 0..1

    // Light map: multiply in ~[0.85..1.10]
    const lightMul = 0.85 + 0.25 * lm
    // Shadow map: only darken; clamp to keep within ~[0.7..1.0]
    const shadowMul = Math.max(0.7, 1.0 - sm)

    const add = sp * 255 * specStrength
    const r = data[i] * lightMul * shadowMul + add
    const g = data[i + 1] * lightMul * shadowMul + add
    const b = data[i + 2] * lightMul * shadowMul + add

    data[i] = clampByte(r)
    data[i + 1] = clampByte(g)
    data[i + 2] = clampByte(b)
  }
}