/**
 * Sheet-vs-slab keep predicates used by the mask worker.
 * Extracted so unit tests can cover sensitivity curves without the worker.
 */

/** Keep slab pixels on a green sheet. Higher s widens the green-sheet match. */
export function greenKeep(r: number, g: number, b: number, s: number): boolean {
  const t = Math.max(0, Math.min(100, s)) / 100;
  // s=0 removes only strongly green sheet; increasing sensitivity widens the match.
  const isSheet = g - Math.max(r, b) > 45 - 35 * t;
  return !isSheet;
}

/**
 * Keep slab pixels on a black sheet.
 * At s=0 only near-black sheet (very low lum) is removed so dark live-edge /
 * bark (lum ~25–50) stays. The match widens monotonically toward s=100 (#74).
 */
export function blackKeep(r: number, g: number, b: number, s: number): boolean {
  const t = Math.max(0, Math.min(100, s)) / 100;
  const lum = 0.2126 * r + 0.7152 * g + 0.0722 * b;
  // Old floor 40 ate dark wood at minimum sensitivity. Floor 10 isolates near-black.
  const isSheet = lum < 10 + 140 * t;
  return !isSheet;
}

export function autoPickSheet(
  samples: { r: number; g: number; b: number }[],
): 'green' | 'black' {
  let gr = 0, gl = 0;
  for (const p of samples) {
    if (p.g - Math.max(p.r, p.b) > 20) gr++;
    if (0.2126 * p.r + 0.7152 * p.g + 0.0722 * p.b < 70) gl++;
  }
  return gl >= gr ? 'black' : 'green';
}