// Shared utilities for mq_editor

// Evaluate cubic bezier curve at time t (robust: handles dt<=0)
function evalBezier(curve, t) {
  const dt = curve.t3 - curve.t0;
  if (dt <= 0) return curve.v0;
  let u = (t - curve.t0) / dt;
  u = Math.max(0, Math.min(1, u));
  const u1 = 1.0 - u;
  return u1*u1*u1 * curve.v0 +
         3*u1*u1*u * curve.v1 +
         3*u1*u*u  * curve.v2 +
         u*u*u     * curve.v3;
}

// Get canvas-relative {x, y} from a mouse event
function getCanvasCoords(e, canvas) {
  const rect = canvas.getBoundingClientRect();
  return { x: e.clientX - rect.left, y: e.clientY - rect.top };
}

// Build upper/lower band point arrays for a frequency curve.
// factorAbove/factorBelow are fractional offsets (e.g. 0.02 = ±2%).
// Returns { upper: [[x,y],...], lower: [[x,y],...] }
function buildBandPoints(viewer, curve, factorAbove, factorBelow) {
  const STEPS = 60;
  const upper = [], lower = [];
  for (let i = 0; i <= STEPS; ++i) {
    const t = curve.t0 + (curve.t3 - curve.t0) * i / STEPS;
    if (t < viewer.t_view_min - 0.01 || t > viewer.t_view_max + 0.01) continue;
    const f = evalBezier(curve, t);
    upper.push([viewer.timeToX(t), viewer.freqToY(f * (1 + factorAbove))]);
    lower.push([viewer.timeToX(t), viewer.freqToY(f * (1 - factorBelow))]);
  }
  return { upper, lower };
}