// meters/scale_helpers.js — shared helpers for drawing center-scale grid lines

export const METER_HEADER_FONT = 'bold 12px ui-monospace, monospace';

/**
 * Draws a hairline-style grid (like the RMS meter) across a center column.
 * The caller provides the existing mapY function so non-linear scales are supported.
 */
export function drawHairlineGrid(
  g,
  rect,
  mapY,
  topValue,
  bottomValue,
  step = 1,
  color = 'rgba(255,255,255,0.08)',
  lineWidth = 0.6
) {
  if (!g || !rect || typeof mapY !== 'function') return;
  if (!Number.isFinite(step) || step <= 0) return;

  const hi = Math.max(topValue, bottomValue);
  const lo = Math.min(topValue, bottomValue);

  g.save();
  g.beginPath();
  g.rect(rect.x, rect.y, rect.w, rect.h);
  g.clip();

  for (let v = hi; v >= lo - 1e-6; v -= step) {
    const y = Math.round(mapY(v)) + 0.5;
    if (!Number.isFinite(y)) continue;
    if (y < rect.y - 2 || y > rect.y + rect.h + 2) continue;

    g.strokeStyle = color;
    g.lineWidth = lineWidth;
    g.beginPath();
    g.moveTo(rect.x, y);
    g.lineTo(rect.x + rect.w, y);
    g.stroke();
  }

  g.restore();
}