// Generates a hand-tunable wavy ground polyline: a human picks the
// amplitude/frequency knobs per level, this just avoids typing out every point.
export function generateWave(startX, endX, step, baseY, amplitude, frequency, phase = 0) {
  const points = [];
  for (let x = startX; x <= endX; x += step) {
    const y = baseY + Math.sin(x / frequency + phase) * amplitude;
    points.push({ x, y: Math.round(y) });
  }
  return points;
}

// Splices a straight ramp of the given rise (positive = downhill to the right)
// between two x positions into an existing point array, in place.
export function withRamp(points, fromX, toX, rise) {
  const from = points.find((p) => p.x >= fromX) || points[points.length - 1];
  const to = points.find((p) => p.x >= toX) || points[points.length - 1];
  const fromIndex = points.indexOf(from);
  const toIndex = points.indexOf(to);
  if (toIndex <= fromIndex) return points;
  const baseY = from.y;
  for (let i = fromIndex; i <= toIndex; i++) {
    const t = (points[i].x - from.x) / (to.x - from.x);
    points[i].y = Math.round(baseY + rise * t);
  }
  // flatten everything after the ramp to the new height
  const newY = points[toIndex].y;
  for (let i = toIndex + 1; i < points.length; i++) {
    points[i].y = newY;
  }
  return points;
}