const OUTPUT_PIXELS = 64;

function positiveNumber(value, field) {
  const number = Number(value);
  if (!Number.isFinite(number) || number <= 0) {
    throw new TypeError(field + " must be a positive number");
  }
  return number;
}

export function cropGeometry({
  viewportWidth, viewportHeight, sourceWidth, sourceHeight, zoom, centerX, centerY,
}) {
  const viewWidth = positiveNumber(viewportWidth, "viewportWidth");
  const viewHeight = positiveNumber(viewportHeight, "viewportHeight");
  const imageWidth = positiveNumber(sourceWidth, "sourceWidth");
  const imageHeight = positiveNumber(sourceHeight, "sourceHeight");
  const scaleZoom = positiveNumber(zoom, "zoom");
  const x = Number(centerX), y = Number(centerY);
  if (!Number.isFinite(x) || !Number.isFinite(y)) {
    throw new TypeError("crop center must be finite");
  }
  const scale = Math.min(viewWidth / imageWidth, viewHeight / imageHeight) * scaleZoom;
  const width = imageWidth * scale;
  const height = imageHeight * scale;
  return {
    width,
    height,
    left: viewWidth / 2 - x * width,
    top: viewHeight / 2 - y * height,
  };
}

export function cropCenterBounds({
  viewportWidth, viewportHeight, sourceWidth, sourceHeight, zoom,
}) {
  const geometry = cropGeometry({
    viewportWidth, viewportHeight, sourceWidth, sourceHeight, zoom,
    centerX: 0.5, centerY: 0.5,
  });
  const visibleX = Math.min(Number(viewportWidth) / OUTPUT_PIXELS, geometry.width);
  const visibleY = Math.min(Number(viewportHeight) / OUTPUT_PIXELS, geometry.height);
  return {
    minX: (visibleX - Number(viewportWidth) / 2) / geometry.width,
    maxX: 1 + (Number(viewportWidth) / 2 - visibleX) / geometry.width,
    minY: (visibleY - Number(viewportHeight) / 2) / geometry.height,
    maxY: 1 + (Number(viewportHeight) / 2 - visibleY) / geometry.height,
  };
}

export function clampCropCenter(value, bounds) {
  return {
    centerX: Math.max(bounds.minX, Math.min(bounds.maxX, Number(value.centerX))),
    centerY: Math.max(bounds.minY, Math.min(bounds.maxY, Number(value.centerY))),
  };
}