export type ReaderSize = {
  width: number;
  height: number;
};

export const READER_ZOOM_MIN = 50;
export const READER_ZOOM_MAX = 300;
export const READER_ZOOM_STEP = 25;
export const READER_ZOOM_DEFAULT = 100;

export function clampReaderZoom(zoom: number) {
  const steppedZoom = Math.round(zoom / READER_ZOOM_STEP) * READER_ZOOM_STEP;
  return Math.max(READER_ZOOM_MIN, Math.min(steppedZoom, READER_ZOOM_MAX));
}

export function readerZoomLabel(zoom: number) {
  return `${clampReaderZoom(zoom)} %`;
}

export function readerZoomFactor(zoom: number) {
  return clampReaderZoom(zoom) / 100;
}

export function clampReaderPage(page: number, pageCount: number) {
  const safePageCount = Math.max(1, Math.floor(pageCount));
  return Math.max(1, Math.min(Math.floor(page), safePageCount));
}

export function previousReaderPage(page: number, pageCount: number) {
  return clampReaderPage(page - 1, pageCount);
}

export function nextReaderPage(page: number, pageCount: number) {
  return clampReaderPage(page + 1, pageCount);
}

export function readerPositionLabel(page: number, pageCount: number) {
  return `Page ${clampReaderPage(page, pageCount)} / ${Math.max(1, Math.floor(pageCount))}`;
}

export function containPageSize(viewport: ReaderSize, page: ReaderSize): ReaderSize {
  if (viewport.width <= 0 || viewport.height <= 0 || page.width <= 0 || page.height <= 0) {
    return { width: 0, height: 0 };
  }
  const scale = Math.min(viewport.width / page.width, viewport.height / page.height);
  return {
    width: Math.max(1, Math.floor(page.width * scale)),
    height: Math.max(1, Math.floor(page.height * scale))
  };
}

export function orientedContainPageSize(viewport: ReaderSize, page: ReaderSize): ReaderSize {
  if (viewport.width <= 0 || viewport.height <= 0 || page.width <= 0 || page.height <= 0) {
    return { width: 0, height: 0 };
  }
  const fitByHeight = page.height >= page.width;
  const primaryScale = fitByHeight ? viewport.height / page.height : viewport.width / page.width;
  const crossScale = fitByHeight ? viewport.width / page.width : viewport.height / page.height;
  const scale = Math.min(primaryScale, crossScale);
  return {
    width: Math.max(1, Math.floor(page.width * scale)),
    height: Math.max(1, Math.floor(page.height * scale))
  };
}

export function zoomReaderSize(size: ReaderSize, zoom: number): ReaderSize {
  const factor = readerZoomFactor(zoom);
  return {
    width: Math.max(1, Math.floor(size.width * factor)),
    height: Math.max(1, Math.floor(size.height * factor))
  };
}

export function readableViewportSize(size: ReaderSize): ReaderSize | null {
  if (size.width < 32 || size.height < 32) return null;
  return {
    width: Math.floor(size.width),
    height: Math.floor(size.height)
  };
}