import type { ReaderSize } from "./readerLayout";

const PDF_SENTINEL_BACKGROUND = { red: 247, green: 240, blue: 223 };
const PDF_BACKGROUND_TOLERANCE = 5;
const PDF_VISIBLE_DELTA = 10;
const PDF_MIN_VISIBLE_PIXELS = 12;

export type PdfRenderResult = "rendered-ok" | "blank-detected";

export function pdfRenderScale(frameSize: ReaderSize, pageSize: ReaderSize) {
  if (frameSize.width <= 0 || frameSize.height <= 0 || pageSize.width <= 0 || pageSize.height <= 0) return 1;
  return Math.min(frameSize.width / pageSize.width, frameSize.height / pageSize.height);
}

export function pdfCanvasVisible(pageRendered: boolean, hasPageError: boolean) {
  return pageRendered && !hasPageError;
}

function isNearSentinel(red: number, green: number, blue: number) {
  return (
    Math.abs(red - PDF_SENTINEL_BACKGROUND.red) <= PDF_BACKGROUND_TOLERANCE &&
    Math.abs(green - PDF_SENTINEL_BACKGROUND.green) <= PDF_BACKGROUND_TOLERANCE &&
    Math.abs(blue - PDF_SENTINEL_BACKGROUND.blue) <= PDF_BACKGROUND_TOLERANCE
  );
}

function isVisibleInk(red: number, green: number, blue: number, alpha: number) {
  if (alpha < 24) return false;
  if (isNearSentinel(red, green, blue)) return false;
  const distanceFromWhite = Math.max(255 - red, 255 - green, 255 - blue);
  return distanceFromWhite >= PDF_VISIBLE_DELTA;
}

export function pdfCanvasHasVisibleContent(imageData: Pick<ImageData, "data">) {
  let visiblePixels = 0;
  const data = imageData.data;
  for (let index = 0; index < data.length; index += 4) {
    if (isVisibleInk(data[index] ?? 255, data[index + 1] ?? 255, data[index + 2] ?? 255, data[index + 3] ?? 255)) {
      visiblePixels += 1;
      if (visiblePixels >= PDF_MIN_VISIBLE_PIXELS) return true;
    }
  }
  return false;
}

export function classifyPdfCanvas(imageData: Pick<ImageData, "data">): PdfRenderResult {
  return pdfCanvasHasVisibleContent(imageData) ? "rendered-ok" : "blank-detected";
}

export function pdfSentinelBackground() {
  return `rgb(${PDF_SENTINEL_BACKGROUND.red}, ${PDF_SENTINEL_BACKGROUND.green}, ${PDF_SENTINEL_BACKGROUND.blue})`;
}