import * as pdfjsLib from 'pdfjs-dist';
import pdfjsWorker from 'pdfjs-dist/build/pdf.worker?worker&url';

// eslint-disable-next-line @typescript-eslint/no-explicit-any
(pdfjsLib as any).GlobalWorkerOptions.workerSrc = pdfjsWorker;

type RotationsMap = Record<number, number>;

export async function generateThumbnails(
  arrayBuffer: ArrayBuffer,
  maxHeight = 150
): Promise<string[]> {
  return generateThumbnailsInternal(arrayBuffer, {}, maxHeight);
}

export async function generateThumbnailsWithRotations(
  arrayBuffer: ArrayBuffer,
  rotations: RotationsMap,
  maxHeight = 150
): Promise<string[]> {
  return generateThumbnailsInternal(arrayBuffer, rotations, maxHeight);
}

async function generateThumbnailsInternal(
  arrayBuffer: ArrayBuffer,
  rotations: RotationsMap,
  maxHeight: number
): Promise<string[]> {
  const loadingTask = pdfjsLib.getDocument({ data: arrayBuffer });
  const pdf = await loadingTask.promise;

  const thumbs: string[] = [];

  for (let pageNum = 1; pageNum <= pdf.numPages; pageNum++) {
    const page = await pdf.getPage(pageNum);
    const viewport = page.getViewport({ scale: 1 });
    const scale = maxHeight / viewport.height;
    const scaledViewport = page.getViewport({ scale });

    const baseCanvas = document.createElement('canvas');
    const baseCtx = baseCanvas.getContext('2d');
    if (!baseCtx) {
      thumbs.push('');
      continue;
    }

    baseCanvas.width = scaledViewport.width;
    baseCanvas.height = scaledViewport.height;

    const renderTask = page.render({
      canvasContext: baseCtx,
      viewport: scaledViewport,
    });
    await renderTask.promise;

    const originalIndex = pageNum - 1;
    const rotationDegRaw = rotations[originalIndex] ?? 0;
    const rotationDeg = ((rotationDegRaw % 360) + 360) % 360;

    if (rotationDeg === 0) {
      thumbs.push(baseCanvas.toDataURL('image/png'));
      continue;
    }

    const rotatedCanvas = document.createElement('canvas');
    const rotatedCtx = rotatedCanvas.getContext('2d');
    if (!rotatedCtx) {
      thumbs.push(baseCanvas.toDataURL('image/png'));
      continue;
    }

    const rad = (rotationDeg * Math.PI) / 180;

    if (rotationDeg === 90 || rotationDeg === 270) {
      rotatedCanvas.width = baseCanvas.height;
      rotatedCanvas.height = baseCanvas.width;
    } else {
      rotatedCanvas.width = baseCanvas.width;
      rotatedCanvas.height = baseCanvas.height;
    }

    rotatedCtx.save();

    switch (rotationDeg) {
      case 90:
        rotatedCtx.translate(rotatedCanvas.width, 0);
        rotatedCtx.rotate(rad);
        break;
      case 180:
        rotatedCtx.translate(rotatedCanvas.width, rotatedCanvas.height);
        rotatedCtx.rotate(rad);
        break;
      case 270:
        rotatedCtx.translate(0, rotatedCanvas.height);
        rotatedCtx.rotate(rad);
        break;
      default:
        break;
    }

    rotatedCtx.drawImage(baseCanvas, 0, 0);
    rotatedCtx.restore();

    thumbs.push(rotatedCanvas.toDataURL('image/png'));
  }

  return thumbs;
}