import type { PDFDocumentProxy } from 'pdfjs-dist';
import type { ImageType } from './types.js';

interface Environment {
  getDocument: (pdf: ArrayBuffer | Uint8Array) => Promise<PDFDocumentProxy>;
  createCanvas: (width: number, height: number) => HTMLCanvasElement | OffscreenCanvas;
  canvasToArrayBuffer: (
    canvas: HTMLCanvasElement | OffscreenCanvas,
    imageType: ImageType,
  ) => ArrayBuffer;
}

export interface Pdf2ImgOptions {
  scale?: number;
  imageType?: ImageType;
  range?: {
    start?: number;
    end?: number;
  };
}

export async function pdf2img(
  pdf: ArrayBuffer | Uint8Array,
  options: Pdf2ImgOptions = {},
  env: Environment,
): Promise<ArrayBuffer[]> {
  try {
    const { scale = 1, imageType = 'jpeg', range = {} } = options;
    const { start = 0, end = Infinity } = range;

    const { getDocument, createCanvas, canvasToArrayBuffer } = env;

    const pdfDoc = await getDocument(pdf);
    const numPages = pdfDoc.numPages;

    const startPage = Math.max(start + 1, 1);
    const endPage = Math.min(end + 1, numPages);

    const results: ArrayBuffer[] = [];

    for (let pageNum = startPage; pageNum <= endPage; pageNum++) {
      const page = await pdfDoc.getPage(pageNum);
      const viewport = page.getViewport({ scale });

      const canvas = createCanvas(viewport.width, viewport.height);
      if (!canvas) {
        throw new Error('Failed to create canvas');
      }

      const context = canvas.getContext('2d') as CanvasRenderingContext2D;
      if (!context) {
        throw new Error('Failed to get canvas context');
      }

      await page.render({ canvasContext: context, viewport }).promise;
      const arrayBuffer = canvasToArrayBuffer(canvas, imageType);
      results.push(arrayBuffer);
    }

    return results;
  } catch (error) {
    throw new Error(`[@pdfme/converter] pdf2img failed: ${(error as Error).message}`);
  }
}