import extract from "png-chunks-extract";

export default class FileHelper {
  /**
   * Checks if a file is an image.
   *
   * @param file The file to check
   * @returns True if the file is an image
   */
  static isImage(file: File) {
    return file.type.startsWith("image/");
  }

  /**
   * Checks if a file is a video.
   *
   * @param file The file to check
   * @returns True if the file is an video
   */
  static isVideo(file: File) {
    return file.type.startsWith("video/");
  }

  /**
   * Loads the dimensions of a video file.
   *
   * @param file The file to load the dimensions for
   * @returns The dimensions of the video
   */
  static getVideoDimensions(
    file: File
  ): Promise<{ width: number; height: number }> {
    return new Promise((resolve, reject) => {
      const video = document.createElement("video");
      video.preload = "metadata";
      video.crossOrigin = "anonymous";
      video.onloadedmetadata = () => {
        window.URL.revokeObjectURL(video.src);
        resolve({ width: video.videoWidth, height: video.videoHeight });
      };
      video.onerror = reject;
      video.src = URL.createObjectURL(file);
    });
  }

  /**
   * Loads the dimensions of an image file – currently only PNGs are supported – but we mainly use
   * this to get the "real" dimensions of a retina image.
   *
   * @param file The file to load the dimensions for
   * @returns The dimensions of the image, if known.
   */
  static async getImageDimensions(
    file: File
  ): Promise<{ width: number; height: number } | undefined> {
    if (file.type !== "image/png") {
      return;
    }

    function parsePhys(view: DataView) {
      return {
        ppux: view.getUint32(0),
        ppuy: view.getUint32(4),
        unit: view.getUint8(4),
      };
    }

    function parseIHDR(view: DataView) {
      return {
        width: view.getUint32(0),
        height: view.getUint32(4),
      };
    }

    try {
      const buffer = await file.arrayBuffer();
      const chunks = extract(new Uint8Array(buffer));
      const pHYsChunk = chunks.find((chunk) => chunk.name === "pHYs");
      const iHDRChunk = chunks.find((chunk) => chunk.name === "IHDR");

      if (!pHYsChunk || !iHDRChunk) {
        return;
      }

      const idhrData = parseIHDR(new DataView(iHDRChunk.data.buffer));
      const physData = parsePhys(new DataView(pHYsChunk.data.buffer));

      if (physData.unit === 0 && physData.ppux === physData.ppuy) {
        const pixelRatio = Math.round(physData.ppux / 2834.5);
        return {
          width: idhrData.width / pixelRatio,
          height: idhrData.height / pixelRatio,
        };
      }
    } catch (_e) {
      return undefined;
    }

    return undefined;
  }
}