/**
 * A basic IO handler for file drop (Drag-and-drop).
 *
 * Example use:
 * ```javascript
 *  var body = document.getElememtByTagName("body")[0];
 *  var fileDrop = new FileDrop(body);
 *    fileDrop.onFileJSONDropped(function (jsonObject) {
 *    console.log("jsonObject", jsonObject);
 *  });
 * ```
 *
 * @author   Ikaros Kappler
 * @date     2021-10-13
 * @modified 2022-01-31 (ported from the ngdg project, then generalized)
 * @modified 2023-01-03 Fixing some minor type issues and adding SVG reading capabilities.
 * @version  2.1.0
 */

type IDroppedCallbackJSON = (jsonData: object) => void;
type IDroppedCallbackText = (textData: string) => void;
type IDroppedCallbackSVG = (svgDocument: Document) => void;
type IDroppedCallbackBinary = (binaryData: Blob, file: File) => void;

export class FileDrop {
  /**
   * The 'dropzone' element.
   * @private
   * @memberof FileDrop
   * @member {HTMLElement}
   */
  private element: HTMLElement;

  /**
   * The JSON file drop callback.
   * @private
   * @memberof FileDrop
   * @member {HTMLElement}
   */
  private fileDroppedCallbackJSON: IDroppedCallbackJSON | null;

  /**
   * The text file drop callback.
   * @private
   * @memberof FileDrop
   * @member {HTMLElement}
   */
  private fileDroppedCallbackText: IDroppedCallbackText | null;

  /**
   * The binary file drop callback.
   * @private
   * @memberof FileDrop
   * @member {HTMLElement}
   */
  private fileDroppedCallbackBinary: IDroppedCallbackBinary | null;

  /**
   * The SVG file drop callback.
   * @private
   * @memberof FileDrop
   * @member {HTMLElement}
   */
  private fileDroppedCallbackSVG: IDroppedCallbackSVG | null;

  /**
   *
   * @param {HTMLElement} element - The element you wish to operate as the drop zone (like <body/>).
   */
  constructor(element: HTMLElement) {
    this.element = element;

    // Init the drop listeners
    element.addEventListener("drop", this.handleDropEvent.bind(this));
    element.addEventListener("dragover", this.handleDragOverEvent.bind(this));
    element.addEventListener("dragleave", this.handleDragLeaveEvent.bind(this));
  }

  /**
   * Install the JSON (MIME type json*) file drop callback. Note than only one callback can be installed
   * in this implementation. Calling this method multiple times will overwrite previously
   * installed listeners.
   *
   * The callback will receive the dropped file content as an object (parsed JSON).
   *
   * @param {(data:object)=>void} callback
   */
  onFileJSONDropped(callback: IDroppedCallbackJSON) {
    this.fileDroppedCallbackJSON = callback;
  }

  /**
   * Install the text file (MIME type text/plain) drop callback. Note than only one callback can be installed
   * in this implementation. Calling this method multiple times will overwrite previously
   * installed listeners.
   *
   * The callback will receive the dropped file content as a string.
   *
   * @param {(data:object)=>void} callback
   */
  onFileTextDropped(callback: IDroppedCallbackText) {
    this.fileDroppedCallbackText = callback;
  }

  onFileSVGDropped(callback: IDroppedCallbackSVG) {
    this.fileDroppedCallbackSVG = callback;
  }

  /**
   * Internally handle a drop event.
   *
   * @param {DragEvent} event
   * @returns {void}
   */
  private handleDropEvent = (event: DragEvent) => {
    event.preventDefault();
    event.stopPropagation();
    this.element.style.opacity = "1.0";

    if (!event.dataTransfer || !event.dataTransfer.files || event.dataTransfer.files.length === 0) {
      // No files were dropped
      return;
    }
    if (event.dataTransfer.files.length > 1) {
      // Multiple file drop is not nupported
      return;
    }
    // if (!this.fileDroppedCallbackJSON) {
    //   // No handling callback defined.
    //   return;
    // }
    if (event.dataTransfer.files[0]) {
      const file: File = event.dataTransfer.files[0];
      // console.log("file", file);
      if (file.type.match(/json.*/) && this.fileDroppedCallbackJSON !== null) {
        var reader = new FileReader();
        reader.onload = (readEvent: ProgressEvent<FileReader>) => {
          if (!readEvent.target) {
            console.warn("Cannot process JSON ProgressEvent data: target is null.");
            return;
          }
          // Finished reading file data.
          const jsonObject: object = JSON.parse(readEvent.target.result as string);
          // TODO: what happens on fail?
          this.fileDroppedCallbackJSON && this.fileDroppedCallbackJSON(jsonObject);
        };
        reader.readAsText(file); // start reading the file data.
      } else if (file.type.match(/text\/plain.*/) && this.fileDroppedCallbackText) {
        var reader = new FileReader();
        reader.onload = (readEvent: ProgressEvent<FileReader>) => {
          if (!readEvent.target) {
            console.warn("Cannot process Text ProgressEvent data: target is null.");
            return;
          }
          // Finished reading file data.
          this.fileDroppedCallbackText && this.fileDroppedCallbackText(readEvent.target.result as string);
        };
        reader.readAsText(file); // start reading the file data.
      } else if (this.fileDroppedCallbackBinary) {
        var reader = new FileReader();
        reader.onload = (readEvent: ProgressEvent<FileReader>) => {
          if (!readEvent.target) {
            console.warn("Cannot process Binary ProgressEvent data: target is null.");
            return;
          }
          // Finished reading file data.
          this.fileDroppedCallbackBinary &&
            this.fileDroppedCallbackBinary(new Blob([readEvent.target.result as ArrayBuffer]), file);
        };
        reader.readAsBinaryString(file); // start reading the file data.
      } else if (this.fileDroppedCallbackSVG) {
        var reader = new FileReader();
        reader.onload = (readEvent: ProgressEvent<FileReader>) => {
          if (!readEvent.target) {
            console.warn("Cannot process SVG ProgressEvent data: target is null.");
            return;
          }
          const parser = new DOMParser();
          const doc = parser.parseFromString(readEvent.target.result as string, "image/svg+xml");

          // Finished reading file data.
          this.fileDroppedCallbackSVG && this.fileDroppedCallbackSVG(doc);
        };
        reader.readAsText(file); // start reading the file data.
      }
    }
  };

  /**
   * Toggles the drop sensitive element's opacity to 0.5.
   *
   * @param {DragEvent} event - The event.
   */
  private handleDragOverEvent = (event: DragEvent) => {
    event.preventDefault();
    event.stopPropagation();
    this.element.style.opacity = "0.5";
  };

  /**
   * Restored the drop sensitive element's opacity back to 1.0.
   *
   * @param {DragEvent} event - The event.
   */
  private handleDragLeaveEvent = (event: DragEvent) => {
    event.preventDefault();
    event.stopPropagation();
    this.element.style.opacity = "1.0";
  };

  /**
   * Removes all listeners (drop, dragover and dragleave).
   */
  destroy() {
    this.element.removeEventListener("drop", this.handleDropEvent);
    this.element.removeEventListener("dragover", this.handleDragOverEvent);
    this.element.removeEventListener("dragleave", this.handleDragLeaveEvent);
  }
}