Save to File #

As stated, the FileStorageUseCase implementation will be injected at runtime as a visitor of our LocalStorageUseCase concrete instance.

All it has to do is to provide a save method that accepts a type that our storage service can provide.

save #

The purpose of the save method is to get a content and

• Convert it to be writable to a file.
• Trigger an event for the Client browser to download our file.

But...

• US6 states that the file must be usable locally: let's choose JSON for our file format.
• US7 states that the file must be timestamped. Even if the file system provides a way to organize files by date, we will suppose that time must be readable at a first glance on the file's name.

So, we will have to provide internal methods to 'sanitize' our file saving and to manage with the DOM (as stated in US1 Client is acting from her browser).

Helper methods #

_generateFileName #

We will generate a filename with current date values. At the end, the filename will look like e.g. 20230215-12.54.26.923.json. To make this happen, we will create a method to format the values returned by Date methods.

private _generateFilename(): string {
  const now = new Date();

  return (
    `${now.getFullYear()}` +
    `${this._formatDateItem(now.getMonth() + 1)}` +
    `${this._formatDateItem(now.getDate())}-` +
    `${this._formatDateItem(now.getHours())}.` +
    `${this._formatDateItem(now.getMinutes())}.` +
    `${this._formatDateItem(now.getSeconds())}.` +
    `${now.getMilliseconds()}` +
    `.json`
  );
}

_formatDateItem #

This helper method simply add a 0 before 1 digit date value.

private _formatDateItem(item: string | number): string {
  return ('0' + item).slice(-2);
}

_downloadContent #

To download the content of our 'store' in a file, we provisionally transform the DOM by generating a link that we trigger programmatically.

private _downloadContent(content: string, filename: string): void {
  // Create a link.

  const downloadLink = document.createElement('a');

  // Setup the link to download our file.
  downloadLink.setAttribute('href', content);
  downloadLink.setAttribute('download', filename);

  document.body.appendChild(downloadLink); // Required for Firefox

  // Trigger the link.
  downloadLink.click();

  // Remove it from DOM.
  downloadLink.remove();
}

Finally... save #

As a result, our save function will call these private methods to build and download a file with the content it has been provided.

public save(content: Record<string, any>): void {
  // Prepare file content.

  const fileContent = `data:text/json;charset=utf-8,${encodeURIComponent(
    JSON.stringify(content, null, 2)
  )}`;

  // Prepare file name.

  const filename = this._generateFilename();

  // Download file.

  this._downloadContent(fileContent, filename);
}