Vue File Watcher: Real-time Component Updates

This challenge focuses on building a real-time file watcher within a Vue.js application. You will create a component that monitors changes to a specific text file and automatically updates its content displayed in the UI when the file is modified. This is incredibly useful for scenarios like live configuration editing, dynamic content loading, or collaborative document editing.

Problem Description

Your task is to develop a Vue.js component that acts as a file watcher. This component should:

1. Select a file: Allow the user to select a text file (e.g., .txt, .json, .md) from their local system.
2. Watch for changes: Continuously monitor the selected file for any modifications.
3. Display content: Display the current content of the watched file in a designated area of the component.
4. Auto-update: When the file is saved (modified), the component should automatically re-read the file and update the displayed content without requiring a manual page refresh.

Key Requirements:

• The solution must be implemented in Vue.js with TypeScript.
• Use the fs module (or equivalent browser API if targeting a browser-only environment without Node.js context) for file system operations. For a typical Vue CLI or Vite project running in a browser, you'll need to abstract file reading using the FileReader API.
• The component should clearly indicate which file is being watched.
• Provide a mechanism for the user to stop watching a file.

Expected Behavior:

• Upon component initialization, the user should be presented with an interface to select a file.
• Once a file is selected, its initial content should be displayed.
• Any subsequent changes to the file (e.g., saving the file in a text editor) should trigger an update in the displayed content within the Vue component.
• The user should be able to clear the selection and stop watching the current file.

Edge Cases:

• What happens if the selected file is deleted while being watched?
• What happens if the user selects a very large file? (Consider performance implications.)
• What if the file is not a plain text file? (For this challenge, assume plain text for simplicity, but acknowledge this limitation.)
• Error handling for file access permissions or non-existent files.

Examples

Example 1:

Input: User selects a file named 'config.txt' located at '/path/to/config.txt'.
Initial Content of 'config.txt':

setting1=value1
setting2=value2

Output:
Component displays:
File being watched: config.txt
--------------------
setting1=value1
setting2=value2
--------------------
[Button: Stop Watching]

Explanation: The user has selected a file, and its content is displayed.

Example 2:

Input: User modifies 'config.txt' in their text editor to:

setting1=new_value
setting3=another_setting

And saves the file. Output: Component displays: File being watched: config.txt

setting1=new_value setting3=another_setting

[Button: Stop Watching]

*Explanation:* The file was modified and saved. The component detected the change and updated the displayed content automatically.

**Example 3:** (Edge Case: File Deletion)

Input: User is watching 'config.txt'. The file '/path/to/config.txt' is deleted from the file system. Output: Component displays: File being watched: config.txt

Error: File not found or access denied.

[Button: Stop Watching]

*Explanation:* The component attempts to re-read the file, detects it's missing, and displays an appropriate error message.

## Constraints

*   The Vue.js application should be built using Vue 3 and TypeScript.
*   For browser-based applications (typical for Vue development), you will need to simulate file watching by using a mechanism that can detect changes. This might involve:
    *   **Browser API approach:** Utilizing the `FileReader` API for reading, and potentially a periodic check or a more advanced technique if available to detect system file changes (though direct, real-time system file watching like Node.js `fs.watch` is not directly available in standard browser environments without workarounds or specific browser extensions/APIs). **For this challenge, assume you can achieve a form of "watching" either by instructing the user to manually trigger a re-read or by implementing a simple interval-based check (though less efficient for true real-time). A more robust solution might involve exposing a "Refresh" button.**
    *   **Node.js context (if developing a desktop app with Electron, for instance):** You would use `fs.watch` and `fs.readFile`.
*   File size for display should be manageable within reasonable browser memory limits. Avoid handling extremely large files (e.g., > 10MB) without specific optimizations.
*   The focus is on the file watching and updating mechanism, not complex UI design.

## Notes

*   Consider how you will handle the user's file selection. The `<input type="file">` element is a good starting point.
*   For true real-time file watching in a browser, direct system access is restricted. You'll need to think creatively about how to detect changes. A common pattern for development environments is to have a refresh button that the user clicks after saving their file externally. Alternatively, you could consider polling at a reasonable interval, but be mindful of performance.
*   Think about how to clean up any watchers or intervals when the component is unmounted to prevent memory leaks.
*   The `fs` module is part of Node.js. If you are strictly in a browser environment (Vue CLI/Vite default), you'll use browser APIs like `FileReader` and `File` objects. For this challenge, if you are developing in a Node.js environment (e.g., with Electron), you can use `fs.watch`. If in a standard browser environment, you will likely need to rely on user interaction for re-reading or use a polling mechanism. **The spirit of the challenge is to react to external file changes and update the UI.**