I haven't made a datapack for years, so I decided to make something small and simple.
This datapack add an item called [​Pirate's head patch], which is inspired by pirate's eyepatch, into Minecraft.

Crafting

Throw 5 black stained glasses and a carved pumpkin on the ground to craft a [​Pirate's head patch].

Usage

Throw the item to use it.

On the first activation, the blindness effect will be triggered for 15 seconds.
On the second activation, the night vision effect will be triggered for 15 seconds.
On the next activation, the effect will be changed back to blindness.
These two effects will be swapped every time the item is used.

If you want to throw the item without activating it, you will need to throw it while sneaking.
When all items are removed from the inventory, the activating effect (if any) will be cleared.

Increasing the effect duration is possible by throwing multiple pirate's head patches at once.
Each additional item will increase the effect duration by three seconds.
For example: If you throw 5 items at once, the effect duration will be: 15 + (5 - 1) * 3 = 27 seconds.

Installation

1. Open Minecraft
2. Select your world, click Edit then click Open World Folder
3. Drop the .zip file of the datapack to the datapacks folder
4. Open your world, then type /reload
5. Done!
Type /trigger php_help for more information.

Un-installation

Type /function php:uninstall to remove all scoreboards of this datapack.