# Phase 2

Phase 2 is about error handling. We want to add some variants to `DrawerError` and a `validate` method to `DrawerOperation`
that will catch various problems and ensure that we can do the operation correctly. Here are some error cases in no particular order:

- If the command is `Open` and the drawer file does not exist.
- If the command is `Close` and the target path either does not exist, is not a directory, or is not readable.
- If the `key` is `EnvVar` but the `$DRAWER_KEY` environment variable is not set, or is not set to a path that exists and is readable.
- If the `key` is `Path()` but the path does not exist or is not readable.
- If the command is `Open` and the target is a non-empty directory that exists, and the `force` flag is false
- If the command is `Close` and the target contains the drawer file (at any level; the target is any parent of the drawer file's path)

The `validate` method should take `&self` and return `Result<(), DrawerError>`. Let's have `main`, which is currently
creating a `DrawerOperation` and not using it, also call `validate` and print out the error if there is one. This means
we also need to `impl Display` on `DrawerError`.