:toc: macro
:toclevels: 5
:figure-caption!:

:dotfiles_link: link:https://alchemists.io/projects/dotfiles[Dotfiles]
:runcom_link: link:https://alchemists.io/projects/runcom[Runcom]
:sod_link: link:https://alchemists.io/projects/sod[Sod]

= XDG

Provides a Ruby implementation of the link:https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html[XDG Base Directory Specification] for managing common configurations without polluting your {dotfiles_link}. XDG is great for command line interfaces or any application that needs a common configuration, cache, data, state, or runtime.

💡 If you write a lot of Command Line Interfaces (CLIs) and would like additional behavior built atop this gem, then check out the {runcom_link} gem or the more advanced {sod_link} gem.

toc::[]

== Features

* Provides a `XDG` object that adheres to the _XDG Base Directory Specification_ with access to the following environment variables:
** `XDG_CACHE_HOME`
** `XDG_CONFIG_HOME`
** `XDG_CONFIG_DIRS`
** `XDG_DATA_HOME`
** `XDG_DATA_DIRS`
** `XDG_RUNTIME_DIR`
** `XDG_STATE_HOME`

== Requirements

. https://www.ruby-lang.org[Ruby]

== Setup

To install _with_ security, run:

[source,bash]
----
# 💡 Skip this line if you already have the public certificate installed.
gem cert --add <(curl --compressed --location https://alchemists.io/gems.pem)
gem install xdg --trust-policy HighSecurity
----

To install _without_ security, run:

[source,bash]
----
gem install xdg
----

You can also add the gem directly to your project:

[source,bash]
----
bundle add xdg
----

Once the gem is installed, you only need to require it:

[source,ruby]
----
require "xdg"
----

== Usage

The following describes how to use this implementation.

=== Objects

To get up and running quickly, use `XDG.new` as follows:

[source,ruby]
----
xdg = XDG.new
xdg.cache_home   # Answers computed `XDG_CACHE_HOME` value.
xdg.config_home  # Answers computed `XDG_CONFIG_HOME` value.
xdg.config_dirs  # Answers computed `XDG_CONFIG_DIRS` value.
xdg.data_home    # Answers computed `XDG_DATA_HOME` value.
xdg.data_dirs    # Answers computed `XDG_DATA_DIRS` value.
xdg.runtime_dir  # Answers computed `XDG_RUNTIME_DIR` value.
xdg.state_home   # Answers computed `XDG_STATE_HOME` value.
----

Behinds the scenes, use of `XDG.new` wraps `XDG::Environment.new` which provides a unified Object API to the following objects:

[source,ruby]
----
cache = XDG::Cache.new
config = XDG::Config.new
data = XDG::Data.new
runtime = XDG::Runtime.new
state = XDG::State.new
----

Generally, use of `XDG.new` is all you need but knowing you can create a specialized instance of any aspect of the XDG specification can be handy for specific use cases. Additionally, the `cache`, `config`, `data`, and `state` objects share the same API which means you can send the following messages:

* `#home`: Answers the home directory as computed via the `+XDG_*_HOME+` key.
* `#directories`: Answers an array directories as computed via the `+XDG_*_DIRS+` key.
* `#all`: Answers an array of _all_ directories as computed from the combined `+XDG_*_HOME+` and
  `+XDG_*_DIRS+` values (with `+XDG_*_HOME+` prefixed at the start of the array).
* `#to_s`: Answers an _explicit_ string cast for the current environment.
* `#to_str`: Answers an _implicit_ string cast for the current environment.
* `#inspect`: Answers object inspection complete with object type, object ID, and all environment variables.

The _computed_ value of each method is either the user-defined value of the key or the default value, per specification, when the key is not defined or empty. For more on this, scroll down to the _Variable Defaults_ section to learn more.

=== Examples

The following are examples of what you will see when exploring the XDG objects within an IRB console:

[source,ruby]
----
require "xdg"

# Initialization

xdg = XDG.new
cache = XDG::Cache.new
config = XDG::Config.new
data = XDG::Data.new
runtime = XDG::Runtime.new
state = XDG::State.new

# Paths

xdg.cache_home       # "#<Pathname:/Users/demo/.cache>"
xdg.config_home      # "#<Pathname:/Users/demo/.config>"
xdg.config_dirs      # ["#<Pathname:/etc/xdg>"]
xdg.data_home        # "#<Pathname:/Users/demo/.local/share>"
xdg.data_dirs        # ["#<Pathname:/usr/local/share>", "#<Pathname:/usr/share>"]
xdg.runtime_dir      # "#<Pathname:>"
xdg.state_home       # "#<Pathname:/Users/demo/.local/state>"

cache.home           # "#<Pathname:/Users/demo/.cache>"
cache.directories    # []
cache.all            # ["#<Pathname:/Users/demo/.cache>"]

config.home          # "#<Pathname:/Users/demo/.config>"
config.directories   # ["#<Pathname:/etc/xdg>"]
config.all           # ["#<Pathname:/Users/demo/.config>", "#<Pathname:/etc/xdg>"]

data.home            # "#<Pathname:/Users/demo/.local/share>"
data.directories     # ["#<Pathname:/usr/local/share>", "#<Pathname:/usr/share>"]
data.all             # ["#<Pathname:/Users/demo/.local/share>", "#<Pathname:/usr/local/share>", "#<Pathname:/usr/share>"]

runtime.home         # "#<Pathname:>"
runtime.directories  # []
runtime.all          # ["#<Pathname:>"]

state.home           # "#<Pathname:/Users/demo/.local/state>"
state.directories    # []
state.all            # ["#<Pathname:/Users/demo/.local/state>"]

# Strings (explicit and implicit)

xdg.to_s             # "XDG_CACHE_HOME=/Users/demo/.cache XDG_CONFIG_HOME=/Users/demo/.config XDG_CONFIG_DIRS=/etc/xdg XDG_DATA_HOME=/Users/demo/.local/share XDG_DATA_DIRS=/usr/local/share:/usr/share XDG_RUNTIME_DIR= XDG_STATE_HOME=/Users/demo/.local/state"
cache.to_s           # "XDG_CACHE_HOME=/Users/demo/.cache"
config.to_s          # "XDG_CONFIG_HOME=/Users/demo/.config XDG_CONFIG_DIRS=/etc/xdg"
data.to_s            # "XDG_DATA_HOME=/Users/demo/.local/share XDG_DATA_DIRS=/usr/local/share:/usr/share"
runtime.to_s         # "XDG_RUNTIME_DIR="
state.to_s           # "XDG_STATE_HOME=/Users/demo/.local/state"

xdg.to_str           # "XDG_CACHE_HOME=/Users/demo/.cache XDG_CONFIG_HOME=/Users/demo/.config XDG_CONFIG_DIRS=/etc/xdg XDG_DATA_HOME=/Users/demo/.local/share XDG_DATA_DIRS=/usr/local/share:/usr/share XDG_RUNTIME_DIR= XDG_STATE_HOME=/Users/demo/.local/state"
cache.to_str         # "XDG_CACHE_HOME=/Users/demo/.cache"
config.to_str        # "XDG_CONFIG_HOME=/Users/demo/.config XDG_CONFIG_DIRS=/etc/xdg"
data.to_str          # "XDG_DATA_HOME=/Users/demo/.local/share XDG_DATA_DIRS=/usr/local/share:/usr/share"
runtime.to_str       # "XDG_RUNTIME_DIR="
state.to_str         # "XDG_STATE_HOME=/Users/demo/.local/state"

# Inspection

xdg.inspect          # "#<XDG::Environment:1456 XDG_CACHE_HOME=/Users/demo/.cache XDG_CONFIG_HOME=/Users/demo/.config XDG_CONFIG_DIRS=/etc/xdg XDG_DATA_HOME=/Users/demo/.local/share XDG_DATA_DIRS=/usr/local/share:/usr/share XDG_RUNTIME_DIR= XDG_STATE_HOME=/Users/demo/.local/state>"
cache.inspect        # "#<XDG::Cache:2040 XDG_CACHE_HOME=/Users/demo/.cache>"
config.inspect       # "#<XDG::Config:2060 XDG_CONFIG_HOME=/Users/demo/.config XDG_CONFIG_DIRS=/etc/xdg>"
data.inspect         # "#<XDG::Data:2080 XDG_DATA_HOME=/Users/demo/.local/share XDG_DATA_DIRS=/usr/local/share:/usr/share>"
runtime.inspect      # "#<XDG::Runtime:1496 XDG_RUNTIME_DIR=>"
state.inspect        # "#<XDG::State:2100 XDG_STATE_HOME=/Users/demo/.local/state>"
----

=== Variable Defaults

The _XDG Base Directory Specification_ defines environment variables and associated default values
when not defined or empty. The following defaults, per specification, are implemented by the `XDG`
objects:

* `XDG_CACHE_HOME="$HOME/.cache"`
* `XDG_CONFIG_HOME="$HOME/.config"`
* `XDG_CONFIG_DIRS="/etc/xdg"`
* `XDG_DATA_HOME="$HOME/.local/share"`
* `XDG_DATA_DIRS="/usr/local/share/:/usr/share/"`
* `XDG_RUNTIME_DIR=`
* `XDG_STATE_HOME="$HOME/.local/state"`

The `XDG_RUNTIME_DIR` environment variable deserves special mention because it is more user/environment specific and has no default value. Here is how `XDG_RUNTIME_DIR` is meant to be used should you choose to use it:

* _Must_ reference user-specific non-essential runtime files and other file objects (such as
sockets, named pipes, etc.)
* _Must_ be owned by the user with _only_ the user having read and write access to it.
* _Must_ have a Unix access mode of `0700`.
* _Must_ be bound to the user when logging in.
* _Must_ be removed when the user logs out.
* _Must_ be pointed to the same directory when the user logs in more than once.
* _Must_ exist from first login to last logout on the system and not removed in between.
* _Must_ not allow files in the directory to survive reboot or a full logout/login cycle.
* _Must_ keep the directory on the local file system and not shared with any other file systems.
* _Must_ keep the directory fully-featured by the standards of the operating system. Specifically,
on Unix-like operating systems AF_UNIX sockets, symbolic links, hard links, proper permissions, file
locking, sparse files, memory mapping, file change notifications, a reliable hard link count must be
supported, and no restrictions on the file name character set should be imposed. Files in this
directory _may_ be subjected to periodic clean-up. To ensure files are not removed, they should have
their access time timestamp modified at least once every 6 hours of monotonic time or the '`sticky`'
bit should be set on the file.
* When not set, applications should fall back to a replacement directory with similar capabilities
and print a warning message. Applications should use this directory for communication and
synchronization purposes and should not place larger files in it, since it might reside in runtime
memory and cannot necessarily be swapped out to disk.

=== Variable Behavior

The behavior of the XDG environment variables can be broken down by category:

* `+XDG_*_DIR+`
* `+XDG_*_DIRS+`
* `+XDG_*_HOME+`

Each is described in detail below.

==== Directory

The `+XDG_*_DIR+` category is unique in that it is specific to the `XDG_RUNTIME_DIR` and has no default value. This directory must adhere to all of the `XDG_RUNTIME_DIR` requirements as documented above.

==== Directories

These variables are used to define a colon (`:`) delimited list of directories. Order is important
as the first directory defined will take precedent over the following directory and so forth. For
example, here is a situation where the `XDG_CONFIG_DIRS` key has a custom value:

[source,bash]
----
XDG_CONFIG_DIRS="/demo/one/.config:/demo/two/.settings:/demo/three/.configuration"
----

The above then yields the following, colon delimited, array:

[source,ruby]
----
[
  "/demo/one/.config",
  "/demo/two/.settings",
  "/demo/three/.configuration"
]
----

In the above example, the `"/demo/one/.config"` path takes _highest_ priority since it was
defined first.

==== Home

These variables take precedence over the corresponding `+XDG_*_DIRS+` environment variables. Using
a modified version of the `+XDG_*_DIRS+` example, shown above, we could have the following setup:

[source,bash]
----
XDG_CONFIG_HOME="/demo/priority"
XDG_CONFIG_DIRS="/demo/one/.config:/demo/two/.settings"
----

The above then yields the following, colon delimited, array:

[source,ruby]
----
[
  "/demo/priority",
  "/demo/one/.config",
  "/demo/two/.settings"
]
----

Due to `XDG_CONFIG_HOME` taking precedence over the `XDG_CONFIG_DIRS`, the path with the
_highest_ priority is: `"/demo/priority"`.

=== Variable Priority

Path precedence is determined in the following order (with the first taking highest priority):

. `+XDG_*_HOME+` - Will be used if defined. Otherwise, falls back to specification default.
. `+XDG_*_DIRS+` - Iterates through directories in order defined (with first taking highest
  priority). Otherwise, falls back to specification default.

== Development

To contribute, run:

[source,bash]
----
git clone https://github.com/demo/xdg
cd xdg
bin/setup
----

You can also use the IRB console for direct access to all objects:

[source,bash]
----
bin/console
----

Lastly, there is a `bin/demo` script which displays default functionality for quick visual reference. This is the same script used to generate the usage examples shown at the top of this document.

[source,bash]
----
bin/demo
----

== Tests

To test, run:

[source,bash]
----
bin/rake
----

== link:https://alchemists.io/policies/license[License]

== link:https://alchemists.io/policies/security[Security]

== link:https://alchemists.io/policies/code_of_conduct[Code of Conduct]

== link:https://alchemists.io/policies/contributions[Contributions]

== link:https://alchemists.io/policies/developer_certificate_of_origin[Developer Certificate of Origin]

== link:https://alchemists.io/projects/xdg/versions[Versions]

== link:https://alchemists.io/community[Community]

== Credits

* Built with link:https://alchemists.io/projects/gemsmith[Gemsmith].
* Engineered by link:https://alchemists.io/team/brooke_kuhlmann[Brooke Kuhlmann].
* Created by link:https://github.com/trans[Thomas Sawyer] (link:https://github.com/rubyworks[Rubyworks]) in 2008 then transferred to Brooke in 2019.
