Takeoff
=======

This is a microlibrary for creating Elixir applications that are fully configurable
via the command-line, just as you would configure it using the standard config
scripts. 

**Disclaimer** Arguably, this might not be the _Elixir_ way of doing things.
Nevertheless, I found it usefull in deployment as well as in testing, where I
sometimes would spawn lots of instances of the same service with a randomized
configuration.

## Example

Say we have the following simple configuration:

```elixir
config :maru, MyApp.API,
  http: [port: 8080]

config :myapp, MyApp.Repo,
  adapter: Ecto.MySQL,
  database: "foobar"
```

After following the tutorial and building the executable, we can use something
like `./myapp --http-port 9000 --db-database barbar` to override these default
settings.

## Installation

Fist, add this microlibrary to your dependencies:

```elixir
def deps do
  [{:takeoff, "~> 0.2.0"}]
end
```

Next, enable the generation of an executable:

```elixir
def project do 
  # ...
  escript: [main_module: MyApp.CLI],
  # ...
end
```

We define the respective module somewhere in our source:

```elixir
defmodule MyApp.CLI do
  use Takeoff,
    mod: MyApp.App, # run after configuration
    arguments: # mapping from argument prefixes to paths in Application config
      [http: [:maru, MyApp.API, :http],
      db: [:myapp, MyApp.Repo]]
end
```

This tells Erlang to map the prefix `--db-` to the configuration of our application `:myapp`
with key `MyApp.Repo`, while `--http-` is mapped to the dependency application
`:maru` with key `MyApp.API` and a sub-key `:http`.

The final step is to build the executable with `mix escript.build`. Now you
will be able to run the application with `./myapp`.

## Future Plans

This is just a quick proof-of-concept. If this were to get more robust, it
might be nice to provide some integration with mix itself if this is possible.
Other than that, a few meta-flags could be added such as `--config-file`, which
loads configuration from the specific file or directory.

## License

The MIT License.