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, with nothing special added to the mix.
If this were to get 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 load configuration from the specific file
or directory.

## License

The MIT License.