vim-dadbod integration for applications using Ecto (#481)

* feat: vim-dadbod integration for applications using Ecto

[vim-dadbod][1] is useful library for interacting with databases, this
PR adds support for interacting with applications that are using Ecto
with `Ecto.Adapter.Postgres` and `Ecto.Adapter.MySQL`, thanks to that
user can run:

    :DB ecto:MyApp.Repo SELECT * FROM foo

And it will open new preview window containing result of the query or
even one can use

    :DB ecto:MyApp.Repo

To open interactive shell for DB assigned to given repository.

[1]: https://github.com/tpope/vim-dadbod

* docs: include informations about integration in README

Author: hauleth

README.md

@@ -11,6 +11,8 @@ Features:
 * Syntax highlighting for Elixir and EEx files
 * Filetype detection for `.ex`, `.exs` and `.eex` files
 * Automatic indentation
+* Integration between Ecto projects and [vim-dadbod][] for running SQL queries
+  on defined Ecto repositories
 
 ## Installation
 
@@ -54,3 +56,5 @@ We've decided not to include `mix format` integration into `vim-elixir`. If you'
 
 Run the tests: `bundle exec parallel_rspec spec`
 Spawn a vim instance with dev configs: `bin/spawn_vim`
+
+[vim-dadbod]: https://github.com/tpope/vim-dadbod

autoload/db/adapter/ecto.vim

@@ -0,0 +1,20 @@
+let s:path = expand('<sfile>:h')
+let s:cmd = join(['mix', 'run', '--no-start', '--no-compile', shellescape(s:path.'/get_repos.exs')])
+
+function! s:repo_list() abort
+    return map(systemlist(s:cmd), 'split(v:val)')
+endfunction
+
+function! db#adapter#ecto#canonicalize(url) abort
+    for l:item in s:repo_list()
+        let l:name = get(l:item, 0)
+        let l:url = get(l:item, 1)
+        if !empty(l:name) && 'ecto:'.l:name ==# a:url
+            return l:url
+        endif
+    endfor
+endfunction
+
+function! db#adapter#ecto#complete_opaque(url) abort
+    return map(s:repo_list(), 'v:val[0]')
+endfunction

autoload/db/adapter/get_repos.exs

@@ -0,0 +1,54 @@
+defmodule LoadRepos do
+  defp load_apps do
+    :code.get_path()
+    |> Enum.flat_map(fn app_dir ->
+      Path.join(app_dir, "*.app") |> Path.wildcard()
+    end)
+    |> Enum.map(fn app_file ->
+      app_file |> Path.basename() |> Path.rootname(".app") |> String.to_atom()
+    end)
+    |> Enum.map(&Application.load/1)
+  end
+
+  defp configs do
+    for {app, _, _} <- Application.loaded_applications(),
+        repos = Application.get_env(app, :ecto_repos),
+        is_list(repos) and repos != [],
+        repo <- repos,
+        do: {repo, Map.new(Application.get_env(app, repo))}
+  end
+
+  defp config_to_url(_, %{url: url}), do: url
+
+  defp config_to_url(repo, %{
+         hostname: hostname,
+         username: username,
+         password: password,
+         database: database
+       }) do
+    %URI{
+      scheme: adapter_to_string(repo.__adapter__),
+      userinfo: "#{username}:#{password}",
+      host: hostname,
+      path: Path.join("/", database)
+    }
+    |> URI.to_string()
+  end
+
+  defp adapter_to_string(Ecto.Adapters.Postgres), do: "postgres"
+  defp adapter_to_string(Ecto.Adapters.MySQL), do: "mysql"
+  defp adapter_to_string(mod), do: raise("Unknown adapter #{inspect(mod)}")
+
+  def main do
+    load_apps()
+
+    configs()
+    |> Enum.map(fn {repo, config} ->
+      [inspect(repo), ?\s, config_to_url(repo, config)]
+    end)
+    |> Enum.intersperse(?\n)
+    |> IO.puts()
+  end
+end
+
+LoadRepos.main()