feat(growth): load data on application start

To make this possible, the following changes were made:

* Use `Task` to start the load process
* Create `ets` table before start the async task
  * This is needed to keep the tables alive after the task process exits
* Adjust the application to start the `Growth.Indicators.Load` task

lib/growth/indicators/load.ex

@@ -32,6 +32,8 @@ defmodule Growth.Indicators.Load do
 
   """
 
+  use Task
+
   alias Growth.Score
 
   @measure_to_score [
@@ -45,6 +47,15 @@ defmodule Growth.Indicators.Load do
     weight_for_height: Score.WeightForHeight
   ]
 
+  @doc false
+  def start_link(_) do
+    Enum.map(@measure_to_score, fn {_, measure} ->
+      create_ets(measure)
+    end)
+
+    Task.start_link(__MODULE__, :all, [])
+  end
+
   @spec all :: [[boolean()]]
   @doc """
   Load indicators csv files into their own ets tables.
@@ -57,20 +68,13 @@ defmodule Growth.Indicators.Load do
     |> Task.await_many()
   end
 
-  @spec create_ets(String.t()) :: {atom(), String.t()}
+  @spec create_ets(module()) :: module()
   @doc """
-  Create a public ets table for the csv filename, using the file name as the table name.
+  Create a public ets table for the growth module, using it as the table name.
 
-  Returns a tuple with table name as an atom and the filename.
+  Returns the given module.
   """
-  def create_ets(filename) do
+  def create_ets(measure) do
-    measure =
-      filename
-      |> Path.basename()
-      |> Path.rootname()
-      |> String.to_atom()
-      |> then(&Keyword.get(@measure_to_score, &1, &1))
-
     try do
       :ets.new(measure, [:set, :public, :named_table])
     rescue
@@ -78,6 +82,21 @@ defmodule Growth.Indicators.Load do
         nil
     end
 
+    measure
+  end
+
+  @spec filename_to_measure(String.t()) :: {atom(), String.t()}
+  @doc """
+  Translate the given filename to the related module and return both in a tuple.
+  """
+  def filename_to_measure(filename) do
+    measure =
+      filename
+      |> Path.basename()
+      |> Path.rootname()
+      |> String.to_atom()
+      |> then(&Keyword.get(@measure_to_score, &1, &1))
+
     {measure, filename}
   end
 
@@ -127,7 +146,7 @@ defmodule Growth.Indicators.Load do
           as_float(t)
         end
 
-      key = {String.to_existing_atom(gender), unit, converted_t}
+      key = {String.to_atom(gender), unit, converted_t}
 
       value = %{
         l: as_float(l),

lib/wabanex/application.ex

@@ -16,9 +16,10 @@ defmodule Wabanex.Application do
       # Start the PubSub system
       {Phoenix.PubSub, name: Wabanex.PubSub},
       # Start the Endpoint (http/https)
-      WabanexWeb.Endpoint
+      WabanexWeb.Endpoint,
       # Start a worker by calling: Wabanex.Worker.start_link(arg)
       # {Wabanex.Worker, arg}
+      {Growth.Indicators.Load, []}
     ]
 
     # See https://hexdocs.pm/elixir/Supervisor.html