[extra-01] training has a period validity

We move from start/end date to a period date range to represent the
interval where a training take place.

Besides that, new constraints are added to ensure a trainings of a user
can't overlap. These constraints reflect in changeset validation.

lib/wabanex/training.ex

@@ -3,17 +3,16 @@ defmodule Wabanex.Training do
 
   import Ecto.Changeset
 
+  alias PgRanges.DateRange
   alias Wabanex.{Exercise, User}
 
   @primary_key {:id, :binary_id, autogenerate: true}
   @foreign_key_type :binary_id
 
-  @fields [:start_date, :end_date, :user_id]
+  @fields [:period, :user_id]
-  @required_fields [:start_date, :user_id]
 
   schema "trainings" do
-    field :start_date, :date
+    field :period, DateRange, default: DateRange.new(Date.utc_today(), nil)
-    field :end_date, :date
 
     belongs_to :user, User
 
@@ -25,7 +24,8 @@ defmodule Wabanex.Training do
   def changeset(params) do
     %__MODULE__{}
     |> cast(params, @fields)
-    |> validate_required(@required_fields)
+    |> validate_required(@fields)
+    |> exclusion_constraint(:period, name: :non_overlap_period)
     |> cast_assoc(:exercises)
   end
 end

priv/repo/migrations/20210627114504_create_gist_extension.exs

@@ -0,0 +1,11 @@
+defmodule Wabanex.Repo.Migrations.CreateGistExtension do
+  use Ecto.Migration
+
+  def up do
+    execute("CREATE EXTENSION IF NOT EXISTS \"btree_gist\";")
+  end
+
+  def down do
+    execute("DROP EXTENSION \"btree_gist\";")
+  end
+end

priv/repo/migrations/20210627114539_alter_trainings_add_period.exs

@@ -0,0 +1,46 @@
+defmodule Wabanex.Repo.Migrations.AlterTrainingsAddPeriod do
+  use Ecto.Migration
+
+  def up do
+    alter table(:trainings) do
+      add :period, :daterange
+    end
+
+    execute("""
+      update trainings set
+        period=daterange(start_date, end_date, '[)')
+        , updated_at=date_trunc('second', current_timestamp::timestamp)
+    """)
+
+    alter table(:trainings) do
+      remove :start_date
+      remove :end_date
+      modify :period, :daterange, null: false
+    end
+
+    create constraint(:trainings, :non_overlap_period,
+             exclude: "gist (user_id WITH =, period with &&)"
+           )
+  end
+
+  def down do
+    alter table(:trainings) do
+      add :start_date, :date
+      add :end_date, :date
+    end
+
+    execute("""
+      update trainings set
+        start_date=lower(period)
+        , end_date=upper(period)
+        , update_at=date_trunc('second', current_timestamp::timestamp)
+    """)
+
+    drop constraint(:trainings, :non_overlap_period)
+
+    alter table(:trainings) do
+      remove :period
+      modify :start_date, :date, null: false
+    end
+  end
+end