Add Push notifications backend support

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/mobilizon/users/push_subscription.ex

@@ -0,0 +1,49 @@
+defmodule Mobilizon.Users.PushSubscription do
+  use Ecto.Schema
+  alias Mobilizon.Users.User
+  import Ecto.Changeset
+
+  schema "user_push_subscriptions" do
+    field(:digest, :string)
+    belongs_to(:user, User)
+
+    embeds_one :data, Data, on_replace: :delete do
+      field(:endpoint, :string)
+
+      embeds_one :keys, Keys, on_replace: :delete do
+        field(:auth, :string)
+        field(:p256dh, :string)
+      end
+    end
+
+    timestamps()
+  end
+
+  @doc false
+  def changeset(push_subscription, attrs) do
+    push_subscription
+    |> cast(attrs, [:user_id])
+    |> cast_embed(:data, with: &cast_data/2)
+    |> put_change(:digest, compute_digest(attrs.data))
+    |> validate_required([:digest, :user_id, :data])
+  end
+
+  defp cast_data(schema, attrs) do
+    schema
+    |> cast(attrs, [:endpoint])
+    |> cast_embed(:keys, with: &cast_keys/2)
+    |> validate_required([:endpoint, :keys])
+  end
+
+  defp cast_keys(schema, attrs) do
+    schema
+    |> cast(attrs, [:auth, :p256dh])
+    |> validate_required([:auth, :p256dh])
+  end
+
+  defp compute_digest(data) do
+    :sha256
+    |> :crypto.hash(data)
+    |> Base.encode16()
+  end
+end