3 files changed, 120 insertions, 0 deletions
diff --git a/src/flagd-ui/lib/flagd_ui/application.ex b/src/flagd-ui/lib/flagd_ui/application.ex
new file mode 100644
index 0000000..732e4d0
--- /dev/null
+++ b/src/flagd-ui/lib/flagd_ui/application.ex
@@ -0,0 +1,43 @@
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
+defmodule FlagdUi.Application do
+  # See https://hexdocs.pm/elixir/Application.html
+  # for more information on OTP Applications
+  @moduledoc false
+
+  use Application
+
+  @impl true
+  def start(_type, _args) do
+    # Ensure inets is started before OpenTelemetry initialization
+    :ok = Application.ensure_started(:inets)
+
+    children = [
+      FlagdUiWeb.Telemetry,
+      {DNSCluster, query: Application.get_env(:flagd_ui, :dns_cluster_query) || :ignore},
+      {Phoenix.PubSub, name: FlagdUi.PubSub},
+      FlagdUi.Storage,
+      # Start a worker by calling: FlagdUi.Worker.start_link(arg)
+      # {FlagdUi.Worker, arg},
+      # Start to serve requests, typically the last entry
+      FlagdUiWeb.Endpoint
+    ]
+
+    OpentelemetryBandit.setup()
+    OpentelemetryPhoenix.setup(adapter: :bandit)
+
+    # See https://hexdocs.pm/elixir/Supervisor.html
+    # for other strategies and supported options
+    opts = [strategy: :one_for_one, name: FlagdUi.Supervisor]
+    Supervisor.start_link(children, opts)
+  end
+
+  # Tell Phoenix to update the endpoint configuration
+  # whenever the application is updated.
+  @impl true
+  def config_change(changed, _new, removed) do
+    FlagdUiWeb.Endpoint.config_change(changed, removed)
+    :ok
+  end
+end
diff --git a/src/flagd-ui/lib/flagd_ui/mailer.ex b/src/flagd-ui/lib/flagd_ui/mailer.ex
new file mode 100644
index 0000000..c22a862
--- /dev/null
+++ b/src/flagd-ui/lib/flagd_ui/mailer.ex
@@ -0,0 +1,6 @@
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
+defmodule FlagdUi.Mailer do
+  use Swoosh.Mailer, otp_app: :flagd_ui
+end
diff --git a/src/flagd-ui/lib/flagd_ui/storage.ex b/src/flagd-ui/lib/flagd_ui/storage.ex
new file mode 100644
index 0000000..eefcb13
--- /dev/null
+++ b/src/flagd-ui/lib/flagd_ui/storage.ex
@@ -0,0 +1,71 @@
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
+defmodule FlagdUi.Storage do
+  @moduledoc """
+  Storage module. This module initializes a process as a separate GenServer
+  to linearize reads and writes preventing conflicts and last-writer-wins.
+  """
+
+  use GenServer
+  require Logger
+
+  @file_path Application.compile_env!(:flagd_ui, :storage_file_path)
+
+  def start_link(opts) do
+    name = Keyword.get(opts, :name, Storage)
+
+    GenServer.start_link(__MODULE__, %{}, name: name)
+  end
+
+  @impl true
+  def init(_) do
+    state = @file_path |> File.read!() |> Jason.decode!()
+    Logger.info("Read new state from file")
+
+    {:ok, state}
+  end
+
+  @impl true
+  def handle_call(:read, _from, state) do
+    {:reply, state, state}
+  end
+
+  @impl true
+  def handle_cast({:replace, json_string}, _) do
+    new_state = Jason.decode!(json_string)
+
+    write_state(json_string)
+
+    {:noreply, new_state}
+  end
+
+  @impl true
+  def handle_cast({:write, flag_name, flag_value}, state) do
+    new_state =
+      Map.update(state, "flags", %{}, fn flags ->
+        update_flag(flags, flag_name, flag_value)
+      end)
+
+    json_state = Jason.encode!(new_state, pretty: true)
+
+    write_state(json_state)
+
+    {:noreply, new_state}
+  end
+
+  defp update_flag(flags, flag_name, value) do
+    flags
+    |> Enum.map(fn
+      {flag, data} when flag == flag_name -> {flag, Map.replace(data, "defaultVariant", value)}
+      {flag, data} -> {flag, data}
+    end)
+    |> Map.new()
+  end
+
+  defp write_state(json_string) do
+    File.write!(@file_path, json_string)
+
+    Logger.info("Wrote new state to file")
+  end
+end