Refactor as per Rin's suggestions, add endpoint tests

lib/pleroma/thread_mute.ex

@@ -0,0 +1,45 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.ThreadMute do
+  use Ecto.Schema
+  alias Pleroma.{Repo, User, ThreadMute}
+  require Ecto.Query
+
+  schema "thread_mutes" do
+    belongs_to(:user, User, type: Pleroma.FlakeId)
+    field(:context, :string)
+  end
+
+  def changeset(mute, params \\ %{}) do
+    mute
+    |> Ecto.Changeset.cast(params, [:user_id, :context])
+    |> Ecto.Changeset.foreign_key_constraint(:user_id)
+    |> Ecto.Changeset.unique_constraint(:user_id, name: :unique_index)
+  end
+
+  def query(user_id, context) do
+    user_id = Pleroma.FlakeId.from_string(user_id)
+
+    ThreadMute
+    |> Ecto.Query.where(user_id: ^user_id)
+    |> Ecto.Query.where(context: ^context)
+  end
+
+  def add_mute(user_id, context) do
+    %ThreadMute{}
+    |> changeset(%{user_id: user_id, context: context})
+    |> Repo.insert()
+  end
+
+  def remove_mute(user_id, context) do
+    query(user_id, context)
+    |> Repo.delete_all()
+  end
+
+  def check_muted(user_id, context) do
+    query(user_id, context)
+    |> Repo.all()
+  end
+end