# Copyright 2019 Hubert Chathi <hubert@uhoreg.ca>
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

defmodule Polyjuice.Util.Event do
  @moduledoc """
  Event-related functions.
  """

  defmodule Module.concat(Polyjuice.Util.Event.RoomVersion, "1") do
    @moduledoc false

    # the common keys that should be kept in the top level of all events
    # (except for "content", which has special handling).
    @keys_to_keep ~w(
      event_id
      type
      room_id
      sender
      state_key
      hashes
      signatures
      depth
      prev_events
      prev_state
      auth_events
      origin
      origin_server_ts
      membership
    )

    def redact(event) do
      redacted_no_content = Map.take(event, @keys_to_keep)

      with {:ok, content} <- Map.fetch(event, "content"),
           {:ok, type} <- Map.fetch(event, "type") do
        content_keys_to_keep =
          case type do
            "m.room.member" ->
              ~w(membership)

            "m.room.create" ->
              ~w(creator)

            "m.room.join_rules" ->
              ~w(join_rule)

            "m.room.power_levels" ->
              ~w(ban events events_default kick redact state_default users users_default)

            "m.room.aliases" ->
              ~w(aliases)

            "m.room.history_visibility" ->
              ~w(history_visibility)

            _ ->
              []
          end

        Map.put(
          redacted_no_content,
          "content",
          Map.take(content, content_keys_to_keep)
        )
      else
        _ -> redacted_no_content
      end
    end
  end

  defmodule Module.concat(Polyjuice.Util.Event.RoomVersion, "2") do
    @moduledoc false
    defdelegate redact(event), to: Module.concat(Polyjuice.Util.Event.RoomVersion, "1")
  end

  defmodule Module.concat(Polyjuice.Util.Event.RoomVersion, "3") do
    @moduledoc false
    defdelegate redact(event), to: Module.concat(Polyjuice.Util.Event.RoomVersion, "1")
  end

  defmodule Module.concat(Polyjuice.Util.Event.RoomVersion, "4") do
    @moduledoc false
    defdelegate redact(event), to: Module.concat(Polyjuice.Util.Event.RoomVersion, "1")
  end

  defmodule Module.concat(Polyjuice.Util.Event.RoomVersion, "5") do
    @moduledoc false
    defdelegate redact(event), to: Module.concat(Polyjuice.Util.Event.RoomVersion, "1")
  end

  @doc ~S"""
  Calculate the redacted version of an event for the given room version.

  Examples:

      iex> Polyjuice.Util.Event.redact(
      ...>   "1",
      ...>   %{
      ...>     "content" => %{
      ...>       "body" => "Here is the message content"
      ...>     },
      ...>     "event_id" => "$0:domain",
      ...>     "origin" => "domain",
      ...>     "origin_server_ts" => 1000000,
      ...>     "type" => "m.room.message",
      ...>     "room_id" => "!r:domain",
      ...>     "sender" => "@u:domain",
      ...>     "signatures" => %{},
      ...>     "unsigned" => %{
      ...>       "age_ts" => 1000000
      ...>     }
      ...>   }
      ...> )
      {
        :ok,
        %{
          "content" => %{},
          "event_id" => "$0:domain",
          "origin" => "domain",
          "origin_server_ts" => 1000000,
          "type" => "m.room.message",
          "room_id" => "!r:domain",
          "sender" => "@u:domain",
          "signatures" => %{}
        }
      }

      iex> Polyjuice.Util.Event.redact(
      ...>   "unknown room version",
      ...>   %{}
      ...> )
      :error
  """
  @spec redact(room_version :: String.t(), event :: map) :: {:ok, map} | :error
  def redact(room_version, event) when is_binary(room_version) and is_map(event) do
    try do
      module = Module.safe_concat(Polyjuice.Util.Event.RoomVersion, room_version)
      {:ok, apply(module, :redact, [event])}
    rescue
      _ -> :error
    end
  end
end