# Copyright 2021 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.URI do
  @doc """
  Functions for using Matrix URIs

  Supports `matrix.to`, `matrix:`, and `mxc:` URIs, and supports referencing
  users, rooms (by ID or alias), events (using room ID or room alias), and
  media (`mxc:` URIs only).

  """

  import URI, only: [encode_www_form: 1]

  @typedoc """
  For users, room IDs and room aliases, `identifier` is a string.  For events,
  it is of the form `{room_id_or_alias, event_id}`.  And for media, it is of the
  form `{server, id}`.

  """
  @type t() :: %__MODULE__{
          type: :user | :event | :event_by_room_alias | :room_id | :room_alias | :media,
          identifier: String.t() | {String.t(), String.t()},
          query_params: list({String.t(), String.t()})
        }
  @enforce_keys [:type, :identifier]
  defstruct [:type, :identifier, query_params: []]

  @doc ~S"""
  Parse a Matrix URI.

  ## Examples

      iex> Polyjuice.Util.URI.parse("matrix:u/hubert:uhoreg.ca")
      {:ok, %Polyjuice.Util.URI{
         type: :user,
         identifier: "@hubert:uhoreg.ca",
         query_params: []
      }}

      iex> Polyjuice.Util.URI.parse("https://matrix.to/#/%40hubert:uhoreg.ca")
      {:ok, %Polyjuice.Util.URI{
         type: :user,
         identifier: "@hubert:uhoreg.ca",
         query_params: []
      }}
  """
  @spec parse(uri :: String.t() | URI.t()) :: {:ok, Polyjuice.Util.URI.t()} | {:error, atom}
  def parse(uri) when is_binary(uri) do
    parse(URI.parse(uri))
  end

  def parse(%URI{scheme: "mxc", host: host, path: path}) do
    path = String.trim_leading(path, "/")

    {:ok,
     %Polyjuice.Util.URI{
       type: :media,
       identifier: {host, URI.decode(path)},
       query_params: []
     }}
  end

  def parse(%URI{scheme: scheme, host: "matrix.to", fragment: fragment})
      when scheme == "https" or scheme == "http" do
    fragment = String.trim_leading(fragment, "/")

    {location, query} =
      case String.split(fragment, "?", parts: 2) do
        [l, q] -> {l, URI.query_decoder(q) |> Enum.to_list()}
        [l] -> {l, []}
      end

    location =
      case location do
        <<?%, esc_sigil::binary-size(2), rest::binary>> ->
          <<String.to_integer(esc_sigil, 16), rest::binary>>

        _ ->
          location
      end

    case location do
      <<?@, _rest::binary>> ->
        {:ok,
         %Polyjuice.Util.URI{
           type: :user,
           identifier: URI.decode(location),
           query_params: query
         }}

      <<?\#, _rest::binary>> ->
        case String.split(location, "/", parts: 2) do
          [_] ->
            {:ok,
             %Polyjuice.Util.URI{
               type: :room_alias,
               identifier: URI.decode(location),
               query_params: query
             }}

          [room, event] ->
            {:ok,
             %Polyjuice.Util.URI{
               type: :event_by_room_alias,
               identifier: {URI.decode(room), URI.decode(event)},
               query_params: query
             }}
        end

      <<?!, _rest::binary>> ->
        case String.split(location, "/", parts: 2) do
          [_] ->
            {:ok,
             %Polyjuice.Util.URI{
               type: :room_id,
               identifier: URI.decode(location),
               query_params: query
             }}

          [room, event] ->
            {:ok,
             %Polyjuice.Util.URI{
               type: :event,
               identifier: {URI.decode(room), URI.decode(event)},
               query_params: query
             }}
        end

      _ ->
        {:error, :unknown_sigil}
    end
  end

  def parse(%URI{scheme: "matrix", path: path, query: query}) do
    [type, identifier | rest] = String.split(path, "/")
    query = if query, do: URI.query_decoder(query) |> Enum.to_list(), else: []

    case type do
      "u" ->
        if rest == [] do
          {:ok,
           %Polyjuice.Util.URI{
             type: :user,
             identifier: "@" <> URI.decode(identifier),
             query_params: query
           }}
        else
          {:error, :unknown_format}
        end

      "r" ->
        case rest do
          ["e", event] ->
            {:ok,
             %Polyjuice.Util.URI{
               type: :event_by_room_alias,
               identifier: {"#" <> URI.decode(identifier), "$" <> URI.decode(event)},
               query_params: query
             }}

          [] ->
            {:ok,
             %Polyjuice.Util.URI{
               type: :room_alias,
               identifier: "#" <> URI.decode(identifier),
               query_params: query
             }}

          _ ->
            {:error, :unknown_format}
        end

      "roomid" ->
        case rest do
          ["e", event] ->
            {:ok,
             %Polyjuice.Util.URI{
               type: :event,
               identifier: {"!" <> URI.decode(identifier), "$" <> URI.decode(event)},
               query_params: query
             }}

          [] ->
            {:ok,
             %Polyjuice.Util.URI{
               type: :room_id,
               identifier: "!" <> URI.decode(identifier),
               query_params: query
             }}

          _ ->
            {:error, :unknown_format}
        end

      _ ->
        {:error, :unknown_format}
    end
  end

  def parse(_, _) do
    {:error, :unknown_format}
  end

  @doc ~S"""
  Generate a Matrix URI.

  `format` indicates what URI format to generate.  Currently, it defaults to
  `matrix_to`; in the future when the `matrix` format is supported by more
  clients, the default may change to that.  If you require a certain format,
  you should specify it rather than relying on the default behaviour.  `:media`
  URIs will always be `mxc:` URIs, regardless of the `format`.

  ## Examples

      iex> Polyjuice.Util.URI.to_string(
      ...>   %Polyjuice.Util.URI{type: :user, identifier: "@hubert:uhoreg.ca"},
      ...>   :matrix
      ...> )
      "matrix:u/hubert%3Auhoreg.ca"

      iex> Polyjuice.Util.URI.to_string(
      ...>   %Polyjuice.Util.URI{type: :user, identifier: "@hubert:uhoreg.ca"},
      ...>   :matrix_to
      ...> )
      "https://matrix.to/#/%40hubert%3Auhoreg.ca"
  """
  @spec to_string(uri :: Polyjuice.Util.URI.t(), format :: :matrix | :matrix_to | nil) ::
          String.t()
  def to_string(uri, format \\ :matrix_to)

  def to_string(%Polyjuice.Util.URI{} = uri, nil) do
    Polyjuice.Util.URI.to_string(uri, :matrix_to)
  end

  def to_string(%Polyjuice.Util.URI{type: :media, identifier: {server, id}}, _)
      when is_binary(server) and is_binary(id) do
    "mxc://#{encode_www_form(server)}/#{encode_www_form(id)}"
  end

  def to_string(%Polyjuice.Util.URI{} = uri, :matrix) do
    query_part =
      case uri.query_params do
        nil -> ""
        [] -> ""
        x when is_list(x) -> [??, URI.encode_query(uri.query_params)]
      end

    case uri do
      %{type: :user, identifier: <<?@, unprefixed::binary>>} ->
        "matrix:u/#{URI.encode_www_form(unprefixed)}#{query_part}"

      %{
        type: :event,
        identifier: {<<?!, unprefixed_room::binary>>, <<?$, unprefixed_event::binary>>}
      } ->
        "matrix:roomid/#{URI.encode_www_form(unprefixed_room)}/e/#{
          URI.encode_www_form(unprefixed_event)
        }#{query_part}"

      %{
        type: type,
        identifier: {<<?\#, unprefixed_room::binary>>, <<?$, unprefixed_event::binary>>}
      }
      when type == :event or type == :event_by_room_alias ->
        "matrix:r/#{URI.encode_www_form(unprefixed_room)}/e/#{
          URI.encode_www_form(unprefixed_event)
        }#{query_part}"

      %{type: :room_id, identifier: <<?!, unprefixed_room::binary>>} ->
        "matrix:roomid/#{URI.encode_www_form(unprefixed_room)}#{query_part}"

      %{type: :room_alias, identifier: <<?\#, unprefixed_room::binary>>} ->
        "matrix:r/#{URI.encode_www_form(unprefixed_room)}#{query_part}"
    end
  end

  def to_string(%Polyjuice.Util.URI{} = uri, :matrix_to) do
    query_part =
      case uri.query_params do
        nil -> ""
        [] -> ""
        x when is_list(x) -> [??, URI.encode_query(uri.query_params)]
      end

    case uri.identifier do
      identifier when is_binary(identifier) ->
        "https://matrix.to/#/#{URI.encode_www_form(identifier)}#{query_part}"

      {first, second} ->
        "https://matrix.to/#/#{URI.encode_www_form(first)}/#{URI.encode_www_form(second)}#{
          query_part
        }"
    end
  end

  defimpl String.Chars do
    def to_string(uri) do
      Polyjuice.Util.URI.to_string(uri)
    end
  end
end