# 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.Client.Endpoint do
  defmodule HttpSpec do
    @typedoc """
    The description of how to handle the endpoint.

    - `method` is the HTTP verb
    - `headers` is a list of the HTTP headers
    - `path` is the path of the endpoint, relative to the homeserver's base URL
    - `query` is an enumerable of `{key, value}` tuples giving the query parameters
    - `body` is the HTTP body (if any) as a binary, or `{:file, filename}`
    - `transform` is a function to transform the result (status code, headers,
      content) to a return value
    - `auth_required` indicates whether the end point requires authentication
    """
    @type t :: %__MODULE__{
            method: atom,
            path: String.t(),
            headers: [{String.t(), String.t()}],
            query: Keyword.t(),
            body: iodata() | {:file, String.t()} | {Enumerable.t(), integer},
            auth_required: boolean,
            stream_response: boolean
          }
    @enforce_keys [:method, :path, :headers]
    defstruct [
      :method,
      :path,
      :headers,
      :query,
      body: "",
      auth_required: true,
      stream_response: false
    ]

    @doc "The r0 client URL prefix"
    def prefix_r0, do: "_matrix/client/r0"
    @doc "The unstable client URL prefix"
    def prefix_unstable, do: "_matrix/client/unstable"
    @doc "The r0 media URL prefix"
    def prefix_media_r0, do: "_matrix/media/r0"

    @doc "Headers for endpoints that accept JSON."
    def accept_json,
      do: [
        {"Accept", "application/json"},
        {"Accept-Encoding", "gzip, deflate"}
      ]

    @doc "Headers for endpoints that send and accept JSON."
    def send_json,
      do: [
        {"Accept", "application/json"},
        {"Accept-Encoding", "gzip, deflate"},
        {"Content-Type", "application/json"}
      ]

    @doc """
    Create a `GET` request.

    `prefix` is a prefix for the path.  It can be one of `r0` (indicating
    `_matrix/client/r0`), `unstable` (indicating `_matrix/client/unstable`),
    `media_r0` (indicating `_matrix/media/r0`), or a string giving any other
    prefix.

    `opts` is a keyword list giving any of the other parameters for `Polyjuice.Client.Endpoint.HttpSpec.t()`.

    """
    def get(prefix, path, opts \\ []) when is_binary(path) and is_list(opts) do
      create(:get, prefix, path, accept_json(), opts)
    end

    @doc """
    Create a `POST` request.

    See `get/3`.
    """
    def post(prefix, path, opts \\ []) when is_binary(path) and is_list(opts) do
      create(:post, prefix, path, send_json(), opts)
    end

    @doc """
    Create a `PUT` request.

    See `get/3`.
    """
    def put(prefix, path, opts \\ []) when is_binary(path) and is_list(opts) do
      create(:put, prefix, path, send_json(), opts)
    end

    @doc """
    Create a `DELETE` request.

    See `get/3`.
    """
    def delete(prefix, path, opts \\ []) when is_binary(path) and is_list(opts) do
      create(:delete, prefix, path, accept_json(), opts)
    end

    defp create(method, prefix, path, default_headers, opts) do
      prefix =
        case prefix do
          :r0 -> Polyjuice.Client.Endpoint.HttpSpec.prefix_r0()
          :unstable -> Polyjuice.Client.Endpoint.HttpSpec.prefix_unstable()
          :media_r0 -> Polyjuice.Client.Endpoint.HttpSpec.prefix_media_r0()
          p when is_binary(p) -> String.trim_leading(p, "/")
        end

      path = if String.starts_with?(path, "/"), do: [path], else: ["/", path]

      %Polyjuice.Client.Endpoint.HttpSpec{
        method: method,
        headers: Keyword.get(opts, :headers, default_headers),
        path: IO.iodata_to_binary([prefix, path]),
        query: Keyword.get(opts, :query, nil),
        body: Keyword.get(opts, :body, ""),
        auth_required: Keyword.get(opts, :auth_required, true),
        stream_response: Keyword.get(opts, :stream_response, false)
      }
    end
  end

  defprotocol Proto do
    @moduledoc """
    Matrix client endpoint.
    """

    @doc """
    Generate the spec for calling the endpoint via HTTP.
    """
    @spec http_spec(endpoint_args :: __MODULE__.t()) :: Polyjuice.Client.Endpoint.HttpSpec.t()
    def http_spec(endpoint_args)

    @doc """
    Transform the HTTP result into a return value.
    """
    @spec transform_http_result(
            endpoint_args :: __MODULE__.t(),
            status_code :: integer(),
            headers :: [{String.t(), String.t()}, ...],
            body :: String.t()
          ) :: any
    def transform_http_result(endpoint_args, status_code, headers, body)
  end

  defprotocol BodyParser do
    @fallback_to_any true
    @spec parse(endpoint_args :: __MODULE__.t(), body :: any) :: any
    def parse(endpoint_args, body)
  end

  defimpl BodyParser, for: Any do
    def parse(_endpoint_args, body), do: {:ok, body}
  end

  @spec parse_response(
          endpoint_args :: map,
          status_code :: integer(),
          headers :: [{String.t(), String.t()}, ...],
          body :: String.t()
        ) :: any
  def parse_response(%{} = endpoint_args, status_code, headers, body)
      when is_integer(status_code) and is_list(headers) and is_binary(body) do
    {:ok, decoded_body} = content_decode(body, headers)
    # make sure it's JSON content
    with "application/json" <- get_header(headers, "content-type"),
         {:ok, json} <- Jason.decode(decoded_body) do
      case status_code do
        200 ->
          Polyjuice.Client.Endpoint.BodyParser.parse(endpoint_args, json)

        _ ->
          {:error, status_code, json}
      end
    else
      _ ->
        {:error, if(status_code == 200, do: 500, else: status_code),
         %{"errcode" => "CA_UHOREG_POLYJUICE_BAD_RESPONSE", "body" => decoded_body}}
    end
  end

  @spec get_header(
          headers :: list({String.t(), String.t()}),
          name :: String.t(),
          default :: any
        ) :: any
  def get_header(headers, name, default \\ nil) do
    name = String.downcase(name, :ascii)

    {_, value} =
      Enum.find(
        headers,
        {nil, default},
        fn {n, _} -> String.downcase(n, :ascii) == name end
      )

    value
  end

  def content_decode(encoded, headers) do
    case get_header(headers, "content-encoding", "identity") do
      "identity" ->
        {:ok, encoded}

      "gzip" ->
        {:ok, :zlib.gunzip(encoded)}

      "deflate" ->
        {:ok, :zlib.uncompress(encoded)}

      "x-gzip" ->
        {:ok, :zlib.gunzip(encoded)}

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