defmodule Rolodex do
  @moduledoc """
  Rolodex generates documentation for your Phoenix API.

  Rolodex inspects a Phoenix Router and transforms the `@doc` annotations on your
  controller actions into documentation in the format of your choosing.

  `Rolodex.run/1` encapsulates the full documentation generation process. When
  invoked, it will:

  1. Traverse your Phoenix Router
  2. Collect documentation data for the API endpoints exposed by your router
  3. Serialize the data into a format of your choosing (e.g. Swagger JSON)
  4. Write the serialized data out to a destination of your choosing.

  Rolodex can be configured in the `config/` files for your Phoenix project. See
  `Rolodex.Config` for more details on configuration options.

  ## Features and resources

  - **Reusable components** - See `Rolodex.Schema` for details on how define reusable
  parameter schemas. See `Rolodex.RequestBody` for details on how to use schemas
  in your API request body definitions. See `Rolodex.Response` for details on
  how to use schemas in your API response definitions. See `Rolodex.Headers` for
  details on how to define reusable headers for your route doc annotations and your
  responses.
  - **Structured annotations** - See `Rolodex.Route` for details on how to format
  annotations on your API route action functions for the Rolodex parser to handle
  - **Generic serialization** - The `Rolodex.Processor` behaviour encapsulates
  the basic steps needed to serialize API metadata into documentation. Rolodex
  ships with a valid Swagger JSON processor (see: `Rolodex.Processors.Swagger`)
  - **Generic writing** - The `Rolodex.Writer` behaviour encapsulates the basic
  steps needed to write out formatted docs. Rolodex ships with a file writer (
  see: `Rolodex.Writers.FileWriter`)

  ## High level example

      # Your Phoenix router
      defmodule MyRouter do
        pipeline :api do
          plug MyPlug
        end

        scope "/api" do
          pipe_through [:api]

          get "/test", MyController, :index
        end
      end

      # Your controller
      defmodule MyController do
        @doc [
          auth: :BearerAuth,
          headers: ["X-Request-ID": uuid, required: true],
          query_params: [include: :string],
          path_params: [user_id: :uuid],
          body: MyRequestBody,
          responses: %{200 => MyResponse},
          metadata: [public: true],
          tags: ["foo", "bar"]
        ]
        @doc "My index action"
        def index(conn, _), do: conn
      end

      # Your request body
      defmodule MyRequestBody do
        use Rolodex.RequestBody

        request_body "MyRequestBody" do
          desc "A request body"

          content "application/json" do
            schema MySchema
            example :request, %{id: "123", name: "Ada Lovelace"}
          end
        end
      end

      # Some shared headers for your response
      defmodule RateLimitHeaders do
        use Rolodex.Headers

        headers "RateLimitHeaders" do
          header "X-Rate-Limited", :boolean, desc: "Have you been rate limited"
          header "X-Rate-Limit-Duration", :integer
        end
      end

      # Your response
      defmodule MyResponse do
        use Rolodex.Response

        response "MyResponse" do
          desc "A response"
          headers RateLimitHeaders

          content "application/json" do
            schema MySchema
            example :response, %{id: "123", name: "Ada Lovelace"}
          end
        end
      end

      # Your schema
      defmodule MySchema do
        use Rolodex.Schema

        schema "MySchema", desc: "A schema" do
          field :id, :uuid
          field :name, :string, desc: "The name"
        end
      end

      # Your Rolodex config
      defmodule MyConfig do
        use Rolodex.Config

        def spec() do
          [
            title: "MyApp",
            description: "An example",
            version: "1.0.0",
            router: MyRouter
          ]
        end

        def auth_spec() do
          [
            BearerAuth: [
              type: "http",
              scheme: "bearer"
            ]
          ]
        end

        def pipelines_spec() do
          [
            api: [
              headers: ["Include-Meta": :boolean]
            ]
          ]
        end
      end

      # In mix.exs
      config :rolodex, module: MyConfig

      # Then...
      Application.get_all_env(:rolodex)[:module]
      |> Rolodex.Config.new()
      |> Rolodex.run()

      # The JSON written out to file should look like
      %{
        "openapi" => "3.0.0",
        "info" => %{
          "title" => "MyApp",
          "description" => "An example",
          "version" => "1.0.0"
        },
        "paths" => %{
          "/api/test" => %{
            "get" => %{
              "security" => [%{"BearerAuth" => []}],
              "metadata" => %{"public" => true},
              "parameters" => [
                %{
                  "in" => "header",
                  "name" => "X-Request-ID",
                  "required" => true,
                  "schema" => %{
                    "type" => "string",
                    "format" => "uuid"
                  }
                },
                %{
                  "in" => "path",
                  "name" => "user_id",
                  "schema" => %{
                    "type" => "string",
                    "format" => "uuid"
                  }
                },
                %{
                  "in" => "query",
                  "name" => "include",
                  "schema" => %{
                    "type" => "string"
                  }
                }
              ],
              "responses" => %{
                "200" => %{
                  "$ref" => "#/components/responses/MyResponse"
                }
              },
              "requestBody" => %{
                "type" => "object",
                "properties" => %{
                  "id" => %{"type" => "string", "format" => "uuid"}
                }
              },
              "tags" => ["foo", "bar"]
            }
          }
        },
        "components" => %{
          "requestBodies" => %{
            "MyRequestBody" => %{
              "description" => "A request body",
              "content" => %{
                "application/json" => %{
                  "schema" => %{
                    "$ref" => "#/components/schemas/MySchema"
                  },
                  "examples" => %{
                    "request" => %{"id" => "123", "name" => "Ada Lovelace"}
                  }
                }
              }
            }
          },
          "responses" => %{
            "MyResponse" => %{
              "description" => "A response",
              "headers" => %{
                "X-Rate-Limited" => %{
                  "description" => "Have you been rate limited",
                  "schema" => %{
                    "type" => "string"
                  }
                },
                "X-Rate-Limit-Duration" => %{
                  "schema" => %{
                    "type" => "integer"
                  }
                }
              },
              "content" => %{
                "application/json" => %{
                  "schema" => %{
                    "$ref" => "#/components/schemas/MySchema"
                  },
                  "examples" => %{
                    "response" => %{"id" => "123", "name" => "Ada Lovelace"}
                  }
                }
              }
            }
          },
          "schemas" => %{
            "MySchema" => %{
              "type" => "object",
              "description" => "A schema",
              "properties" => %{
                "id" => %{"type" => "string", "format" => "uuid"},
                "name" => %{"type" => "string", "description" => "The name"}
              }
            }
          },
          "securitySchemes" => %{
            "BearerAuth" => %{
              "type" => "http",
              "scheme" => "bearer"
            }
          }
        }
      }
  """

  alias Rolodex.{
    Config,
    Field,
    Headers,
    RenderGroupConfig,
    RequestBody,
    Response,
    Route,
    Schema
  }

  @route_fields_with_refs [:body, :headers, :responses]
  @ref_types [:headers, :request_body, :response, :schema]

  @doc """
  Runs Rolodex and writes out documentation to the specified destination
  """
  @spec run(Rolodex.Config.t()) :: :ok | {:error, any()}
  def run(config) do
    config
    |> generate_routes()
    |> process_render_groups(config)
  end

  defp generate_routes(%Config{router: router} = config) do
    router.__routes__()
    |> Enum.map(&Route.new(&1, config))
  end

  defp process_render_groups(routes, %Config{render_groups: groups} = config) do
    Enum.map(groups, &process_render_group(routes, config, &1))
  end

  defp process_render_group(routes, config, %RenderGroupConfig{processor: processor} = group) do
    routes = filter_routes(routes, group)
    refs = generate_refs(routes)

    config
    |> processor.process(routes, refs)
    |> write(group)
  end

  defp filter_routes(routes, %RenderGroupConfig{filters: filters}) do
    Enum.reject(routes, &(&1 == nil || Route.matches_filter?(&1, filters)))
  end

  defp write(processed, %RenderGroupConfig{writer: writer, writer_opts: opts}) do
    with {:ok, device} <- writer.init(opts),
         :ok <- writer.write(device, processed),
         :ok <- writer.close(device) do
      {:ok, processed}
    else
      err -> {:error, err}
    end
  end

  # Inspects the request and response parameter data for each `Rolodex.Route`.
  # From these routes, it collects a unique list of `Rolodex.RequestBody`,
  # `Rolodex.Response`, `Rolodex.Headers`, and `Rolodex.Schema` references. The
  # serialized refs will be passed along to a `Rolodex.Processor` behaviour.
  defp generate_refs(routes) do
    Enum.reduce(
      routes,
      %{schemas: %{}, responses: %{}, request_bodies: %{}, headers: %{}},
      &refs_for_route/2
    )
  end

  defp refs_for_route(route, all_refs) do
    route
    |> unserialized_refs_for_route(all_refs)
    |> Enum.reduce(all_refs, fn
      {:schema, ref}, %{schemas: schemas} = acc ->
        %{acc | schemas: Map.put(schemas, ref, Schema.to_map(ref))}

      {:response, ref}, %{responses: responses} = acc ->
        %{acc | responses: Map.put(responses, ref, Response.to_map(ref))}

      {:request_body, ref}, %{request_bodies: request_bodies} = acc ->
        %{acc | request_bodies: Map.put(request_bodies, ref, RequestBody.to_map(ref))}

      {:headers, ref}, %{headers: headers} = acc ->
        %{acc | headers: Map.put(headers, ref, Headers.to_map(ref))}
    end)
  end

  # Looks at the route fields where users can provide refs that it now needs to
  # serialize. Performs a DFS on each field to collect any unserialized refs. We
  # look at both the refs in the maps of data, PLUS refs nested within the
  # responses/schemas themselves. We recursively traverse this graph until we've
  # collected all unseen refs for the current context.
  defp unserialized_refs_for_route(route, all_refs) do
    serialized_refs = serialized_refs_list(all_refs)

    route
    |> Map.take(@route_fields_with_refs)
    |> Enum.reduce(MapSet.new(), fn {_, field}, acc ->
      collect_unserialized_refs(field, acc, serialized_refs)
    end)
    |> Enum.to_list()
  end

  defp collect_unserialized_refs(field, result, serialized_refs) when is_map(field) do
    field
    |> Field.get_refs()
    |> Enum.reduce(result, &collect_ref(&1, &2, serialized_refs))
  end

  # Shared schemas, responses, and request bodies can each have nested refs within,
  # so we recursively collect those. Headers shouldn't have nested refs.
  defp collect_unserialized_refs(ref, result, serialized_refs) when is_atom(ref) do
    case Field.get_ref_type(ref) do
      :schema ->
        ref
        |> Schema.get_refs()
        |> Enum.reduce(result, &collect_ref(&1, &2, serialized_refs))

      :response ->
        ref
        |> Response.get_refs()
        |> Enum.reduce(result, &collect_ref(&1, &2, serialized_refs))

      :request_body ->
        ref
        |> RequestBody.get_refs()
        |> Enum.reduce(result, &collect_ref(&1, &2, serialized_refs))

      :headers ->
        result

      :error ->
        result
    end
  end

  defp collect_unserialized_refs(_, acc, _), do: acc

  # If the current schema ref is unserialized, add to the MapSet of unserialized
  # refs, and then continue the recursive traversal
  defp collect_ref(ref, result, serialized_refs) do
    ref_type = Field.get_ref_type(ref)

    cond do
      {ref_type, ref} in (Enum.to_list(result) ++ serialized_refs) ->
        result

      ref_type in @ref_types ->
        result = MapSet.put(result, {ref_type, ref})
        collect_unserialized_refs(ref, result, serialized_refs)

      true ->
        result
    end
  end

  defp serialized_refs_list(%{
         schemas: schemas,
         responses: responses,
         request_bodies: bodies,
         headers: headers
       }) do
    [schema: schemas, response: responses, request_body: bodies, headers: headers]
    |> Enum.reduce([], fn {ref_type, refs}, acc ->
      refs
      |> Map.keys()
      |> Enum.map(&{ref_type, &1})
      |> Enum.concat(acc)
    end)
  end
end