defmodule Waffle.Storage.Google.CloudStorage do
  @moduledoc """
  The main storage integration for Waffle, this acts primarily as a wrapper
  around `Google.Api.Storage.V1`. To use this module with Waffle, simply set
  your `:storage` config appropriately:

  ```elixir
  config :waffle, storage: Waffle.Storage.Google.CloudStorage
  ```

  Ensure you have a valid bucket set, either through the configs or as an
  environment variable, otherwise all calls will fail. The credentials available
  through `Goth` must have the appropriate level of access to the bucket,
  otherwise some (or all) calls may fail.
  """

  @full_control_scope "https://www.googleapis.com/auth/devstorage.full_control"

  alias GoogleApi.Storage.V1.Connection
  alias GoogleApi.Storage.V1.Api.Objects
  alias GoogleApi.Storage.V1.Model.Object
  alias Waffle.Storage.Google.Util
  alias Waffle.Types

  @type object_or_error :: {:ok, GoogleApi.Storage.V1.Model.Object.t} | {:error, Tesla.Env.t}

  @doc """
  Put a Waffle file in a Google Cloud Storage bucket.
  """
  @spec put(Types.definition, Types.version, Types.meta) :: object_or_error
  def put(definition, version, meta) do
    path = path_for(definition, version, meta)
    acl = definition.acl(version, meta)
    insert(conn(), bucket(definition), path, data(meta), acl)
  end

  @doc """
  Delete a file from a Google Cloud Storage bucket.
  """
  @spec put(Types.definition, Types.version, Types.meta) :: object_or_error
  def delete(definition, version, meta) do
    Objects.storage_objects_delete(
      conn(),
      bucket(definition),
      path_for(definition, version, meta)
    )
  end

  @doc """
  Retrieve the public URL for a file in a Google Cloud Storage bucket. Uses
  `Waffle.Storage.Google.UrlV2` by default, which uses v2 signing if a signed
  URL is requested, but this can be overriden in the options list or in the
  application configs by setting `:url_builder` to any module that imlements the
  behavior of `Waffle.Storage.Google.Url`.
  """
  @spec url(Types.definition, Types.version, Types.meta, Keyword.t) :: String.t
  def url(definition, version, meta, opts \\ []) do
    signer = Util.option(opts, :url_builder, Waffle.Storage.Google.UrlV2)
    signer.build(definition, version, meta, opts)
  end

  @doc """
  Constructs a new connection object with scoped authentication. If no scope is
  provided, the `devstorage.full_control` scope is used as a default.
  """
  @spec conn(String.t) :: Tesla.Env.client
  def conn(scope \\ @full_control_scope) do
    {:ok, token} = Goth.Token.for_scope(scope)
    Connection.new(token.token)
  end

  @doc """
  Returns the bucket for file uploads.
  """
  @spec bucket(Types.definition) :: String.t
  def bucket(definition), do: Util.var(definition.bucket())

  @doc """
  Returns the storage directory **within a bucket** to store the file under.
  """
  @spec storage_dir(Types.definition, Types.version, Types.meta) :: String.t
  def storage_dir(definition, version, meta) do
    version
    |> definition.storage_dir(meta)
    |> Util.var()
  end

  @doc """
  Returns the full file path for the upload destination.
  """
  @spec path_for(Types.definition, Types.version, Types.meta) :: String.t
  def path_for(definition, version, meta) do
    definition
    |> storage_dir(version, meta)
    |> Path.join(definition.filename(version, meta))
  end

  @spec data(Types.file) :: {:file | :binary, String.t}
  defp data({%{binary: nil, path: path}, _}), do: {:file, path}
  defp data({%{binary: data}, _}), do: {:binary, data}

  @spec insert(Tesla.Env.client, String.t, String.t, {:file | :binary, String.t}, String.t) :: object_or_error
  defp insert(conn, bucket, name, {:file, path}, acl) do
    Objects.storage_objects_insert_simple(
      conn,
      bucket,
      "multipart",
      %Object{name: name, acl: acl},
      path
    )
  end
  defp insert(conn, bucket, name, {:binary, data}, acl) do
    Util.storage_objects_insert_binary(
      conn,
      bucket,
      %Object{name: name, acl: acl},
      data
    )
  end
end