defmodule NLdoc.Ecto.Validator.URI do
  @moduledoc """
  Validator for URI's.

  ## Example

      defmodule User do
        use Ecto.Schema

        import NLdoc.Ecto.Validator.URI, only: [:validate_uri: 3]

        schema "users" do
          field :name, :string
          field :profile_url, :string
        end

        def changeset(user, params) do
          user
          |> Ecto.Changeset.cast(params, [:name, :profile_url])
          |> validate_uri(:profile_url, schemes: ["https"])
        end
      end
  """

  @type validate_url_opt() :: {:schemes, [String.t()]}

  @spec validate_uri(
          changeset :: Ecto.Changeset.t(),
          field :: atom(),
          opts :: [validate_url_opt()]
        ) :: Ecto.Changeset.t()
  def validate_uri(changeset, field, opts \\ []) do
    allowed_schemes = Keyword.get(opts, :schemes, [])

    Ecto.Changeset.validate_change(
      changeset,
      field,
      fn ^field, value ->
        case do_validate_uri(value, allowed_schemes) do
          :ok -> []
          {:error, reason} -> [{field, reason}]
        end
      end
    )
  end

  @spec do_validate_uri(value :: binary(), allowed_schemes :: [String.t()]) ::
          :ok | {:error, String.t()}
  def do_validate_uri(value, allowed_schemes) when is_binary(value) do
    case URI.new(value) do
      {:ok, %URI{scheme: scheme}} ->
        cond do
          is_nil(scheme) ->
            {:error, "must have scheme"}

          Enum.empty?(allowed_schemes) ->
            :ok

          Enum.member?(allowed_schemes, scheme) ->
            :ok

          true ->
            {:error, "has invalid scheme"}
        end

      {:error, _} ->
        {:error, "must be a URI"}
    end
  end
end