defmodule EctoCommons.URLValidator do
  @moduledoc ~S"""
  This validator is used to validate URLs.

  ## Options
  There are some available options depending on the strictness of what you want to validate:

    - `:parsable`: Checks to see if the URL is parsable by `:http_uri.parse/1` Erlang function.
       This can have issues with international URLs where it should be disabled (see tests). Defaults to enabled
    - `:empty`: Checks to see if the parsed `%URI{}` struct is not empty (all fields set to nil). Defaults to enabled
    - `:scheme`: Checks to see if the parsed `%URI{}` struct contains a `:scheme`. Defaults to enabled
    - `:host`: Checks to see if the parsed `%URI{}` struct contains a `:host`. Defaults to enabled
    - `:valid_host`: Does a `:inet.getbyhostname/1` call to check if the host exists. Defaults to disabled
    - `:path`: Checks to see if the parsed `%URI{}` struct contains a `:path`. Defaults to disabled
    - `:regexp`: Tries to match URL to a regexp known to catch many unwanted URLs (see below). Defaults to disabled

  The approach is not yet very satisfactory IMHO, if you have suggestions, Pull Requests are welcome :)

  ## Example:

      iex> types = %{url: :string}
      iex> params = %{url: "https://www.example.com/"}
      iex> Ecto.Changeset.cast({%{}, types}, params, Map.keys(types))
      ...> |> validate_url(:url)
      #Ecto.Changeset<action: nil, changes: %{url: "https://www.example.com/"}, errors: [], data: %{}, valid?: true>

      iex> types = %{url: :string}
      iex> params = %{url: "https://www.example.com/"}
      iex> Ecto.Changeset.cast({%{}, types}, params, Map.keys(types))
      ...> |> validate_url(:url, checks: [:empty, :path, :scheme, :host])
      #Ecto.Changeset<action: nil, changes: %{url: "https://www.example.com/"}, errors: [], data: %{}, valid?: true>

      iex> types = %{url: :string}
      iex> params = %{url: "some@invalid_url"}
      iex> Ecto.Changeset.cast({%{}, types}, params, Map.keys(types))
      ...> |> validate_url(:url)
      #Ecto.Changeset<action: nil, changes: %{url: "some@invalid_url"}, errors: [url: {"is not a valid url", [validation: :url]}], data: %{}, valid?: false>

      iex> types = %{url: :string}
      iex> params = %{url: "Just some random text"}
      iex> Ecto.Changeset.cast({%{}, types}, params, Map.keys(types))
      ...> |> validate_url(:url)
      #Ecto.Changeset<action: nil, changes: %{url: "Just some random text"}, errors: [url: {"is not a valid url", [validation: :url]}], data: %{}, valid?: false>

  """

  import Ecto.Changeset

  # Taken from here https://mathiasbynens.be/demo/url-regex
  # credo:disable-for-next-line Credo.Check.Readability.MaxLineLength
  @url_regex ~r/^(?:(?:https?|ftp):\/\/)(?:\S+(?::\S*)?@)?(?:(?!10(?:\.\d{1,3}){3})(?!127(?:\.\d{1,3}){3})(?!169\.254(?:\.\d{1,3}){2})(?!192\.168(?:\.\d{1,3}){2})(?!172\.(?:1[6-9]|2\d|3[0-1])(?:\.\d{1,3}){2})(?:[1-9]\d?|1\d\d|2[01]\d|22[0-3])(?:\.(?:1?\d{1,2}|2[0-4]\d|25[0-5])){2}(?:\.(?:[1-9]\d?|1\d\d|2[0-4]\d|25[0-4]))|(?:(?:[a-z\x{00a1}-\x{ffff}0-9]+-?)*[a-z\x{00a1}-\x{ffff}0-9]+)(?:\.(?:[a-z\x{00a1}-\x{ffff}0-9]+-?)*[a-z\x{00a1}-\x{ffff}0-9]+)*(?:\.(?:[a-z\x{00a1}-\x{ffff}]{2,})))(?::\d{2,5})?(?:\/[^\s]*)?$/ius

  def validate_url(changeset, field, opts \\ []) do
    validate_change(changeset, field, {:url, opts}, fn _, value ->
      checks = Keyword.get(opts, :checks, [:parsable, :empty, :scheme, :host])
      parsed = URI.parse(value)

      case do_validate_url(value, parsed, checks) do
        :ok -> []
        :error -> [{field, {message(opts, "is not a valid url"), [validation: :url]}}]
      end
    end)
  end

  defp do_validate_url(value, parsed, checks) when is_list(checks) do
    check_all = Enum.map(checks, fn check -> do_validate_url(value, parsed, check) end)

    if Enum.member?(check_all, :error), do: :error, else: :ok
  end

  defp do_validate_url(value, _parsed, :parsable) do
    case :http_uri.parse(String.to_charlist(value)) do
      {:ok, _uri} -> :ok
      {:error, _msg} -> :error
    end
  end

  defp do_validate_url(value, _parsed, :regexp) do
    case String.match?(value, @url_regex) do
      true -> :ok
      false -> :error
    end
  end

  # Caution: this check does a network call and can be slow.
  defp do_validate_url(_value, %URI{host: host}, :valid_host) do
    case :inet.gethostbyname(String.to_charlist(host)) do
      {:ok, _value} -> :ok
      {:error, :nxdomain} -> :error
    end
  end

  defp do_validate_url(_value, parsed, :empty) do
    values = parsed |> Map.from_struct() |> Enum.map(fn {_key, val} -> blank?(val) end)

    if Enum.member?(values, false), do: :ok, else: :error
  end

  defp do_validate_url(_value, %URI{path: path} = _parsed, :path) do
    if blank?(path), do: :error, else: :ok
  end

  defp do_validate_url(_value, %URI{scheme: scheme} = _parsed, :scheme) do
    if blank?(scheme), do: :error, else: :ok
  end

  defp do_validate_url(_value, %URI{host: host} = _parsed, :host) do
    if blank?(host), do: :error, else: :ok
  end

  defp message(opts, key \\ :message, default) do
    Keyword.get(opts, key, default)
  end

  @compile {:inline, blank?: 1}
  def blank?(""), do: true
  def blank?([]), do: true
  def blank?(nil), do: true
  def blank?({}), do: true
  def blank?(%{} = map) when map_size(map) == 0, do: true
  def blank?(_), do: false
end