opencadc_registry_client

defmodule OpencadcRegistryClient do
  @moduledoc """
  IVOA compliant Registry client to lookup service URL endpoints.
  """

  @doc """
  Lookup the URL that can be used to obtain the Capabilities ASCII document.  Specify the REGISTRY_ENDPOINT_HOST 
  environment variable as <http(s)://myhost.com> or leave the default to use the CADC's Production host address.
  This assumes that the host will support the /reg/resource-caps endpoint.

  Capability XML document specification here: http://www.ivoa.net/xml/VOSICapabilities/v1.0
  Sample CADC document containing Capabilities URLs: http://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/reg/resource-caps

  Returns a string URL.

    ## Examples

      iex> OpencadcRegistryClient.lookupCapabilitiesURL("ivo://cadc.nrc.ca/vospace")
      "http://www.canfar.phys.uvic.ca/vospace/capabilities"

  @param  resourceURI   The Resource URI to use to lookup the URL.
  """
  def lookupCapabilitiesURL(resourceURI) do
    registryEntries(
      System.get_env("REGISTRY_ENDPOINT_HOST") || "http://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca"
    )
    |> handleResponse(resourceURI)
  end

  @doc """
  Lookup the Service URL to be used to issue requests to.  This function will navigate the Capabilities XML document
  and pull the appropriate public (non-secure) service URL.

  Capability XML document specification here: http://www.ivoa.net/xml/VOSICapabilities/v1.0
  Sample CADC document containing Capabilities URLs: http://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/reg/resource-caps

  Returns a string URL.

    ## Examples

      iex> OpencadcRegistryClient.lookupServiceURL("ivo://cadc.nrc.ca/vospace", "ivo://ivoa.net/std/VOSpace/v2.0#nodes", "vs:ParamHTTP")
      "http://www.canfar.phys.uvic.ca/vospace/nodes"

  @param  resourceURI   The Resource URI to use to lookup the Capabilities URL.
  @param  standardURI   The Standard URI identified on the capability.
  @param  xsiType       The XSI value used in the capability's interface attribute.
  """
  def lookupServiceURL(resourceURI, standardURI, xsiType) do
    with capResponse = lookupCapabilitiesURL(resourceURI) |> HTTPoison.get!() do
      Parser.all(
        Parser.from_string(capResponse.body),
        "//capability[@standardID=\"" <>
          standardURI <>
          "\"]/interface[@xsi:type=\"" <> xsiType <> "\"][not(securityMethod)]/accessURL"
      )
      |> extractServiceURL
    end
  end

  @doc """
  Lookup the Service URL to be used to issue requests to.  This function will navigate the Capabilities XML document
  and pull the appropriate public secure service URL.  The 

  Capability XML document specification here: http://www.ivoa.net/xml/VOSICapabilities/v1.0
  Sample CADC document containing Capabilities URLs: http://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/reg/resource-caps

  Returns a string URL.

    ## Examples

      iex> OpencadcRegistryClient.lookupServiceURL("ivo://cadc.nrc.ca/vospace", "ivo://ivoa.net/std/VOSpace/v2.0#nodes", "vs:ParamHTTP", "ivo://ivoa.net/sso#tls-with-certificate")
      "https://www.canfar.phys.uvic.ca/vospace/nodes"

  @param  resourceURI   The Resource URI to use to lookup the Capabilities URL.
  @param  standardURI   The Standard URI identified on the capability.
  @param  xsiType       The XSI value used in the capability's interface attribute.
  @param  securityURI   The URI identifying what kind of security to use.  Valid values are 
  """
  def lookupServiceURL(resourceURI, standardURI, xsiType, securityURI) do
    with capResponse = lookupCapabilitiesURL(resourceURI) |> HTTPoison.get!(),
         capabilitiesURL = capResponse.body do
      Parser.all(
        Parser.from_string(capabilitiesURL),
        "//capability[@standardID=\"" <>
          standardURI <>
          "\"]/interface[@xsi:type=\"" <>
          xsiType <> "\"][securityMethod[@standardID=\"" <> securityURI <> "\"]]/accessURL"
      )
      |> extractServiceURL
    end
  end

  defp registryEntries(host) do
    (host <> "/reg/resource-caps") |> HTTPoison.get!()
  end

  defp extractCapabilitiesURL([]) do
    raise ArgumentError, message: "No capabilities found"
  end

  defp extractCapabilitiesURL(capabilities) do
    capabilities |> Enum.at(0) |> String.split("=") |> Enum.at(1) |> String.trim()
  end

  defp handleResponse(%HTTPoison.Response{status_code: 200} = response, resourceURI) do
    response.body
    |> String.split("\n", trim: true)
    |> Enum.filter(fn str -> String.starts_with?(str, resourceURI) == true end)
    |> extractCapabilitiesURL
  end

  defp handleResponse(response, _) do
    raise ArgumentError,
      message: "Unable to query service registry: Response code " <> response.status_code
  end

  defp extractServiceURL([]) do
    raise ArgumentError, message: "No service endpoints found"
  end

  defp extractServiceURL(endpoints) do
    endpoints |> Enum.at(0) |> Parser.text()
  end
end