defmodule Tower.Slack.Client do
  def deliver(message) do
    post(webhook_url(), message)
  end

  defp post(url, payload) when is_map(payload) do
    :httpc.request(
      :post,
      {
        ~c"#{url}",
        [],
        ~c"application/json",
        Jason.encode!(payload)
      },
      [
        ssl: tls_client_options()
      ],
      []
    )
  end

  defp tls_client_options do
    [
      verify: :verify_peer,
      cacerts: :public_key.cacerts_get(),
      # Support wildcard certificates
      customize_hostname_check: [
        match_fun: :public_key.pkix_verify_hostname_match_fun(:https)
      ]
    ]
  end

  defp webhook_url do
    Application.fetch_env!(:tower_slack, :webhook_url)
  end
end