# Copyright(c) 2015-2023 ACCESS CO., LTD. All rights reserved.

use Croma
alias Croma.Result, as: R

defmodule AntikytheraAws.Ec2.ClusterConfiguration do
  @behaviour AntikytheraEal.ClusterConfiguration.Behaviour

  alias Antikythera.Httpc
  require AntikytheraCore.Logger, as: L

  @region Application.fetch_env!(:antikythera_aws, :region)
  @auto_scaling_group_name Application.fetch_env!(:antikythera_aws, :auto_scaling_group_name)
  @availability_zone_metadata_url "http://169.254.169.254/latest/meta-data/placement/availability-zone"

  @impl true
  defun running_hosts() :: R.t(%{String.t() => boolean}) do
    run_cli(
      [
        "autoscaling",
        "describe-auto-scaling-groups",
        "--auto-scaling-group-names",
        @auto_scaling_group_name
      ],
      fn j1 ->
        id_status_map = make_id_status_map(j1)

        run_cli(
          ["ec2", "describe-instances", "--instance-ids" | Map.keys(id_status_map)],
          fn j2 ->
            make_id_private_dns_name_map(j2)
            |> Map.new(fn {id, dns_name} -> {dns_name, Map.fetch!(id_status_map, id)} end)
            |> R.pure()
          end
        )
      end
    )
  end

  defp run_cli(args, f) do
    args_all = ["--region", @region | args]

    case System.cmd("aws", args_all, stderr_to_stdout: true) do
      {json, 0} ->
        f.(Jason.decode!(json))

      {output, _nonzero} ->
        L.error("aws-cli with args #{inspect(args_all)} returned nonzero status: #{output}")
        {:error, :script_error}
    end
  end

  defp make_id_status_map(decoded) do
    decoded
    |> Map.fetch!("AutoScalingGroups")
    # Only 1 auto scaling group name is given to aws-cli describe-auto-scaling-groups command
    |> hd()
    |> Map.fetch!("Instances")
    |> Enum.filter(fn %{"HealthStatus" => s} -> s == "Healthy" end)
    |> Map.new(fn %{"InstanceId" => id, "LifecycleState" => state} ->
      {id, state == "InService"}
    end)
  end

  defp make_id_private_dns_name_map(decoded) do
    decoded
    |> Map.fetch!("Reservations")
    |> Enum.flat_map(fn %{"Instances" => is} -> is end)
    |> Map.new(fn %{"InstanceId" => id, "PrivateDnsName" => name} -> {id, name} end)
    |> Enum.reject(fn {_id, name} -> String.length(name) == 0 end)
  end

  @impl true
  defun zone_of_this_host() :: String.t() do
    %Httpc.Response{body: body} = Httpc.get!(@availability_zone_metadata_url)
    body
  end

  @default_health_check_grace_period 300

  @impl true
  defun health_check_grace_period_in_seconds() :: non_neg_integer do
    run_cli(
      [
        "autoscaling",
        "describe-auto-scaling-groups",
        "--auto-scaling-group-names",
        @auto_scaling_group_name
      ],
      fn j ->
        Map.fetch!(j, "AutoScalingGroups")
        # Only 1 auto scaling group name is given to aws-cli describe-auto-scaling-groups command
        |> hd()
        |> Map.fetch!("HealthCheckGracePeriod")
      end
    )
    |> case do
      {:error, :script_error} ->
        msg =
          "Failed to fetch the health check grace period by aws-cli describe-auto-scaling-groups command," <>
            " so the default value: #{@default_health_check_grace_period} will be used"

        L.error(msg)
        @default_health_check_grace_period

      health_check_grace_period ->
        health_check_grace_period
    end
  end
end