defmodule Defdo.Cloudflare.Monitor do
  @moduledoc """
  Keep watching the ip
  """
  require Logger
  import Defdo.Cloudflare.DDNS
  use GenServer

  defmodule State do
    @moduledoc false
    defstruct refetch_every: nil
  end

  # server
  @impl true
  def init(%State{} = state) do
    {:ok, state, {:continue, :start_monitor}}
  end

  @impl true
  def handle_continue(:start_monitor, state) do
    execute_monitor()
    Process.send_after(self(), :keep_monitoring, state.refetch_every)

    {:noreply, state}
  end

  @impl true
  def handle_call(:checkup, _from, state) do
    result = execute_monitor()

    {:reply, result, state}
  end

  @impl true
  def handle_info(:keep_monitoring, state) do
    execute_monitor()
    Process.send_after(self(), :keep_monitoring, state.refetch_every)

    {:noreply, state}
  end

  # client
  def start_link(state \\ []) do
    refetch_every = Keyword.get(state, :refetch_every, :timer.minutes(5))
    GenServer.start_link(__MODULE__, %State{refetch_every: refetch_every}, name: __MODULE__)
  end

  def checkup do
    GenServer.call(__MODULE__, :checkup)
  end

  def checkup_once do
    execute_monitor()
  end

  defp execute_monitor do
    Logger.info("Executing checkup...")

    get_all_cloudflare_config_domains()
    |> Enum.map(&safe_process/1)
  rescue
    error ->
      # Second line of defence. A checkup must never take the monitor down: the
      # supervisor would restart it straight into the same failing call and, after
      # the restart intensity is exhausted, shut the whole application down. A
      # failed checkup is logged and retried on the next tick instead.
      message = "Error - checkup aborted: #{Exception.message(error)}"
      Logger.error(message)
      [message]
  end

  defp safe_process(domain) do
    process(domain)
  rescue
    error ->
      message = "Error - checkup failed for domain=#{domain}: #{Exception.message(error)}"
      Logger.error(message)
      [message]
  end

  defp process(domain) do
    Logger.info("Processing domain: #{domain}")
    zone_id = get_zone_id(domain)

    if is_nil(zone_id) do
      message = "Error - unable to resolve Cloudflare zone id for domain=#{domain}"
      Logger.error(message)
      [message]
    else
      a_records_to_monitor =
        if domain_configured?(domain, :domain_mappings) do
          records_to_monitor(domain, :domain_mappings)
        else
          []
        end

      aaaa_records_to_monitor =
        if domain_configured?(domain, :aaaa_domain_mappings) do
          records_to_monitor(domain, :aaaa_domain_mappings)
        else
          []
        end

      a_record_name_set = MapSet.new(a_records_to_monitor)
      aaaa_record_name_set = MapSet.new(aaaa_records_to_monitor)

      local_ipv4 =
        if MapSet.size(a_record_name_set) > 0 do
          get_current_ipv4()
        else
          nil
        end

      local_ipv6 =
        if MapSet.size(aaaa_record_name_set) > 0 do
          get_current_ipv6()
        else
          nil
        end

      if MapSet.size(a_record_name_set) > 0 and is_nil(local_ipv4) do
        Logger.error("Unable to detect public IPv4 address; A records cannot be synchronized")
      end

      if MapSet.size(aaaa_record_name_set) > 0 and is_nil(local_ipv6) do
        Logger.warning(
          "Unable to detect public IPv6 address; AAAA records will be skipped for this cycle"
        )
      end

      configured_cname_records = get_cname_records_for_domain(domain)
      cname_record_names = configured_cname_records |> Enum.map(& &1["name"]) |> MapSet.new()

      dns_records_to_monitor =
        a_records_to_monitor
        |> Kernel.++(aaaa_records_to_monitor)
        |> Kernel.++(MapSet.to_list(cname_record_names))
        |> Enum.uniq()

      auto_create_missing_records = get_cloudflare_key(:auto_create_missing_records)

      # Note: Making separate API calls for each DNS record due to Cloudflare API deprecation
      # of comma-separated name filtering (deprecated 2025-02-21)
      online_dns_records =
        dns_records_to_monitor
        |> Enum.flat_map(fn record_name ->
          records = list_dns_records(zone_id, name: record_name)

          created_records =
            maybe_create_missing_ip_records(
              zone_id,
              record_name,
              records,
              local_ipv4,
              local_ipv6,
              a_record_name_set,
              aaaa_record_name_set,
              cname_record_names,
              auto_create_missing_records
            )

          records ++ created_records
        end)

      ip_dns_records =
        online_dns_records
        |> Enum.filter(&(&1["type"] in ~w(A AAAA)))

      ip_result =
        ip_dns_records
        |> input_for_update_dns_records(%{"A" => local_ipv4, "AAAA" => local_ipv6})
        |> Enum.map(fn input ->
          {success, result} = apply_update(zone_id, input)

          message =
            if success do
              "Success - #{result["name"]} DNS record updated (ip=#{result["content"]}, proxied=#{result["proxied"]})"
            else
              "Error - #{inspect(input)}"
            end

          if success do
            Logger.info(message)
          else
            Logger.error(message)
          end

          message
        end)

      cname_result = sync_cname_records(zone_id, configured_cname_records)
      result = ip_result ++ cname_result

      # Re-read records after updates to evaluate final state.
      final_dns_records =
        dns_records_to_monitor
        |> Enum.flat_map(fn record_name -> list_dns_records(zone_id, name: record_name) end)
        |> Enum.filter(&(&1["type"] in ~w(A AAAA CNAME)))

      log_advanced_certificate_warnings(domain, final_dns_records)

      ssl_mode = get_zone_ssl_mode(zone_id)
      expected_proxied = get_cloudflare_key(:proxy_a_records, false)
      posture = evaluate_domain_posture(final_dns_records, ssl_mode, expected_proxied)
      posture_message = log_domain_posture(domain, posture)

      result =
        if result == [] do
          message = "Nothing to do"
          Logger.info(message)

          [message, posture_message]
        else
          result ++ [posture_message]
        end

      Logger.info("Checkup completed")

      result
    end
  end

  defp create_missing_ip_records(
         zone_id,
         record_name,
         local_ipv4,
         local_ipv6,
         a_record_name_set,
         aaaa_record_name_set,
         existing_records
       ) do
    proxied = get_cloudflare_key(:proxy_a_records, false)
    ttl = if proxied, do: 1, else: 300

    existing_record_types =
      existing_records
      |> Enum.map(&Map.get(&1, "type", ""))
      |> MapSet.new()

    record_types_to_create =
      []
      |> maybe_add_missing_record_type(
        "A",
        record_name,
        a_record_name_set,
        local_ipv4,
        existing_record_types
      )
      |> maybe_add_missing_record_type(
        "AAAA",
        record_name,
        aaaa_record_name_set,
        local_ipv6,
        existing_record_types
      )

    Enum.flat_map(record_types_to_create, fn {record_type, record_ip} ->
      Logger.info("Creating missing DNS record: #{record_type} #{record_name}")

      record_data = %{
        "type" => record_type,
        "name" => record_name,
        "content" => record_ip,
        "ttl" => ttl,
        "proxied" => proxied
      }

      case create_dns_record(zone_id, record_data) do
        {true, result} ->
          Logger.info(
            "Created DNS record: #{record_type} #{record_name} with promotional comment"
          )

          [result]

        {false, _} ->
          Logger.error("Failed to create DNS record: #{record_type} #{record_name}")
          []
      end
    end)
  end

  defp maybe_add_missing_record_type(
         acc,
         record_type,
         record_name,
         monitored_names,
         detected_ip,
         existing_record_types
       ) do
    if MapSet.member?(monitored_names, record_name) and
         not MapSet.member?(existing_record_types, record_type) do
      if is_binary(detected_ip) and detected_ip != "" do
        [{record_type, detected_ip} | acc]
      else
        Logger.warning(
          "Skipping #{record_type} auto-create for #{record_name}: no detected #{record_type} public address"
        )

        acc
      end
    else
      acc
    end
  end

  defp maybe_create_missing_ip_records(
         zone_id,
         record_name,
         records,
         local_ipv4,
         local_ipv6,
         a_record_name_set,
         aaaa_record_name_set,
         cname_record_names,
         auto_create_missing_records
       ) do
    cond do
      MapSet.member?(cname_record_names, record_name) ->
        if Enum.empty?(records) do
          Logger.warning("DNS record '#{record_name}' not found in Cloudflare")

          Logger.info(
            "Skipping A auto-create for '#{record_name}' because it is managed as CNAME"
          )
        end

        []

      Enum.empty?(records) and auto_create_missing_records ->
        Logger.warning("DNS record '#{record_name}' not found in Cloudflare")

        create_missing_ip_records(
          zone_id,
          record_name,
          local_ipv4,
          local_ipv6,
          a_record_name_set,
          aaaa_record_name_set,
          records
        )

      Enum.empty?(records) ->
        Logger.warning("DNS record '#{record_name}' not found in Cloudflare")
        Logger.info("Set AUTO_CREATE_DNS_RECORDS=true to auto-create missing records")
        []

      not auto_create_missing_records ->
        []

      Enum.any?(records, &(&1["type"] == "CNAME")) ->
        Logger.warning(
          "Skipping A/AAAA auto-create for '#{record_name}': CNAME record already exists"
        )

        []

      true ->
        create_missing_ip_records(
          zone_id,
          record_name,
          local_ipv4,
          local_ipv6,
          a_record_name_set,
          aaaa_record_name_set,
          records
        )
    end
  end

  defp sync_cname_records(_zone_id, []), do: []

  defp sync_cname_records(zone_id, desired_cname_records) do
    desired_cname_records
    |> Enum.flat_map(&sync_cname_record(zone_id, &1))
  end

  defp sync_cname_record(zone_id, desired_record) do
    record_name = desired_record["name"]
    existing_records = list_dns_records(zone_id, name: record_name)
    cname_records = Enum.filter(existing_records, &(&1["type"] == "CNAME"))
    conflicting_records = Enum.reject(existing_records, &(&1["type"] == "CNAME"))

    cond do
      conflicting_records != [] ->
        conflicting_types =
          conflicting_records
          |> Enum.map(& &1["type"])
          |> Enum.uniq()
          |> Enum.join(",")

        message =
          "Error - cannot manage CNAME #{record_name}: conflicting DNS record type(s) exist (#{conflicting_types})"

        Logger.error(message)
        [message]

      cname_records == [] ->
        case create_dns_record(zone_id, desired_record) do
          {true, result} ->
            message =
              "Success - #{result["name"]} CNAME record created (target=#{result["content"]}, proxied=#{result["proxied"]})"

            Logger.info(message)
            [message]

          {false, _} ->
            message = "Error - failed to create CNAME record: #{record_name}"
            Logger.error(message)
            [message]
        end

      true ->
        cname_records
        |> input_for_update_cname_records(desired_record)
        |> Enum.map(fn input ->
          {success, result} = apply_update(zone_id, input)

          message =
            if success do
              "Success - #{result["name"]} CNAME record updated (target=#{result["content"]}, proxied=#{result["proxied"]})"
            else
              "Error - #{inspect(input)}"
            end

          if success do
            Logger.info(message)
          else
            Logger.error(message)
          end

          message
        end)
    end
  end

  defp log_domain_posture(domain, posture) do
    status = posture.overall |> to_string() |> String.upcase()

    summary =
      "[HEALTH][#{status}] domain=#{domain} ssl_mode=#{posture.ssl_mode} edge_tls=#{posture.edge_tls} " <>
        "proxied=#{posture.proxied_count}/#{posture.records_total} dns_only=#{posture.dns_only_count} " <>
        "proxy_mismatch=#{posture.proxy_mismatch_count} hairpin_risk=#{posture.hairpin_risk}"

    case posture.overall do
      :green ->
        Logger.info(summary)

      :yellow ->
        Logger.warning(
          summary <> " recommendation=Use Full (strict) and proxied records for web apps"
        )

      :red ->
        Logger.error(summary <> " recommendation=Set Cloudflare SSL/TLS mode to Full (strict)")
    end

    summary
  end

  defp log_advanced_certificate_warnings(domain, records) do
    deep_hosts =
      records
      |> Enum.map(&Map.get(&1, "name"))
      |> Enum.reject(&is_nil/1)
      |> Enum.filter(&requires_advanced_certificate?(&1, domain))
      |> Enum.uniq()

    proxied_deep_hosts =
      records
      |> Enum.filter(
        &(Map.get(&1, "proxied", false) and requires_advanced_certificate?(&1["name"], domain))
      )
      |> Enum.map(& &1["name"])
      |> Enum.uniq()

    excluded_deep_hosts =
      deep_hosts
      |> Enum.filter(&proxy_excluded?/1)
      |> Enum.uniq()

    if proxied_deep_hosts != [] do
      Logger.warning(
        "[CERT][ACM] domain=#{domain} proxied_hosts=#{Enum.join(proxied_deep_hosts, ",")} " <>
          "may not be covered by Cloudflare Universal SSL and can require Advanced Certificate Manager."
      )
    end

    if excluded_deep_hosts != [] do
      Logger.warning(
        "[CERT][ACM] domain=#{domain} excluded_hosts=#{Enum.join(excluded_deep_hosts, ",")} " <>
          "matched CLOUDFLARE_PROXY_EXCLUDE; keeping DNS only helps avoid edge TLS handshake failures without Advanced Certificate Manager."
      )
    end
  end
end