defmodule ServerWeb.OverviewLive do
  use ServerWeb, :live_view

  alias Server.{Hosts, Metrics, Status}

  @impl true
  def mount(_params, _session, socket) do
    if connected?(socket), do: Phoenix.PubSub.subscribe(Server.PubSub, "metrics")
    {:ok, assign(socket, hosts: load_hosts(), page_title: "Overview")}
  end

  @impl true
  def handle_info({:metric_inserted, _host_id, _interval}, socket) do
    {:noreply, assign(socket, :hosts, load_hosts())}
  end

  defp load_hosts do
    for host <- Hosts.list_all() do
      sample = Metrics.latest_sample(host.id, "fast")
      payload = sample && sample.payload
      %{host: host, sample: sample, status: Status.compute(host.status, payload)}
    end
  end

  @impl true
  def render(assigns) do
    ~H"""
    <ServerWeb.DashboardNav.nav active={:overview} />

    <div class="page">
      <div class="pagehead">
        <h1>Hosts</h1>
        <span class="sub">{summary_line(@hosts)}</span>
      </div>

      <div :if={@hosts == []} class="panel">
        <div class="empty">
          No hosts registered. Add one at
          <.link navigate={~p"/admin/hosts"}>/admin/hosts</.link>.
        </div>
      </div>

      <div class="cards">
        <.link :for={entry <- @hosts} navigate={~p"/hosts/#{entry.host.name}"} class="card"
              data-status={Atom.to_string(entry.status)} data-role="host-card">
          <div class="row">
            <span class="name">{entry.host.name}</span>
            <span class="right badge" data-status={Atom.to_string(entry.status)}>
              {entry.status}
            </span>
          </div>
          <div class="seen">last seen {last_seen(entry.host.last_seen_at)}</div>
          <%= if entry.sample do %>
            <div class="stat"><span class="k">load</span><span class="v">{load(entry.sample.payload)}</span></div>
            <div class="stat"><span class="k">ram</span><span class="v">{mem(entry.sample.payload)}</span></div>
            <div class="stat"><span class="k">pools</span><span class="v">{pool_summary(entry.sample.payload)}</span></div>
            <div class="stat"><span class="k">vms</span><span class="v">{vm_count(entry.sample.payload)}</span></div>
          <% else %>
            <div class="dim">no samples yet</div>
          <% end %>
        </.link>
      </div>
    </div>
    """
  end

  defp summary_line([]), do: "0 hosts"
  defp summary_line(hosts) do
    n = length(hosts)
    by = Enum.frequencies_by(hosts, & &1.status)
    parts =
      [:ok, :warning, :critical, :offline]
      |> Enum.filter(&Map.has_key?(by, &1))
      |> Enum.map(fn s -> "#{by[s]} #{s}" end)
    "#{n} host#{if n == 1, do: "", else: "s"} · " <> Enum.join(parts, " · ")
  end

  defp last_seen(nil), do: "never"
  defp last_seen(%DateTime{} = dt) do
    secs = DateTime.diff(DateTime.utc_now(), dt, :second)
    cond do
      secs < 60 -> "#{secs}s ago"
      secs < 3600 -> "#{div(secs, 60)}m ago"
      true -> "#{div(secs, 3600)}h ago"
    end
  end

  defp load(payload) do
    case get_in(payload, ["host", "load1"]) do
      nil -> "—"
      l -> :io_lib.format("~.2f", [l]) |> to_string()
    end
  end

  defp mem(payload) do
    used = get_in(payload, ["host", "mem_used_bytes"])
    total = get_in(payload, ["host", "mem_total_bytes"])
    case {used, total} do
      {u, t} when is_integer(u) and is_integer(t) and t > 0 ->
        "#{Float.round(u / t * 100, 1)}%"
      _ -> "—"
    end
  end

  defp pool_summary(payload) do
    pools = get_in(payload, ["zfs_pools", "pools"]) || []
    total = length(pools)
    bad = Enum.count(pools, &(&1["health"] != "ONLINE"))
    if total == 0, do: "—", else: "#{total - bad}/#{total}"
  end

  defp vm_count(payload) do
    vms = get_in(payload, ["vms_runtime", "vms"]) || []
    length(vms) |> to_string()
  end
end