feat(server): pure Status.compute/2 for ok/warning/critical/offline

server/lib/server/status.ex

@@ -0,0 +1,41 @@
+defmodule Server.Status do
+  @moduledoc """
+  Derive a status level for a host from its latest fast sample.
+    :offline   host has no active agent connection
+    :critical  pool DEGRADED/FAULTED or capacity > 90
+    :warning   capacity 80..90 or pending OS updates
+    :ok        everything nominal
+  """
+
+  @bad_pool_states ~w(DEGRADED FAULTED SUSPENDED UNAVAIL)
+
+  @spec compute(String.t(), map() | nil) :: :offline | :critical | :warning | :ok
+  def compute(host_status, _payload) when host_status in ~w(offline never_connected),
+    do: :offline
+
+  def compute(_host_status, nil), do: :ok
+
+  def compute(_host_status, %{} = payload) do
+    pools = get_in(payload, ["zfs_pools", "pools"]) || []
+    pending = get_in(payload, ["system_info", "pending_updates"]) || 0
+
+    cond do
+      Enum.any?(pools, &critical_pool?/1) -> :critical
+      Enum.any?(pools, &warning_pool?/1) -> :warning
+      pending > 0 -> :warning
+      true -> :ok
+    end
+  end
+
+  defp critical_pool?(pool) do
+    health = pool["health"]
+    cap = pool["capacity_percent"] || 0
+
+    health in @bad_pool_states or cap > 90
+  end
+
+  defp warning_pool?(pool) do
+    cap = pool["capacity_percent"] || 0
+    cap >= 80 and cap <= 90
+  end
+end