Reworks plugin loading and structure

Implements #4358

scripts/plugins/alerts/internals/slow_purge/user_scripts/interface/slow_purge.lua

@@ -0,0 +1,78 @@
+--
+-- (C) 2019-20 - ntop.org
+--
+
+local alerts_api = require("alerts_api")
+local alert_consts = require("alert_consts")
+local user_scripts = require("user_scripts")
+
+-- #################################################################
+
+local function check_interface_idle(params)
+  local threshold = tonumber(params.user_script_config.threshold)
+  local engage = false
+  local max_idle = 0
+  local max_idle_perc = 0
+
+  local hash_tables_stats = interface.getHashTablesStats()
+  for ht_name, ht_stats in pairsByKeys(hash_tables_stats, asc) do
+    local idle = ht_stats["hash_entry_states"]["hash_entry_state_idle"] or "0"
+    local active = ht_stats["hash_entry_states"]["hash_entry_state_active"] or "0"
+    local idle_perc = math.min(idle * 100.0 / (idle + active + 1), 100)
+    if (idle + active) > 1000 and idle_perc > threshold then
+      if idle_perc > max_idle_perc then
+        max_idle = idle
+        max_idle_perc = idle_perc
+      end
+    end
+  end
+
+  local idle_type = alert_consts.alert_types.alert_slow_purge.create(
+     alert_consts.alert_severities.warning,
+     alert_consts.alerts_granularities.min,
+     max_idle,
+     max_idle_perc,
+     threshold
+  )
+
+  if max_idle_perc > threshold then
+    alerts_api.trigger(params.alert_entity, idle_type, nil, params.cur_alerts)
+  else
+    alerts_api.release(params.alert_entity, idle_type, nil, params.cur_alerts)
+  end
+end
+
+-- #################################################################
+
+local script = {
+  -- Script category
+  category = user_scripts.script_categories.internals,
+
+  default_enabled = true,
+  default_value = {
+    -- "> 50%"
+    operator = "gt",
+    threshold = 50,
+  },
+
+  -- This script is only for alerts generation
+  is_alert = true,
+
+  hooks = {
+    min = check_interface_idle,
+  },
+
+  gui = {
+    i18n_title = "alerts_thresholds_config.alert_slow_purge_threshold",
+    i18n_description = "alerts_thresholds_config.alert_slow_purge_threshold_descr",
+    i18n_field_unit = user_scripts.field_units.percentage,
+    input_builder = "threshold_cross",
+    field_max = 99,
+    field_min = 1,
+    field_operator = "gt";
+  }
+}
+
+-- #################################################################
+
+return script