Implemented countries host check (#5713)

* Added check and alert implementation

* Fixed size of estimation and some typo

* Added HLL counters and DES structure
Co-authored-by: Paolo Junior Mollica <p.mollica@studenti.unipi.it>

* fixes according comments of PR

* decreased memory footprint

* resolved conflicts

* fixed HostCheckID

* Removed wrongly committed file

Co-authored-by: paolo-junior-mollica <paolo.junior.mollica@gmail.com>
Co-authored-by: Matteo Biscosi <49585191+MatteoBiscosi@users.noreply.github.com>

scripts/lua/modules/alert_definitions/host/host_alert_countries_contacts.lua

@@ -0,0 +1,66 @@
+--
+-- (C) 2019-21 - ntop.org
+--
+
+-- ##############################################
+
+local host_alert_keys = require "host_alert_keys"
+package.path = dirs.installdir .. "/scripts/lua/modules/?.lua;" .. package.path
+
+local alert_creators = require "alert_creators"
+local json = require("dkjson")
+-- Import the classes library.
+local classes = require "classes"
+-- Make sure to import the Superclass!
+local alert = require "alert"
+
+-- ##############################################
+
+local host_alert_countries_contacts = classes.class(alert)
+
+-- ##############################################
+
+host_alert_countries_contacts.meta = {
+  alert_key = host_alert_keys.host_alert_countries_contacts,
+  i18n_title = "alerts_dashboard.host_alert_countries_contacts",
+  icon = "fas fa-fw fa-life-ring",
+  has_victim = true,
+}
+
+-- ##############################################
+
+-- @brief Prepare an alert table used to generate the alert
+-- @param one_param The first alert param
+-- @param another_param The second alert param
+-- @return A table with the alert built
+function host_alert_countries_contacts:init(metric, value, operator, threshold)
+   -- Call the parent constructor
+   self.super:init()
+
+   self.alert_type_params = alert_creators.createThresholdCross(metric, value, operator, threshold)
+end
+
+-- #######################################################
+
+-- @brief Format an alert into a human-readable string
+-- @param ifid The integer interface id of the generated alert
+-- @param alert The alert description table, including alert data such as the generating entity, timestamp, granularity, type
+-- @param alert_type_params Table `alert_type_params` as built in the `:init` method
+-- @return A human-readable string
+function host_alert_countries_contacts.format(ifid, alert, alert_type_params)
+  local alert_consts = require("alert_consts")
+  local entity = alert_consts.formatHostAlert(ifid, alert["ip"], alert["vlan_id"])
+  local value = alert_type_params.value
+
+  if(value == nil) then value = 0 end
+  
+  return i18n("alert_messages.host_alert_countries_contacts", {
+    entity = entity,
+    value = string.format("%u", math.ceil(value or 0)),
+    threshold = alert_type_params.threshold or 0,
+  })
+end
+
+-- #######################################################
+
+return host_alert_countries_contacts