--
-- (C) 2021-22 - ntop.org
--
-- Module to keep things in common across alert_store of various type

local dirs = ntop.getDirs()

-- Import the classes library.
local classes = require "classes"
require "lua_utils"
local json = require "dkjson"
local format_utils = require "format_utils"
local alert_consts = require "alert_consts"
local alert_utils = require "alert_utils"
local alert_severities = require "alert_severities"
local alert_roles = require "alert_roles"
local tag_utils = require "tag_utils"
local alert_entities = require "alert_entities"

-- ##############################################

local alert_store = classes.class()

-- ##############################################

local EARLIEST_AVAILABLE_EPOCH_CACHE_KEY = "ntopng.cache.alerts.ifid_%d.table_%s.status_%d.earliest_available_epoch"

-- Default number of time slots to be returned when aggregating by time
local NUM_TIME_SLOTS = 31
local TOP_LIMIT = 10

local user = "no_user"

if (_SESSION) and (_SESSION["user"]) then
    user = _SESSION["user"]
end

local ALERT_SORTING_ORDER = "ntopng.cached.alert.%s.%s.sort_order.%s"
local ALERT_SORTING_COLUMN = "ntopng.cached.alert.%s.%s.sort_column.%s"

local CSV_SEPARATOR = "|"

-- ##############################################

function alert_store:init(args)
   self._group_by = nil
   self._top_limit = TOP_LIMIT

   -- Note: _where contains conditions for the where clause.
   -- Example:
   -- {
   --   -- List of items
   --   'alert_id' = { 
   --     all = {
   --       -- List of AND conditions
   --       {
   --         field = 'alert_id',
   --         op = 'neq',
   --         value = 1,
   --         value_type = 'number', -- default: string
   --         sql = 'alert_id = 1', -- special conditions only
   --       }
   --     },
   --     any = {
   --       -- List of OR conditions
   --     } 
   --   }
   -- }
   self._where = {}

   -- tprint(debug.traceback())
end

-- ##############################################

function alert_store:_escape(str)
   if not str then
      return ""
   end

   str = str:gsub("'", "''")
   if(str == '\\') then str = '' end

   return str
end

-- ##############################################

--@brief Converts interface IDs into their database type
--       Normal interface IDs are untouched.
--       The system interface ID is converted from -1 to (u_int16_t)-1 to handle everything as unsigned integer
function alert_store:_convert_ifid(ifid)
   -- The system interface ID becomes (u_int16_t)-1
   return 0xFFFF & tonumber(ifid)
end

-- ##############################################

--@brief Check if the submitted fields are avalid (i.e., they are not injection attempts)
function alert_store:_valid_fields(fields)
   local f = fields:split(",") or { fields }

   for _, field in pairs(f) do
      -- only allow alphanumeric characters and underscores
      if not string.match(field, "^[%w_(*) ]+$") then
	 traceError(TRACE_ERROR, TRACE_CONSOLE, string.format("Invalid field found in query [%s]", field:gsub('%W','') --[[ prevent stored injections --]]))
	 return false
      end
   end

   return true
end

-- ##############################################

--@brief Return the alert family name
function alert_store:get_family()
   local family_name

   if self._alert_entity then
      family_name = self._alert_entity.alert_store_name
   end

   return family_name
end

-- ##############################################

--@brief Add filters on status (engaged, historical, or acknowledged, one of `alert_consts.alert_status`)
--@param status A key of `alert_consts.alert_status`
--@return True if set is successful, false otherwise
function alert_store:add_status_filter(status)
   if not self._status then
      if alert_consts.alert_status[status] then
	 self._status = alert_consts.alert_status[status].alert_status_id

	 -- Engaged alerts don't add a database filter as they are in-memory only
	 if status ~= "engaged" then
	    self:add_filter_condition_raw('alert_status',
					  string.format(" alert_status = %u ", self._status))
	 end
      end

      return true
   end

   return false
end

-- ##############################################

--@brief Add filters on time
--@param epoch_begin The start timestamp
--@param epoch_end The end timestamp
--@return True if set is successful, false otherwise
function alert_store:add_time_filter(epoch_begin, epoch_end)
   if not self._epoch_begin and 
      tonumber(epoch_begin) and 
      tonumber(epoch_end) then

      self._epoch_begin = tonumber(epoch_begin)
      self._epoch_end = tonumber(epoch_end)

      self:add_filter_condition_raw('tstamp',
        string.format("tstamp >= %u AND tstamp <= %u", self._epoch_begin, self._epoch_end))
   end

   return true
end

-- ##############################################

function alert_store:build_sql_cond(cond)
   if cond.sql then
      return cond.sql -- special condition
   end

   local sql_cond

   local sql_op = tag_utils.tag_operators[cond.op]

   -- Special case: l7_proto
   if cond.field == 'l7_proto' and cond.value ~= 0 then
      -- Search also in l7_master_proto, unless value is 0 (Unknown)
      sql_cond = string.format("(l7_proto %s %u %s l7_master_proto %s %u)",
         sql_op, cond.value, ternary(cond.op == 'neq', 'AND', 'OR'), sql_op, cond.value)
   
   -- Special case: ip (with vlan)
   elseif cond.field == 'ip' or
          cond.field == 'cli_ip' or 
          cond.field == 'srv_ip' then
      local host = hostkey2hostinfo(cond.value)
      if not isEmptyString(host["host"]) then
         if not host["vlan"] or host["vlan"] == 0 then
            if cond.field == 'ip' and self._alert_entity == alert_entities.flow then
               sql_cond = string.format("(%s %s '%s' %s %s %s '%s')",
                  'cli_ip', sql_op, cond.value,
                  ternary(cond.op == 'neq', 'AND', 'OR'), 
                  'srv_ip', sql_op, cond.value)
            else
               sql_cond = string.format("%s %s '%s'", cond.field, sql_op, cond.value)
            end
         else
            if cond.field == 'ip' and self._alert_entity == alert_entities.flow then
               sql_cond = string.format("((%s %s '%s' %s %s %s '%s') %s vlan_id %s %u)",
                  'cli_ip', sql_op, host["host"], 
                  ternary(cond.op == 'neq', 'AND', 'OR'),
                  'srv_ip', sql_op, host["host"], 
                  ternary(cond.op == 'neq', 'OR', 'AND'), sql_op, host["vlan"])
            else
               sql_cond = string.format("(%s %s '%s' %s vlan_id %s %u)", cond.field, sql_op, host["host"], ternary(cond.op == 'neq', 'OR', 'AND'), sql_op, host["vlan"])
            end
         end
      end

   -- Special case: role (host)
   elseif cond.field == 'host_role' then
      if cond.value == 'attacker' then
         sql_cond = "is_attacker = 1"
      elseif cond.value == 'victim' then
         sql_cond = "is_victim = 1"
      else -- 'no_attacker_no_victim'
         sql_cond = "(is_attacker = 0 AND is_victim = 0)"
      end

   -- Special case: role (flow)
   elseif cond.field == 'flow_role' then
      if cond.value == 'attacker' then
         sql_cond = "(is_cli_attacker = 1 OR is_srv_attacker = 1)"
      elseif cond.value == 'victim' then
         sql_cond = "(is_cli_victim = 1 OR is_srv_victim = 1)"
      else -- 'no_attacker_no_victim'
         sql_cond = "(is_cli_attacker = 0 AND is_srv_attacker = 0 AND is_srv_victim = 0 AND is_cli_victim = 0)"
      end

   -- Special case: role_cli_srv)
   elseif cond.field == 'role_cli_srv' then
      if cond.value == 'client' then
         sql_cond = "is_client = 1"
      else -- 'server'
         sql_cond = "is_server = 1"
      end

   -- Number
   elseif cond.value_type == 'number' then
     sql_cond = string.format("%s %s %u", cond.field, sql_op, cond.value)

   -- String
   else
     sql_cond = string.format("%s %s '%s'", cond.field, sql_op, cond.value)
   end

   return sql_cond
end

-- ##############################################

--@brief Build where string from filters
--@return the where condition in SQL syntax
function alert_store:build_where_clause()
   local where_clause = ""
   local and_clauses = {}
   local or_clauses = {}

   for name, groups in pairs(self._where) do
     -- Build AND clauses for all fields
     for _, cond in ipairs(groups.all) do
        local sql_cond = self:build_sql_cond(cond)

        if and_clauses[name] then
           and_clauses[name] = and_clauses[name] .. " AND " .. sql_cond
        else
           and_clauses[name] = sql_cond
        end
     end

     -- Build OR clauses for all fields
     for _, cond in ipairs(groups.any) do
        local sql_cond = self:build_sql_cond(cond)

        if or_clauses[name] then
           or_clauses[name] = or_clauses[name] .. " OR " .. sql_cond
        else
           or_clauses[name] = sql_cond
        end
     end
   end

   -- Join all groups
  
   -- AND groups
   for name, clause in pairs(and_clauses) do
      if isEmptyString(where_clause) then
         where_clause = "(" .. clause .. ")"
      else
         where_clause = where_clause .. " AND " .. "(" .. clause .. ")"
      end
   end

   -- OR groups
   for name, clause in pairs(or_clauses) do
      if isEmptyString(where_clause) then
         where_clause = "(" .. clause .. ")"
      else
         where_clause = where_clause .. " AND " .. "(" .. clause .. ")"
      end
   end

   if isEmptyString(where_clause) then
      where_clause = "1 = 1"
   end

   -- tprint(where_clause)

   return where_clause
end

-- ##############################################

--@brief Filter (engaged) alerts in lua) evaluating self:_where conditions
function alert_store:eval_alert_cond(alert, cond)

   -- Special case: l7_proto
   if cond.field == 'l7_proto' and cond.value ~= 0 then
      -- Search also in l7_master_proto, unless value is 0 (Unknown)
      if cond.op == 'neq' then
         return tag_utils.eval_op(alert['l7_proto'], cond.op, cond.value) and 
                tag_utils.eval_op(alert['l7_master_proto'], cond.op, cond.value)
      else
         return tag_utils.eval_op(alert['l7_proto'], cond.op, cond.value) or 
                tag_utils.eval_op(alert['l7_master_proto'], cond.op, cond.value)
      end

   -- Special case: ip (with vlan)
   elseif cond.field == 'ip' or
          cond.field == 'cli_ip' or
          cond.field == 'srv_ip' then
      local host = hostkey2hostinfo(cond.value)
      if not isEmptyString(host["host"]) then
         if not host["vlan"] or host["vlan"] == 0 then
            if cond.field == 'ip' and self._alert_entity == alert_entities.flow then
               return tag_utils.eval_op(alert['cli_ip'], cond.op, host["host"]) or
                      tag_utils.eval_op(alert['srv_ip'], cond.op, host["host"])
            else
               return tag_utils.eval_op(alert[cond.field], cond.op, host["host"])
            end
         else
            if cond.op == 'neq' then
               if cond.field == 'ip' and self._alert_entity == alert_entities.flow then
                  return tag_utils.eval_op(alert['cli_ip'], cond.op, host["host"]) or
                         tag_utils.eval_op(alert['srv_ip'], cond.op, host["host"]) or
                         tag_utils.eval_op(alert['vlan_id'], cond.op, host["vlan"])
               else
                  return tag_utils.eval_op(alert[cond.field], cond.op, host["host"]) or
                         tag_utils.eval_op(alert['vlan_id'], cond.op, host["vlan"])
               end
            else
               if cond.field == 'ip' and self._alert_entity == alert_entities.flow then
                  return (tag_utils.eval_op(alert['cli_ip'], cond.op, host["host"]) or
                          tag_utils.eval_op(alert['srv_ip'], cond.op, host["host"])) and
                         tag_utils.eval_op(alert['vlan_id'], cond.op, host["vlan"])
               else
                  return tag_utils.eval_op(alert[cond.field], cond.op, host["host"]) and
                         tag_utils.eval_op(alert['vlan_id'], cond.op, host["vlan"])
               end
            end
         end
      end

   -- Special case: role (host)
   elseif cond.field == 'host_role' then
      if cond.value == 'attacker' then
         return tag_utils.eval_op(alert['is_attacker'], cond.op, 1)
      elseif cond.value == 'victim' then
         return tag_utils.eval_op(alert['is_victim'], cond.op, 1)
      else -- 'no_attacker_no_victim'
         return tag_utils.eval_op(alert['is_attacker'], cond.op, 0) and
                tag_utils.eval_op(alert['is_victim'], cond.op, 0)
      end

   -- Special case: role (flow)
   elseif cond.field == 'flow_role' then
      if cond.value == 'attacker' then
         return tag_utils.eval_op(alert['is_cli_attacker'], cond.op, 1) or
                tag_utils.eval_op(alert['is_srv_attacker'], cond.op, 1)
      elseif cond.value == 'victim' then
         return tag_utils.eval_op(alert['is_cli_victim'], cond.op, 1) or
                tag_utils.eval_op(alert['is_srv_victim'], cond.op, 1)
      else -- 'no_attacker_no_victim'
         return tag_utils.eval_op(alert['is_cli_attacker'], cond.op, 0) and
                tag_utils.eval_op(alert['is_srv_attacker'], cond.op, 0) and
                tag_utils.eval_op(alert['is_cli_victim'], cond.op, 0) and
                tag_utils.eval_op(alert['is_srv_victim'], cond.op, 0)
      end

   -- Special case: role_cli_srv)
   elseif cond.field == 'role_cli_srv' then
      if cond.value == 'client' then
         return tag_utils.eval_op(alert['is_client'], cond.op, 1)
      else -- 'server'
         return tag_utils.eval_op(alert['is_server'], cond.op, 1)
      end
   end

   return tag_utils.eval_op(alert[cond.field], cond.op, cond.value)
end

-- ##############################################

--@brief Filter (engaged) alerts in lua) evaluating self:_where conditions
function alert_store:filter_alerts(alerts)
   local result = {}

   -- For all alerts
   for _, alert in ipairs(alerts) do
      local pass = true
     
      -- For all fields
      for name, groups in pairs(self._where) do

         -- Eval AND conditions
         for _, cond in ipairs(groups.all) do
            if not self:eval_alert_cond(alert, cond) then
               pass = false
               break
            end
         end
         if not pass then
            break
         end

         -- Eval OR conditions
         if #groups.any > 0 then
            local or_pass = false
            for _, cond in ipairs(groups.any) do
               if self:eval_alert_cond(alert, cond) then
                  or_pass = true
                  break
               end
            end
            if not or_pass then
               pass = false
               break
            end
         end
      end

      if pass then
         result[#result + 1] = alert
      end
   end

   return result
end

-- ##############################################

--@brief Add raw/sql condition to the 'where' filters
--@param field The field name (e.g. 'alert_id')
--@param sql_cond The raw sql condition
function alert_store:add_filter_condition_raw(field, sql_cond, any)
   local cond = {
      field = field,
      sql = sql_cond,
   }

   if not self._where[field] then
      self._where[field] = { all = {}, any = {} }
   end

   if any then
      self._where[field].any[#self._where[field].any + 1] = cond
   else
      self._where[field].all[#self._where[field].all + 1] = cond
   end
end

-- ##############################################

--@brief Add condition to the 'where' filters
--@param field The field name (e.g. 'alert_id')
--@param op The operator (e.g. 'neq')
--@param value The value
--@param value_type The value type (e.g. 'number')
function alert_store:add_filter_condition(field, op, value, value_type)

   if not op or not tag_utils.tag_operators[op] then
      op = 'eq'
   end

   if value_type == 'number' then
     value = tonumber(value)
   end

   local cond = {
      field = field,
      op = op,
      value = value,
      value_type = value_type,
   }

   if not self._where[field] then
      self._where[field] = { all = {}, any = {} }
   end

   if op == 'neq' or field == 'score' then
      self._where[field].all[#self._where[field].all + 1] = cond
   else
      self._where[field].any[#self._where[field].any + 1] = cond
   end
end

-- ##############################################

--@brief Handle filter operator (eq, lt, gt, gte, lte)
function alert_store:strip_filter_operator(value)
   if isEmptyString(value) then return nil, nil end
   local filter = split(value, tag_utils.SEPARATOR)
   local value = filter[1]
   local op = filter[2]
   return value, op
end

-- ##############################################

--@brief Add list of conditions to the 'where' filters
--@param field The field name (e.g. 'alert_id')
--@param values The comma-separated list of values and operators
--@param value_type The value type (e.g. 'number')
--@return True if set is successful, false otherwise
function alert_store:add_filter_condition_list(field, values, values_type)
   if not values then
      return false
   end

   local list = split(values, ',')

   for _, value_op in ipairs(list) do
      local value, op = self:strip_filter_operator(value_op)
      if values_type == 'number' then
         value = tonumber(value)
      end

      if value then
         self:add_filter_condition(field, op, value, values_type)
      end
   end

   return true
end

-- ##############################################

--@brief Pagination options to fetch partial results
--@param limit The number of results to be returned
--@param offset The number of records to skip before returning results
--@return True if set is successful, false otherwise
function alert_store:add_limit(limit, offset)
   if not self._limit and tonumber(limit) then
      self._limit = limit

      if not self._offset and tonumber(offset) then
	 self._offset = offset
      end

      return true
   end

   return false
end

-- ##############################################

--@brief Specify the sort criteria of the query
--@param sort_column The column to be used for sorting
--@param sort_order Order, either `asc` or `desc`
--@return True if set is successful, false otherwise
function alert_store:add_order_by(sort_column, sort_order)
   -- Caching the order by depending on the user, the page and the interface id
   if sort_order and sort_column then
      local user = "no_user"
      
      if (_SESSION) and (_SESSION["user"]) then
         user = _SESSION["user"]
      end

      ntop.setCache(string.format(ALERT_SORTING_ORDER, _GET["ifid"] or "0", user, _GET["page"]), sort_order)
      ntop.setCache(string.format(ALERT_SORTING_COLUMN, _GET["ifid"] or "0", user, _GET["page"]), sort_column)
   end

   -- Creating the order by if not defined and valid
   if not self._order_by 
      and sort_column and self:_valid_fields(sort_column)
      and (sort_order == "asc" or sort_order == "desc") then
      self._order_by = {sort_column = sort_column, sort_order = sort_order}
      return true
   end

   return false
end

-- ##############################################

function alert_store:group_by(fields)
   if not self._group_by 
      and fields and self:_valid_fields(fields) then
      self._group_by = fields
      return true
   end

   return false
end

-- ##############################################

function alert_store:insert(alert)
   traceError(TRACE_NORMAL, TRACE_CONSOLE, "alert_store:insert")
   return false
end

-- ##############################################

--@brief Deletes data according to specified filters
function alert_store:delete()
   local where_clause = self:build_where_clause()

   -- Prepare the final query
   local q
   if ntop.isClickHouseEnabled() then
      q = string.format("ALTER TABLE `%s` DELETE WHERE %s ", self._table_name, where_clause)
   else
      q = string.format("DELETE FROM `%s` WHERE %s ", self._table_name, where_clause)
   end

   local res = interface.alert_store_query(q)
   return res and table.len(res) == 0
end

-- ##############################################

--@brief Labels alerts according to specified filters
function alert_store:acknowledge(label)
   local where_clause = self:build_where_clause()

   -- Prepare the final query
   local q
   if ntop.isClickHouseEnabled() then
      q = string.format("ALTER TABLE `%s` UPDATE `alert_status` = %u, `user_label` = '%s', `user_label_tstamp` = %u WHERE %s", self._table_name, alert_consts.alert_status.acknowledged.alert_status_id, self:_escape(label), os.time(), where_clause)
   else
      q = string.format("UPDATE `%s` SET `alert_status` = %u, `user_label` = '%s', `user_label_tstamp` = %u WHERE %s", self._table_name, alert_consts.alert_status.acknowledged.alert_status_id, self:_escape(label), os.time(), where_clause)
   end

   local res = interface.alert_store_query(q)
   return res and table.len(res) == 0
end

-- ##############################################

-- NOTE parameter 'filter' is ignored
function alert_store:select_historical(filter, fields)
   local res = {}
   local where_clause = ''
   local group_by_clause = ''
   local order_by_clause = ''
   local limit_clause = ''
   local offset_clause = ''

   local begin_time = ntop.gettimemsec()

   -- TODO handle fields (e.g. add entity value to WHERE)

   if ((fields == "*" and not(ntop.isClickHouseEnabled()))) then
      -- SQLite needs BLOB conversion to HEX
      fields = "*, hex(alerts_map) alerts_map"
   end

   -- Select everything by default
   fields = fields or '*'

   if not self:_valid_fields(fields) then
      return res
   end

   where_clause = self:build_where_clause()

   -- [OPTIONAL] Add the group by
   if self._group_by then
      group_by_clause = string.format("GROUP BY %s", self._group_by)
   end

   -- [OPTIONAL] Add sort criteria
   if self._order_by then
      order_by_clause = string.format("ORDER BY %s %s", self._order_by.sort_column, self._order_by.sort_order)
   end

   -- [OPTIONAL] Add limit for pagination
   if self._limit then
      limit_clause = string.format("LIMIT %u", self._limit)
   end

   -- [OPTIONAL] Add offset for pagination
   if self._offset then
      offset_clause = string.format("OFFSET %u", self._offset)
   end

   -- Prepare the final query
   -- NOTE: entity_id is necessary as alert_utils.formatAlertMessage assumes it to always be present inside the alert
   local q
   if ntop.isClickHouseEnabled() then
      q = string.format(" SELECT %u entity_id, (toUnixTimestamp(tstamp_end) - toUnixTimestamp(tstamp)) duration, %s FROM `%s` WHERE %s %s %s %s %s",
         self._alert_entity.entity_id, fields, self._table_name, where_clause, group_by_clause, order_by_clause, limit_clause, offset_clause)
   else
      q = string.format(" SELECT %u entity_id, (tstamp_end - tstamp) duration, %s FROM `%s` WHERE %s %s %s %s %s",
         self._alert_entity.entity_id, fields, self._table_name, where_clause, group_by_clause, order_by_clause, limit_clause, offset_clause)
   end

   res = interface.alert_store_query(q)

   if ntop.isClickHouseEnabled() then
      -- convert DATETIME to epoch
      for _, record in ipairs(res or {}) do
         if record.tstamp then record.tstamp = format_utils.parseDateTime(record.tstamp) end
         if record.tstamp_end then record.tstamp_end = format_utils.parseDateTime(record.tstamp_end) end
         if record.first_seen then record.first_seen = format_utils.parseDateTime(record.first_seen) end
         if record.user_label_tstamp then record.user_label_tstamp = format_utils.parseDateTime(record.user_label_tstamp) end
      end
   end

   -- count records
   local count_res = 0
   if isEmptyString(group_by_clause) then
      local count_q = string.format("SELECT COUNT(*) AS totalRows FROM `%s` WHERE %s", self._table_name, where_clause)
      local count_r = interface.alert_store_query(count_q)
      if table.len(count_r) > 0 then
         count_res = tonumber(count_r[1]["totalRows"])
      end
   else
      count_res = #res
   end

   local end_time = ntop.gettimemsec() -- Format: 1637330701.5767
   local duration = (end_time - begin_time) * 1000
   local records_sec = round((count_res / duration)*1000)

   local info = {
      query = q,
      query_duration_msec = duration,
      num_records_processed = i18n("db_search.processed_records", {records=formatValue(count_res), rps=formatValue(records_sec)}),
   }

   return res, info
end

-- ##############################################

--@brief Selects engaged alerts from memory
--@return Selected engaged alerts, and the total number of engaged alerts
function alert_store:select_engaged(filter)
   local entity_id_filter = tonumber(self._alert_entity and self._alert_entity.entity_id) -- Possibly set in subclasses constructor
   local entity_value_filter = filter
   -- The below filters are evaluated in Lua to support all operators
   local alert_id_filter = nil
   local severity_filter = nil
   local role_filter = nil

   local alerts = interface.getEngagedAlerts(entity_id_filter, entity_value_filter, alert_id_filter, severity_filter, role_filter)

   alerts = self:filter_alerts(alerts)

   local total_rows = 0
   local sort_2_col = {}

   -- Sort and filtering
   for idx, alert in pairs(alerts) do
      -- Exclude alerts falling outside requested time ranges
      local tstamp = tonumber(alert.tstamp)
      if self._epoch_begin and tstamp < self._epoch_begin then goto continue end
      if self._epoch_end and tstamp > self._epoch_end then goto continue end
      if self._subtype and alert.subtype ~= self._subtype then goto continue end

      if self._order_by and self._order_by.sort_column and alert[self._order_by.sort_column] ~= nil then
	 sort_2_col[#sort_2_col + 1] = {idx = idx, val = tonumber(alert[self._order_by.sort_column]) or string.format("%s", alert[self._order_by.sort_column])}
      else
	 sort_2_col[#sort_2_col + 1] = {idx = idx, val = tstamp}
      end

      total_rows = total_rows + 1

      ::continue::
   end

   -- Pagination
   local offset = self._offset or 0        -- The offset, or zero (start from the beginning) if no offset is set
   local limit = self._limit or total_rows -- The limit, or the actual number of records, ie., no limit

   local res = {}
   local i = 0

   for _, val in pairsByField(sort_2_col, "val", ternary(self._order_by and self._order_by.sort_order and self._order_by.sort_order == "asc", asc, rev)) do
      if i >= offset + limit then
	 break
      end

      if i >= offset then
	 res[#res + 1] = alerts[val.idx]
      end

      i = i + 1
   end

   return res, total_rows
end

-- ##############################################

--@brief Performs a query and counts the number of records
function alert_store:count()
   local where_clause = ''

   where_clause = self:build_where_clause()

   local q = string.format(" SELECT count(*) as count FROM `%s` WHERE %s",
      self._table_name, where_clause)

   local count_query = interface.alert_store_query(q)

   local num_results = 0
   if count_query then
      num_results = tonumber(count_query[1]["count"])
   end
      
   return num_results
end

-- ##############################################

--@brief Checks whether there are alerts, wither engaged or historical
function alert_store:has_alerts()
   -- First, check for engaged alerts (fastest)
   local _, num_alerts = self:select_engaged()
   local ifid = tonumber(_GET["ifid"]) or tonumber(interface.getId())

   if num_alerts > 0 then
      return true
   end

   -- The System Interface has the id -1 and in u_int16_t is 65535 
   if (ifid == -1) then
      ifid = 65535
   end

   -- Now check for historical alerts written in the database. Slightly slower.
      
   -- Fastest way to query SQLite for existance of records. Response will be either a string '1' if records exist,
   -- or '0' if records don't exist
   local q, res, has_historical_alerts

   if(ntop.isClickHouseEnabled()) then
      q = string.format(" SELECT COUNT(*) as num_alerts FROM `%s` WHERE interface_id = %d", self._table_name, ifid)
      res = interface.alert_store_query(q)

      has_historical_alerts = res and res[1] and (tonumber(res[1].num_alerts) > 0) or false
   else
      q = string.format(" SELECT EXISTS (SELECT 1 FROM `%s` WHERE interface_id = %d) has_historical_alerts", self._table_name, ifid)
      res = interface.alert_store_query(q)
      has_historical_alerts = res and res[1] and res[1]["has_historical_alerts"] == "1" or false
   end
   
   return has_historical_alerts
end

-- ##############################################

--@brief Returns minimum and maximum timestamps and the time slot width to
-- be used for queries performing group-by-time operations
function alert_store:_count_by_time_get_bounds()
   local now = os.time()
   local min_slot = self._epoch_begin or (now - 3600)
   local max_slot = self._epoch_end or now
   local slot_width

   -- Compute the width to obtain a fixed number of points
   local slot_span = max_slot - min_slot

   if slot_span < 0 or slot_span < NUM_TIME_SLOTS then
      -- Slot width is 1 second, can't be smaller than this
      slot_width = 1
   else
      -- Result is the floor to return an integer number
      slot_width = math.floor(slot_span / NUM_TIME_SLOTS)
   end

   -- Align the range using the width of the time slot to always return aligned data
   min_slot = min_slot - (min_slot % slot_width)
   max_slot = min_slot + slot_width * NUM_TIME_SLOTS

   return min_slot, max_slot, slot_width
end

-- ##############################################

--@brief Pad missing points with zeroes and prepare the series
function alert_store:_prepare_count_by_severity_and_time_series(all_severities, min_slot, max_slot, time_slot_width)
   local res = {}

   if table.len(all_severities) == 0 then
      -- No series, add a dummy series for "no alerts"
      local noalert_res = {}
      for slot = min_slot, max_slot + 1, time_slot_width do
	 noalert_res[#noalert_res + 1] = {slot * 1000 --[[ In milliseconds --]], 0}
      end
      res[0] = noalert_res
      return res
   end

   -- Pad missing points with zeroes
   for _, severity in pairs(alert_severities) do
      local severity_id = tonumber(severity.severity_id)

      -- Empty series for this severity, skip
      if not all_severities[severity_id] then goto skip_severity_pad end

      for slot = min_slot, max_slot + 1, time_slot_width do
	 if not all_severities[severity_id].all_slots[slot] then
	    all_severities[severity_id].all_slots[slot] = 0
	 end
      end

      ::skip_severity_pad::
   end

   -- Prepare the result as a Lua array ordered by time slot
   for _, severity in pairs(alert_severities) do
      local severity_id = tonumber(severity.severity_id)

      -- Empty series for this severity, skip
      if not all_severities[severity_id] then goto skip_severity_prep end

      local severity_res = {}

      for slot, count in pairsByKeys(all_severities[severity_id].all_slots, asc) do
	 severity_res[#severity_res + 1] = {slot * 1000 --[[ In milliseconds --]], count}
      end

      res[severity_id] = severity_res

      ::skip_severity_prep::
   end

   return res
end

-- ##############################################

--@brief Counts the number of engaged alerts in multiple time slots
function alert_store:count_by_severity_and_time_engaged(filter, severity)
   local min_slot, max_slot, time_slot_width = self:_count_by_time_get_bounds()
   local entity_id_filter = tonumber(self._alert_entity and self._alert_entity.entity_id) -- Possibly set in subclasses constructor
   local entity_value_filter = filter
   -- The below filters are evaluated in Lua to support all operators
   local alert_id_filter = nil
   local severity_filter = nil
   local role_filter = nil

   local alerts = interface.getEngagedAlerts(entity_id_filter, entity_value_filter, alert_id_filter, severity_filter)

   alerts = self:filter_alerts(alerts)

   local all_severities = {}
   local all_slots = {}

   -- Calculate minimum and maximum slots to make sure the response always returns consecutive time slots, possibly filled with zeroes
   for _, alert in ipairs(alerts) do
      local severity_id = alert.severity

      local tstamp = tonumber(alert.tstamp)
      local cur_slot = tstamp - (tstamp % time_slot_width)

      -- Exclude alerts falling outside requested time ranges
      if self._epoch_begin and tstamp < self._epoch_begin then goto continue end
      if self._epoch_end and tstamp > self._epoch_end then goto continue end

      if not all_severities[severity_id] then all_severities[severity_id] = {} end
      if not all_severities[severity_id].all_slots then all_severities[severity_id].all_slots = {} end

      all_severities[severity_id].all_slots[cur_slot] = (all_severities[severity_id].all_slots[cur_slot] or 0) + 1

      ::continue::
   end

   return self:_prepare_count_by_severity_and_time_series(all_severities, min_slot, max_slot, time_slot_width)
end

-- ##############################################

--@brief Performs a query and counts the number of records in multiple time slots
function alert_store:count_by_severity_and_time_historical()
   -- Preserve all the filters currently set
   local min_slot, max_slot, time_slot_width = self:_count_by_time_get_bounds()
   local where_clause = self:build_where_clause()
   local q

   -- Group by according to the timeslot, that is, the alert timestamp MODULO the slot width
   if(ntop.isClickHouseEnabled()) then
      q = string.format("SELECT severity, (toUnixTimestamp(tstamp) - toUnixTimestamp(tstamp) %% %u) as slot, count(*) count FROM %s WHERE %s GROUP BY severity, slot ORDER BY severity, slot ASC",
         time_slot_width, self._table_name, where_clause)
   else
      q = string.format("SELECT severity, (tstamp - tstamp %% %u) as slot, count(*) count FROM %s WHERE %s GROUP BY severity, slot ORDER BY severity, slot ASC",
         time_slot_width, self._table_name, where_clause)
   end

   local q_res = interface.alert_store_query(q) or {}

   local all_severities = {}

   -- Read points from the query
   for _, p in ipairs(q_res) do
      local severity_id = tonumber(p.severity)

      if not all_severities[severity_id] then all_severities[severity_id] = {} end
      if not all_severities[severity_id].all_slots then all_severities[severity_id].all_slots = {} end

      -- Make sure slots are within the requested bounds
      local cur_slot = tonumber(p.slot)
      local cur_count = tonumber(p.count)
      if cur_slot >= min_slot and cur_slot <= max_slot then
	 all_severities[severity_id].all_slots[cur_slot] = cur_count
      end
   end

   return self:_prepare_count_by_severity_and_time_series(all_severities, min_slot, max_slot, time_slot_width)
end

-- ##############################################

--@brief Performs a query and counts the number of records in multiple time slots using the old response format (CheckMK integration)
function alert_store:count_by_24h_historical()
   local group_by = "hour"
   local time_slot_width = "3600"
   local where_clause = self:build_where_clause()

   -- Group by according to the timeslot, that is, the alert timestamp MODULO the slot width
   local q   
   if ntop.isClickHouseEnabled() then
      q = string.format("SELECT (toUnixTimestamp(tstamp) - toUnixTimestamp(tstamp) %% %u) as hour, count(*) count FROM %s WHERE %s GROUP BY hour",
         time_slot_width, self._table_name, where_clause)
   else
      q = string.format("SELECT (tstamp - tstamp %% %u) as hour, count(*) count FROM %s WHERE %s GROUP BY hour",
         time_slot_width, self._table_name, where_clause)
   end

   local q_res = interface.alert_store_query(q) or {}

   local res = alert_utils.formatOldTimeseries(q_res, self._epoch_begin, self._epoch_end)

   return res
end

-- ##############################################

--@brief Performs a query and counts the number of records in multiple time slots using the old response format (CheckMK integration)
function alert_store:count_by_24h_engaged(filter, severity)
   local group_by = "hour"
   local time_slot_width = "3600"
   local where_clause = self:build_where_clause()
   local entity_id_filter = tonumber(self._alert_entity and self._alert_entity.entity_id) -- Possibly set in subclasses constructor
   local entity_value_filter = filter
   local alert_id_filter = nil
   local severity_filter = nil
   local role_filter = nil

   local alerts = interface.getEngagedAlerts(entity_id_filter, entity_value_filter, alert_id_filter, severity_filter)

   q_res = self:filter_alerts(alerts)

   -- Query done, now format the array
   local res = alert_utils.formatOldTimeseries(q_res, self._epoch_begin, self._epoch_end)

   return res
end

-- ##############################################

-- Old timeseries --
--@brief Count from memory (engaged) or database (historical)
--@return Alert counters divided into severity and time slots
function alert_store:count_by_24h()
   -- Add filters
   self:add_request_filters()
   -- Add limits and sort criteria
   self:add_request_ranges()

   if self._status == alert_consts.alert_status.engaged.alert_status_id then -- Engaged
      return self:count_by_24h_engaged() or {}
   else -- Historical
      return self:count_by_24h_historical() or {}
   end
end

-- ##############################################

--@brief Count from memory (engaged) or database (historical)
--@return Alert counters divided into severity and time slots
function alert_store:count_by_severity_and_time()
   -- Add filters
   self:add_request_filters()
   -- Add limits and sort criteria
   self:add_request_ranges()

   -- old queries, integration with CheckMK
   if self._status == alert_consts.alert_status.engaged.alert_status_id then -- Engaged
      return self:count_by_severity_and_time_engaged() or 0
   else -- Historical
      return self:count_by_severity_and_time_historical() or 0
   end
end

-- ##############################################

--@brief Performs a query for the top alerts by alert count
function alert_store:top_alert_id_historical()
   -- Preserve all the filters currently set
   local where_clause = self:build_where_clause()
   local limit = 10
   
   local q = string.format("SELECT alert_id, count(*) count FROM %s WHERE %s GROUP BY alert_id ORDER BY count DESC LIMIT %u",
			   self._table_name, where_clause, limit)

   local q_res = interface.alert_store_query(q) or {}

   return q_res
end

-- ##############################################

--@brief Child stats
function alert_store:_get_additional_stats()
   return {}
end

-- ##############################################

--@brief Stats used by the dashboard
function alert_store:get_stats()
   -- Add filters
   self:add_request_filters()

   -- Get child stats
   local stats = self:_get_additional_stats()

   stats.count = self:count()
   stats.top = stats.top or {}
   stats.top.alert_id = self:top_alert_id_historical()

   return stats
end

-- ##############################################

--@brief Format top alerts returned by get_stats() for general_stats.lua
function alert_store:format_top_alerts(stats)
   local top_alerts = {}

   for n, value in pairs(stats.top.alert_id) do
      if self._top_limit > 0 and n > self._top_limit then break end

      local label = alert_consts.alertTypeLabel(tonumber(value.alert_id), true, self._alert_entity.entity_id)

      top_alerts[#top_alerts + 1] = {
         count = (tonumber(value.count) * 100) / stats.count,
         key = "alert_id",
         value = tonumber(value.alert_id),
         label = shortenString(label, s_len),
         title = label,
      }
   end

   return top_alerts 
end

-- ##############################################

--@brief Stats used by the dashboard
function alert_store:get_top_limit()
   return self._top_limit
end

-- ##############################################
-- REST API Utility Functions
-- ##############################################

--@brief Handle count requests (GET) from memory (engaged) or database (historical)
--@return Alert counters divided into severity and time slots
function alert_store:count_by_severity_and_time_request()
   local res = {
      series = {},
      colors = {}
   }

   local count_data = 0
   local by_24h = toboolean(_GET["by_24h"]) or false

   if by_24h then
      return self:count_by_24h()
   else
      count_data = self:count_by_severity_and_time()
   end

   for _, severity in pairsByField(alert_severities, "severity_id", rev) do
      if(count_data[severity.severity_id] ~= nil) then
	 res.series[#res.series + 1] = {
	    name = i18n(severity.i18n_title),
	    data = count_data[severity.severity_id],
	 }
	 res.colors[#res.colors + 1] = severity.color
      end
   end

   if table.len(res.series) == 0 and count_data[0] ~= nil then
      res.series[#res.series + 1] = {
        name = i18n("alerts_dashboard.no_alerts"),
        data = count_data[0],
      }
      res.colors[#res.colors + 1] = "#ccc"
   end

   return res
end

-- ##############################################

--@brief Handle alerts select request (GET) from memory (engaged) or database (historical)
--@param filter A filter on the entity value (no filter by default)
--@param select_fields The fields to be returned (all by default or in any case for engaged)
--@return Selected alerts, and the total number of alerts
function alert_store:select_request(filter, select_fields)

   -- Add filters
   self:add_request_filters()

   if self._status == alert_consts.alert_status.engaged.alert_status_id then -- Engaged
      -- Add limits and sort criteria
      self:add_request_ranges()

      local alerts, total_rows =  self:select_engaged(filter)

      return alerts, total_rows, {}
   else -- Historical
      
      -- Count
      local total_row = self:count()

      -- Add limits and sort criteria only after the count has been done
      self:add_request_ranges()

      local res, info = self:select_historical(filter, select_fields)

      return res, total_row, info
   end
end

-- ##############################################

function alert_store:get_earliest_available_epoch(status)   
   -- Add filters (only needed for the status, must ignore all other filters)
   self:add_status_filter(status)
   local cached_epoch_key = string.format(EARLIEST_AVAILABLE_EPOCH_CACHE_KEY, _GET["ifid"] or interface.getId(), self._table_name, self._status)
   local earliest = 0

   -- Check if epoch has already been cached
   local cached_epoch = ntop.getCache(cached_epoch_key)
   if not isEmptyString(cached_epoch) then
      -- If found in cache, return it
      return tonumber(cached_epoch)
   end

   if status == "engaged" then
      local res = self:select_engaged()
      for k, v in  pairsByField(res, "tstamp", asc) do
	 -- Take the first
	 earliest = v["tstamp"]
	 break
      end
   else -- Historical
      local q
      if ntop.isClickHouseEnabled() then
	 q = string.format(" SELECT toUnixTimestamp(tstamp) earliest_epoch FROM `%s` WHERE interface_id = %d AND alert_status = %d ORDER BY tstamp ASC LIMIT 1",
			   self._table_name, interface.getId(), self._status)
      else
	 q = string.format(" SELECT tstamp earliest_epoch FROM `%s` WHERE interface_id = %d AND alert_status = %d ORDER BY tstamp ASC LIMIT 1",
			   self._table_name, interface.getId(), self._status)
      end

      local res = interface.alert_store_query(q)
      if res and res[1] and tonumber(res[1]["earliest_epoch"]) then
	 -- Cache and return the number as read from the DB
	 ntop.setCache(cached_epoch_key, res[1]["earliest_epoch"], 600 --[[ Cache for 5 mins --]])
	 earliest = tonumber(res[1]["earliest_epoch"])
      end
   end

   -- Cache the value
   ntop.setCache(cached_epoch_key, string.format("%u", earliest), earliest == 0 and 60 or 600)

   return earliest
end

-- ##############################################

--@brief Possibly overridden in subclasses to add additional filters from the request
function alert_store:_add_additional_request_filters()
end

-- ##############################################

--@brief Add ip filter
function alert_store:add_alert_id_filter(alert_id)
   self:add_filter_condition('alert_id', 'eq', alert_id, 'number');
end

-- ##############################################

--@brief Add filters according to what is specified inside the REST API
function alert_store:add_request_filters()
   local ifid = _GET["ifid"] or interface.getId()
   local epoch_begin = tonumber(_GET["epoch_begin"])
   local epoch_end = tonumber(_GET["epoch_end"])
   local alert_id = _GET["alert_id"] or _GET["alert_type"] --[[ compatibility ]]--
   local alert_severity = _GET["severity"] or _GET["alert_severity"]
   local score = _GET["score"]
   local rowid = _GET["row_id"]
   local status = _GET["status"]

   -- Remember the score filter (see also alert_stats.lua)
   local alert_score_cached = "ntopng.alert.score.ifid_" .. ifid .. ""
   if isEmptyString(score) then
      ntop.delCache(alert_score_cached)
   else
      ntop.setCache(alert_score_cached, score)
   end

   if ifid == "-1" then
      ifid = 65535
   end

   self:add_status_filter(status)
   self:add_time_filter(epoch_begin, epoch_end)

   self:add_filter_condition_list('alert_id', alert_id, 'number')
   self:add_filter_condition_list('severity', alert_severity, 'number')
   self:add_filter_condition_list('score', score, 'number')

   
   if(ntop.isClickHouseEnabled()) then
      -- Clickhouse db has the column 'interface_id', filter by that per interface
      self:add_filter_condition_list('rowid', rowid, 'string')
      self:add_filter_condition_list('interface_id', ifid, 'number')
   else
      self:add_filter_condition_list('rowid', rowid, 'number')
   end

   self:_add_additional_request_filters()
end

-- ##############################################

--@brief Possibly overridden in subclasses to get info about additional available filters
function alert_store:_get_additional_available_filters()
   return {}
end

-- ##############################################

--@brief Get info about available filters
function alert_store:get_available_filters()
   local additional_filters = self:_get_additional_available_filters()

   local filters = {
      alert_id = {
         value_type = 'alert_id',
	 i18n_label = i18n('db_search.tags.alert_id'),
      }, 
      severity = {
         value_type = 'severity',
	 i18n_label = i18n('db_search.tags.severity'),
      },
      score = {
         value_type = 'score',
	 i18n_label = i18n('db_search.tags.score'),
      },
   }

   return table.merge(filters, additional_filters)
end

-- ##############################################

--@brief Add offset, limit, and group by filters according to what is specified inside the REST API
function alert_store:add_request_ranges()
   local start = tonumber(_GET["start"])   --[[ The OFFSET: default no offset --]]
   local length = tonumber(_GET["length"]) --[[ The LIMIT: default no limit   --]]
   local sort_column = _GET["sort"]
   local sort_order = _GET["order"]

   self:add_limit(length, start)
   self:add_order_by(sort_column, sort_order)
end

-- ##############################################

-- define the base record names of the document, both json and csv
-- add a new record name here if you want to add a new base element
-- name: the actual record name 
-- export: use only in csv export, true the record is included in the csv, false otherwise
-- in case an element is a table by default the 'value' key is exported, if you want to export multiple fields
-- add an 'element' array specifing the field names to export, for example:
-- MSG = { name = "msg", export = true, elements = {"name", "value"}}
local BASE_RNAME = {
   FAMILY = { name = "family", export = true},
   ROW_ID = { name = "row_id", export = false},
   TSTAMP = { name = "tstamp", export = true},
   ALERT_ID = { name = "alert_id", export = true},
   SCORE = { name = "score", export = true},
   SEVERITY = { name = "severity", export = true},
   DURATION = { name = "duration", export = true},
   COUNT = { name = "count", export = true},
   SCRIPT_KEY = { name = "script_key", export = false},
   USER_LABEL = { name = "user_label", export = true},
}

--@brief Convert an alert coming from the DB (value) to a record returned by the REST API
function alert_store:format_json_record_common(value, entity_id)
   local record = {}

   -- Note: this record is rendered by 
   -- httpdocs/templates/pages/alerts/families/{host,..}/table[.js].template 
   
   record[BASE_RNAME.FAMILY.name] = self:get_family()

   record[BASE_RNAME.ROW_ID.name] = value["rowid"]

   local score = tonumber(value["score"])
   local severity_id = ntop.mapScoreToSeverity(score)
   local severity = alert_consts.alertSeverityById(severity_id)

   local tstamp = tonumber(value["alert_tstamp"] or value["tstamp"])
   record[BASE_RNAME.TSTAMP.name] = {
      value = tstamp,
      label = format_utils.formatPastEpochShort(tstamp),
      highlight = severity.color,
   }

   record[BASE_RNAME.ALERT_ID.name] = {
      value = value["alert_id"],
      label = alert_consts.alertTypeLabel(tonumber(value["alert_id"]), false, entity_id),
   }

   record[BASE_RNAME.SCORE.name] = {
      value = score,
      label = format_utils.formatValue(score),
      color = severity.color,
   }

   local severity_label = ""
   if severity then
      severity_label = "<i class='"..severity.icon.."' style='color: "..severity.color.."!important' title='"..i18n(severity.i18n_title).."'></i> "
   end

   record[BASE_RNAME.SEVERITY.name] = {
      value = severity_id,
      label = severity_label,
      color = severity.color,
   }

   record[BASE_RNAME.USER_LABEL.name] = value["user_label"]

   record[BASE_RNAME.DURATION.name] = tonumber(value["duration"]) or (tonumber(value["tstamp_end"]) - tonumber(value["tstamp"]))
   record[BASE_RNAME.COUNT.name] = tonumber(value["count"]) or 1

   local alert_json = json.decode(value["json"]) or {}
   record[BASE_RNAME.SCRIPT_KEY.name] = alert_json["alert_generation"] and alert_json["alert_generation"]["script_key"]

   return record
end

-- Convert from table to CSV string
function alert_store:to_csv(documents)
   local csv = ""

   local rnames = self:get_rnames_to_export()

   -- column heading output
   local row = self:build_csv_row_header(rnames)
   csv = csv .. row .. '\n'

   for _, document in ipairs(documents) do
      row = self:build_csv_row(rnames, document)
      csv = csv .. row .. '\n'
   end

   return csv
end

function alert_store:get_rnames_to_export()
   local rnames = {}

   for key, value in pairs(self:get_export_base_rnames()) do
      if value.export then
         rnames[key] = value
      end
   end
   
   for key, value in pairs(self:get_rnames()) do
      if value.export then
         rnames[key] = value
      end
   end

   return rnames
end

-- do not override in subclasses
function alert_store:get_export_base_rnames()
   return BASE_RNAME
end

-- to add new elements in subclasses define a RNAME table in subclass and returned it overring this function
function alert_store:get_rnames()
   return {}
end

-- do not override in subclasses
function alert_store:build_csv_row_header(rnames)
   local row = ""

   for _, value in pairsByKeys(rnames) do
      if value["elements"] == nil then
         row = row .. CSV_SEPARATOR .. value.name
      else
         for _, element in ipairs(value.elements) do
            row = row .. CSV_SEPARATOR .. value.name .. "_" .. string.gsub(element, "%.", "_")
         end
      end
   end

   row = string.sub(row, 2) -- remove first separator
   
   return row;
end

function alert_store:build_csv_row(rnames, document)
   local row = ""
   
   for _, rname in pairsByKeys(rnames) do
      local doc_value = document[rname.name]
      if type(doc_value) ~= "table" then
         row = row .. self:build_csv_row_single_element(doc_value)
      else
         if rname["elements"] ~= nil then
            row = row .. self:build_csv_row_multiple_elements(doc_value, rname.elements)
         else
            row = row .. self:build_csv_row_single_element(doc_value.value)
         end
      end
   end
   
   row = string.sub(row, 2) -- remove first separator
   
   return row
end

function alert_store:build_csv_row_single_element(value)
   return CSV_SEPARATOR .. self:escape_csv(tostring(value))
end

function alert_store:build_csv_row_multiple_elements(value, elements)
   local row = ""
   for _, element in ipairs(elements) do
      local splitted = string.split(element, "%.")
      if(splitted == nil) then
         row = row .. CSV_SEPARATOR .. self:escape_csv(tostring(value[element]))
      else 
         if #splitted > 2 then
            row = row .. self:build_csv_row_multiple_elements(value[splitted[1]], self:rebuild_sub_elements(splitted))
         else
            row = row .. CSV_SEPARATOR .. self:escape_csv(tostring(value[splitted[1]][splitted[2]]))   
         end
      end
   end   
   return row
end

function alert_store:rebuild_sub_elements(splitted)
   local tmp_elements = {}
   for i = 2, #splitted, 1 do
      tmp_elements[#tmp_elements+1] = splitted[i]
   end
   return { table.concat(tmp_elements, ".") }
end

-- Used to escape "'s by to_csv
function alert_store:escape_csv(s)
   if string.find(s, '[,"|\n]') then
      s = '"' .. string.gsub(s, '"', '""') .. '"'
   end
   return s
end
-- ##############################################

--@brief Deletes old data according to the configuration or up to a safe limit
function alert_store:housekeeping(ifid)
   local prefs = ntop.getPrefs()

   -- By Number of records
   
   local max_entity_alerts = prefs.max_entity_alerts
   local limit = math.floor(max_entity_alerts * 0.8) -- deletes 20% more alerts than the maximum number

   local q
   if ntop.isClickHouseEnabled() then
      q = string.format("ALTER TABLE `%s` DELETE WHERE interface_id = %d AND rowid <= (SELECT rowid FROM `%s` WHERE interface_id = %u ORDER BY rowid DESC LIMIT 1 OFFSET %u)",
			self._table_name, ifid, self._table_name, ifid, limit)
   else
      q = string.format("DELETE FROM `%s` WHERE rowid <= (SELECT rowid FROM `%s` ORDER BY rowid DESC LIMIT 1 OFFSET %u)",
			self._table_name, self._table_name, limit)
   end

   local deleted = interface.alert_store_query(q)

   -- By Time
   
   local now = os.time()
   local max_time_sec = prefs.max_num_secs_before_delete_alert
   local expiration_epoch = now - max_time_sec

   if ntop.isClickHouseEnabled() then
      q = string.format("ALTER TABLE `%s` DELETE WHERE interface_id = %d AND tstamp < %u", self._table_name, ifid, expiration_epoch)
   else
      q = string.format("DELETE FROM `%s` WHERE tstamp < %u", self._table_name, expiration_epoch)
   end

   deleted = interface.alert_store_query(q)
end

-- ##############################################

return alert_store