--
-- (C) 2019-21 - ntop.org
--
-- The functions below are called with a LuaC "flow" context set.
-- See user_scripts.load() documentation for information
-- on adding custom scripts.
--
-- NOTE: this script is loaded once and cached into the vm and then invoked
-- multiple times. The setup() function is only called with the first load.
--

local dirs = ntop.getDirs()
package.path = dirs.installdir .. "/scripts/lua/modules/?.lua;" .. package.path

require "lua_utils"
require "flow_utils"
local user_scripts = require("user_scripts")
local alert_consts = require("alert_consts")
local flow_consts = require("flow_consts")
local json = require("dkjson")
local alerts_api = require("alerts_api")
local recipients = require "recipients"
local ids_utils = nil

if ntop.isPro() then
  package.path = dirs.installdir .. "/pro/scripts/lua/modules/?.lua;" .. package.path
end

local do_benchmark = false         -- Compute benchmarks and store their results
local do_print_benchmark = false   -- Print benchmarks results to standard output
local do_trace = false             -- Trace lua calls
local flows_config = nil
local flows_filters = nil
local score_enabled = nil

local available_modules = nil

-- Keeps information about the current alerted alerted status
local alerted_status
local alert_type_params
local alerted_status_score
local alerted_user_script
local cur_user_script
local cur_l4_proto

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

local function trace_f(trace_msg)
   local fmt = string.format("[ifid: %i] %s\n", interface.getId(), trace_msg or '')
   print(fmt)
end

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

local function addL4Callaback(l4_hooks, l4_proto, hook_name, script_key, callback)
   local l4_scripts = l4_hooks[l4_proto]

   if not l4_scripts then
      l4_scripts = {}
      l4_hooks[l4_proto] = l4_scripts
   end

   l4_scripts[hook_name] = l4_scripts[hook_name] or {}
   l4_scripts[hook_name][script_key] = callback
end

local function skip_disabled_flow_scripts(user_script)
   -- NOTE: this filter can only be applied here because there is no
   -- concept of entity_value for a flow.
   return(user_scripts.getTargetHookConfig(flows_config, user_script).enabled)
end

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

local function prioritizeL4Callabacks(l4_hooks)
   local group_mods_by_prio = {}
   local mods_by_prio = {}

   -- Set the priority to the `prio` indicated in the module, or to zero,
   -- if no `prio` is indicated
   for mod_key, mod in pairs(available_modules.modules) do
      local prio = tonumber(mod.prio) or 0
      if not group_mods_by_prio[prio] then
        group_mods_by_prio[prio] = {}
      end
      group_mods_by_prio[prio][mod_key] = mod
   end

   -- Sort available modules by descending `prio`
   -- That is from lower (negative) to higher (positive) priorities
   -- E.g., a prio -20 is executed after a prio 0 which, in turn, is executed
   -- after a prio 20
   -- Modules with the same prio are sorted by key, to determinitically
   -- evaluate modules and produce results
   for prio, mods in pairsByKeys(group_mods_by_prio, rev) do
      for key, mod in pairsByKeys(mods, asc) do
         mods_by_prio[#mods_by_prio + 1] = key
      end
   end

   -- Updates l4_hooks and convert modules to ordered lua arrays
   for l4_proto, hooks in pairs(l4_hooks) do
      -- e.g.:
      -- 1 (l4_proto) -> protocolDetected (hooks table)
      -- 1 (l4_proto) -> periodicUpdate (hooks table)
      for hook_name, modules in pairs(hooks) do
	 -- e.g.:
	 -- protocolDetected (hook_name) -> invalid_dns_query
	 -- protocolDetected (hook_name) -> web_mining
	 local sorted_modules = {}
	 for _, mod_key in ipairs(mods_by_prio) do
	    if modules[mod_key] then
	       sorted_modules[#sorted_modules + 1] = {mod_key = mod_key, mod_fn = modules[mod_key]}
	    end
	 end

	 -- Update the hooks with sorted hooks
	 hooks[hook_name] = sorted_modules
      end
   end

   -- Sets l4_hooks with the sorted hooks
   available_modules.l4_hooks = l4_hooks
end

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

-- The function below is called once (#pragma once)
function setup()
   if do_trace then
      trace_f(string.format("flow.lua:setup() called"))
   end

   local ifid = interface.getId()
   local view_ifid
   if interface.isViewed() then
      view_ifid = interface.viewedBy()
   end

   local configset = user_scripts.getConfigset()

   -- Flows config and filters are system-wide, always take the DEFAULT_CONFIGSET_ID
   flows_config = user_scripts.getConfig(configset, "flow")
   flows_filters = user_scripts.getFilters(configset, "flow")
   alerted_user_script = nil

   -- To execute flows, the viewed interface id is used instead, as flows reside in the viewed interface, not in the view
   available_modules = user_scripts.load(ifid, user_scripts.script_types.flow, "flow", {
      do_benchmark = true,
      scripts_filter = skip_disabled_flow_scripts,
   })

   -- Reorganize the modules to optimize lookup by L4 protocol
   -- E.g. l4_hooks = {tcp -> {periodicUpdate -> {check_tcp_retr}}, other -> {protocolDetected -> {mud, score}}}

   -- Prepare the l4 hooks
   local l4_hooks = {}

   for hook_name, hooks in pairs(available_modules.hooks) do
      -- available_modules.l4_hooks
      for script_key, callback in pairs(hooks) do
         local script = available_modules.modules[script_key]

         if script.l4_proto then
            local l4_proto = l4_proto_to_id(script.l4_proto)

            if not l4_proto then
               traceError(TRACE_ERROR, TRACE_CONSOLE, string.format("Unknown l4_proto '%s' in module '%s', skipping", script.l4_proto, script_key))
            else
               addL4Callaback(l4_hooks, l4_proto, hook_name, script_key, callback)
            end
         else
            -- No l4 filter is active for the specified module
            -- Attach the protocol to all the L4 protocols
            for _, l4_proto in pairs(l4_keys) do
               local l4_proto = l4_proto[3]

               if l4_proto > 0 then
                  addL4Callaback(l4_hooks, l4_proto, hook_name, script_key, callback)
               end
            end
         end
      end
   end

   prioritizeL4Callabacks(l4_hooks)

   if(ntop.isEnterpriseM()) then
      ids_utils = require("ids_utils")
   end
end

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

-- The function below is called once (#pragma once) right before
-- the lua virtual machine is destroyed
function teardown()
   if do_trace then
      trace_f("flow.lua:teardown() called")
   end

   if available_modules then
      user_scripts.teardown(available_modules, do_benchmark, do_print_benchmark)
   end
end

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

-- @brief Store more information into the flow status. Such information
-- does not depend the specific flow status being triggered
-- @param flow_status the status table to augument
local function augumentFlowStatusInfo(flow_status)
   flow_status["ntopng.key"] = flow.getKey()
   flow_status["hash_entry_id"] = flow.getHashEntryId()
   flow_status["info"] = flow.getInfo()["info"] or ''

   if cur_l4_proto == 1 --[[ ICMP ]] then
      -- NOTE: this information is parsed by getFlowStatusInfo()
      flow_status["icmp"] = flow.getICMPStatusInfo()
   end
end

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

-- @brief Trigger a flow alert (and dispatch the alert to the notification modules)
-- @param now A unix epoch of the present time
-- @param trigger_status The status that is being triggered, obtained as `status_info.status_type`
-- @param trigger_type_params A table of params associated to the status
-- @param trigger_status_score The score associated to the status that is being triggered
-- @return True if the alert has been triggered, false otherwise
local function triggerFlowAlert(now, trigger_status, trigger_type_params, trigger_status_score)
   if not areAlertsEnabled() then
      return(false)
   end

   local cli_key = flow.getClientKey()
   local srv_key = flow.getServerKey()
   local status_key = trigger_status.status_key

   if do_trace then
      trace_f(string.format("flow.triggerAlert(type=%s, severity=%s)",
			 alert_consts.alertTypeRaw(trigger_status.alert_type.alert_key),
			 alert_consts.alertSeverityRaw(trigger_status.alert_severity.severity_id)))
   end

   trigger_type_params = trigger_type_params or {}

   if type(trigger_type_params) == "table" then
      -- NOTE: porting this to C is not feasable as the lua table can contain
      -- arbitrary data
      augumentFlowStatusInfo(trigger_type_params)
      alerts_api.addAlertGenerationInfo(trigger_type_params, alerted_user_script)

      trigger_type_params = json.encode(trigger_type_params)
   end

   local res = flow.triggerAlert(
      status_key,
      trigger_status.alert_type.alert_key,
      trigger_status.alert_severity.severity_id,
      trigger_status_score,
      now,
      trigger_status.alert_type.status_always_notify == true,
      trigger_type_params)

   -- There's no lua table for the flow alert. Flow alert is generated from C and is returned to
   -- Lua as a JSON string. Hence, to dispatch it to the recipient, alert must be decoded from JSON.
   -- Then, the dispatch will re-encode it, thus wasting more time. This needs to be fixed.
   if res.alert_json then
      recipients.dispatch_notification(json.decode(res.alert_json), alerted_user_script)
   end

   return(res.triggered)
end

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

-- Function for the actual module execution. Iterates over available (and enabled)
-- modules, calling them one after one.
-- @param l4_proto the L4 protocol of the flow
-- @param master_id the L7 master protocol of the flow
-- @param app_id the L7 app protocol of the flow
-- @param mod_fn the callback to call
-- @return true if some module was called, false otherwise
local function call_modules(l4_proto, master_id, app_id, mod_fn, update_ctr)
   if not available_modules then
      return true
   end

   local all_modules = available_modules.modules
   local hooks = available_modules.l4_hooks[l4_proto]

   -- Reset alerted status information
   alerted_status = nil
   alert_type_params = nil
   alerted_status_score = -1
   cur_l4_proto = l4_proto

   if hooks then
      hooks = hooks[mod_fn]
   end

   if not hooks then
      if do_trace then
	 trace_f(string.format("No flow.lua modules, skipping %s(%d) for %s", mod_fn, l4_proto, shortFlowLabel(flow.getInfo())))
      end

      return true
   end

   if do_trace then
      trace_f(string.format("%s()[START]: bitmap=0x%x alerted=%d", mod_fn, flow.getStatus(), flow.getAlertedStatus()))
   end

   local now = os.time()
   local twh_in_progress = l4_proto == 6 --[[TCP]] and not flow.isTwhOK()

   for _, mod in ipairs(hooks) do
      local mod_key = mod.mod_key
      local hook_fn = mod.mod_fn
      local script = all_modules[mod_key]

      -- Check if the script requires the flow to have successfully completed the three-way handshake
      if script.three_way_handshake_ok and twh_in_progress then
	 -- Check if the script wants the three way handshake completed
	 if do_trace then
	    trace_f(string.format("%s() [check: %s]: skipping flow with incomplete three way handshake", mod_fn, mod_key))
	 end

	 goto continue
      end

      local script_l7 = script.l7_proto_id

      if script_l7 and master_id ~= script_l7 and app_id ~= script_l7 then
	 if do_trace then
	    trace_f(string.format("%s() [check: %s]: skipping flow with proto=%s/%s [wants: %s]", mod_fn, mod_key, master_id, app_id, script_l7))
	 end

	 goto continue
      end

      if do_trace then
	 local info = flow.getInfo()

	 if do_trace then
	    trace_f(string.format("%s() [check: %s]: %s", mod_fn, mod_key, shortFlowLabel(info)))
	 end
      end

      local conf = user_scripts.getTargetHookConfig(flows_config, script)

      cur_user_script = script
      hook_fn(now, conf.script_conf or {})

      ::continue::
   end

   if do_trace then
      trace_f(string.format("%s()[END]: bitmap=0x%x alerted=%d score=%d flow.score=%d", 
         mod_fn, flow.getStatus(), flow.getAlertedStatus(), 
         alerted_status_score, flow.getAlertedStatusScore())
)
   end

   -- Only trigger the alert if its score is greater than the currently
   -- triggered alert score (when score is supported)
   if areAlertsEnabled() and alerted_status and (not flow.isAlerted() or alerted_status_score > flow.getAlertedStatusScore()) then
      -- Only trigger if the `alerted_status` has no `status_always_notify`. When the `alerted_status`
      -- has `status_always_notify` set to true, the alert has already been triggered.
      if not alerted_status.alert_type.status_always_notify then
	 triggerFlowAlert(now, alerted_status, alert_type_params, alerted_status_score)
      end
   end

   return true
end

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

local function setStatus(status_info, flow_score, cli_score, srv_score)
   -- A status is always set multiple times, causing flow scores to be increased every time, unless
   -- an explicity flag `status_keep_increasing_scores` is telling not to do so.
   -- There are flows (e.g., those representing security risks) where it is meaningful to increase scores multiple times
   -- so the longer the flow the higher the risk.
   -- There are other flows (e.g., long-lived flows kept active with keepalive) where it is pointless and misleading to
   -- keep increasing the score as this would result in flows with high scores only because they are long lived (See #4993),
   if not flow.isStatusSet(status_info.status_type.status_key) or status_info.status_type.alert_type.status_keep_increasing_scores then
      return flow.setStatus(status_info.status_type.status_key, flow_score, cli_score, srv_score, cur_user_script.key, cur_user_script.category.id)
   end

   -- Status already set and multiple score increases disabled with `status_keep_increasing_scores`
   return true
end

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

-- @brief This provides an API that flow user_scripts can call in order to
-- set a flow status bit. The status_info of the alerted status is
-- saved for later use.
function flow.triggerStatus(status_info, flow_score, cli_score, srv_score)
   flow_score = math.min(math.max(flow_score or 0, 0), flow_consts.max_score)
   cli_score = math.min(math.max(cli_score or 0, 0), flow_consts.max_score)
   srv_score = math.min(math.max(srv_score or 0, 0), flow_consts.max_score)

   if(tonumber(status_info) ~= nil) then
      tprint("Invalid status_info")
      tprint(debug.traceback())
      return
   end

   -- Check if there is an alert filter for this guy and possibly exclude the generation
   if cur_user_script and cur_user_script.key and flows_filters then
      if user_scripts.matchExcludeFilter(flows_filters, cur_user_script, "flow") then
	 -- This flow is matching an exclusion filter. return, and don't trigger anything
	 return
      end
   end

   -- Decide if this triggered status is also the alerted status, that is, the predominant
   -- alerted status for this flow
   if not alerted_status or flow_score > alerted_status_score then
      -- The new alerted status as an higher score
      alerted_status = status_info.status_type
      alert_type_params = status_info["alert_type_params"] or {}
      alerted_status_score = flow_score
      alerted_user_script = cur_user_script
   end

   setStatus(status_info, flow_score, cli_score, srv_score)

   -- A notification is only emitted for the predominant status, once all flow checks have been processed
   -- and all statuses have been set.
   -- However, if the current status has the `status_always_notify`, a notification MUST always be emitted
   -- even if it is not the predominant status.
   if status_info.status_type.alert_type.status_always_notify then
      triggerFlowAlert(os.time(), status_info.status_type, status_info["alert_type_params"], flow_score)
   end
end

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

-- Given an L4 protocol, we must call both the hooks registered for that protocol and
-- the hooks registered for any L4 protocol (id 255)
function protocolDetected(l4_proto, master_id, app_id)
   return call_modules(l4_proto, master_id, app_id, "protocolDetected")
end

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

function statusChanged(l4_proto, master_id, app_id)
   return call_modules(l4_proto, master_id, app_id, "statusChanged")
end

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

function flowEnd(l4_proto, master_id, app_id)
   return call_modules(l4_proto, master_id, app_id, "flowEnd")
end

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

function periodicUpdate(l4_proto, master_id, app_id, update_ctr)
   return call_modules(l4_proto, master_id, app_id, "periodicUpdate", update_ctr)
end