--[[
Copyright (c) 2019, Vsevolod Stakhov <vsevolod@highsecure.ru>
Copyright (c) 2019, Carsten Rosenberg <c.rosenberg@heinlein-support.de>

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
]]--

--[[[
-- @module spamassassin
-- This module contains spamd access functions.
--]]

local lua_util = require "lua_util"
local tcp = require "rspamd_tcp"
local upstream_list = require "rspamd_upstream_list"
local rspamd_logger = require "rspamd_logger"
local common = require "lua_scanners/common"

local N = 'spamassassin'

local function spamassassin_config(opts)

  local spamassassin_conf = {
    N = N,
    scan_mime_parts = false,
    scan_text_mime = false,
    scan_image_mime = false,
    default_port = 783,
    timeout = 15.0,
    log_clean = false,
    retransmits = 2,
    cache_expire = 3600, -- expire redis in one hour
    symbol = "SPAMD",
    message = '${SCANNER}: Spamassassin bulk message found: "${VIRUS}"',
    detection_category = "spam",
    default_score = 1,
    action = false,
    extended = false,
    symbol_type = 'postfilter',
    dynamic_scan = true,
  }

  spamassassin_conf = lua_util.override_defaults(spamassassin_conf, opts)

  if not spamassassin_conf.prefix then
    spamassassin_conf.prefix = 'rs_' .. spamassassin_conf.name .. '_'
  end

  if not spamassassin_conf.log_prefix then
    if spamassassin_conf.name:lower() == spamassassin_conf.type:lower() then
      spamassassin_conf.log_prefix = spamassassin_conf.name
    else
      spamassassin_conf.log_prefix = spamassassin_conf.name .. ' (' .. spamassassin_conf.type .. ')'
    end
  end

  if not spamassassin_conf.servers then
    rspamd_logger.errx(rspamd_config, 'no servers defined')

    return nil
  end

  spamassassin_conf.upstreams = upstream_list.create(rspamd_config,
    spamassassin_conf.servers,
    spamassassin_conf.default_port)

  if spamassassin_conf.upstreams then
    lua_util.add_debug_alias('external_services', spamassassin_conf.N)
    return spamassassin_conf
  end

  rspamd_logger.errx(rspamd_config, 'cannot parse servers %s',
    spamassassin_conf.servers)
  return nil
end

local function spamassassin_check(task, content, digest, rule)
  local function spamassassin_check_uncached ()
    local upstream = rule.upstreams:get_upstream_round_robin()
    local addr = upstream:get_addr()
    local retransmits = rule.retransmits

    -- Build the spamd query
    -- https://svn.apache.org/repos/asf/spamassassin/trunk/spamd/PROTOCOL
    local request_data = {
      "HEADERS SPAMC/1.5\r\n",
      "User: root\r\n",
      "Content-length: ".. #content .. "\r\n",
      "\r\n",
      content,
    }

    local function spamassassin_callback(err, data, conn)

      local function spamassassin_requery(error)
        -- set current upstream to fail because an error occurred
        upstream:fail()

        -- retry with another upstream until retransmits exceeds
        if retransmits > 0 then

          retransmits = retransmits - 1

          lua_util.debugm(rule.N, task, '%s: Request Error: %s - retries left: %s',
            rule.log_prefix, error, retransmits)

          -- Select a different upstream!
          upstream = rule.upstreams:get_upstream_round_robin()
          addr = upstream:get_addr()

          lua_util.debugm(rule.N, task, '%s: retry IP: %s:%s',
            rule.log_prefix, addr, addr:get_port())

          tcp.request({
            task = task,
            host = addr:to_string(),
            port = addr:get_port(),
            timeout = rule['timeout'],
            data = request_data,
            callback = spamassassin_callback,
          })
        else
          rspamd_logger.errx(task, '%s: failed to scan, maximum retransmits '..
            'exceed - err: %s', rule.log_prefix, error)
          common.yield_result(task, rule, 'failed to scan and retransmits exceed: ' .. error, 0.0, 'fail')
        end
      end

      if err then

        spamassassin_requery(err)

      else
        -- Parse the response
        if upstream then upstream:ok() end

        --lua_util.debugm(rule.N, task, '%s: returned result: %s', rule.log_prefix, data)

        --[[
        patterns tested against Spamassassin 3.4.2

        Spam: False ; 1.1 / 5.0

        X-Spam-Status: No, score=1.1 required=5.0 tests=HTML_MESSAGE,MIME_HTML_ONLY,
          TVD_RCVD_SPACE_BRACKET,UNPARSEABLE_RELAY autolearn=no
          autolearn_force=no version=3.4.2
        ]] --
        local header = string.gsub(tostring(data), "[\r\n]+[\t ]", " ")
        --lua_util.debugm(rule.N, task, '%s: returned header: %s', rule.log_prefix, header)

        local symbols
        local spam_score
        for s in header:gmatch("[^\r\n]+") do
          if string.find(s, 'X%-Spam%-Status: %S+, score') then
            local pattern_symbols = "X%-Spam%-Status: %S+, score%=(%d+%.%d+) .* tests=(.*,)( +%S+).*"
            spam_score = string.gsub(s, pattern_symbols, "%1")
            lua_util.debugm(rule.N, task, '%s: spamd Spam line: %s', rule.log_prefix, spam_score)
            symbols = string.gsub(s, pattern_symbols, "%2%3")
            symbols = string.gsub(symbols, "%s", "")
          end
        end

        if tonumber(spam_score) > 0 and #symbols > 0 and symbols ~= "none" then

          if rule.extended == false then
            common.yield_result(task, rule, symbols, spam_score)
            common.save_cache(task, digest, rule, symbols, spam_score)
          else
            local symbols_table = {}
            symbols_table = lua_util.str_split(symbols, ",")
            lua_util.debugm(rule.N, task, '%s: returned symbols as table: %s', rule.log_prefix, symbols_table)

            common.yield_result(task, rule, symbols_table, spam_score)
            common.save_cache(task, digest, rule, symbols_table, spam_score)
          end
        else
          common.save_cache(task, digest, rule, 'OK')
          common.log_clean(task, rule, 'no spam detected - spam score: ' .. spam_score .. ', symbols: ' .. symbols)
        end
      end
    end

    tcp.request({
      task = task,
      host = addr:to_string(),
      port = addr:get_port(),
      timeout = rule['timeout'],
      data = request_data,
      callback = spamassassin_callback,
    })
  end

  if common.condition_check_and_continue(task, content, rule, digest, spamassassin_check_uncached) then
    return
  else
    spamassassin_check_uncached()
  end

end

return {
  type = {N,'spam', 'scanner'},
  description = 'spamassassin spam scanner',
  configure = spamassassin_config,
  check = spamassassin_check,
  name = N
}
