--[[
Copyright (c) 2016, Vsevolod Stakhov <vsevolod@highsecure.ru>

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.
]]--

-- MX check plugin
local rspamd_logger = require "rspamd_logger"
local rspamd_tcp = require "rspamd_tcp"
local rspamd_util = require "rspamd_util"
local fun = require "fun"

local settings = {
  timeout = 1.0, -- connect timeout
  symbol_bad_mx = 'MX_INVALID',
  symbol_no_mx = 'MX_MISSING',
  symbol_good_mx = 'MX_GOOD',
  expire = 86400, -- 1 day by default
  expire_novalid = 7200, -- 2 hours by default for no valid mxes
  greylist_invalid = false, -- Greylist first message with invalid MX (require greylist plugin)
  key_prefix = 'rmx'
}
local redis_params

local function mx_check(task)
  local ip_addr = task:get_ip()
  if task:get_user() or (ip_addr and ip_addr:is_local()) then
    return
  end

  local from = task:get_from('smtp')
  local mx_domain
  if from and from[1] and from[1]['domain'] and not from[2] then
    mx_domain = from[1]['domain']
  else
    mx_domain = task:get_helo()

    if mx_domain then
      mx_domain = rspamd_util.get_tld(mx_domain)
    end
  end

  if not mx_domain then
    return
  end

  local valid = false

  local function check_results(mxes)
    if fun.all(function(_, elt) return elt.checked end, mxes) then
      -- Save cache
      local key = settings.key_prefix .. mx_domain
      local function redis_cache_cb(err)
        if err ~= nil then
          rspamd_logger.errx(task, 'redis_cache_cb received error: %1', err)
          return
        end
      end
      if not valid then
        -- Greylist message
        if settings.greylist_invalid then
          local grey_is_whitelisted = task:get_mempool():get_variable("grey_whitelisted")
          if not grey_is_whitelisted then
            task:get_mempool():set_variable("grey_greylisted_required", "1")
            task:insert_result(settings.symbol_bad_mx, 1.0, "greylisted")
          end
        else
          task:insert_result(settings.symbol_bad_mx, 1.0)
        end
        local ret = rspamd_redis_make_request(task,
          redis_params, -- connect params
          key, -- hash key
          true, -- is write
          redis_cache_cb, --callback
          'SETEX', -- command
          {key, tostring(settings.expire_novalid), '0'} -- arguments
        )
        if not ret then
          rspamd_logger.errx(task, 'got error connecting to redis')
        end
      else
        local valid_mx = {}
        fun.each(function(k)
          table.insert(valid_mx, k)
        end, fun.filter(function (_, elt) return elt.working end, mxes))
        task:insert_result(settings.symbol_good_mx, 1.0, valid_mx)
        local ret = rspamd_redis_make_request(task,
          redis_params, -- connect params
          key, -- hash key
          true, -- is write
          redis_cache_cb, --callback
          'SETEX', -- command
          {key, tostring(settings.expire), table.concat(valid_mx, ';')} -- arguments
        )
        if not ret then
          rspamd_logger.errx(task, 'error connecting to redis')
        end
      end
    end
  end

  local function gen_mx_a_callback(name, mxes)
    return function(_, _, results, err)
      mxes[name].ips = results

      local function io_cb(io_err)
        if io_err then
          mxes[name].checked = true
        else
          mxes[name].checked = true
          mxes[name].working = true
          valid = true
        end
        check_results(mxes)
      end
      local function on_connect_cb(conn)
        if err then
          mxes[name].checked = true
        else
          mxes[name].checked = true
          valid = true
          mxes[name].working = true
        end
        conn:close()
        check_results(mxes)
      end

      if err or not results then
        mxes[name].checked = true
      else
        -- Try to open TCP connection to port 25
        for _,res in ipairs(results) do
          local t_ret = rspamd_tcp.new({
            task = task,
            host = res:to_string(),
            callback = io_cb,
            on_connect = on_connect_cb,
            timeout = settings.timeout,
            port = 25
          })

          if not t_ret then
            mxes[name].checked = true
          end
        end
      end
      check_results(mxes)
    end
  end

  local function mx_callback(_, _, results, err)
    local mxes = {}
    if err or not results then
      local r = task:get_resolver()
      -- XXX: maybe add ipv6?
      -- fallback to implicit mx
      mxes[mx_domain] = {checked = false, working = false, ips = {}}
      r:resolve('a', {
        name = mx_domain,
        callback = gen_mx_a_callback(mx_domain, mxes),
        task = task,
        forced = true
      })
      task:insert_result(settings.symbol_no_mx, 1.0, err)
    else
      table.sort(results, function(r1, r2)
        return r1['priority'] < r2['priority']
      end)
      for _,mx in ipairs(results) do
        -- Not checked
        mxes[mx['name']] = {checked = false, working = false, ips = {}}
      end

      for _,mx in ipairs(results) do
        local r = task:get_resolver()
        -- XXX: maybe add ipv6?
        r:resolve('a', {
          name = mx['name'],
          callback = gen_mx_a_callback(mx['name'], mxes),
          task = task,
          forced = true
        })
      end
      check_results(mxes)
    end
  end

  if not redis_params then
    local r = task:get_resolver()
    r:resolve('mx', {
      name = mx_domain,
      callback = mx_callback,
      task = task,
      forced = true
    })
  else
    local function redis_cache_get_cb(err, data)
      if err or type(data) ~= 'string' then
        local r = task:get_resolver()
        r:resolve('mx', {
          name = mx_domain,
          callback = mx_callback,
          task = task,
          forced = true
        })
      else
        if data == '0' then
          task:insert_result(settings.symbol_bad_mx, 1.0, 'cached')
        else
          local mxes = rspamd_str_split(data, ';')
          task:insert_result(settings.symbol_good_mx, 1.0, 'cached: ' .. mxes[1])
        end
      end
    end

    local key = settings.key_prefix .. mx_domain
    local ret = rspamd_redis_make_request(task,
      redis_params, -- connect params
      key, -- hash key
      false, -- is write
      redis_cache_get_cb, --callback
      'GET', -- command
      {key} -- arguments
    )

    if not ret then
      local r = task:get_resolver()
      r:resolve('mx', {
        name = mx_domain,
        callback = mx_callback,
        task = task,
        forced = true
      })
    end
  end
end

-- Module setup
local opts = rspamd_config:get_all_opt('mx_check')
if not (opts and type(opts) == 'table') then
  rspamd_logger.infox(rspamd_config, 'module is unconfigured')
  return
end
if opts then
  redis_params = rspamd_parse_redis_server('mx_check')
  if not redis_params then
    rspamd_logger.errx(rspamd_config, 'no redis servers are specified, disabling module')
    return
  end
  for k,v in pairs(opts) do
    settings[k] = v
  end

  local id = rspamd_config:register_symbol({
    name = settings.symbol_bad_mx,
    type = 'normal',
    callback = mx_check,
  })
  rspamd_config:register_symbol({
    name = settings.symbol_no_mx,
    type = 'virtual',
    parent = id
  })
  rspamd_config:register_symbol({
    name = settings.symbol_good_mx,
    type = 'virtual',
    parent = id
  })

  rspamd_config:set_metric_symbol({
    name = settings.symbol_bad_mx,
    score = 4.0,
    description = 'Domain has no working MX',
    group = 'MX',
    one_shot = true,
    one_param = true,
  })
  rspamd_config:set_metric_symbol({
    name = settings.symbol_good_mx,
    score = -0.1,
    description = 'Domain has working MX',
    group = 'MX',
    one_shot = true,
    one_param = true,
  })
  rspamd_config:set_metric_symbol({
    name = settings.symbol_no_mx,
    score = 1.5,
    description = 'Domain has no resolvable MX',
    group = 'MX',
    one_shot = true,
    one_param = true,
  })
end
