--[[
nomoVM answering machine detection for FreeSWITCH.

Streams the answered call's audio to nomoVM with mod_audio_stream, waits for the verdict and sets:

  AMDSTATUS = HUMAN | MACHINE | FALLBACK
  AMDCAUSE  = HUMAN | MACHINE | SCREENING | SILENCE | TONE | BUSY | UNKNOWN      (HUMAN / MACHINE)
              AUTH | SUSPENDED | QUOTA | NOSERVER                                (FALLBACK)

FALLBACK means nomoVM can't judge this call (bad or disabled key, plan limit, service unreachable, or
mod_audio_stream not loaded). It is decided before the call's audio is used, so your dialplan can use
another detector or treat the call as before. A timeout or error after streaming started gives
MACHINE / UNKNOWN: only a confirmed HUMAN goes to an agent.

Needs mod_lua (standard) and mod_audio_stream (https://github.com/amigniter/mod_audio_stream, loaded with
`load mod_audio_stream`). Copy this file to FreeSWITCH's scripts folder (usually /usr/share/freeswitch/scripts
or /etc/freeswitch/scripts) and call it right after the call is answered:

  <action application="lua" data="nomovm_amd.lua wss://amd.nomovm.com/ YOUR_KEY 4500"/>
  <action application="log" data="INFO nomoVM: ${AMDSTATUS} ${AMDCAUSE}"/>

Arguments: WebSocket URL, API key, overall timeout in ms (default 4500; it must cover the service's
longest listening window, 3.2 s, plus network time).
]]

local VERSION = "1.0.0"
local HANDSHAKE_MS = 1000   -- no connection after this long: FALLBACK while the call is still fresh
local POLL_MS = 50

local function log(level, msg)
  freeswitch.consoleLog(level, "nomovm_amd: " .. msg .. "\n")
end

-- "amdstatus": "HUMAN" -> HUMAN (the verdict is small, flat JSON: no parser needed)
local function json_field(body, key)
  return body and body:match('"' .. key .. '"%s*:%s*"([^"]*)"') or nil
end

-- AMDSTATUS / AMDCAUSE from the service's verdict, with the HUMAN rule enforced
local function verdict_vars(body)
  local status, cause = json_field(body, "amdstatus"), json_field(body, "amdcause")
  if status == "FALLBACK" then
    return "FALLBACK", cause or "NOSERVER"
  end
  if status ~= "HUMAN" and status ~= "MACHINE" then
    return "MACHINE", "UNKNOWN"
  end
  if (status == "HUMAN") ~= (cause == "HUMAN") then
    return "MACHINE", (cause and cause ~= "HUMAN") and cause or "UNKNOWN"
  end
  return status, cause
end

local function run(session, api, url, key, timeout_ms)
  local uuid = session:get_uuid()
  if not url or url == "" or not key or key == "" then
    return "FALLBACK", "NOSERVER"
  end
  if key:find('[%s"\\]') then  -- the key goes into a JSON header value
    return "FALLBACK", "AUTH"
  end

  -- mod_audio_stream reads these when the stream starts
  session:setVariable("STREAM_EXTRA_HEADERS", '{"Authorization":"Bearer ' .. key .. '"}')
  session:setVariable("STREAM_NO_RECONNECT", "true")   -- the service closes after its verdict: don't reconnect
  session:setVariable("STREAM_SUPPRESS_LOG", "true")
  session:setVariable("STREAM_BUFFER_SIZE", "100")      -- 100 ms frames, like the Asterisk client

  local events = freeswitch.EventConsumer("CUSTOM", "mod_audio_stream::json")
  events:bind("CUSTOM", "mod_audio_stream::connect")
  events:bind("CUSTOM", "mod_audio_stream::disconnect")
  events:bind("CUSTOM", "mod_audio_stream::error")

  local start = '{"type":"start","call_id":"' .. uuid .. '"}'
  local reply = api:executeString("uuid_audio_stream " .. uuid .. " start " .. url .. " mono 8k " .. start) or ""
  if not reply:find("^%+OK") then
    log("WARNING", "uuid_audio_stream failed (is mod_audio_stream loaded?): " .. reply)
    return "FALLBACK", "NOSERVER"
  end

  -- api:getTime() is FreeSWITCH's clock in ms; without it, count poll steps (slightly long on busy servers)
  local function now() local ok, t = pcall(function() return tonumber(api:getTime()) end); return ok and t or nil end
  local t0 = now()
  local elapsed, connected = 0, false
  local status, cause = "MACHINE", "UNKNOWN"
  while elapsed < timeout_ms do
    if not session:ready() then break end     -- caller hung up
    local e = events:pop(1, POLL_MS)
    if e then
      local id = e:getHeader("Unique-ID") or e:getHeader("Channel-Call-UUID")
      if id == uuid then
        local sub = e:getHeader("Event-Subclass") or ""
        local body = e:getBody() or ""
        if sub == "mod_audio_stream::connect" then
          connected = true
        elseif sub == "mod_audio_stream::json" then
          status, cause = verdict_vars(body)
          break
        elseif sub == "mod_audio_stream::error" then
          log("WARNING", "stream error: " .. body)
          if not connected then status, cause = "FALLBACK", "NOSERVER" end  -- nothing was streamed yet
          break
        elseif sub == "mod_audio_stream::disconnect" then
          break                               -- closed without a verdict: MACHINE / UNKNOWN
        end
      end
    end
    local t = t0 and now()
    if t then elapsed = t - t0 else elapsed = elapsed + POLL_MS end
    if not connected and elapsed >= HANDSHAKE_MS then
      log("WARNING", "no connection to " .. url .. " after " .. HANDSHAKE_MS .. " ms")
      status, cause = "FALLBACK", "NOSERVER"
      break
    end
  end
  api:executeString("uuid_audio_stream " .. uuid .. " stop")
  return status, cause
end

-- when FreeSWITCH runs the script (tests load it with `session` unset and call the returned table)
if session then
  local api = freeswitch.API()
  local status, cause = run(session, api, argv[1], argv[2], tonumber(argv[3] or "") or 4500)
  session:setVariable("AMDSTATUS", status)
  session:setVariable("AMDCAUSE", cause)
  log("INFO", status .. " " .. cause)
end

return { run = run, verdict_vars = verdict_vars, VERSION = VERSION }