-- TrapOS networking: service-name bus on a single channel.
--
-- Servers register handlers on the boot eventloop:
--   net.serve('ping', function(msg, reply) reply('pong') end)
--   net.listen('events.foo', function(msg, packet) ... end)
--
-- Clients (CLI programs) call or send without an eventloop:
--   local ok, res = net.call('ping', 'ping', { destId = 5, timeout = 0.5 })
--   net.send('events.foo', payload, { destId = 'alice' })
--
-- A router service (servers/router-server.lua) must run on exactly one machine.
-- It resolves label-addressed packets, stamps routerId, and rebroadcasts.
local createEventLoop = require('/apis/eventloop');

local BUS_CHANNEL = 10;
local DEFAULT_TIMEOUT = 0.5;

local nextRequestSeq = 1;
local function newRequestId()
  local id = tostring(os.getComputerID()) .. ':' .. tostring(nextRequestSeq) .. ':' .. tostring(os.clock());
  nextRequestSeq = nextRequestSeq + 1;
  return id;
end

local function isPacketOk(packet)
  if type(packet) ~= 'table' then return false end
  if not packet.routerId or not packet.sourceId then return false end
  if packet.destId == nil then return true end
  if type(packet.destId) == 'number' and packet.destId == os.getComputerID() then return true end
  if type(packet.destId) == 'string' and packet.destId == os.getComputerLabel() then return true end
  return false
end

local function createNetwork(el, modem, modemSide)
  el = el or createEventLoop();
  modem = modem or peripheral.find('modem') or error('modem not found');
  modem.open(BUS_CHANNEL);

  local isRouter = false;
  modemSide = modemSide or peripheral.getName(modem);

  local function buildPacket(service, kind, payload, destId, requestId)
    return {
      sourceId = os.getComputerID(),
      sourceLabel = os.getComputerLabel(),
      destId = tonumber(destId) or destId,
      service = service,
      kind = kind,
      requestId = requestId,
      payload = payload,
      routerId = isRouter and os.getComputerID() or nil,
    };
  end

  local function transmit(packet)
    local selfId = os.getComputerID();
    local selfLabel = os.getComputerLabel();

    local destIsSelfId = packet.destId == selfId;
    local destIsSelfLabel = selfLabel ~= nil and packet.destId == selfLabel;
    local destIsSelf = destIsSelfId or destIsSelfLabel;
    local matchesSelf = packet.destId == nil or destIsSelf;

    if matchesSelf then
      local localPacket = {};
      for k, v in pairs(packet) do localPacket[k] = v end
      localPacket.routerId = localPacket.routerId or selfId;
      os.queueEvent('modem_message', modemSide, BUS_CHANNEL, BUS_CHANNEL, localPacket, 0);
    end

    if not destIsSelf then
      modem.transmit(BUS_CHANNEL, BUS_CHANNEL, packet);
    end
  end

  local function serve(serviceName, handler)
    return el.register('modem_message', function(_, _, replyChannel, packet)
      if replyChannel ~= BUS_CHANNEL then return end
      if not isPacketOk(packet) then return end
      if packet.service ~= serviceName or packet.kind ~= 'req' then return end

      local function reply(responsePayload)
        local response = buildPacket(serviceName, 'res', responsePayload, packet.sourceId, packet.requestId);
        transmit(response);
      end

      handler(packet.payload, reply, packet);
    end);
  end

  local function listen(serviceName, handler)
    return el.register('modem_message', function(_, _, replyChannel, packet)
      if replyChannel ~= BUS_CHANNEL then return end
      if not isPacketOk(packet) then return end
      if packet.service ~= serviceName or packet.kind ~= 'evt' then return end

      handler(packet.payload, packet);
    end);
  end

  local function send(serviceName, payload, opts)
    opts = opts or {};
    transmit(buildPacket(serviceName, 'evt', payload, opts.destId, nil));
  end

  local function awaitResponse(serviceName, requestId, timeout, collectMultiple)
    local timerId = os.startTimer(timeout);
    local results = {};
    local packets = {};

    while true do
      local event, p1, _, p3, p4 = os.pullEvent();
      if event == 'timer' and p1 == timerId then
        if collectMultiple then
          if #results == 0 then return false, 'net.call timeout', {} end
          return true, results, packets;
        end
        return false, 'net.call timeout', nil;
      elseif event == 'modem_message' then
        local replyChannel = p3;
        local recvPacket = p4;
        if replyChannel == BUS_CHANNEL
            and isPacketOk(recvPacket)
            and recvPacket.service == serviceName
            and recvPacket.kind == 'res'
            and recvPacket.requestId == requestId then
          if collectMultiple then
            table.insert(results, recvPacket.payload);
            table.insert(packets, recvPacket);
          else
            os.cancelTimer(timerId);
            return true, recvPacket.payload, recvPacket;
          end
        end
      end
    end
  end

  local function call(serviceName, payload, opts)
    opts = opts or {};
    local timeout = opts.timeout or DEFAULT_TIMEOUT;
    local requestId = newRequestId();
    transmit(buildPacket(serviceName, 'req', payload, opts.destId, requestId));
    return awaitResponse(serviceName, requestId, timeout, false);
  end

  local function callMultiple(serviceName, payload, opts)
    opts = opts or {};
    local timeout = opts.timeout or DEFAULT_TIMEOUT;
    local requestId = newRequestId();
    transmit(buildPacket(serviceName, 'req', payload, opts.destId, requestId));
    return awaitResponse(serviceName, requestId, timeout, true);
  end

  local function setRouter(enabled)
    isRouter = enabled and true or false;
  end

  local function onUnrouted(handler)
    return el.register('modem_message', function(_, _, replyChannel, packet)
      if replyChannel ~= BUS_CHANNEL then return end
      if type(packet) ~= 'table' then return end
      if packet.routerId then return end
      if not packet.sourceId then return end
      handler(packet);
    end);
  end

  local function rebroadcast(packet)
    packet.routerId = packet.routerId or os.getComputerID();
    local selfId = os.getComputerID();
    local selfLabel = os.getComputerLabel();
    local destIsSelfId = packet.destId == selfId;
    local destIsSelfLabel = selfLabel ~= nil and packet.destId == selfLabel;
    local destIsSelf = destIsSelfId or destIsSelfLabel;
    local matchesSelf = packet.destId == nil or destIsSelf;

    if matchesSelf then
      os.queueEvent('modem_message', modemSide, BUS_CHANNEL, BUS_CHANNEL, packet, 0);
    end
    if not destIsSelf then
      modem.transmit(BUS_CHANNEL, BUS_CHANNEL, packet);
    end
  end

  return {
    BUS_CHANNEL = BUS_CHANNEL,
    DEFAULT_TIMEOUT = DEFAULT_TIMEOUT,
    eventloop = el,
    isPacketOk = isPacketOk,
    serve = serve,
    listen = listen,
    send = send,
    call = call,
    callMultiple = callMultiple,
    setRouter = setRouter,
    onUnrouted = onUnrouted,
    rebroadcast = rebroadcast,
  };
end

local singleton = nil;

return function(el, modem, modemSide)
  if el == nil and modem == nil and _G.bootEventLoop then
    if not singleton then
      singleton = createNetwork(_G.bootEventLoop, nil, nil);
    end
    return singleton;
  end
  return createNetwork(el, modem, modemSide);
end