-- TrapOS router state machine: (label -> id) map with TTL.
--
-- Pure logic so it can be unit-tested without a modem or eventloop.
-- The wire glue lives in /programs/router.lua.
local DEFAULT_TTL = 90;

local function createRouter(options)
  options = options or {};
  local ttl = options.ttl or DEFAULT_TTL;
  local nowFn = options.now or os.clock;

  local labelMap = {};

  local function isExpired(entry)
    return entry.expiresAt < nowFn();
  end

  local function register(label, id)
    local existing = labelMap[label];
    if existing and existing.id ~= id and not isExpired(existing) then
      return false, 'duplicate label';
    end
    labelMap[label] = { id = id, expiresAt = nowFn() + ttl };
    return true;
  end

  local function resolve(label)
    local entry = labelMap[label];
    if not entry then return nil end
    if isExpired(entry) then
      labelMap[label] = nil;
      return nil;
    end
    return entry.id;
  end

  local function forget(label)
    labelMap[label] = nil;
  end

  return {
    register = register,
    resolve = resolve,
    forget = forget,
    ttl = ttl,
  };
end

return createRouter;