I've heard it said many times that "everyone who wasn't Joseph Stalin" could see the German attack on Russia coming a mile away. Is this true? Were the Western Powers aware that Germany was planning to attack Russia? What about Japan? I know that Germany didn't inform Japan until hours before the attack, but did their intelligence service predict it?
And what about within Russia itself? Did members of the government who weren't Stalin see the attack coming? Finally, why did Stalin himself fail to predict the attack?
The Swedes actually had almost full access to the German deployments for Operation Barbarossa.
When the Germans invaded Norway, they demanded that Sweden keep the telephone and telegraph lines from Norway to the continent (which ran over Sweden) open. Sweden obliged and wiretapped them.
The Germans used a slightly less advanced derivate of the Enigma for wired communications, called the Geheimschreiber. The Swedish mathematician Arne Beurling managed to crack this device and from late 1940 until late 1943 Sweden could read about 80-95% of all messages sent between Norway and Germany. This included army level staff reports and deployments, including the plans for Operation Barbarossa.
Sweden did pass on warnings to the Soviets, who refused to listen.
Source: "Svenska kryptobedrifter" by Bengt Beckman.
I can recommend a book called 'The Grand Delusion' on the issue of warnings about Barbarossa.