Since the first day of training camp last year, when they announced a new deal for defensive end Everson Griffen as players checked into the dorm at Minnesota State-Mankato, the Vikings have been working diligently to check off items on a shopping list that only figured to get more complicated with time.

The success of their 2015 draft, and the expiration of initial deals for Griffen and defensive tackle Linval Joseph, meant the Vikings had six key players set to hit the open market after the 2018 season. Five of them — Griffen, Joseph, cornerback Xavier Rhodes, linebackers Eric Kendricks and Anthony Barr and defensive end Danielle Hunter — were on a defense that had formed the bedrock of the team's rebuilding project under Mike Zimmer, and it was no secret the Vikings (who have been among the league's most aggressive teams in the draft under general manager Rick Spielman) were going to do what they could to keep the group together.

So the Vikings hammered out deals with Griffen and Joseph during training camp last year, breaking precedent by reworking the veterans' deals with two years remaining and earning praise from Griffen's agent Brian Murphy for their proactive approach. Xavier Rhodes, who was due to become a free agent after 2017, got a five-year deal during training camp that made him one of the league's highest paid cornerbacks.

The next step in the process came on Monday, when players reported for the first day of offseason workouts at the team's new facility in Eagan. The Vikings' announcement of Kendricks' five-year deal — timed, as the team's extensions often are, to coincide with a key date in the NFL calendar for dramatic effect — made the middle linebacker one of the league's four highest-paid players at his position. It came a month and a day after the Vikings gave Kirk Cousins his fully-guaranteed contract, and signaled once again that the team has no intention of decimating its defense after giving big money to a quarterback.

It's an ambitious plan made easier by the shrewd salary cap management of Rob Brzezinski, the team's vice president of football operations, and the Vikings now have just three players remaining on their list of possible contract extensions: Barr, Hunter and wide receiver Stefon Diggs. There's reason to think, however, that the last three players on the list might be the trickiest to re-sign.

Hunter, who has 25 1/2 sacks in his first three seasons, doesn't turn 24 until Oct. 29. At a position where the franchise tag currently sits at $17.143 million and eight players (including Griffen) currently command salaries of more than $10 million a year, Hunter will have a strong hand to play in the open market, should he get there. He'd hit free agency at the same time as pass rushers like Cameron Wake, Ezekiel Ansah and Cliff Avril, but he's younger than all of them.

If Hunter is in line for a handsome payday as a premium pass rusher, Barr is already in line to receive one because of the position he plays (or, perhaps more accurately, because of the position his cohorts play). As the ninth overall pick in the 2014 draft, he's playing on a fifth-year option equal to the transition tag at linebacker, which will be worth $12.3 million this season. Because the NFL doesn't separate 4-3 linebackers from players who rack up sacks and get paid for their pass-rushing production in a 3-4 system, like Von Miller and Justin Houston, Barr's fifth-year option reflects the hefty salaries those players earn. He'll be the highest-paid 4-3 outside linebacker in the NFL this season, with all of his money guaranteed. It puts him in an enviable negotiating position, if the Vikings are interested in designing an extension that starts by reducing his 2018 cap number. And while Barr is now represented by Brian Murphy — the Athletes First agent whose long relationship with the Vikings includes deals for Griffen, Harrison Smith, Kyle Rudolph and John Sullivan — the particulars of his play at his position could make for an interesting set of negotiations.

And Diggs, as our Andrew Krammer outlined earlier this month, is in a strong position to get paid next spring, as well, thanks to deals for Davante Adams in Green Bay, Allen Robinson in Chicago and Jarvis Landry in Cleveland. He's represented by Adisa Bakari, who counts Le'Veon Bell among his clients, and Diggs is coming off a scene-stealing playoff moment that undoubtedly raised his national profile. In his case, too, things will be interesting for the Vikings. Do they pay him more than Adam Thielen, who caught 91 passes and earned a trip to the Pro Bowl on a deal that already looks like a bargain? Do they rework Thielen's deal to keep his salary in line with what Diggs would earn? One idea might be for the Vikings to give Thielen a raise now (to, say, $10 million a year), to effectively establish a ceiling for what they would pay Diggs and head off a potentially awkward situation with a popular local player next summer. Thielen won't be a free agent until 2021, and he's not in possession of much leverage for the time being, but the Vikings might be able to use his situation to help themselves in their talks with Diggs.

It all adds up to a complex, and intriguing, 11 months until those players hit free agency. The Vikings have worked through four extensions in the past nine months, first picking off the deals that might have been the most straightforward. With the next three, the choices could get harder.