SAN FRANCISCO — The most important thing you need to know about what the Giants are thinking ahead of tonight’s draft is this: Nobody ever knows what they’re thinking.

Brian Sabean, Bobby Evans, John Barr and the rest guard their draft preferences more closely than anything else. For better or worse, the Giants tend to surprise on draft night.

They have not, generally, had that much success with prospects in recent years. But sometimes they surprise the industry and it turns out they were right on the mark. Seven years ago, with the 29th overall pick, they selected a shortstop out of St. John’s who wasn’t considered even a second-rounder by most draft experts. One prominent draft writer tweeted that the kid would be a utility infielder.

It turns out Joe Panik is pretty good.

Last year, the Giants surprised everyone by taking Heliot Ramos in the middle of the first round, and they feel they got a steal there, too. There’s a decent chance tonight will be unpredictable. But there’s a lot we do know. Here’s a rundown…

When is the draft? MLB Network and MLB.com will start pre-draft coverage at 3 p.m. and the actual draft will begin at 4 p.m. Round 1 and Competitive Balance Round A (this is a real thing) will air live and coverage will move online for Round 2. The second day of the draft (Tuesday) will feature Round 3-10. The next day will be rapid-fire from Round 11-40. There are four minutes between picks in Round 1, so the Giants should have their top selection well before manager Bruce Bochy does his daily media session at 4:30.

Why are the Giants picking second? Because 2017 was a slow, lifeless march to 98 losses, during which the lineup failed to hit for power, the bullpen piled up blown saves, the ace crashed on an off day, the other ace had the worst year of his career, and every call-up got hurt. Oh, and on the final day, Pablo Sandoval hit a walk-off to avoid a 99th loss. So the Detroit Tigers will pick first. The Phillies, White Sox and Reds round out the top five. The Giants will make their second round selection at No. 45 after the compensatory rounds.

Have the Giants picked this high before? Yes, and it worked out! This is their highest pick since 1985, when they chose Will Clark second overall. Clark hit .299 in eight years with the Giants, with 176 homers and 709 RBI, and changed the outlook of the franchise. The last time they picked in the top five the Giants took Buster Posey out of Florida State.

What’s the success rate for No. 2 picks? Justin Verlander, Alex Gordon, Mike Moustakas, Kris Bryant and Alex Bregman are among the players selected second overall in the past two decades. So are Dustin Ackley, Danny Hultzen and Greg Reynolds. It's a bit of a crapshoot. But if you choose the right guy, there's a very good chance he will move up through the minors quickly.

Who do the experts think the Giants will take? The consensus is that the Giants are leaning toward Joey Bart, a right-handed catcher from Georgia Tech. He hit .359 this season with a .471 on-base percentage and 16 homers in 57 starts.

But will they take him? As mentioned above, it’s foolish to connect the Giants to a specific player. Did you see a Giants scout right behind the plate at a college game? Well, Dick Tidrow was hiding behind a tree at a high school game somewhere else and that's what really matters.

A few draft experts have written that Bart can be the succession plan to Buster Posey, but that’s flawed thinking. Posey is signed through 2021 and the Giants are in no rush to move him to first, in part because he still is elite behind the plate and in part because the team’s actual best hitter plays first base. Also, remember this: The top of the draft is generally about "best player available," but the men making this selection might not have much time to turn this mess around, and it seems unlikely that they would select someone who would be blocked at the big league level for years.

So, what’s the prediction? The front office has gone dark in recent weeks, but some sources believe the Giants are leaning toward a college pitcher. Casey Mize is expected to go first overall, so the pick here is Brady Singer, a right-hander from Florida.

Will Ryan Vogelsong be involved? Of course. Vogey and Mike Murphy, the legend, will represent the Giants at the MLB Network Studio in New Jersey. Vogelsong, selected in the fifth round of the 1998 draft, has been doing some work for the front office recently.