Foresightful Fighting (Unrestricted by race or class)

Activation is needed:

This feat allows a character to gain a bonus to attack and defense in close combat after activation. The bonus from this feat equals the character's Wisdom score divided by two (rounded down, but always at least 1, and no more than 3, or at the discretion of the Dungeon Master).

If two foresightful fighters clash, the character with the higher "Foresightful Fighting" value gains the corresponding bonus minus the opponent's value, if the value of both opponents is the same, it is subtracted from both. If the value is less than 1, the character has no bonus. This feat cannot be used against ranged or firearm weapons (basically against attacks from more than 3 or 4 meters away).

It can be activated as many times as the character's Proficiency Bonus value after completing a long rest.

It always applies even without activation:

The character cannot be unexpectedly ambushed from behind (applies absolutely always), if they can actively defend themselves (e.g. not bound, paralyzed, etc.), but for this case the bonus is not counted (the character receives only the ability to actively defend themselves). In combat in absolute darkness, if the character is blinded or the "Foresightful Fighting" bonus is reduced to 0, they can only defend themselves without penalty, but do not gain other bonuses from the feat and still cannot be ambushed from behind in close combat.

Okay, so, a few things.

There is no “from behind” in this edition of D&D, all creatures have a full 360º awareness at all times.

That whole “when two foresight fighters clash” section is way to convoluted. It’s also unnecessary since the math works out the same statistically if you just completely omit that part since the relative bonuses would just negate each other anyway.

Barring some extremely unusual homebrew, a PCs max Wis modifier can’t ever exceed +6, and that requires some significantly powerful magic items, so you could probably drop the maximum bonus of +3. The chances of anyone having a bonus of +8 or higher to exceed +3 after rounding down are so low as to be not worth worrying about.

You wrote that after activating the feat they gain a bonus to “attack and defense in close combat,” but didn’t specify if that bonus only applies to AC or also to saving throws or anything.

You never specified how long the feat stays active once activated.

From how I have interpreted what you wrote, this is what I think you’re going for with your feat:

Foresightful Fighting

While not blinded, deafened, or incapacitated, you cannot be surprised.

In addition while you are not blinded, deafened, or incapacitated, you can activate this feat as an action to gain additional advantages in combat. When you do so, for the next 1 minute you gain the following benefits:

• You gain a bonus to your melee attack rolls equal to half your Wisdom modifier (rounded down, minimum 1).
• You gain a bonus to your AC against melee attacks equal to half your Wisdom modifier (rounded down, minimum 1).

You can activate this feat a number of times equal to your proficiency bonus, and regain all uses of this feat whenever you finish a long rest.

Does that seem about right as for what you wanted?

First thing: you don't have to specify it is unrestricted by race or class; this is the default rule, and exceptions are rare.

The wording for this is a bit confusing, so I'm going to rewrite what I think it's supposed to do. italic is vague wording/interpretation, bold is balance changes. correct me if I'm wrong.

When initiative is rolled or at any time during your turn, you can activate forsightful fighting to gain a bonus to attack rolls and AC equal to half your wisdom modifier rounded down (to a minimum of 1) against creatures within 5 feet.  You cannot do this while blinded. You lose this bonus once initiative ends. You can do this a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

This is what I assume the majority of this feat is supposed to do. A "bonus to attack and defense" was translated to numeric values, being AC and a hit bonus. Additionally, I assume you meant Wisdom modifier and score, as most wisdom scores won't be less than 4, unless they rolled poorly with stats. I changed 3 or 4 meters to 5, because unless your in a grapple, all attacks are at least 5 feet away. (5 is the default range for melee attacks) The "absolute darkness" line from the final paragraph was merged into this, but as the blinded condition for more clarity. Additionally, the second paragraph was entirely removed, as bonuses to AC and attack rolls will naturally cancel each other out. Because the use case for the portion is already small (a monster has to have the same feat as a PC and be within melee range of two, one with the feat and one without) I removed it for clarity. Now for the second part:

You cannot be surprised as long as you are not incapacitated, grappled, or blinded. However, if you would have been surprised, you cannot activate forsightful fighting until the second round of combat.

I had a lot of trouble understanding the final paragraph, but this is what I think it means. I don't anything to comment here.

Balance comments: AC bonuses are very powerful, and I would be careful handing them out. However, it's only a +1 or 2, and only in melee range, so that might balance out. I would make it a half feat (+1 to wisdom score) and remove the last paragraph about being surprised, as that has too much overlap with the Alert feat. melee characters struggle a lot compared to ranged ones anyway, so this probably wouldn't OP.