#AHK, 208 bytes

AutoTrim,Off
w=%1%
b=%2%
f:=Mod(b,w)
Loop,%w%
s=%s%---
s=|%s%|`n
If (f>0) {
Loop,%f%
t=%t%|X|
Loop,% w-f
t=%t% ` ` `
t=|%t%|`n
t:=s t t t s
}
Loop,%w%
r=%r%|X|
r=|%r%|`n
Loop,% (b-f)/w
t:=t s r r r s
Send,%t%

There are a few things frustating me from golfing further:

• AutoHotkey doesn't have a built-in repeat function
• You can't directly use the passed in arguments (%1% & %2%) in math functions because those expect variable or number input and it will assume the unescaped 1 to be the number one rather than the variable name
• I am not very good at golfing

An easier to read version of the above looks like this:

AutoTrim,Off
w=%1%
b=%2%
f:=Mod(b,w)

Loop,%w%
   s=%s%---
s=|%s%|`n

If (f>0) {
   Loop,%f%
      t=%t%|X|
   Loop,% w-f
      t=%t% ` ` `
   t=|%t%|`n
   t:=s t t t s
}

Loop,%w%
   r=%r%|X|
r=|%r%|`n

Loop,% (b-f)/w
   t:=t s r r r s

Send,%t%

If a Loop doesn't use brackets {}, then only the next line is part of the loop. If setting a variable's value using := instead of =, you can drop the percent sign escape characters. Tilde n is the newline character.

AHK, 208 bytes

AutoTrim,Off
w=%1%
b=%2%
f:=Mod(b,w)
Loop,%w%
s=%s%---
s=|%s%|`n
If (f>0) {
Loop,%f%
t=%t%|X|
Loop,% w-f
t=%t% ` ` `
t=|%t%|`n
t:=s t t t s
}
Loop,%w%
r=%r%|X|
r=|%r%|`n
Loop,% (b-f)/w
t:=t s r r r s
Send,%t%

There are a few things frustating me from golfing further:

• AutoHotkey doesn't have a built-in repeat function
• You can't directly use the passed in arguments (%1% & %2%) in math functions because those expect variable or number input and it will assume the unescaped 1 to be the number one rather than the variable name
• I am not very good at golfing

An easier to read version of the above looks like this:

AutoTrim,Off
w=%1%
b=%2%
f:=Mod(b,w)

Loop,%w%
   s=%s%---
s=|%s%|`n

If (f>0) {
   Loop,%f%
      t=%t%|X|
   Loop,% w-f
      t=%t% ` ` `
   t=|%t%|`n
   t:=s t t t s
}

Loop,%w%
   r=%r%|X|
r=|%r%|`n

Loop,% (b-f)/w
   t:=t s r r r s

Send,%t%

If a Loop doesn't use brackets {}, then only the next line is part of the loop. If setting a variable's value using := instead of =, you can drop the percent sign escape characters. Tilde n is the newline character.