eacal, 386 bytes

init .
define @ curry push .
define ~ curry exec .--func
alias $ strap
alias ' string
set n set m cast number arg number 0
set s empty string
label l
@ get n
set n ~ dec
@ space
@ get n
$ ~ repeat
$ ' /----/
@ space
@ get m
@ get n
@ ~ sub
@ ~ dec
@ number 2
@ ~ mul
$ ~ repeat
$ ' \
$ newline
@ get n
@ number 0
if ~ more
goto l
@ $
@ regex gm '   ( {4})(?=.$)
@ '  \$1
print ~ replace

I have officially made the most verbose language possible. Instructions on how to run in the github repo linked in the header.

Ungolfed

init .
set n set m cast number arg number 0
set s empty string
label loop
    push . get n
    set n exec .--func dec
    push . space
    push . get n
    strap exec .--func repeat
    strap string /----/
    push . space
    push . get m
    push . get n
    push . exec .--func sub
    push . exec .--func dec
    push . number 2
    push . exec .--func mul
    strap exec .--func repeat
    strap string \
    strap newline
    push . get n
    push . number 0
    if exec .--func more
        goto loop

push . strap
push . regex gm string   ( {4})(?=.$)
push . string  \$1
print exec .--func replace