Estex-DSS/SHELL/Commands/IF.ASM

;///////////////////////////////////////////////////
;
; IF - conditional command (MS-DOS style)
;
;   IF [NOT] ERRORLEVEL number  command
;   IF [NOT] EXIST     filename command
;   IF [NOT] string1 == string2 command
;
; If the condition is true, the rest of the line is
; executed as an ordinary command (GOTO, ECHO, a
; program, another IF, ...).
;
;///////////////////////////////////////////////////

; in: de -> argument string (everything after "IF ")
cmd_if:
	ex	de,hl			; hl -> args
	xor	a
	ld	(.neg),a
	call	IF_SKIPB		; skip leading blanks
	; --- optional NOT ---
	ld	de,.kw_not
	call	IF_KW
	jr	nc,.noNOT
	ld	a,1
	ld	(.neg),a
.noNOT:
	; --- ERRORLEVEL n ? ---
	ld	de,.kw_errlvl
	call	IF_KW
	jr	nc,.notErr
	ld	de,Buffers.work.buffer1
	ld	c,Dss.GSwitch		; extract the number token
	RST	ToDSS
	ld	(.cmd),hl		; rest of line = command part
	ld	de,Buffers.work.buffer1
	call	IF_ATOI8		; a = number (0..255)
	ld	b,a			; b = threshold
	ld	c,Dss.Get_Err		; a = exit code of last program
	RST	ToDSS
	cp	b			; A >= n ?  (NC = yes)
	ld	a,0
	jr	c,.decide		; A < n -> false
	inc	a			; true
	jr	.decide
.notErr:
	; --- EXIST filename ? ---
	ld	de,.kw_exist
	call	IF_KW
	jr	nc,.strcmp
	ld	de,Buffers.work.buffer1
	ld	c,Dss.GSwitch		; extract the filename token
	RST	ToDSS
	ld	(.cmd),hl		; rest of line = command part
	ld	a,FAT_ATTR.NoVolID	; any file/dir (not the volume label)
	ld	hl,Buffers.work.buffer1	; filespec (NUL-term DOS name)
	ld	de,Buffers.work.buffer2	; F_First work buffer
	ld	bc,Dss.F_First.DOSname	; B=1, C=#19
	RST	ToDSS
	ld	a,0
	jr	c,.decide		; CF=1 -> not found -> false
	inc	a			; exists -> true
	jr	.decide
.strcmp:
	; hl -> string1 "==" string2 [blank] command
	push	hl			; s1 start
.find:	ld	a,(hl)
	or	a
	jr	z,.bad			; no "==" -> malformed
	cp	"="
	jr	nz,.fnext
	inc	hl
	ld	a,(hl)
	cp	"="
	jr	z,.foundEq
	dec	hl
.fnext:	inc	hl
	jr	.find
.bad:	pop	hl
	ret				; syntax error -> no-op
.foundEq:
	dec	hl			; hl -> first '=' of "=="
	pop	de			; de = s1 start
	push	de
	or	a
	sbc	hl,de			; hl = len1 (line < 256 -> h=0)
	ld	a,l
	ld	(.len1),a
	pop	de			; de = s1 start
	ld	hl,0
	ld	l,a
	add	hl,de			; hl = s1 + len1 = first '='
	inc	hl
	inc	hl			; hl = s2 start
	ld	(.s2),hl
	ld	b,0			; len2
.s2l:	ld	a,(hl)
	cp	" "+1			; <=' ' (space/tab/CR/0) -> token end
	jr	c,.s2e
	inc	hl
	inc	b
	jr	.s2l
.s2e:	ld	(.cmd),hl		; command part starts here
	ld	a,(.len1)
	cp	b			; len1 == len2 ?
	jr	nz,.neq
	or	a
	jr	z,.eq			; both empty -> equal
	ld	c,a			; c = length
	ld	hl,(.s2)
.cl:	ld	a,(de)			; de = s1
	cp	(hl)			; case-sensitive (MS-DOS)
	jr	nz,.neq
	inc	de
	inc	hl
	dec	c
	jr	nz,.cl
.eq:	ld	a,1
	jr	.decide
.neq:	xor	a
	;
.decide:
	; a = raw condition (0/1)
	ld	b,a
	ld	a,(.neg)
	xor	b			; cond ^ NOT
	and	1
	ret	z			; false -> nothing to do
	ld	hl,(.cmd)
	jp	IF_RUN			; true -> run the command part
	;
.kw_not:	db	"NOT",0
.kw_errlvl:	db	"ERRORLEVEL",0
.kw_exist:	db	"EXIST",0
.neg:		db	0
.cmd:		dw	0
.len1:		db	0
.s2:		dw	0

;-------------------------------------------------
; Skip blanks (space / TAB) at (hl)
;-------------------------------------------------
IF_SKIPB:
.l:	ld	a,(hl)
	cp	" "
	jr	z,.i
	cp	"\t"
	ret	nz
.i:	inc	hl
	jr	.l

;-------------------------------------------------
; Case-insensitive keyword test.
; in:  hl -> text, de -> keyword (UPPER, 0-term)
; out: CF=1 - matched, hl past keyword + blanks
;      CF=0 - no match, hl unchanged
;-------------------------------------------------
IF_KW:	push	hl
.l:	ld	a,(de)
	or	a
	jr	z,.kend			; keyword consumed
	ld	c,a
	ld	a,(hl)
	call	COMPARE.cmp_AZ		; -> upper
	cp	c
	jr	nz,.no
	inc	hl
	inc	de
	jr	.l
.kend:	ld	a,(hl)			; must be a blank delimiter
	cp	" "
	jr	z,.ok
	cp	"\t"
	jr	z,.ok
.no:	pop	hl			; restore, no match
	or	a			; CF=0
	ret
.ok:	inc	hl			; skip delimiter + following blanks
.ok2:	ld	a,(hl)
	cp	" "
	jr	z,.oki
	cp	"\t"
	jr	nz,.done
.oki:	inc	hl
	jr	.ok2
.done:	pop	bc			; discard saved hl
	scf
	ret

;-------------------------------------------------
; ASCII decimal -> A (0..255, saturating)
; in: de -> digits
;-------------------------------------------------
IF_ATOI8:
	ld	hl,0
.l:	ld	a,(de)
	sub	"0"
	jr	c,.end
	cp	10
	jr	nc,.end
	ld	c,a			; c = digit
	ld	b,0
	push	de
	ld	d,h
	ld	e,l
	add	hl,hl			; *2
	add	hl,hl			; *4
	add	hl,de			; *5
	add	hl,hl			; *10
	add	hl,bc			; + digit
	pop	de
	inc	de
	jr	.l
.end:	ld	a,h
	or	a
	jr	nz,.sat
	ld	a,l
	ret
.sat:	ld	a,255
	ret

;-------------------------------------------------
; Run the conditional command.
; in: hl -> command text (NUL-term at line end)
;-------------------------------------------------
IF_RUN:
	call	IF_SKIPB
	ld	a,(hl)
	or	a
	ret	z			; empty -> no-op
	ld	d,h
	ld	e,l			; de = command start
	ld	bc,0			; b=0, c = token length
.tl:	ld	a,(hl)
	cp	" "+1			; <=' ' -> end of command token
	jr	c,.tle
	inc	hl
	inc	c
	jr	.tl
.tle:	ld	hl,BATLIST		; bat + dos commands
	jp	COMP.start		; dispatch (recurses for nested IF)