XDEF _NeedleInHaystack
    XREF _DOSBase

    SECTION CODE,CODE_P

    incdir  VINCLUDEOS3ASM:
    include exec/libraries.i
    include dos/dos.i
    include dos/dos_lib.i

    include macros.i

DEBUG_ENABLE = 1

;dos.library equates
PutStr  = -$3b4
VPrintf = -$3ba

_NeedleInHaystack:
    ;Haystack = a0
    ;Needle   = a1
    ;Returns 0 in d0 if found, -1 if not found

    ;preserve a2/d3
    PUSHL   a2
    PUSHL   d3

    ;Debugging.
    IF DEBUG_ENABLE

    PUSHL   a0-a6
    PUSHL   d0-d7

    ;Print Haystack
    PUSHL   a1
    move.l  _DOSBase,a6      ;Get dos.library addr
    move.l  #dbg_Haystack,d1 ;d1 = format string
    move.l  a0,dbg_str_ptr
    move.l  #dbg_str_ptr,d2  ;d2 = ptr to argument list (in this case just a ptr to a string)
    jsr     VPrintf(a6)

    ;Print Needle
    POPL    a1
    move.l  #dbg_Needle,d1
    move.l  a1,dbg_str_ptr
    move.l  #dbg_str_ptr,d2
    jsr     VPrintf(a6)

    POPL    d0-d7
    POPL   a0-a6

    ENDIF

    move.l  a1,a2 ;copy Needle into a2

    move.b  #-1,d0
    move.b  (a1)+,d2 ;d2 = current needle
    jsr LowerNeedleChar

.outer:
    move.b  (a0)+,d1 ;d1 = current haystack
    cmp.b   #$0,d1   ;is this a terminator?
    beq .failure ;fail if so
    jsr LowerHaystackChar

    cmp.b   d2,d1       ;same, caps-insensitive?
    beq .found      ;yes, advance Needle ptr
    jsr ResetNeedle     ;no, reset to the start of needle
    cmp.b   d2,d1       ;try again
    beq .found      ;match the start of Needle
    bra .outer      ;no match. go back to the outer loop

.found:
    move.b  (a1)+,d2    ;advance Needle ptr
    cmp #0,d2       ;is it a null?
    beq .success    ;yes, we found the whole substring
    bne .outer      ;no, still more to look for

.failure:   ;needle is not in haystack
    move.b  #-1,d0
    bra .done

.success:   ;needle is in haystack
    move.b  #0,d0
    bra .done

.done:
    ;retrieve a2/d3

    IF DEBUG_ENABLE

    move.l  #dbg_Separator,d1
    move.l  #0,d2
    jsr     VPrintf(a6)

    ENDIF

    POPL    d3
    POPL    a2
    rts

;----------------------
ResetNeedle:    ;reset the Needle ptr and load d2 w/starting char
    move.l  a2,a1
    move.b  (a1)+,d2
    rts

LowerHaystackChar:
    cmp #$5A,d1 ;$5A = Z
    bhi .abort
    cmp #$41,d1 ;$41 = A
    blo .abort

    ;d2 is in the range $41 to $5A
    add.b   #$20,d1
    rts

.abort:
    rts

LowerNeedleChar:
    cmp #$5A,d2
    bhi .abort
    cmp #$41,d2
    blo .abort

    add.b   #$20,d1
    rts

.abort:
    rts

    SECTION DATA,DATA_P
dbg_Haystack    dc.b    'Haystack: %s',10,0
dbg_Needle      dc.b    'Needle  : %s',10,0
dbg_Separator   dc.b    '********',10,0

dbg_str_ptr     dc.l    0

    END