; This function just returns the address of the UDG of the given str.
; If the str is EMPTY or not a letter, 0 is returned and ERR_NR set
; to "A: Invalid Argument"

; On entry HL points to the string
; and A register is non-zero if the string must be freed (TMP string)

#include once <error.asm>
#include once <sysvars.asm>
#include once <mem/free.asm>

    push namespace core

USR_STR:
    PROC
    ex af, af'     ; Saves A flag

    ld a, h
    or l
    jr z, USR_ERROR ; a$ = NULL => Invalid Arg

    ld d, h         ; Saves HL in DE, for
    ld e, l         ; later usage

    ld c, (hl)
    inc hl
    ld a, (hl)
    or c
    jr z, USR_ERROR ; a$ = "" => Invalid Arg

    inc hl
    ld a, (hl) ; Only the 1st char is needed
    and %11011111 ; Convert it to UPPER CASE
    sub 144   ; CODE(UDG "A")
    jr nc, CONT
    add a, 144   ; It was a letter
    sub 'A'

    LOCAL CONT
CONT:

    ld l, a
    ld h, 0
    add hl, hl
    add hl, hl
    add hl, hl	 ; hl = A * 8
    ld bc, (UDG)
    add hl, bc

    ;; Now checks if the string must be released
    ex af, af'  ; Recovers A flag
    or a
    ret z   ; return if not

    push hl ; saves result since __MEM_FREE changes HL
    ex de, hl   ; Recovers original HL value
    call __MEM_FREE
    pop hl
    ret

USR_ERROR:
    ex de, hl   ; Recovers original HL value
    ex af, af'  ; Recovers A flag
    or a
    call nz, __MEM_FREE

    ld a, ERROR_InvalidArg
    ld (ERR_NR), a
    ld hl, 0
    ret
    ENDP

    pop namespace
