.global scan_cards
.global find_first_card
.global get_all_cards

scan_cards:
; Read the types of all the cards in the system
; The values in HL, BC, and A are destroyed
ld hl, card_types+255
ld bc, 0xFFFF ; Start at card 255
scan_loop: ; Read the types of card 255 through to card 1
in a, (c)
ld (hl), a
dec hl
djnz scan_loop
in a, (c) ; Read card 0's type
ld (hl), a
ret

get_all_cards:
; Gets the indexes of the cards with the specified type
; IX is a pointer to the buffer to store the results in
; B is the length of the buffer (0 is a 256 byte length)
; C is the type of card to find
; The zero flag is set if the buffer is full
; The values in A, B, HL, and IX are destroyed
ld hl, card_types+1
gac_loop:
ld a, (hl) ; Get card type
cp c ; Check whether the type of the current card is the type we want
jp nz, gac_next ; Skip the card if it is not
ld (ix), l
inc ix
dec b
gac_next:
inc hl ; Go to the next card
ld a, l ; Check if we have gone through all the cards
or a ; (or a == cp 0)
jp Z, gac_done ; If so, return
ld a, b ; Check if we have filled the buffer
or a ; (or a == cp 0)
jp Z, gac_full ; If so, return with the zero flag set
jp gac_loop 
gac_done:
or 1 ; Reset zero flag to provide correct "buffer filed" indication
gac_full:
ret

find_first_card:
; Finds the first instance of a card type specified in B
; A is zero if no such card was found, and nonzero if a card was found
; If a card was found, the ID of the card is returned in L
; If a card was not found, 0 is returned in L
; The values in A and H are destroyed
ld hl, card_types+1
ffc_loop:
ld a, (hl) ; Get card type
cp b ; Check whether the type of the current card is the type we want
jp Z, ffc_done ; If so, return the type in L
or a ; (or a == cp 0) Check whether the card type is 0 (nonexistent card)
jp Z, ffc_notfound ; If so, return 0 in L
inc hl ; Go to the next card
jp ffc_loop 
ffc_notfound:
ld l, 0
ffc_done: 
ret

.bss
.balign 256
card_types: .ds.b 256