DEF vSelectedSpreadIndex EQU VARIABLES_START
DEF vPreviousSpreadIndex EQU vSelectedSpreadIndex + 1
def vSelectedSpreadCard equ vPreviousSpreadIndex + 1

ScreenSpreadSelect:
  dw SpreadSelectSetup
  dw SpreadSelectUpdate
  dw SpreadSelectDraw
  dw SpreadSelectTeardown
  
SpreadSelectSetup:
  ld a, 0 
  ldh [vSelectedCardInSpread], a 
  ldh [vPreviousSpreadIndex], a 
  ldh [vSelectedSpreadIndex], a 
  
  ld hl, ZEROES
  ld de, $9800
  ld b, 18
  ld c, 20

  ld a, LOW(CopyTilesToMapThreadsafe)
  ld [vAsyncNext], a 
  ld a, HIGH(CopyTilesToMapThreadsafe)
  ld [vAsyncNext+1], a 
  ld a, LOW(.loadUITiles)
  ld [vAsyncAfter], a 
  ld a, HIGH(.loadUITiles)
  ld [vAsyncAfter+1], a 
  call DoInAsyncVBlank
  
  ld a, HIGH(ZEROES)
  ld de, $ffc0
  call RunDMA
  ret
  
.loadUITiles
  ld hl, UITiles ; source
  ld de, $8000 + $80*16; destination of copy
  ld bc, UITilesEnd - UITiles ; length to copy

  ld a, LOW(CopyRangeUnsafe)
  ld [vAsyncNext], a 
  ld a, HIGH(CopyRangeUnsafe)
  ld [vAsyncNext+1], a 
  ld a, LOW(DrawSpreadAsync)
  ld [vAsyncAfter], a 
  ld a, HIGH(DrawSpreadAsync)
  ld [vAsyncAfter+1], a 
  ret  
  
SpreadSelectUpdate:
  ld hl, rMYBTNP
  bit 4, [hl]
  jp z, .doneB
  ld hl, ScreenMainMenu
  call ChangeScene
  ret
.doneB
  ld a, [vSelectedSpreadIndex]
  
  bit 3, [hl]  ; select the down key
  jp z, .doneDown ; skip the following code if down is not pressed
  dec a ; increment when they press down because the deck has card 0 at the top
.doneDown
  bit 2, [hl] ; select up key
  jp z, .doneUp ; skip the following code if up is not pressed
  inc a ; decrement when they press up because the deck has card 0 at the top
.doneUp
  ld hl, Spreads 
  call ArrayClampLooping
  ldh [vSelectedSpreadIndex], a ; load current selected tile index
  
  ld hl, vPreviousSpreadIndex
  cp a, [hl]
  ret z ; we're done if previous index is same as new index
  
  ; execute an async call to DrawSpreadAsync.
  ld a, LOW(DrawSpreadAsync)
  ld [vAsyncNext], a 
  ld a, HIGH(DrawSpreadAsync)
  ld [vAsyncNext+1], a 
  
  call DoInAsyncVBlank
  ret ; return from main thread. go back to looping.
  
DrawSpreadAsync:
  ldh a, [vSelectedSpreadIndex]
  ldh [vPreviousSpreadIndex], a 
  
  ; find the correct spread address
  ld hl, Spreads
  inc hl ; skip length of spreads
  ld a, [vSelectedSpreadIndex]
  inc a ; we're decing at the start so we inc first to prepare...
  ld d, 0
.findSpread
  dec a
  jp z, .spreadFound
  
  ld e, [hl] ; skip cards in spread
  inc hl 
  add hl, de
  
  ld e, [hl] ; skip title of spread
  inc hl
  add hl, de
  
  ld e, [hl] ; skip description
  inc hl
  add hl, de
  
  jp .findSpread
.spreadFound
  ld a, l 
  ld [vCurrentSpread], a
  ld a, h
  ld [vCurrentSpread+1], a ; save the current spread (hl) into vcurrentspread. 

  ld de, $9800 + 32*4 + 3
  ld hl, ZEROES
  ld b, 8
  ld c, 10
  
  ld a, LOW(CopyTilesToMapThreadsafe)
  ld [vAsyncNext], a 
  ld a, HIGH(CopyTilesToMapThreadsafe)
  ld [vAsyncNext+1], a 
  ld a, LOW(.afterClear)
  ld [vAsyncAfter], a
  ld a, HIGH(.afterClear)
  ld [vAsyncAfter+1], a
  ret  ; return from async execution now that we've registered desire
  ; to call copytilestomapthreadsafe
  ; and then drawspread

.afterClear
  ld a, [vCurrentSpread]
  ld l, a 
  ld a, [vCurrentSpread+1]
  ld h, a
  ld d, 0 
  ld e, [hl]
  inc e
  add hl, de
  ld de, $9800 + 32
  ld a, LOW(PrintString)
  ld [vAsyncNext], a 
  ld a, HIGH(PrintString)
  ld [vAsyncNext+1], a 
  ld a, LOW(.afterTitle)
  ld [vAsyncAfter], a 
  ld a, HIGH(.afterTitle)
  ld [vAsyncAfter+1], a 
  ret

.afterTitle
  ld de, $9800 + (32*2)
  ld a, LOW(PrintString)
  ld [vAsyncNext], a 
  ld a, HIGH(PrintString)
  ld [vAsyncNext+1], a 
  ld a, LOW(.afterDescription)
  ld [vAsyncAfter], a 
  ld a, HIGH(.afterDescription)
  ld [vAsyncAfter+1], a 
  ret
  
.afterDescription
  
  ld hl, $9800 + 32*4 + 3
  ldh a, [vSelectedSpreadCard]
  ld e, a ; e contains the selected index
  
  ld a, LOW(DrawSpreadBigAndThreadsafe)
  ld [vAsyncNext], a 
  ld a, HIGH(DrawSpreadBigAndThreadsafe)
  ld [vAsyncNext+1], a 
  ld a, LOW(.finishAsyncUpdate)
  ld [vAsyncAfter], a 
  ld a, HIGH(.finishAsyncUpdate)
  ld [vAsyncAfter+1], a 
  ret
  
.finishAsyncUpdate
  ; signal that we're done with execution of the async thread
  ld a, 0 
  ld [vAsyncNext], a 
  ld [vAsyncNext+1], a 
  ld [vAsyncAfter], a 
  ld [vAsyncAfter+1], a 
  ret
  
SpreadSelectDraw:
  ret
SpreadSelectTeardown:
  ret  

DrawSpreadBigAndThreadsafe:
; hl for location on screen
; bc for current spread address ; actually holding that in vCurrentSpread
; e for index of selected card
  di
  ld a, [vCurrentSpread]
  ld c, a 
  ld a, [vCurrentSpread+1]
  ld b, a 
  ld a, [bc]
  cp a, 0 ; length of spread
  ret z ; return early if the spread is empty
  ld d, a ; length of spread in d
  inc d
.drawCards
  ei
  nop
  di
  dec d
  jp z, .doneWithSpread ; if we're drawing zero remaining cards, stop drawing
  inc bc ; step forward
  push hl  ; need this bc drawsmallcard changes hl
  ld a, [bc]
  call DrawBigCard
  pop hl  
  jp .drawCards
.doneWithSpread 
; stack has spread address
; d is zero
; e should have currently selected index
  ld b, h
  ld c, l ; stash hl in bc for a mo; this should be a location in vram
  
  ld a, [vCurrentSpread]
  ld l, a
  ld a, [vCurrentSpread+1]
  ld h, a 
  ;spread address in hl

  inc e ; skip the tiles length
  
  add hl, de
  ld a, [hl] ; load card descriptor into a 
  
  ld h, b
  ld l, c; retrieve vram address
  ei
  nop
  di
  call DrawBigCardSelected
  
  ei
  ret



DrawSpreadBig:
; hl for location on screen
; bc for current spread address
; e for index of selected card
  ld a, [bc]
  cp a, 0 ; length of spread
  ret z ; return early if the spread is empty
  push bc
  ld d, a ; length of spread in d
  inc d
.drawCards
  dec d
  jp z, .doneWithSpread ; if we're drawing zero remaining cards, stop drawing
  inc bc ; step forward
  push hl  ; need this bc drawsmallcard changes hl
  ld a, [bc]
  call DrawBigCard
  pop hl  
  jp .drawCards
.doneWithSpread 
; stack has spread address
; d is zero
; e should have currently selected index
  ld b, h
  ld c, l ; stash hl in bc for a mo; this should be a location in vram
  pop hl ; put bc from stack into hl, this is the spread address

  inc e ; skip the tiles length
  
  add hl, de
  ld a, [hl]
  
  ld h, b
  ld l, c; retrieve
  ;call DrawBigCardSelected
  
  ret
  
DrawBigCard: ; starting from screen location hl, draw a card at 
;the location described in a
; saves de and is therefore not threadsafe
  push de
  ld d, a 
  swap a
  and a, %0000_1111
  sla a
  ld e, a 

  ld a, d
  and a, %0000_1111

  ld d, 0
  add hl, de ; step right
  
  ld e, 64
  jp z, .drawCard
.stepDown
  add hl, de ; step down
  dec a
  jp nz, .stepDown
.drawCard
  ld de, 32
  ld [hl], $12
  inc hl 
  ld [hl], $1e
  add hl, de
  ld [hl], $1f
  dec hl 
  ld [hl], $13
  add hl, de 
  ld [hl], $13
  inc hl 
  ld [hl], $1f 
  add hl, de
  ld [hl], $23
  dec hl 
  ld [hl], $17
  
  pop de
  ret 

DrawBigCardSelected: ; starting from screen location hl, draw a card at 
;the location described in a
  push de
  push af 
  swap a
  ld d, 0
  and a, %0000_1111
  sla a
  ld e, a 
  add hl, de ; step right
  
  ld e, 64
  pop af
  and a, %0000_1111
  jp z, .drawCard
.stepDown
  add hl, de ; step down
  dec a
  jp nz, .stepDown
.drawCard
  ld de, 32
  ld [hl], $12
  inc hl 
  ld [hl], $1e
  add hl, de
  ld [hl], $1f
  dec hl 
  ld [hl], $13
  add hl, de 
  ld [hl], $13
  inc hl 
  ld [hl], $1f 
  add hl, de
  ld [hl], $23
  dec hl 
  ld [hl], $17
  
  pop de
  ret 

DrawSpreadMinimap:
; hl for location on screen
; bc for current spread address
; a for index of selected card
  push af
  push bc
  
  ld a, [bc]
  ld d, 0
  ld e, a ; length of spread in de
.drawCards
  ld a, e 
  cp a, 0
  jp z, .doneWithSpread ; if we're drawing zero remaining cards, stop drawing
  dec e
  inc bc ; step forward
  
  push hl ; need this bc drawsmallcard changes hl
  push bc
  ld a, [bc]
  ld bc, $8384
  call DrawSmallCard
  pop bc
  pop hl
  
  jp .drawCards
.doneWithSpread ; stack has hl, bc, af at the time of jumping here
  pop bc ; stack: af 
  pop af
  ld d, 0
  ld e, a ; index of selected card in spread
  inc e ; skip the length
  
  push hl ; stack: hl
  ld h, b
  ld l, c ; put bc in hl temporarily so we can add to hl 
  
  add hl, de
  
  ld a, [hl]
  pop hl ; stack: empty
  ld bc, $8586
  call DrawSmallCard
  
  ret
  
DrawSmallCard: ; starting from screen location hl, draw a card at 
;the location described in a, top and bottom sprite in b and c
  push de
  push af 
  swap a
  ld d, 0
  and a, %0000_1111
  ld e, a 
  add hl, de ; step right
  
  ld e, 32
  pop af
  and a, %0000_1111
  jp z, .drawCard
:
  dec a
  add hl, de ; step down
  cp a, 0
  jp nz, :-
.drawCard
  ld [hl], b
  add hl, de
  ld [hl], c
  
  pop de
  ret