INCLUDE "hardware.inc"
INCLUDE "sprobjs_lib.asm"

SECTION "Header", ROM0[$100]

	jp Init

	ds $150 - @, 0 ; Make room for the header

SECTION "Main", ROM0
Init:
	; Shut down audio circuitry
	ld a, 0
	ld [rNR52], a

	; Do not turn the LCD off outside of VBlank
WaitVBlank:
	ld a, [rLY]
	cp 144
	jp c, WaitVBlank

	; Turn the LCD off
	ld a, 0
	ld [rLCDC], a

	; Initialize Sprite Object Library
	call InitSprObjLib

	; Reset hardware OAM
	ld a, 0
	ld b, 160
	ld hl, _OAMRAM
.resetOAM
	ld [hli], a
	dec b
	jp nz, .resetOAM

	; Copy cat sprite
	ld de, GfxCat
	ld hl, $8000
	ld bc, GfxCat.end - GfxCat
	call Memcopy

	; Reset positions
	ld d, 0
	ld hl, wMetaspriteBegin
	ld bc, wMetaspriteEnd - wMetaspriteBegin
	call Memset

	; Clear player data
	ld a, $05
	ld [wMetaspritePosition.x+1], a 
	ld [wMetaspritePosition.y+1], a

	; Copy the tile data
	ld de, Tiles
	ld hl, $9000
	ld bc, TilesEnd - Tiles
	call Memcopy

	; Clear the tilemap
	ld hl, $9800
	ld bc, (32 * 20)
	ld d, 0
	call Memset

	; Clear shadown OAM
	ld hl, wShadowOAM
	ld bc, 160
	ld d, 0
	call Memset
	
	; Turn the LCD on
	ld a, LCDCF_ON | LCDCF_BGON | LCDCF_OBJON | LCDCF_OBJ8
	ld [rLCDC], a

	; During the first (blank) frame, initialize display registers
	ld a, %11100100
	ld [rBGP], a
	ld [rOBP0], a
	ld [rOBP1], a

	; Enable vblank interrupt
	ld a, IEF_VBLANK
	ldh [rIE], a
	; Clear interrupt register to 0
	xor a, a
	ldh [rIF], a
	; Enable interrupts 
	ei

Main::
	call ResetShadowOAM
	call UpdateJoypadState
	call HandleInput
	call HandlePhysics
	call HandleRender

	halt
	nop

	jp Main
 
HandleInput::
	ld a, [wJoypadState]
	bit PADB_LEFT, a
	jr nz, .leftend

	ld a, [wMetaspritePosition.x]
	add a, 16
	ld b, a
	ld [wMetaspritePosition.x], a
	ld a, [wMetaspritePosition.x+1]
	adc 0
	ld c, a
	ld [wMetaspritePosition.x+1], a
.leftend:

	ld a, [wJoypadState]
	bit PADB_RIGHT, a
	jr nz, .rightend

	ld a, [wMetaspritePosition.x]
	sub a, 16
	ld b, a
	ld [wMetaspritePosition.x], a
	ld a, [wMetaspritePosition.x+1]
	sbc 0
	ld c, a
	ld [wMetaspritePosition.x+1], a
.rightend:

	ld a, [wJoypadState]
	bit PADB_UP, a
	jr nz, .upend

	ld a, [wMetaspritePosition.y]
	add a, 16
	ld b, a
	ld [wMetaspritePosition.y], a
	ld a, [wMetaspritePosition.y+1]
	adc 0
	ld c, a
	ld [wMetaspritePosition.y+1], a
.upend:
 
	ld a, [wJoypadState]
	bit PADB_DOWN, a
	jr nz, .downend

	ld a, [wMetaspritePosition.y]
	sub a, 16
	ld b, a
	ld [wMetaspritePosition.y], a
	ld a, [wMetaspritePosition.y+1]
	sbc 0
	ld c, a
	ld [wMetaspritePosition.y+1], a
.downend: 

	; Skip jump code if not on ground
	ld a, [wMetaspritePosition.z]
	ld b, a
	ld a, [wMetaspritePosition.z + 1]
	or a, b
	jr nz, .jumpend

	; While on ground, set boost
	ld a, $8
	ld [wMetaspriteVelocity.boost], a

	ld a, [wJoypadPressed]
	bit PADB_A, a
	jr z, .boostclear

	ld a, [wMetaspriteVelocity.z]
	sub a, $20
	ld b, a
	ld [wMetaspriteVelocity.z], a
	ld a, [wMetaspriteVelocity.z+1]
	sbc a, $00
	ld c, a
	ld [wMetaspriteVelocity.z+1], a 
	jr .boostend
.jumpend:
	ld a, [wJoypadState]
	bit PADB_A, a
	jr z, .boostclear
	ld a, $FF
	ld [wMetaspriteVelocity.boosting], a
	jr .boostend
.boostclear:
	ld a, $00
	ld [wMetaspriteVelocity.boosting], a 
.boostend:

	ret

HandleRender::
	; Render the player
	; load de
	ld a, [wMetaspritePosition.x]
	ld e, a
	ld a, [wMetaspritePosition.x + 1]
	ld d, a

	; load bc
	ld a, [wMetaspritePosition.z]
	ld c, a
	ld a, [wMetaspritePosition.y]
	add a, c
	ld c, a
	ld a, [wMetaspritePosition.z + 1]
	ld b, a
	ld a, [wMetaspritePosition.y + 1]
	adc a, b
	ld b, a

	ld hl, CatMetasprite
	call RenderMetasprite

	; Render the shadow
	; load de
	ld a, [wMetaspritePosition.x]
	ld e, a
	ld a, [wMetaspritePosition.x + 1]
	ld d, a

	; load bc
	ld a, [wMetaspritePosition.y]
	ld c, a
	ld a, [wMetaspritePosition.y + 1]
	ld b, a

	ld hl, ShadowMetasprite
	call RenderMetasprite
	ret

HandlePhysics::

	; Skip gravity if on ground
	ld a, [wMetaspritePosition.z]
	ld b, a
	ld a, [wMetaspritePosition.z + 1]
	or a, b
	jr z, .endGravity

	; Skip gravity if boosting
	ld a, [wMetaspriteVelocity.boosting]
	ld b, a
	ld a, [wMetaspriteVelocity.boost]
	and a, b
	cp 0 
	jr z, .startGravity
	ld a, [wMetaspriteVelocity.boost]
	dec a
	ld [wMetaspriteVelocity.boost], a
	jr .endGravity

.startGravity
	; Apply gravity
	ld a, [wMetaspriteVelocity.z]
	add a, $04
	ld [wMetaspriteVelocity.z], a
	ld a, [wMetaspriteVelocity.z+1]
	adc a, $00
	ld [wMetaspriteVelocity.z+1], a
.endGravity:
 

	; Calculate new z, place in bc
	ld a, [wMetaspriteVelocity.z]
	ld c, a
	ld a, [wMetaspritePosition.z]
	add c
	ld c, a
	ld a, [wMetaspriteVelocity.z + 1]
	ld b, a
	ld a, [wMetaspritePosition.z + 1]
	adc b
	ld b, a

	; If z is greater than or equal to 0, pos/vel to 0
	jr nz, .endLanding
	jr nc, .endLanding
.startLanding
	ld a, 0
	ld [wMetaspritePosition.z], a
	ld [wMetaspritePosition.z+1], a
	ld [wMetaspriteVelocity.z], a
	ld [wMetaspriteVelocity.z+1], a
	ld b, a
	ld c, a
.endLanding

	; Update z position
	ld a, c
	ld [wMetaspritePosition.z], a
	ld a, b
	ld [wMetaspritePosition.z+1], a

	ret

SECTION "Joypad Routine", ROM0
UpdateJoypadState::
	ld hl, rP1
	ld [hl], P1F_GET_BTN
	; Read button state twice to ensure we get the proper state
	ld a, [hl]
	ld a, [hl]
	ld [hl], P1F_GET_DPAD
	cpl ; Inputs are active low - invert so it makes more sense
	and PADF_A | PADF_B | PADF_SELECT | PADF_START
	ld c, a ; Store lower 4 button bits in c

	; On real hardware, rP1 needs to be read 8 times to ensure proper state is read
	ld b, 8
.dpadDebounceLoop:
	ld a, [hl]
	dec b
	jr nz, .dpadDebounceLoop
	ld [hl], P1F_GET_NONE ; Disable joypad inputs

	swap a ; Swap the nibbles to store dpad in upper 4 bits
	cpl    ; invert the bits
	and PADF_RIGHT | PADF_LEFT | PADF_UP | PADF_DOWN
	or c
	ld c, a

	; Compare with previously stored state
	ld hl, wJoypadState
	xor [hl]
	and c
	ld [wJoypadPressed], a
	ld a, c
	ld [wJoypadState], a
	ret

SECTION "Memcopy Routine", ROM0
Memcopy::
	dec bc
	inc b
	inc c
.loop:
	ld a, [de]
	ld [hli], a
	inc de
	dec c
	jr nz, .loop
	dec b
	jr nz, .loop
	ret  

; @param hl - Location
; @param bc - Length
; @param d - Value
SECTION "Memset Routine", ROM0
Memset::
	dec bc
	inc b
	inc c
.loop:
	ld a, d
	ld [hli], a
	dec c
	jr nz, .loop
	dec b
	jr nz, .loop
	ret  

SECTION "VBlank Interrupt", ROM0[$0040]
VBlankInterrupt:
	; Store registers to prevent clobbering
	push af
	push bc
	push de
	push hl
	jp VBlankHandler

SECTION "VBlank Handler", ROM0
VBlankHandler:
	ldh a, [hFrameCounter]

	ld a, HIGH(wShadowOAM)
	call hOAMDMA

	; Reset registers to orignal state
	pop hl
	pop de
	pop bc
	pop af
	reti

SECTION "Frame Counter", HRAM
hFrameCounter: 
	db

SECTION "Tile data", ROM0

Tiles:
	INCBIN "tileset.2bpp"
TilesEnd:

SECTION "Tilemap", ROM0

Tilemap:
	INCBIN "tileset.tilemap"
TilemapEnd:

SECTION "Level data", ROM0
	db $03 ; width
	db $03 ; height

	; Each byte stores whether it is solid or not

	; Z = 1
	db $01
	db $01
	db $01

	db $01
	db $01
	db $01

	db $01
	db $01
	db $00

	; Z = 2
	db $01
	db $01
	db $01

	db $01
	db $01
	db $01

	db $00
	db $00
	db $00

	; Z = 3
	db $01
	db $00
	db $00

	db $00
	db $00
	db $00

	db $00
	db $00
	db $00


SECTION "Graphics", ROM0
GfxCat:
	INCBIN "sprites.2bpp"
.end::

CatMetasprite:
	db 0, 0, 2, 0
	db 8, 0, 6, 0
	db 128

ShadowMetasprite:
	db 12, 0, 1, 0
	db 128

SECTION "Position Vars", WRAM0 
 wMetaspriteBegin:
; Q12.4 fixed-point X posiition
wMetaspritePosition::
.x:
	dw
.y:
	dw
.z:
	dw

; Q4.4 fixed-point velocity
wMetaspriteVelocity::
.x:
	dw
.y:
	dw
.z:
	dw
.boost:
	db
.boosting:
	db
 wMetaspriteEnd:

SECTION "Joypad Vars", WRAM0
wJoypadState:
	ds 1
wJoypadPressed:
	ds 1