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; Metroid                                                                            ;
; By: Schwa, additional functionality by Chdata                                      ;
;                                                                                    ;
; This sprite hovers in the air, moving back and forth while bobbing up and down.    ;
; When approached by Mario, it suddenly gives chase, and this thing is FAST. It      ;
; will continue to chase Mario until it is outrun or until it catches him. If it     ;
; catches him, it will latch on to him and drain his coins very fast. It can then    ;
; be shaken off by mashing the controller buttons repeatedly, and when this happens  ;
; the Metroid falls off and dies.                                                    ;
;                                                                                    ;
; Setting the extra bit will make the sprite hurt (or immediately kill) the player   ;
; don't have any coins.                                                              ;
;                                                                                    ;
; The detection range can be modified by changing Extra Property Byte 2 in the CFG.  ;
;										     ;
; It'll drain Air from Air Meter If Extra Property Byte 1 is set to anything.	     ;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; The define below specifies if the Metroid should automatically kill the player     ;
; (used when the extra bit is set), or just hurt them. Set to 1 if you want the      ;
; player to be killed immediately, otherwise leave it at 0.                          ;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

!KillImmediately = 0

!FreeRam = $140C|!Base2			;MUST BE THE SAME AS IN THE AIR METER SPRITE!!!

;;;;;;;;;;;;;;;;
; Init Routine ;
;;;;;;;;;;;;;;;;

print "INIT ",pc
    %SubHorzPos()       ; Face Mario
    TYA
    STA !157C,x
    STZ !1528,x         ; \ set Mode and Button Count to 0
    STZ !C2,x           ; /
    RTL

;;;;;;;;;;;;;;;;
; Main Routine ;
;;;;;;;;;;;;;;;;

print "MAIN ",pc
    PHB : PHK : PLB
    JSR MainCode
    PLB
    RTL

;;;;;;;;;;;;;;;;;;;;
; Main Sprite Code ;
;;;;;;;;;;;;;;;;;;;;

X_Speed:    db $08,$F8
Y_Speed:    db $00,$F8,$F2,$F8,$00,$08,$0E,$08

;;;;;;;;;;;;;;;;;;;;;;;;;;
; Normal Behavor Routine ;
;;;;;;;;;;;;;;;;;;;;;;;;;;

Return1:
    RTS

MainCode:
    JSR Graphics        ; call gfx routine

    LDA !14C8,x         ; \  handle sprite if off screen or dead
    CMP #$08            ;  |
    BNE Return1         ;  |
    LDA $9D             ;  |
    BNE Return1         ;  |
    LDA #$00            ;  |
    %SubOffScreen()     ; / 

    INC !1570,x         ; increase how many frames sprite has been on screen

    LDA !C2,x           ; load sprite Mode ... 0 is normal, 1 is chasing, 2 is latched onto Mario
    CMP #$01            ; \ branch to Chasing code if needed
    BEQ Mode_Chasing    ; /
    CMP #$02            ; \ branch to Latched On code if needed
    BEQ Mode_Draining   ; /

Mode_Normal:
    LDA !1570,x         ; \ change direction every once in a while
    AND #$7F            ;  |
    BNE .noChangeDir    ;  |
    LDA !157C,x         ;  |
    EOR #$01            ;  |
    STA !157C,x         ; /
.noChangeDir
    LDY !157C,x             ; \ set x speed based on facing direction
    LDA X_Speed,y           ;  |
    STA !sprite_speed_x,x   ; /

    LDA !1570,x             ; \ 
    LSR A                   ;  | set y speed based on frame count, so it does the wave motion
    LSR A                   ;  | every 8th frame, change
    LSR A                   ;  |
    AND #$07                ;  |
    TAY                     ;  |
    LDA Y_Speed,y           ;  |
    STA !sprite_speed_y,x   ; / 

    JSR Proximity           ; \ check to see if Mario is close to the sprite
    BEQ FinishStuff         ;  | If so, set mode to Chasing Mode
    LDA #$01                ;  |
    STA !C2,x               ; /
    BRA FinishStuff

Mode_Chasing:
    JSR DoChase

FinishStuff:
    JSL $01802A|!BankB      ; update speed (X/Y with gravity)
    JSL $01A7DC|!BankB      ; check for Mario contact
    BCC .return

    STZ !1534,x
    LDA #$02
    STA !C2,x
.return
    RTS

Mode_Draining:
    STZ !sprite_speed_y,x
    STZ !sprite_speed_x,x

    LDA $94                 ; Set sprite X = player X
    STA !sprite_x_low,x
    LDA $95
    STA !sprite_x_high,x

    LDA $19
    BNE .big
    LDA $96                 ; Set sprite Y = player Y + #$04
    CLC : ADC #$04
    STA !sprite_y_low,x
    LDA $97
    ADC #$00
    STA !sprite_y_high,x
    BRA .notBig

.big
    LDA $96                 ; Set sprite Y = player Y
    STA !sprite_y_low,x
    LDA $97
    STA !sprite_y_high,x

.notBig
    LDA $1490|!Base2        ; \ kill sprite if Mario has a star
    BEQ .NoStar             ; /
    JMP StarKill
.NoStar
    LDA $7D                 ; \ prevent Mario from jumping
    BPL .noMarioJump        ;  |
    LDA $77                 ;  |
    BNE .noMarioJump        ;  |
    STZ $7D                 ; /
.noMarioJump
    %BEC(.drainCoins)       ; Don't try to hurt if extra bit is clear

    LDA $0DBF|!Base2        ; Don't hurt if we still have coins
    BNE .drainCoins

    if !KillImmediately == 0
        JSL $00F5B7|!BankB
    else
        JSL $00F606|!BankB
    endif

.drainCoins
    LDA !extra_prop_1,x
    BEQ .Coins
    LDA #$01		    ; Set Drain Flag
    STA !FreeRam
    BRA .DrainOrNot
.Coins
    LDA $0DBF|!Base2        ; \ drain coins (Or Air) from Mario if he has any
.DrainOrNot		    ;  |
    BEQ .noDrainCoin        ;  |
    LDA $14                 ;  |
    AND #$07                ;  | change AND #$07 to different values to change the rate of coin drainage
    BNE .noDrainCoin        ;  | Make sure it's a power of 2, though (i.e. 2, 4, 8, 16, 32, etc. but in hex)
    LDA !extra_prop_1,x	    ;  |
    BEQ .CoinsAgain	    ;  | Don't drain coins if set to drain air.
    BRA .Sound		    ;  |
.CoinsAgain 		    ;  |
    DEC $0F33|!Base2        ;  | Will drain the time
.Sound			    ;  |
    LDA #$01                ;  |
    STA $1DFC|!Base2        ; /
.noDrainCoin
    LDA $16                 ; \ if buttons are being pressed, increase the button counter
    BEQ .noPressButton      ;  |
    INC !1534,x             ; /
    LDA !1534,x
    CMP #$14                ; change CMP #$14 to other values to change how many button presses are
    BCC .noPressButton      ;   required to shake off the Metroid
    BRA StarKill
.noPressButton
    RTS

;;;;;;;;;;;;;;;;;
; Death Routine ;
;;;;;;;;;;;;;;;;;

Killed_X_Speed:     db $F0,$10

StarKill:
    LDA #$02                ; Kill sprite
    STA !14C8,x
    LDA #$D0                ; Set killed Y speed
    STA !sprite_speed_y,x
    %SubHorzPos()           ; Set killed X speed
    LDA Killed_X_Speed,y
    STA !sprite_speed_x,x

    LDA #$02
    STA !1602,x             ;  write frame to show
    RTS

;;;;;;;;;;;;;;;;;
; Chase Routine ;
;;;;;;;;;;;;;;;;;

X_Accel:        db $02,$FE
X_MaxSpeed:     db $20,$E0
Y_Accel:        db $04,$FC
Y_MaxSpeed:     db $10,$F0

DoChase:
    %SubHorzPos()           ; \ 
    LDA !sprite_speed_x,x   ;  | chase Mario horizontally
    CMP X_MaxSpeed,y        ;  |
    BEQ .doY                ;  |
    CLC : ADC X_Accel,y     ;  |
    STA !sprite_speed_x,x   ; /
.doY
    %SubVertPos()           ; \ 
    LDA !sprite_speed_y,x   ;  | chase Mario vertically
    CMP Y_MaxSpeed,y        ;  |
    BEQ .return             ;  |
    CLC : ADC Y_Accel,y     ;  |
    STA !sprite_speed_y,x    ; /
.return
    RTS

;;;;;;;;;;;;;;;;;;;;;
; Detection Routine ;
;;;;;;;;;;;;;;;;;;;;;

InvertTable:    db $FF,$00

Proximity:
    LDA !sprite_x_high,x        ; A = sprite X position (16-bit)
    XBA
    LDA !sprite_x_low,x
    REP #$20
    SEC : SBC $94               ; Subtract player X
    SEP #$20
    PHA
    %SubHorzPos()
    PLA
    EOR InvertTable,y           ; Invert if needed
    CMP !extra_prop_2,x         ; Range define by Extra Prop 2
    BCS .outOfRange             ; return if not within range
    LDA #$01                    ; Z = 0
    RTS

.outOfRange
    LDA #$00                    ; Z = 1
    RTS

;;;;;;;;;;;;;;;;;;;;
; Graphics Routine ;
;;;;;;;;;;;;;;;;;;;;

Tilemap:    db $C8,$A8,$C8      ; the third frame is the death frame

Graphics:
    %GetDrawInfo()

    LDA !157C,x         ; $02 = direction
    STA $02

    LDA !14C8,x         ; If killed...
    CMP #$02
    BNE NotKilled
    LDA #$02            ;    ...set killed frame
    STA $03
    LDA !15F6,x         ;    ...flip vertically
    ORA #$80
    STA !15F6,x
    BRA DrawSprite

NotKilled:
    LDA $14             ; Set walking frame based on frame counter
    rep 3 : LSR A
    CLC : ADC $15E9|!Base2
    AND #$01
    STA $03
DrawSprite:
    PHX

    LDA $00                 ; Tile x position = sprite x location ($00)
    STA $0300|!Base2,y
    LDA $01                 ; Tile y position = sprite y location ($01)
    STA $0301|!Base2,y

    LDA !15F6,x             ; Tile properties YXPPCCCT
    ORA $64                 ; Add in tile priority of level
    STA $0303|!Base2,y

    LDX $03                 ; Store tile
    LDA Tilemap,x
    STA $0302|!Base2,y
    PLX

    LDY #$02                ; Set tiles to 16x16
    LDA #$00                ; We drew 1 tile
    JSL $01B7B3|!BankB
    RTS