module Cpu

( executeOpcode,

extractOpcodeFromMemory,

decodeOpcode,

parseDigitsFromOpcode,

decrementDelayTimer,

decrementSoundTimer

) where

import Data.Word

import Data.Bits

import qualified Data.Vector as V

import Types

import Opcodes.Assignment

import Opcodes.BitwiseOps

import Opcodes.Conditionals

import Opcodes.ConstantOps

import Opcodes.Display

import Opcodes.Flow

import Opcodes.KeyOps

import Opcodes.Math

import Opcodes.Memory

import Opcodes.Timer

executeOpcode :: Chip8 -> Chip8

executeOpcode chip8State = operation chip8State

where

originalProgramCounter = programCounter chip8State

originalMemory = memory chip8State

opcode = extractOpcodeFromMemory originalMemory originalProgramCounter

operation = decodeOpcode opcode

extractOpcodeFromMemory :: V.Vector Word8 -> Word16 -> Word16

extractOpcodeFromMemory givenMemory givenProgramCounter =

leftShiftedOpcodeFirstHalf .|. opcodeSecondHalf

where

memoryIndex = fromIntegral givenProgramCounter :: Int

opcodeFirstHalf = (fromIntegral $ givenMemory V.! memoryIndex) :: Word16

opcodeSecondHalf = (fromIntegral $ givenMemory V.! (memoryIndex + 1)) :: Word16

leftShiftedOpcodeFirstHalf = opcodeFirstHalf `shiftL` 8

decodeOpcode :: Word16 -> (Chip8 -> Chip8)

decodeOpcode opcode =

case parseDigitsFromOpcode opcode of

(0x0, _, 0x0) -> clearScreen

(0x0, _, 0xE) -> returnFromSubroutine

(0x1, _, _) -> jumpToAddress

(0x2, _, _) -> callSubroutine

(0x3, _, _) -> registerEqualsConstant

(0x4, _, _) -> registerDoesNotEqualConstant

(0x5, _, _) -> registersAreEqual

(0x6, _, _) -> setRegisterToConstant

(0x7, _, _) -> addConstantToRegister

(0x8, _, 0x0) -> assignToRegister

(0x8, _, 0x1) -> bitwiseOr

(0x8, _, 0x2) -> bitwiseAnd

(0x8, _, 0x3) -> bitwiseXor

(0x8, _, 0x4) -> addTwoRegisters

(0x8, _, 0x5) -> subtractRegister

(0x8, _, 0x6) -> shiftRight

(0x8, _, 0x7) -> subtractTwoRegisters

(0x8, _, 0xE) -> shiftLeft

(0x9, _, _) -> registersAreNotEqual

(0xA, _, _) -> setIndexRegisterToAddress

(0xB, _, _) -> jumpToAddressPlusRegisterZero

(0xC, _, _) -> randomBitwiseAnd

(0xD, _, _) -> drawGraphics

(0xE, _, 0xE) -> keyIsPressed

(0xE, _, 0x1) -> keyIsNotPressed

(0xF, _, 0x7) -> setRegisterToDelayTimer

(0xF, _, 0xA) -> awaitKeyPress

(0xF, 1, 0x5) -> setDelayTimerToRegister

(0xF, _, 0x8) -> setSoundTimerToRegister

(0xF, _, 0xE) -> addRegisterToIndexRegister

(0xF, _, 0x9) -> storeSpriteLocation

(0xF, _, 0x3) -> storeBCD

(0xF, 0x5, 0x5) -> registerDump

(0xF, 0x6, 0x5) -> registerLoad

_ -> error "Invalid Opcode"

parseDigitsFromOpcode :: Word16 -> (Word16, Word16, Word16)

parseDigitsFromOpcode opcode = (firstDigit, thirdDigit, lastDigit)

where

firstDigit = (opcode .&. 0xF000) `shiftR` 12

thirdDigit = (opcode .&. 0x00F0) `shiftR` 4

lastDigit = opcode .&. 0x000F

decrementDelayTimer :: Chip8 -> Chip8

decrementDelayTimer chip8State =

chip8State {

delayTimer = if originalDelayTimer > 0 then originalDelayTimer - 1 else originalDelayTimer

}

where

originalDelayTimer = delayTimer chip8State

decrementSoundTimer :: Chip8 -> Chip8

decrementSoundTimer chip8State =

chip8State {

soundTimer = if originalSoundTimer > 0 then originalSoundTimer - 1 else originalSoundTimer

}

where

originalSoundTimer = soundTimer chip8State