import bit from "./bit";
import { memory } from "./memory";
import { Ram } from "./ram";
import { Word, emptyWord, wordFromNumber, wordFromString } from "./word";

export function machine<Width extends number>(ram: Ram<Width>) {

    const programCounterRegister = memory(wordFromNumber(1, ram.addressLength))

    const startAddress = ram.read(emptyWord(ram.addressLength)).subword(ram.wordSize - ram.addressLength, ram.addressLength)
    
    const addressRegister = memory(startAddress)

    const instructionCounterSize = Math.ceil(Math.log2(Math.floor(ram.wordSize / 2)))
    const instructionCounterRegister = memory(emptyWord(instructionCounterSize))

    function programCounter() {
        return programCounterRegister
    }

    function instructionCounter() {
        return instructionCounterRegister
    }

    function tick() {
        
        const currentInstruction = ram.read(programCounterRegister.value()).subword(instructionCounterRegister.value().toNumber() * 2, 2)
        if (currentInstruction.equals(wordFromString("00"))) {
            const firstOperand = ram.read(addressRegister.value())
            const secondOperand = ram.read(addressRegister.value().plus(wordFromNumber(1)).sum)
            const result = firstOperand.plus(secondOperand).sum as Word<number>
            
            ram.write(result as Word<Width>, addressRegister.value().plus(wordFromString("10")).sum)
            incrementInstruction()
        } else if (currentInstruction.equals(wordFromString("01"))) {
            addressRegister.set(ram.read(addressRegister.value()))
            incrementInstruction()
        } else if (currentInstruction.equals(wordFromString("10"))) {
            const current = ram.read(addressRegister.value())
            const jumpAddress = ram.read(addressRegister.value().plus(wordFromNumber(1)).sum).subword(ram.wordSize - ram.addressLength, ram.addressLength)

            if (current.toNumber() !== 0) {
                programCounterRegister.set(jumpAddress)
                instructionCounterRegister.set(emptyWord(instructionCounterSize))
            } else {
                incrementInstruction()
            }
        } else if (currentInstruction.equals(wordFromString("11"))) {
            const nextValue = addressRegister.value().plus(wordFromNumber(1)).sum
            addressRegister.set(nextValue)

            incrementInstruction()
        }
    }
    
    function incrementInstruction() {
        const nextInstructionIndex = instructionCounterRegister.value().plus(wordFromNumber(1, instructionCounterSize))
        instructionCounterRegister.set(nextInstructionIndex.sum)
        
        if (nextInstructionIndex.carry.equals(bit(1))) {
            const nextProgramCounterAddress = programCounterRegister.value().plus(wordFromNumber(1, ram.addressLength))
            programCounterRegister.set(nextProgramCounterAddress.sum)
        }
    }

    return {
        programCounter,
        addressRegister,
        instructionCounter,
        tick,
        ram
    }
}