const Net = require('net');

const port = 8002
const host = "ctf10k.root-me.org"

const client = new Net.Socket

client.on('data', (data) => {
    console.log("received data:\n", data.toString())

    regex =/(?<equation>^\d+.*$)/m
    let message = regex.exec(data.toString()).groups["equation"]
    console.log("equation:", message)

    let response = interpretRPN(message)
    console.log("response:", response)
    let buf = Buffer.from(response+"\n")
    client.write(buf)
})

client.on('end', () => {
    console.log("connection terminated by remote host")
})

client.connect({port: port, host: host}, () => {
    console.log("connected")
})

function interpretRPN(message){
    const operators = ['-', '+', 'x', '/']
    let elements = message.split(' ')
    for (let i = 0; i < elements.length; i++) {
        if (operators.includes(elements[i])) {
            let operation = elements.slice(i-2, i+1)
            let result = computeOperation(operation)
            elements.splice(i-2, 3, result)
            i = 0
        }
    }

    return elements.toString()
}

function computeOperation(operation) {
    switch (operation[2]) {
        case '-':
            return BigInt(operation[0]) - BigInt(operation[1])
        case 'x':
            return BigInt(operation[0]) * BigInt(operation[1])
        case '/':
            return BigInt(operation[0]) / BigInt(operation[1])
        case '+':
            return BigInt(operation[0]) + BigInt(operation[1])
    }
}

// const example = "994 611 + 357 733 + 82 543 - x x 740 + 136 x 996 +"
// console.log("response:", interpretRPN(example))