MoneyRecord.kt

import java.io.File

fun main() {
    println("1) Log in, 2) Create a new account")
    val logInOperation = try {readLine()!!.toInt()} catch (e: NumberFormatException) {null}
    when (logInOperation) {

        1 /* Log into an existing account */ -> {
            print("Enter your account: ")
                                                                        // Changes whitespaces to underscores
            val filePath = "src/main/textFiles/${readStringLower()}.txt".replace("\\s".toRegex(), "_")

            if (doesExist(filePath)) {
                println("1) Make a deposit, 2) Make a withdrawal, 3) Check account's total balance")
                val accountOperation = try {readLine()!!.toInt()} catch (e: NumberFormatException) {null}
                when (accountOperation) {

                    1 /* Make deposit */ -> {
                        print("Amount to deposit: ")
                        try {
                            val amount = readLine()!!.toLong()

                            if (amount > 0) makeDeposit(filePath, amount)
                            else println("Amount cannot be zero nor negative.")

                        } catch (e: NumberFormatException) {
                            println("Amount must be a number.")
                        }
                    }

                    2 /* Make withdrawal */ -> {
                        print("Amount to withdraw: ")
                        try {
                            val amount = readLine()!!.toLong()
                            val accountBalance = getBalance(filePath)

                            if (amount <= 0) println("Amount cannot be zero nor negative.")
                            else if (amount > accountBalance) println("There's not enough money in the account to complete the withdrawal.")
                            else makeWithdrawal(filePath, amount)

                        } catch (e: NumberFormatException) {
                            println("Amount must be a number.")
                        }
                    }

                    3 /* Get balance */ -> println("%,d".format(getBalance(filePath)))

                    else -> println("Invalid option. Try again.")
                }
            }
            else {
                println("This account doesn't exist. Do you want to create it?")
                val doContinue = readStringLower()
                if (doContinue == "yes" || doContinue == "y") {
                    createFile(filePath)
                } else {
                    println("All right. Closing program...")
                }
            }
        }

        2 /* Create a new account */ -> {
            print("Enter the name of your future account: ")
                                                                        // Changes whitespaces to underscores
            val newAccount = "src/main/textFiles/${readStringLower()}.txt".replace("\\s".toRegex(), "_")
            createFile(newAccount)
        }

        else -> println("Invalid option. Try again.")
    }
}

fun createFile(filePath: String) {
    val file = File(filePath)
    if (file.exists()) println("This account already exists.")
    else {
        file.createNewFile()
        println("Account created.")
    }
}

fun makeDeposit(filePath: String, amount: Long) {
    val file = File(filePath)

    if (file.exists()) file.appendText("+ $amount\n")
    else println("This account doesn't exist.")
}

fun makeWithdrawal(filePath: String, amount: Long) {
    val file = File(filePath)

    if (file.exists()) file.appendText("- $amount\n")
    else println("This account doesn't exist.")
}

fun getBalance(filePath: String): Long {
    val file = File(filePath)
    val upAmounts: MutableList<Long> = mutableListOf()
    val downAmounts: MutableList<Long> = mutableListOf()

    file.forEachLine {
        // Checks if it's a deposit or a withdrawal,
        // makes a slice of the amount and adds it to the corresponding list
        if (it[0] == '+') upAmounts.add(it.slice(2..it.lastIndex).toLong())
        else downAmounts.add(it.slice(2..it.lastIndex).toLong())
    }

    return upAmounts.sum() - downAmounts.sum()
}

fun doesExist(name: String): Boolean {
    val file = File(name)
    return file.exists()
}

private fun readStringLower(): String = readLine()!!.lowercase()