genRand.kt

package com.pavlos.efstathiou.genid

import android.os.Build
import androidx.annotation.RequiresApi
import java.io.BufferedReader
import java.io.File
import java.nio.file.Files
import java.nio.file.StandardOpenOption
import java.lang.IllegalArgumentException

data class User(val id: Int, val fileName: String, var file: File,) {
    init {
        if (this.id < 1000 || this.id < 99999) id else throw IllegalArgumentException("id can't be less than 1000 and more than 99999")
    }
}

var user = User(genRand(1000..99999), "id.txt", File("placeholder"))

@RequiresApi(Build.VERSION_CODES.O)
fun main() {
    user.file = File(user.fileName)
//    Files.write(user.file.toPath(), user.id.toString().toByteArray(), StandardOpenOption.APPEND)
//    Files.readAllBytes(user.file.toPath())
    if (user.file.length() >= 5) read()
    else write()
}
fun genRand(range: IntRange) : Int {
    return (range).random()
}

@RequiresApi(Build.VERSION_CODES.O)
fun write() {
    val isFileCreated : Boolean = user.file.createNewFile()
    // Thanks https://www.tutorialkart.com/kotlin/kotlin-create-file/
    if(isFileCreated) println("File created successfully.")
    user.file = File(user.fileName)
    Files.write(user.file.toPath(), user.id.toString().toByteArray(), StandardOpenOption.WRITE) // Deletes data and writes new data
    read()
}

@RequiresApi(Build.VERSION_CODES.O)
fun read() {
    user.file = File(user.fileName)
    Files.readAllBytes(user.file.toPath())
    val bufferedReader: BufferedReader = user.file.bufferedReader()
    val inputString = bufferedReader.use { it.readText() }
    println("Id is $inputString")

}