use std::cmp;

const UNITS: [&str; 4] = ["B", "kB", "MB", "GB"];

pub struct Bytes {
    bytes: f64,
}

impl Bytes {
    pub fn new(bytes: u64) -> Self {
        Self {
            bytes: bytes as f64,
        }
    }
}

impl std::fmt::Display for Bytes {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let num = self.bytes;
        debug_assert!(num >= 0.0);        
        if num < 1_f64 {
            return write!(f, "{} B", num);
        }
        let delimiter = 1000_f64;
        let exponent = cmp::min((num.ln() / 6.90775).floor() as i32, 4);

        write!(f, "{:.2} ", num / delimiter.powi(exponent))?;
        write!(f, "{}", UNITS[exponent as usize])
    }
}