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use std::fmt;
use std::net::Ipv4Addr;

/// A smart IPv4 iterator.
///
/// A smart iterator is an iterator that doesn't store all the items in memory. It's usefull for long series.
///
/// # Examples
///
/// ```
/// use std::net::Ipv4Addr;
///
/// use net_adds::Ipv4AddrSmartIterator;
///
/// let mut iter = Ipv4AddrSmartIterator::new(Ipv4Addr::from(0), Ipv4Addr::from(1));
///
/// assert_eq!(iter.next(), Some(Ipv4Addr::new(0, 0, 0, 0)));
/// assert_eq!(iter.next(), Some(Ipv4Addr::new(0, 0, 0, 1)));
/// assert_eq!(iter.next(), None);
///
/// let mut iter = Ipv4AddrSmartIterator::new(Ipv4Addr::from(0), Ipv4Addr::from(0));
///
/// assert_eq!(iter.next(), Some(Ipv4Addr::new(0, 0, 0, 0)));
/// assert_eq!(iter.next(), None);
///
/// let mut iter = Ipv4AddrSmartIterator::new(Ipv4Addr::from(1), Ipv4Addr::from(0));
///
/// assert_eq!(iter.next(), Some(Ipv4Addr::new(0, 0, 0, 1)));
/// assert_eq!(iter.next(), Some(Ipv4Addr::new(0, 0, 0, 0)));
/// assert_eq!(iter.next(), None);
/// ```
#[derive(Clone, Debug)]
pub struct Ipv4AddrSmartIterator {
    start: u32,
    end: u32,
    curr: u32,
    next: Option<u32>,
    updater: fn(u32) -> u32
}

impl Ipv4AddrSmartIterator {
    /// Returns a `Ipv4AddrSmartIterator`.
    pub fn new (start: Ipv4Addr, end: Ipv4Addr) -> Ipv4AddrSmartIterator {
        let start = u32::from(start);
        let end = u32::from(end);
        let updater = if start < end { |x| x + 1 } else { |x| x - 1 };
        Ipv4AddrSmartIterator {
            start,
            end,
            curr: start.clone(),
            next: Some(start.clone()),
            updater
        }
    } 
}

impl Iterator for Ipv4AddrSmartIterator {
    type Item = Ipv4Addr;

    fn next (&mut self) -> Option<Self::Item> {
        self.curr = self.next?;
        let update = self.updater;
        self.next = if self.curr == self.end { None } else { Some(update(self.curr)) };
        Some(Ipv4Addr::from(self.curr))
    }
}

impl fmt::Display for Ipv4AddrSmartIterator {
    fn fmt (&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}-{}-{}", self.start, self.curr, self.end)
    }
}

impl From<(Ipv4Addr, Ipv4Addr)> for Ipv4AddrSmartIterator {
    /// Create an `Ipv4AddrSmartIterator` from a tuple `(Ipv4Addr, Ipv4Addr)`.
    ///
    /// # Examples:
    ///
    /// ```
    /// use std::net::Ipv4Addr;
    ///
    /// use net_adds::Ipv4AddrSmartIterator;
    ///
    /// let mut iter = Ipv4AddrSmartIterator::from((Ipv4Addr::from(0), Ipv4Addr::from(1)));
    ///
    /// assert_eq!(iter.next(), Some(Ipv4Addr::from(0)));
    /// assert_eq!(iter.next(), Some(Ipv4Addr::from(1)));
    /// assert_eq!(iter.next(), None);
    /// ```
    fn from (ips: (Ipv4Addr, Ipv4Addr)) -> Ipv4AddrSmartIterator {
        Ipv4AddrSmartIterator::new(ips.0, ips.1)
    }
}