use std::cmp::Ordering;
use std::default::Default;

pub enum ValueType {
    TypeDeletion = 0,
    TypeValue = 1,
}

/// Represents a sequence number of a single entry.
pub type SequenceNumber = u64;

#[allow(dead_code)]
pub enum Status {
    OK,
    NotFound(String),
    Corruption(String),
    NotSupported(String),
    InvalidArgument(String),
    IOError(String),
}

/// Trait used to influence how SkipMap determines the order of elements. Use StandardComparator
/// for the normal implementation using numerical comparison.
pub trait Comparator: Copy + Default {
    fn cmp(&[u8], &[u8]) -> Ordering;
}

#[derive(Clone, Copy, Default)]
pub struct StandardComparator;

impl Comparator for StandardComparator {
    fn cmp(a: &[u8], b: &[u8]) -> Ordering {
        a.cmp(b)
    }
}

pub struct Range<'a> {
    pub start: &'a [u8],
    pub limit: &'a [u8],
}

/// An extension of the standard `Iterator` trait that supports some methods necessary for LevelDB.
/// This works because the iterators used are stateful and keep the last returned element.
///
/// Note: Implementing types are expected to hold `!valid()` before the first call to `next()`.
pub trait LdbIterator: Iterator {
    // We're emulating LevelDB's Slice type here using actual slices with the lifetime of the
    // iterator. The lifetime of the iterator is usually the one of the backing storage (Block,
    // MemTable, SkipMap...)
    // type Item = (&'a [u8], &'a [u8]);

    /// Seek the iterator to `key` or the next bigger key.
    fn seek(&mut self, key: &[u8]);
    /// Resets the iterator to be `!valid()` again (before first element)
    fn reset(&mut self);
    /// Returns true if `current()` would return a valid item.
    fn valid(&self) -> bool;
    /// Return the current item.
    fn current(&self) -> Option<Self::Item>;
    /// Go to the previous item.
    fn prev(&mut self) -> Option<Self::Item>;

    /// You should override this with a more efficient solution.
    fn seek_to_last(&mut self) {
        while let Some(_) = self.next() {
        }
    }
    fn seek_to_first(&mut self) {
        self.reset();
        self.next();
    }
}