use std::cmp::Ordering;

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 {
    fn cmp(&[u8], &[u8]) -> Ordering;
}

#[derive(Clone, Copy)]
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.
pub trait LdbIterator<'a>: 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]);
    fn seek(&mut self, key: &[u8]);
    fn valid(&self) -> bool;
    fn current(&'a self) -> Self::Item;
    fn prev(&mut self) -> Option<Self::Item>;
}