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use std::{borrow::Borrow, marker, ops::RangeBounds};

use crate::core::{Diff, Footprint, Index, IndexIter, Reader, Writer};
use crate::core::{Entry, Result};
use crate::error::Error;

/// NoDisk type denotes empty Disk type. Applications can use this
/// type while instantiating `rdms-index` in mem-only mode.
pub struct NoDisk<K, V> {
    phantom_key: marker::PhantomData<K>,
    phantom_val: marker::PhantomData<V>,
}

impl<K, V> NoDisk<K, V> {
    fn new() -> NoDisk<K, V> {
        NoDisk {
            phantom_key: marker::PhantomData,
            phantom_val: marker::PhantomData,
        }
    }
}

impl<K, V> Footprint for NoDisk<K, V> {
    fn footprint(&self) -> isize {
        0
    }
}

impl<K, V> Index<K, V> for NoDisk<K, V>
where
    K: Clone + Ord + Footprint,
    V: Clone + Diff + Footprint,
{
    type W = NoDisk<K, V>;
    type R = NoDisk<K, V>;

    fn make_new(&self) -> Result<Box<Self>> {
        Ok(Box::new(NoDisk::new()))
    }

    fn to_reader(&mut self) -> Result<Self::R> {
        Ok(NoDisk::new())
    }

    fn to_writer(&mut self) -> Result<Self::W> {
        panic!("write operations are not allowed");
    }
}

impl<K, V> Reader<K, V> for NoDisk<K, V>
where
    K: Clone + Ord,
    V: Clone + Diff,
{
    fn get<Q>(&self, _key: &Q) -> Result<Entry<K, V>>
    where
        K: Borrow<Q>,
        Q: Ord + ?Sized,
    {
        Err(Error::KeyNotFound)
    }

    fn iter(&self) -> Result<IndexIter<K, V>> {
        Ok(Box::new(NoDiskIter {
            _phantom_key: &self.phantom_key,
            _phantom_val: &self.phantom_val,
        }))
    }

    fn range<'a, R, Q>(&'a self, _range: R) -> Result<IndexIter<K, V>>
    where
        K: Borrow<Q>,
        R: 'a + RangeBounds<Q>,
        Q: 'a + Ord + ?Sized,
    {
        Ok(Box::new(NoDiskIter {
            _phantom_key: &self.phantom_key,
            _phantom_val: &self.phantom_val,
        }))
    }

    fn reverse<'a, R, Q>(&'a self, _range: R) -> Result<IndexIter<K, V>>
    where
        K: Borrow<Q>,
        R: 'a + RangeBounds<Q>,
        Q: 'a + Ord + ?Sized,
    {
        Ok(Box::new(NoDiskIter {
            _phantom_key: &self.phantom_key,
            _phantom_val: &self.phantom_val,
        }))
    }

    fn get_with_versions<Q>(&self, _key: &Q) -> Result<Entry<K, V>>
    where
        K: Borrow<Q>,
        Q: Ord + ?Sized,
    {
        Err(Error::KeyNotFound)
    }

    fn iter_with_versions(&self) -> Result<IndexIter<K, V>> {
        Ok(Box::new(NoDiskIter {
            _phantom_key: &self.phantom_key,
            _phantom_val: &self.phantom_val,
        }))
    }

    fn range_with_versions<'a, R, Q>(&self, _range: R) -> Result<IndexIter<K, V>>
    where
        K: Borrow<Q>,
        R: 'a + RangeBounds<Q>,
        Q: 'a + Ord + ?Sized,
    {
        Ok(Box::new(NoDiskIter {
            _phantom_key: &self.phantom_key,
            _phantom_val: &self.phantom_val,
        }))
    }

    fn reverse_with_versions<'a, R, Q>(&self, _rng: R) -> Result<IndexIter<K, V>>
    where
        K: Borrow<Q>,
        R: 'a + RangeBounds<Q>,
        Q: 'a + Ord + ?Sized,
    {
        Ok(Box::new(NoDiskIter {
            _phantom_key: &self.phantom_key,
            _phantom_val: &self.phantom_val,
        }))
    }
}

impl<K, V> Writer<K, V> for NoDisk<K, V>
where
    K: Clone + Ord + Footprint,
    V: Clone + Diff + Footprint,
{
    fn set(&mut self, _key: K, _value: V) -> Result<Option<Entry<K, V>>> {
        panic!("operation not allowed");
    }

    fn set_cas(&mut self, _k: K, _v: V, _: u64) -> Result<Option<Entry<K, V>>> {
        panic!("operation not allowed");
    }

    fn delete<Q>(&mut self, _key: &Q) -> Result<Option<Entry<K, V>>>
    where
        K: Borrow<Q>,
        Q: ToOwned<Owned = K> + Ord + ?Sized,
    {
        panic!("operation not allowed");
    }
}

struct NoDiskIter<'a, K, V>
where
    K: Clone + Ord,
    V: Clone + Diff,
{
    _phantom_key: &'a marker::PhantomData<K>,
    _phantom_val: &'a marker::PhantomData<V>,
}

impl<'a, K, V> Iterator for NoDiskIter<'a, K, V>
where
    K: Clone + Ord,
    V: Clone + Diff,
{
    type Item = Result<Entry<K, V>>;

    fn next(&mut self) -> Option<Self::Item> {
        None
    }
}