//! Extensions
use super::*;

use std::{
    collections::HashMap,
    hash::Hash,
    borrow::{
	Borrow,
	ToOwned,
    },
    num::NonZeroU8,
};

pub use dedup::DedupIterExt;

/// Iterator that maps `T` -> `U`
pub struct ReplacingIter<'a, I,T, U=T>
{
    iter: I,
    table: &'a HashMap<T, U>,
}

impl<'a, I,T,U> Iterator for ReplacingIter<'a, I,T,U>
where I: Iterator<Item=T>,
      T: Hash+ Eq + ToOwned<Owned=U>,
      U: Borrow<T> + Clone,
{
    type Item = U;
    fn next(&mut self) -> Option<Self::Item> {
	if let Some(item) = self.iter.next()
	{
	    Some(self.table.get(&item)
		 .map(Clone::clone)
		 .unwrap_or(item.to_owned()))
	} else {
	    None
	}
    }

    #[inline] fn size_hint(&self) -> (usize, Option<usize>) {
	self.iter.size_hint()
    }
}

impl<'a, I,T,U> ExactSizeIterator for ReplacingIter<'a, I,T,U>
where I: Iterator<Item=T> + ExactSizeIterator,
      T: Hash+ Eq + ToOwned<Owned=U>,
      U: Borrow<T> + Clone{}

impl<'a, I,T,U> std::iter::FusedIterator for ReplacingIter<'a, I,T,U>
where I: Iterator<Item=T> + std::iter::FusedIterator,
      T: Hash+ Eq + ToOwned<Owned=U>,
      U: Borrow<T> + Clone{}

impl<'a, I,T,U> std::iter::DoubleEndedIterator for ReplacingIter<'a, I,T,U>
where I: Iterator<Item=T> + std::iter::DoubleEndedIterator,
      T: Hash+ Eq + ToOwned<Owned=U>,
      U: Borrow<T> + Clone
{
    fn next_back(&mut self) -> Option<Self::Item> {
	if let Some(item) = self.iter.next_back()
	{
	    Some(self.table.get(&item)
		 .map(Clone::clone)
		 .unwrap_or(item.to_owned()))
	} else {
	    None
	}
    }
}

impl<'a ,I,T,U> ReplacingIter<'a, I,T,U>
{
    pub fn into_inner(self) -> I
    {
	self.iter
    }
    pub fn table(&self) -> &'a HashMap<T,U>
    {
	self.table
    }
}

pub trait ReplacingIterExt<T, U>: Sized
{
    fn replace_with<'a>(self, table: &'a HashMap<T,U>) -> ReplacingIter<'a, Self, T, U>;
}

impl<I,T,U> ReplacingIterExt<T,U> for I
where I: Iterator<Item=T>,
      T: Hash+ Eq + ToOwned<Owned=U>,
      U: Borrow<T> + Clone,
{
    fn replace_with<'a>(self, table: &'a HashMap<T,U>) -> ReplacingIter<'a, Self, T, U> {
	ReplacingIter {
	    iter: self,
	    table,
	}
    }
}


const fn create_hex_map() -> [(u8, u8); 256]
{
    let mut out = [(0, 0); 256];
    const HEX: &[u8; 16] = b"0123456789abcdef";
    let mut i = 0usize;
    while i <= 255
    {
	out[i] = (
	    HEX[i >> 4],
	    HEX[i & 0xf]
	);
	i+=1;
    }
    out
}
const HEX_MAP: [(u8, u8); 256] = create_hex_map();

pub struct HexStrIterator<I>
{
    iter: I,
    buf: Option<NonZeroU8>, //we don't need full `char` here, since we can only have 0-9a-f anyway
}

impl<I> Iterator for HexStrIterator<I>
where I: Iterator<Item = u8>
{
    type Item = char;
    fn next(&mut self) -> Option<Self::Item>
    {
	if let Some(buf) = self.buf.take()
	{
	    return Some(u8::from(buf) as char);
	}

	if let Some(next) = self.iter.next() {
	    let buf = HEX_MAP[next as usize];
	    debug_assert_ne!(buf.1, 0);
	    //SAFETY: We know `HEX_MAP` contains only non-zero bytes.
	    unsafe {
		self.buf = Some(NonZeroU8::new_unchecked(buf.1));
	    }
	    Some(buf.0 as char)
	} else {
	    None
	}
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
	let (min, max) = self.iter.size_hint();

	(min * 2, max.map(|x| x * 2))
    }
}

impl<I> ExactSizeIterator for HexStrIterator<I>
where I: Iterator<Item = u8> + ExactSizeIterator{}

impl<I> std::iter::FusedIterator for HexStrIterator<I>
where I: Iterator<Item = u8> + std::iter::FusedIterator{}

pub trait HexStrIterExt: Sized
{
    fn hex(self) -> HexStrIterator<Self>;
}

impl<I> HexStrIterExt for I
where I: Iterator<Item = u8>
{
    fn hex(self) -> HexStrIterator<Self>
    {
	HexStrIterator{
	    iter: self,
	    buf: None,
	}
    }
}