use std::io::{Read, Result, Write};

#[derive(Debug, Clone)]
enum HT {
    Branch(Box<HT>, Box<HT>),
    Terminal(u8),
}

pub fn write_huff(buf: &[u8], w: &mut impl Write) -> Result<usize> {
    let mut w = BitIO::new(w);
    assert!(buf.len() <= 0xffffff, "huff frame too big");
    w.wbyte((buf.len() & 0xff) as u8)?;
    w.wbyte(((buf.len() >> 8) & 0xff) as u8)?;
    w.wbyte(((buf.len() >> 16) & 0xff) as u8)?;

    let mut probs = [0usize; 256];
    for b in buf {
        probs[*b as usize] += 1;
    }
    let tree = HT::from_probabilities(probs);
    let mut table = [0u32; 256];
    tree.create_lut(&mut table, 1);
    tree.write(&mut w)?;


    for b in buf {
        let mut k = table[*b as usize];
        while k != 1 {
            w.wbit((k & 1) == 1)?;
            k >>= 1;
        }
    }
    
    w.flush()?;
    Ok(w.position)
}

pub fn read_huff(r: &mut impl Read, buf: &mut Vec<u8>) -> Result<usize> {
    let mut r = BitIO::new(r);

    let mut len = 0usize;
    len |= r.rbyte()? as usize;
    len |= (r.rbyte()? as usize) << 8;
    len |= (r.rbyte()? as usize) << 16;

    let root = HT::read(&mut r)?;
    let root = match &root {
        HT::Branch(a, b) => [a, b],
        _ => panic!("no!"),
    };

    let mut cursor = root;
    while buf.len() != len {
        let v = r.rbit()?;
        match cursor[v as usize].as_ref() {
            HT::Branch(a, b) => {
                cursor = [a, b];
            }
            HT::Terminal(n) => {
                buf.push(*n);
                cursor = root;
            }
        }
    }
    Ok(r.position)
}

impl HT {
    pub fn from_probabilities(ps: [usize; 256]) -> Self {
        let mut parts = ps
            .into_iter()
            .enumerate()
            .map(|(n, p)| (p, HT::Terminal(n as u8)))
            .collect::<Vec<_>>();

        while parts.len() != 1 {
            parts.sort_by_key(|e| -(e.0 as isize));
            let ((ap, at), (bp, bt)) = (parts.pop().unwrap(), parts.pop().unwrap());
            parts.push((ap + bp + 1, HT::Branch(box at, box bt)))
        }
        parts[0].1.clone()
    }
    pub fn create_lut(&self, table: &mut [u32; 256], mut prefix: u32) {
        assert!(self.depth() < 30, "too deep! doesnt fit {}", self.depth());
        match self {
            HT::Branch(a, b) => {
                let pz = 32 - prefix.leading_zeros();
                prefix ^= 1 << pz;
                prefix ^= 1 << (pz - 1);
                a.create_lut(table, prefix);
                prefix ^= 1 << (pz - 1);
                b.create_lut(table, prefix);
            }
            HT::Terminal(n) => {
                assert_eq!(table[*n as usize], 0);
                table[*n as usize] = prefix
            }
        }
    }
    pub fn depth(&self) -> usize {
        match self {
            HT::Branch(a, b) => a.depth().max(b.depth()) + 1,
            HT::Terminal(_) => 0,
        }
    }
    pub fn write(&self, w: &mut BitIO<impl Write>) -> Result<()> {
        match self {
            HT::Branch(a, b) => {
                w.wbit(false)?;
                a.write(w)?;
                b.write(w)?;
            }
            HT::Terminal(n) => {
                w.wbit(true)?;
                w.wbyte(*n)?;
            }
        }
        Ok(())
    }
    pub fn read(r: &mut BitIO<impl Read>) -> Result<Self> {
        match r.rbit()? {
            false => Ok(Self::Branch(box Self::read(r)?, box Self::read(r)?)),
            true => Ok(Self::Terminal(r.rbyte()?)),
        }
    }
}

pub struct BitIO<T> {
    inner: T,
    byte: u8,
    position: usize,
}
impl<T> BitIO<T> {
    pub fn new(inner: T) -> Self {
        Self {
            inner,
            byte: 0,
            position: 0,
        }
    }
}
impl<T: Write> BitIO<T> {
    #[inline]
    pub fn wbit(&mut self, b: bool) -> Result<()> {
        self.byte <<= 1;
        self.byte |= b as u8;
        self.position += 1;
        if self.position & 0b111 == 0 {
            self.inner.write_all(&[self.byte])?;
        }
        Ok(())
    }
    #[inline]
    pub fn wbyte(&mut self, v: u8) -> Result<()> {
        for i in 0..8 {
            self.wbit((v & (1 << i)) != 0)?;
        }
        Ok(())
    }
    pub fn flush(&mut self) -> Result<()> {
        while self.position & 0b111 != 0 {
            self.wbit(false)?;
        }
        Ok(())
    }
}

impl<T: Read> BitIO<T> {
    #[inline]
    pub fn rbit(&mut self) -> Result<bool> {
        if self.position & 0b111 == 0 {
            let mut buf = [0];
            self.inner.read_exact(&mut buf)?;
            self.byte = buf[0];
        }

        let v = (self.byte & 0b10000000) != 0;
        self.byte <<= 1;
        self.position += 1;
        Ok(v)
    }
    #[inline]
    pub fn rbyte(&mut self) -> Result<u8> {
        let mut v = 0u8;
        for i in 0..8 {
            v |= (self.rbit()? as u8) << i;
        }
        Ok(v)
    }
}