use num_bigint::BigInt;
use num_traits::cast::ToPrimitive;
use std::convert::TryInto;
use std::io;
use std::io::Write;
use super::constants::Tag;
use crate::{boundary as B, ValueImpl, DomainEncode, Writer, DefaultDomainCodec};

struct Buffers<W: io::Write> {
    base: W,
    stack: Vec<Vec<Vec<u8>>>,
}

impl<W: io::Write> io::Write for Buffers<W> {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        if self.stack.is_empty() {
            self.base.write(buf)
        } else {
            self.stack
                .last_mut().unwrap()
                .last_mut().expect("Internal error: PackedWriter buffer sequence underflow")
                .write(buf)
        }
    }

    fn flush(&mut self) -> io::Result<()> {
        if self.stack.is_empty() {
            self.base.flush()
        } else {
            Ok(())
        }
    }
}

pub struct PackedWriter<W: io::Write>(Buffers<W>);

impl PackedWriter<&mut Vec<u8>> {
    #[inline(always)]
    pub fn encode_domain<'de, V: ValueImpl<'de>, Enc: DomainEncode<'de, V::Embedded>>(
        enc: &mut Enc,
        v: &V,
    ) -> io::Result<Vec<u8>> {
        let mut buf: Vec<u8> = Vec::new();
        v.write(&mut PackedWriter::new(&mut buf), enc)?;
        Ok(buf)
    }

    #[inline(always)]
    pub fn encode<'de, V: ValueImpl<'de>>(v: &V) -> io::Result<Vec<u8>> {
        Self::encode_domain(&mut DefaultDomainCodec, v)
    }
}

pub fn varint<W: io::Write>(w: &mut W, mut v: u64) -> io::Result<usize> {
    let mut byte_count = 0;
    loop {
        byte_count += 1;
        if v < 128 {
            w.write_all(&[v as u8])?;
            return Ok(byte_count);
        } else {
            w.write_all(&[((v & 0x7f) + 128) as u8])?;
            v >>= 7;
        }
    }
}

impl<W: io::Write> PackedWriter<W> {
    #[inline(always)]
    pub fn new(write: W) -> Self {
        PackedWriter(Buffers {
            base: write,
            stack: vec![],
        })
    }

    #[inline(always)]
    pub fn write_byte(&mut self, b: u8) -> io::Result<()> {
        self.0.write_all(&[b])
    }

    #[inline(always)]
    pub fn write_medium_integer(&mut self, bs: &[u8]) -> io::Result<()> {
        let count: u8 = bs.len().try_into().unwrap();
        if !(1..=16).contains(&count) { panic!("Invalid medium_integer count: {}", count) }
        self.write_byte(Tag::MediumInteger(count).into())?;
        self.0.write_all(bs)
    }

    #[inline(always)]
    pub fn write_atom(&mut self, tag: Tag, bs: &[u8]) -> io::Result<()> {
        self.write_byte(tag.into())?;
        varint(&mut self.0, bs.len().try_into().unwrap())?;
        self.0.write_all(bs)
    }

    fn push(&mut self) -> io::Result<()> {
        self.0.stack.push(vec![vec![]]);
        Ok(())
    }

    fn shift(&mut self) {
        match self.0.stack.last_mut() {
            Some(bss) => bss.push(vec![]),
            None => panic!("Internal error: Preserves PackedWriter stack underflow"),
        }
    }

    fn pop(&mut self, sorted: bool) -> io::Result<()> {
        match self.0.stack.pop() {
            Some(mut bss) => {
                if sorted { bss.sort(); }
                for bs in bss { self.0.write_all(&bs)? }
                Ok(())
            }
            None =>
                panic!("Internal error: Preserves PackedWriter stack underflow"),
        }
    }

    #[inline(always)]
    fn write_tag(&mut self, tag: Tag) -> io::Result<()> {
        self.write_byte(tag.into())
    }
}

macro_rules! fits_in_bytes {
    ($v:ident, $limit:literal) => ({
        let bits = $limit * 8 - 1;
        $v >= -(2 << bits) && $v < (2 << bits)
    })
}

impl<W: io::Write> Writer for PackedWriter<W>
{
    #[inline(always)]
    fn boundary(&mut self, b: &B::Type) -> io::Result<()> {
        match b.closing {
            Some(B::Item::DictionaryValue) |
            Some(B::Item::SetValue) =>
                self.shift(),
            _ =>
                ()
        }
        match b.opening {
            Some(B::Item::Annotation) =>
                self.write_tag(Tag::Annotation)?,
            _ =>
                ()
        }
        Ok(())
    }

    #[inline(always)]
    fn start_annotations(&mut self) -> io::Result<()> {
        Ok(())
    }

    #[inline(always)]
    fn end_annotations(&mut self) -> io::Result<()> {
        Ok(())
    }

    #[inline(always)]
    fn write_bool(&mut self, v: bool) -> io::Result<()> {
        self.write_tag(if v { Tag::True } else { Tag::False })
    }

    #[inline(always)]
    fn write_f32(&mut self, v: f32) -> io::Result<()> {
        self.write_tag(Tag::Float)?;
        self.0.write_all(&u32::to_be_bytes(f32::to_bits(v)))
    }

    #[inline(always)]
    fn write_f64(&mut self, v: f64) -> io::Result<()> {
        self.write_tag(Tag::Double)?;
        self.0.write_all(&u64::to_be_bytes(f64::to_bits(v)))
    }

    #[inline(always)]
    fn write_i8(&mut self, v: i8) -> io::Result<()> {
        if v >= -3 && v <= 12 { return self.write_tag(Tag::SmallInteger(v)) }
        self.write_medium_integer(&[v as u8])
    }

    #[inline(always)]
    fn write_u8(&mut self, v: u8) -> io::Result<()> {
        if let Ok(w) = v.try_into() { return self.write_i8(w) }
        self.write_medium_integer(&[0, v])
    }

    #[inline(always)]
    fn write_i16(&mut self, v: i16) -> io::Result<()> {
        if let Ok(w) = v.try_into() { return self.write_i8(w) }
        self.write_medium_integer(&[(v >> 8) as u8, (v & 255) as u8])
    }

    #[inline(always)]
    fn write_u16(&mut self, v: u16) -> io::Result<()> {
        if let Ok(w) = v.try_into() { return self.write_i16(w) }
        self.write_medium_integer(&[0, (v >> 8) as u8, (v & 255) as u8])
    }

    #[inline(always)]
    fn write_i32(&mut self, v: i32) -> io::Result<()> {
        if let Ok(w) = v.try_into() { return self.write_i16(w) }
        if fits_in_bytes!(v, 3) {
            return self.write_medium_integer(&[(v >> 16) as u8,
                                               (v >> 8) as u8,
                                               (v & 255) as u8]);
        }
        self.write_medium_integer(&[(v >> 24) as u8,
                                    (v >> 16) as u8,
                                    (v >> 8) as u8,
                                    (v & 255) as u8])
    }

    #[inline(always)]
    fn write_u32(&mut self, v: u32) -> io::Result<()> {
        if let Ok(w) = v.try_into() { return self.write_i32(w) }
        self.write_medium_integer(&[0,
                                    (v >> 24) as u8,
                                    (v >> 16) as u8,
                                    (v >> 8) as u8,
                                    (v & 255) as u8])
    }

    #[inline(always)]
    fn write_i64(&mut self, v: i64) -> io::Result<()> {
        if let Ok(w) = v.try_into() { return self.write_i32(w) }
        if fits_in_bytes!(v, 5) {
            return self.write_medium_integer(&[(v >> 32) as u8,
                                               (v >> 24) as u8,
                                               (v >> 16) as u8,
                                               (v >> 8) as u8,
                                               (v & 255) as u8]);
        }
        if fits_in_bytes!(v, 6) {
            return self.write_medium_integer(&[(v >> 40) as u8,
                                               (v >> 32) as u8,
                                               (v >> 24) as u8,
                                               (v >> 16) as u8,
                                               (v >> 8) as u8,
                                               (v & 255) as u8]);
        }
        if fits_in_bytes!(v, 7) {
            return self.write_medium_integer(&[(v >> 48) as u8,
                                               (v >> 40) as u8,
                                               (v >> 32) as u8,
                                               (v >> 24) as u8,
                                               (v >> 16) as u8,
                                               (v >> 8) as u8,
                                               (v & 255) as u8]);
        }
        self.write_medium_integer(&[(v >> 56) as u8,
                                    (v >> 48) as u8,
                                    (v >> 40) as u8,
                                    (v >> 32) as u8,
                                    (v >> 24) as u8,
                                    (v >> 16) as u8,
                                    (v >> 8) as u8,
                                    (v & 255) as u8])
    }

    #[inline(always)]
    fn write_u64(&mut self, v: u64) -> io::Result<()> {
        if let Ok(w) = v.try_into() { return self.write_i64(w) }
        self.write_medium_integer(&[0,
                                    (v >> 56) as u8,
                                    (v >> 48) as u8,
                                    (v >> 40) as u8,
                                    (v >> 32) as u8,
                                    (v >> 24) as u8,
                                    (v >> 16) as u8,
                                    (v >> 8) as u8,
                                    (v & 255) as u8])
    }

    #[inline(always)]
    fn write_i128(&mut self, v: i128) -> io::Result<()> {
        if let Ok(w) = v.try_into() { return self.write_i64(w) }
        let bs: [u8; 16] = v.to_be_bytes();
        if fits_in_bytes!(v, 9)  { return self.write_medium_integer(&bs[7..]); }
        if fits_in_bytes!(v, 10) { return self.write_medium_integer(&bs[6..]); }
        if fits_in_bytes!(v, 11) { return self.write_medium_integer(&bs[5..]); }
        if fits_in_bytes!(v, 12) { return self.write_medium_integer(&bs[4..]); }
        if fits_in_bytes!(v, 13) { return self.write_medium_integer(&bs[3..]); }
        if fits_in_bytes!(v, 14) { return self.write_medium_integer(&bs[2..]); }
        if fits_in_bytes!(v, 15) { return self.write_medium_integer(&bs[1..]); }
        self.write_medium_integer(&bs)
    }

    #[inline(always)]
    fn write_u128(&mut self, v: u128) -> io::Result<()> {
        if let Ok(w) = v.try_into() { return self.write_i128(w) }
        let bs: [u8; 16] = v.to_be_bytes();
        self.write_tag(Tag::SignedInteger)?;
        varint(&mut self.0, 17)?;
        self.write_byte(0)?;
        self.0.write_all(&bs)
    }

    #[inline(always)]
    fn write_int(&mut self, v: &BigInt) -> io::Result<()> {
        match v.to_i8() {
            Some(n) => self.write_i8(n),
            None => {
                match v.to_i128() {
                    Some(n) => self.write_i128(n),
                    None => self.write_atom(Tag::SignedInteger, &v.to_signed_bytes_be()),
                }
            }
        }
    }

    #[inline(always)]
    fn write_string(&mut self, v: &str) -> io::Result<()> {
        self.write_atom(Tag::String, v.as_bytes())
    }

    #[inline(always)]
    fn write_bytes(&mut self, v: &[u8]) -> io::Result<()> {
        self.write_atom(Tag::ByteString, v)
    }

    #[inline(always)]
    fn write_symbol(&mut self, v: &str) -> io::Result<()> {
        self.write_atom(Tag::Symbol, v.as_bytes())
    }

    #[inline(always)]
    fn start_record(&mut self) -> io::Result<()> {
        self.write_tag(Tag::Record)
    }

    #[inline(always)]
    fn end_record(&mut self) -> io::Result<()> {
        self.write_tag(Tag::End)
    }

    #[inline(always)]
    fn start_sequence(&mut self) -> io::Result<()> {
        self.write_tag(Tag::Sequence)
    }

    #[inline(always)]
    fn end_sequence(&mut self) -> io::Result<()> {
        self.write_tag(Tag::End)
    }

    #[inline(always)]
    fn start_set(&mut self) -> io::Result<()> {
        self.write_tag(Tag::Set)?;
        self.push()
    }

    #[inline(always)]
    fn end_set(&mut self) -> io::Result<()> {
        self.pop(true)?;
        self.write_tag(Tag::End)
    }

    #[inline(always)]
    fn start_dictionary(&mut self) -> io::Result<()> {
        self.write_tag(Tag::Dictionary)?;
        self.push()
    }

    #[inline(always)]
    fn end_dictionary(&mut self) -> io::Result<()> {
        self.pop(true)?;
        self.write_tag(Tag::End)
    }

    #[inline(always)]
    fn start_embedded(&mut self) -> io::Result<()> {
        self.write_tag(Tag::Embedded)
    }

    #[inline(always)]
    fn end_embedded(&mut self) -> io::Result<()> {
        Ok(())
    }

    #[inline(always)]
    fn flush(&mut self) -> io::Result<()> {
        self.0.flush()
    }

    fn specialized(&mut self) -> Option<(&str, &mut dyn io::Write)> {
        Some(("packed", &mut self.0))
    }
}