//! Implementation of [Reader] for the binary encoding.

use crate::error::{self, io_syntax_error, is_eof_io_error, ExpectedKind, Received};

use num::bigint::BigInt;
use num::traits::cast::{FromPrimitive, ToPrimitive};

use std::borrow::Cow;
use std::convert::TryFrom;
use std::convert::TryInto;
use std::io;
use std::marker::PhantomData;

use super::super::{
    boundary as B,
    reader::{BinarySource, Reader, ReaderResult, Token},
    repr::Annotations,
    signed_integer::SignedInteger,
    CompoundClass, DomainDecode, Map, NestedValue, Record, Set, Value,
};
use super::constants::Tag;

/// The binary encoding Preserves reader.
pub struct PackedReader<
    'de,
    'src,
    N: NestedValue,
    Dec: DomainDecode<N::Embedded>,
    S: BinarySource<'de>,
> {
    /// Underlying source of bytes.
    pub source: &'src mut S,
    /// Decoder for producing Rust values embedded in the binary data.
    pub decode_embedded: Dec,
    phantom: PhantomData<&'de N>,
}

impl<'de, 'src, N: NestedValue, Dec: DomainDecode<N::Embedded>, S: BinarySource<'de>>
    BinarySource<'de> for PackedReader<'de, 'src, N, Dec, S>
{
    type Mark = S::Mark;
    #[inline(always)]
    fn mark(&mut self) -> io::Result<Self::Mark> {
        self.source.mark()
    }
    #[inline(always)]
    fn restore(&mut self, mark: &Self::Mark) -> io::Result<()> {
        self.source.restore(mark)
    }
    #[inline(always)]
    fn skip(&mut self) -> io::Result<()> {
        self.source.skip()
    }
    #[inline(always)]
    fn peek(&mut self) -> io::Result<u8> {
        self.source.peek()
    }
    #[inline(always)]
    fn readbytes(&mut self, count: usize) -> io::Result<Cow<'de, [u8]>> {
        self.source.readbytes(count)
    }
    #[inline(always)]
    fn readbytes_into(&mut self, bs: &mut [u8]) -> io::Result<()> {
        self.source.readbytes_into(bs)
    }
}

fn out_of_range<I: Into<BigInt>>(i: I) -> error::Error {
    error::Error::NumberOutOfRange(i.into())
}

impl<'de, 'src, N: NestedValue, Dec: DomainDecode<N::Embedded>, S: BinarySource<'de>>
    PackedReader<'de, 'src, N, Dec, S>
{
    /// Construct a new reader from a byte source and embedded-value decoder.
    #[inline(always)]
    pub fn new(source: &'src mut S, decode_embedded: Dec) -> Self {
        PackedReader {
            source,
            decode_embedded,
            phantom: PhantomData,
        }
    }

    #[inline(always)]
    fn read(&mut self) -> io::Result<u8> {
        let v = self.peek()?;
        self.skip()?;
        Ok(v)
    }

    fn expected(&mut self, k: ExpectedKind) -> error::Error {
        match self.demand_next(true) {
            Ok(v) => error::Error::Expected(k, Received::ReceivedOtherValue(format!("{:?}", v))),
            Err(e) => e.into(),
        }
    }

    #[inline(always)]
    fn varint(&mut self) -> io::Result<usize> {
        let mut shift = 0;
        let mut acc: usize = 0;
        loop {
            let v = self.read()?;
            acc |= ((v & 0x7f) as usize) << shift;
            shift += 7;
            if v & 0x80 == 0 {
                return Ok(acc);
            }
        }
    }

    #[inline(always)]
    fn peekend(&mut self) -> io::Result<bool> {
        if self.peek()? == Tag::End.into() {
            self.skip()?;
            Ok(true)
        } else {
            Ok(false)
        }
    }

    #[inline(always)]
    fn try_next_nonannotation<T, F>(&mut self, f: F) -> ReaderResult<T>
    where
        F: FnOnce(&mut Self, Tag) -> ReaderResult<T>,
    {
        let m = self.source.mark()?;
        loop {
            match Tag::try_from(self.peek()?)? {
                Tag::Annotation => {
                    self.skip()?;
                    self.skip_value()?;
                }
                tag => match f(self, tag) {
                    Ok(v) => return Ok(v),
                    Err(e) => {
                        self.source.restore(&m)?;
                        return Err(e);
                    }
                }
            }
        }
    }

    fn next_atomic(&mut self, expected_tag: Tag, k: ExpectedKind) -> ReaderResult<Cow<'de, [u8]>> {
        self.try_next_nonannotation(|r, actual_tag| {
            if actual_tag == expected_tag {
                r.skip()?;
                let count = r.varint()?;
                Ok(r.readbytes(count)?)
            } else {
                Err(r.expected(k))
            }
        })
    }

    fn next_compound(&mut self, expected_tag: Tag, k: ExpectedKind) -> ReaderResult<()> {
        self.try_next_nonannotation(|r, actual_tag| {
            if actual_tag == expected_tag {
                r.skip()?;
                Ok(())
            } else {
                Err(r.expected(k))
            }
        })
    }

    #[inline(always)]
    fn read_signed_integer(&mut self, count: usize) -> io::Result<SignedInteger> {
        if count == 0 {
            return Ok(SignedInteger::from(0_i128));
        }

        if count > 16 {
            let bs = self.readbytes(count)?;
            if (bs[0] & 0x80) == 0 {
                // Positive or zero.
                let mut i = 0;
                while i < count && bs[i] == 0 {
                    i += 1;
                }
                if count - i <= 16 {
                    Ok(SignedInteger::from(u128::from_be_bytes(
                        bs[bs.len() - 16..].try_into().unwrap(),
                    )))
                } else {
                    Ok(SignedInteger::from(Cow::Owned(BigInt::from_bytes_be(
                        num::bigint::Sign::Plus,
                        &bs[i..],
                    ))))
                }
            } else {
                // Negative.
                let mut i = 0;
                while i < count && bs[i] == 0xff {
                    i += 1;
                }
                if count - i <= 16 {
                    Ok(SignedInteger::from(i128::from_be_bytes(
                        bs[bs.len() - 16..].try_into().unwrap(),
                    )))
                } else {
                    Ok(SignedInteger::from(Cow::Owned(
                        BigInt::from_signed_bytes_be(&bs),
                    )))
                }
            }
        } else {
            let first_byte = self.read()?;
            let prefix_byte = if (first_byte & 0x80) == 0 { 0x00 } else { 0xff };
            let mut bs = [prefix_byte; 16];
            bs[16 - count] = first_byte;
            self.readbytes_into(&mut bs[16 - (count - 1)..])?;
            Ok(SignedInteger::from(i128::from_be_bytes(bs)))
        }
    }

    #[inline(always)]
    fn next_unsigned<T: FromPrimitive, F>(&mut self, f: F) -> ReaderResult<T>
    where
        F: FnOnce(u128) -> Option<T>,
    {
        self.try_next_nonannotation(|r, tag| {
            match tag {
                Tag::SignedInteger => {
                    r.skip()?;
                    let count = r.varint()?;
                    let n = &r.read_signed_integer(count)?;
                    let i = n.try_into().map_err(|_| out_of_range(n))?;
                    f(i).ok_or_else(|| out_of_range(i))
                }
                _ => Err(r.expected(ExpectedKind::SignedInteger)),
            }
        })
    }

    #[inline(always)]
    fn next_signed<T: FromPrimitive, F>(&mut self, f: F) -> ReaderResult<T>
    where
        F: FnOnce(i128) -> Option<T>,
    {
        self.try_next_nonannotation(|r, tag| {
            match tag {
                Tag::SignedInteger => {
                    r.skip()?;
                    let count = r.varint()?;
                    let n = &r.read_signed_integer(count)?;
                    let i = n.try_into().map_err(|_| out_of_range(n))?;
                    f(i).ok_or_else(|| out_of_range(i))
                }
                _ => Err(r.expected(ExpectedKind::SignedInteger)),
            }
        })
    }

    fn gather_annotations(&mut self) -> io::Result<Vec<N>> {
        let mut annotations = vec![self.demand_next(true)?];
        while Tag::try_from(self.peek()?)? == Tag::Annotation {
            self.skip()?;
            annotations.push(self.demand_next(true)?);
        }
        Ok(annotations)
    }

    fn skip_annotations(&mut self) -> io::Result<()> {
        self.skip_value()?;
        while Tag::try_from(self.peek()?)? == Tag::Annotation {
            self.skip()?;
            self.skip_value()?;
        }
        Ok(())
    }

    fn next_upto_end(&mut self, read_annotations: bool) -> io::Result<Option<N>> {
        match self.peekend()? {
            true => Ok(None),
            false => Ok(Some(self.demand_next(read_annotations)?)),
        }
    }
}

impl<'de, 'src, N: NestedValue, Dec: DomainDecode<N::Embedded>, S: BinarySource<'de>> Reader<'de, N>
    for PackedReader<'de, 'src, N, Dec, S>
{
    fn next(&mut self, read_annotations: bool) -> io::Result<Option<N>> {
        match self.peek() {
            Err(e) if is_eof_io_error(&e) => return Ok(None),
            Err(e) => return Err(e),
            Ok(_) => (),
        }
        Ok(Some(match Tag::try_from(self.read()?)? {
            Tag::False => N::new(false),
            Tag::True => N::new(true),
            Tag::Annotation => {
                if read_annotations {
                    let mut annotations = self.gather_annotations()?;
                    let (existing_annotations, v) = self.demand_next(read_annotations)?.pieces();
                    annotations.extend_from_slice(existing_annotations.slice());
                    N::wrap(Annotations::new(Some(annotations)), v)
                } else {
                    self.skip_annotations()?;
                    self.demand_next(read_annotations)?
                }
            }
            Tag::Embedded => Value::Embedded(
                self.decode_embedded
                    .decode_embedded(self.source, read_annotations)?,
            ).wrap(),
            Tag::Ieee754 => match self.varint()? {
                8 => {
                    let mut bs = [0; 8];
                    self.readbytes_into(&mut bs)?;
                    Value::from(f64::from_bits(u64::from_be_bytes(bs))).wrap()
                }
                _ => return Err(io_syntax_error("Invalid IEEE754 size"))
            }
            Tag::SignedInteger => {
                let count = self.varint()?;
                let n = self.read_signed_integer(count)?;
                Value::SignedInteger(n).wrap()
            }
            Tag::String => {
                let count = self.varint()?;
                Value::String(decodestr(self.readbytes(count)?)?.into_owned()).wrap()
            }
            Tag::ByteString => {
                let count = self.varint()?;
                Value::ByteString(self.readbytes(count)?.into_owned()).wrap()
            }
            Tag::Symbol => {
                let count = self.varint()?;
                Value::Symbol(decodestr(self.readbytes(count)?)?.into_owned()).wrap()
            }
            Tag::Record => {
                let mut vs = Vec::new();
                while let Some(v) = self.next_upto_end(read_annotations)? {
                    vs.push(v);
                }
                if vs.is_empty() {
                    return Err(io_syntax_error("Too few elements in encoded record"));
                }
                Value::Record(Record(vs)).wrap()
            }
            Tag::Sequence => {
                let mut vs = Vec::new();
                while let Some(v) = self.next_upto_end(read_annotations)? {
                    vs.push(v);
                }
                Value::Sequence(vs).wrap()
            }
            Tag::Set => {
                let mut s = Set::new();
                while let Some(v) = self.next_upto_end(read_annotations)? {
                    s.insert(v);
                }
                Value::Set(s).wrap()
            }
            Tag::Dictionary => {
                let mut d = Map::new();
                while let Some(k) = self.next_upto_end(read_annotations)? {
                    match self.next_upto_end(read_annotations)? {
                        Some(v) => {
                            d.insert(k, v);
                        }
                        None => return Err(io_syntax_error("Missing dictionary value")),
                    }
                }
                Value::Dictionary(d).wrap()
            }
            tag @ Tag::End => {
                return Err(io_syntax_error(&format!("Invalid tag: {:?}", tag)));
            }
        }))
    }

    #[inline(always)]
    fn open_record(&mut self, arity: Option<usize>) -> ReaderResult<B::Type> {
        self.next_compound(Tag::Record, ExpectedKind::Record(arity))?;
        let mut b = B::Type::default();
        self.ensure_more_expected(&mut b, &B::Item::RecordLabel)?;
        Ok(b)
    }

    #[inline(always)]
    fn open_sequence_or_set(&mut self) -> ReaderResult<B::Item> {
        self.try_next_nonannotation(|r, tag| {
            match tag {
                Tag::Sequence => {
                    r.skip()?;
                    Ok(B::Item::SequenceValue)
                }
                Tag::Set => {
                    r.skip()?;
                    Ok(B::Item::SetValue)
                }
                _ => Err(r.expected(ExpectedKind::SequenceOrSet)),
            }
        })
    }

    #[inline(always)]
    fn open_sequence(&mut self) -> ReaderResult<()> {
        self.next_compound(Tag::Sequence, ExpectedKind::Sequence)
    }

    #[inline(always)]
    fn open_set(&mut self) -> ReaderResult<()> {
        self.next_compound(Tag::Set, ExpectedKind::Set)
    }

    #[inline(always)]
    fn open_dictionary(&mut self) -> ReaderResult<()> {
        self.next_compound(Tag::Dictionary, ExpectedKind::Dictionary)
    }

    #[inline(always)]
    fn boundary(&mut self, _b: &B::Type) -> ReaderResult<()> {
        Ok(())
    }

    #[inline(always)]
    fn close_compound(&mut self, _b: &mut B::Type, _i: &B::Item) -> ReaderResult<bool> {
        Ok(self.peekend()?)
    }

    #[inline(always)]
    fn open_embedded(&mut self) -> ReaderResult<()> {
        self.next_compound(Tag::Embedded, ExpectedKind::Embedded)
    }

    #[inline(always)]
    fn close_embedded(&mut self) -> ReaderResult<()> {
        Ok(())
    }

    type Mark = S::Mark;

    #[inline(always)]
    fn mark(&mut self) -> io::Result<Self::Mark> {
        self.source.mark()
    }

    #[inline(always)]
    fn restore(&mut self, mark: &Self::Mark) -> io::Result<()> {
        self.source.restore(mark)
    }

    fn next_token(&mut self, read_embedded_annotations: bool) -> io::Result<Token<N>> {
        loop {
            return Ok(match Tag::try_from(self.peek()?)? {
                Tag::Embedded => {
                    self.skip()?;
                    Token::Embedded(
                        self.decode_embedded
                            .decode_embedded(self.source, read_embedded_annotations)?,
                    )
                }
                Tag::False
                    | Tag::True
                    | Tag::Ieee754
                    | Tag::SignedInteger
                    | Tag::String
                    | Tag::ByteString
                    | Tag::Symbol => Token::Atom(self.demand_next(false)?),

                Tag::Record => {
                    self.skip()?;
                    Token::Compound(CompoundClass::Record)
                }
                Tag::Sequence => {
                    self.skip()?;
                    Token::Compound(CompoundClass::Sequence)
                }
                Tag::Set => {
                    self.skip()?;
                    Token::Compound(CompoundClass::Set)
                }
                Tag::Dictionary => {
                    self.skip()?;
                    Token::Compound(CompoundClass::Dictionary)
                }

                Tag::End => {
                    self.skip()?;
                    Token::End
                }

                Tag::Annotation => {
                    self.skip()?;
                    self.skip_value()?;
                    continue;
                }
            });
        }
    }

    fn next_annotations_and_token(&mut self) -> io::Result<(Vec<N>, Token<N>)> {
        match Tag::try_from(self.peek()?)? {
            Tag::Annotation => {
                self.skip()?;
                let annotations = self.gather_annotations()?;
                Ok((annotations, self.next_token(true)?))
            }
            _ => Ok((Vec::new(), self.next_token(true)?)),
        }
    }

    #[inline(always)]
    fn next_boolean(&mut self) -> ReaderResult<bool> {
        self.try_next_nonannotation(|r, tag| {
            match tag {
                Tag::False => {
                    r.skip()?;
                    Ok(false)
                },
                Tag::True => {
                    r.skip()?;
                    Ok(true)
                },
                _ => Err(r.expected(ExpectedKind::Boolean)),
            }
        })
    }

    fn next_signedinteger(&mut self) -> ReaderResult<SignedInteger> {
        self.try_next_nonannotation(|r, tag| {
            match tag {
                Tag::SignedInteger => {
                    r.skip()?;
                    let count = r.varint()?;
                    Ok(r.read_signed_integer(count)?)
                }
                _ => Err(r.expected(ExpectedKind::SignedInteger)),
            }
        })
    }

    fn next_i8(&mut self) -> ReaderResult<i8> {
        self.next_signed(|n| n.to_i8())
    }
    fn next_i16(&mut self) -> ReaderResult<i16> {
        self.next_signed(|n| n.to_i16())
    }
    fn next_i32(&mut self) -> ReaderResult<i32> {
        self.next_signed(|n| n.to_i32())
    }
    fn next_i64(&mut self) -> ReaderResult<i64> {
        self.next_signed(|n| n.to_i64())
    }
    fn next_i128(&mut self) -> ReaderResult<i128> {
        self.next_signed(|n| n.to_i128())
    }

    fn next_u8(&mut self) -> ReaderResult<u8> {
        self.next_unsigned(|n| n.to_u8())
    }
    fn next_u16(&mut self) -> ReaderResult<u16> {
        self.next_unsigned(|n| n.to_u16())
    }
    fn next_u32(&mut self) -> ReaderResult<u32> {
        self.next_unsigned(|n| n.to_u32())
    }
    fn next_u64(&mut self) -> ReaderResult<u64> {
        self.next_unsigned(|n| n.to_u64())
    }
    fn next_u128(&mut self) -> ReaderResult<u128> {
        self.next_unsigned(|n| n.to_u128())
    }

    fn next_f64(&mut self) -> ReaderResult<f64> {
        self.try_next_nonannotation(|r, tag| {
            if tag == Tag::Ieee754 {
                r.skip()?;
                match r.varint()? {
                    8 => {
                        let mut bs = [0; 8];
                        r.readbytes_into(&mut bs)?;
                        Ok(f64::from_bits(u64::from_be_bytes(bs)))
                    }
                    _ => Err(io_syntax_error("Invalid IEEE754 size"))?,
                }
            } else {
                Err(r.expected(ExpectedKind::Double))
            }
        })
    }

    fn next_str(&mut self) -> ReaderResult<Cow<'de, str>> {
        Ok(decodestr(
            self.next_atomic(Tag::String, ExpectedKind::Symbol)?,
        )?)
    }

    fn next_bytestring(&mut self) -> ReaderResult<Cow<'de, [u8]>> {
        self.next_atomic(Tag::ByteString, ExpectedKind::Symbol)
    }

    fn next_symbol(&mut self) -> ReaderResult<Cow<'de, str>> {
        Ok(decodestr(
            self.next_atomic(Tag::Symbol, ExpectedKind::Symbol)?,
        )?)
    }
}

#[inline(always)]
fn decodestr(cow: Cow<'_, [u8]>) -> io::Result<Cow<'_, str>> {
    match cow {
        Cow::Borrowed(bs) => Ok(Cow::Borrowed(
            std::str::from_utf8(bs).map_err(|_| io_syntax_error("Invalid UTF-8"))?,
        )),
        Cow::Owned(bs) => Ok(Cow::Owned(
            String::from_utf8(bs).map_err(|_| io_syntax_error("Invalid UTF-8"))?,
        )),
    }
}