use num::bigint::BigInt;
use num::traits::cast::{FromPrimitive, ToPrimitive};
use std::borrow::Cow;
use std::convert::TryFrom;
use std::convert::TryInto;
use std::marker::PhantomData;

use super::constants::Tag;
use super::super::{
    FALSE,
    IOResult,
    IOValue,
    Map,
    NestedValue,
    Record,
    Set,
    TRUE,
    Value,

    reader::{
        BinarySource,
        BytesBinarySource,
        ConfiguredReader,
        IOBinarySource,
        Reader,
        ReaderResult,
    },
    repr::Annotations,
    signed_integer::SignedInteger,
};

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

pub struct PackedReader<'de, S: BinarySource<'de>> {
    pub source: S,
    phantom: PhantomData<&'de ()>,
}

impl<'de, S: BinarySource<'de>> BinarySource<'de> for PackedReader<'de, S> {
    fn skip(&mut self) -> IOResult<()> {
        self.source.skip()
    }
    fn peek(&mut self) -> IOResult<u8> {
        self.source.peek()
    }
    fn readbytes(&mut self, count: usize) -> IOResult<Cow<'de, [u8]>> {
        self.source.readbytes(count)
    }
    fn readbytes_into(&mut self, bs: &mut [u8]) -> IOResult<()> {
        self.source.readbytes_into(bs)
    }
}

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

impl<'de> PackedReader<'de, BytesBinarySource<'de>> {
    pub fn decode_bytes(bytes: &'de [u8]) -> Self {
        PackedReader::new(BytesBinarySource::new(bytes))
    }
}

impl<'de, 'a, IOR: std::io::Read> PackedReader<'de, IOBinarySource<'a, IOR>> {
    pub fn decode_read(read: &'a mut IOR) -> Self {
        PackedReader::new(IOBinarySource::new(read))
    }
}

impl<'de, S: BinarySource<'de>> PackedReader<'de, S> {
    pub fn new(source: S) -> Self {
        PackedReader { source, phantom: PhantomData }
    }

    fn read(&mut self) -> IOResult<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(v)),
            Err(e) => e.into()
        }
    }

    fn varint(&mut self) -> IOResult<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) }
        }
    }

    fn peekend(&mut self) -> IOResult<bool> {
        if self.peek()? == Tag::End.into() {
            self.skip()?;
            Ok(true)
        } else {
            Ok(false)
        }
    }

    fn peek_next_nonannotation_tag(&mut self) -> ReaderResult<Tag> {
        loop {
            match Tag::try_from(self.peek()?)? {
                Tag::Annotation => {
                    self.skip()?;
                    self.skip_value()?;
                },
                other => return Ok(other),
            }
        }
    }

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

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

    fn read_signed_integer(&mut self, count: usize) -> IOResult<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)))
        }
    }

    fn next_unsigned<T: FromPrimitive, F>(&mut self, f: F) -> ReaderResult<T>
    where
        F: FnOnce(u128) -> Option<T>
    {
        let tag = self.peek_next_nonannotation_tag()?;
        match tag {
            Tag::SmallInteger(v) => {
                self.skip()?;
                if v < 0 {
                    Err(out_of_range(v))
                } else {
                    f(v as u128).ok_or_else(|| out_of_range(v))
                }
            }
            Tag::MediumInteger(count) => {
                self.skip()?;
                let n = &self.read_signed_integer(count.into())?;
                let i = n.try_into().map_err(|_| out_of_range(n))?;
                f(i).ok_or_else(|| out_of_range(i))
            }
            Tag::SignedInteger => {
                self.skip()?;
                let count = self.varint()?;
                let n = &self.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(self.expected(ExpectedKind::SignedInteger))
        }
    }

    fn next_signed<T: FromPrimitive, F>(&mut self, f: F) -> ReaderResult<T>
    where
        F: FnOnce(i128) -> Option<T>
    {
        let tag = self.peek_next_nonannotation_tag()?;
        match tag {
            Tag::SmallInteger(v) => {
                self.skip()?;
                f(v.into()).ok_or_else(|| out_of_range(v))
            }
            Tag::MediumInteger(count) => {
                self.skip()?;
                let n = &self.read_signed_integer(count.into())?;
                let i = n.try_into().map_err(|_| out_of_range(n))?;
                f(i).ok_or_else(|| out_of_range(i))
            }
            Tag::SignedInteger => {
                self.skip()?;
                let count = self.varint()?;
                let n = &self.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(self.expected(ExpectedKind::SignedInteger))
        }
    }
}

impl<'de, S: BinarySource<'de>> Reader<'de> for PackedReader<'de, S> {
    fn next(&mut self, read_annotations: bool) -> IOResult<Option<IOValue>> {
        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 => FALSE.clone(),
            Tag::True => TRUE.clone(),
            Tag::Float => {
                let mut bs = [0; 4];
                self.readbytes_into(&mut bs)?;
                Value::from(f32::from_bits(u32::from_be_bytes(bs))).wrap()
            }
            Tag::Double => {
                let mut bs = [0; 8];
                self.readbytes_into(&mut bs)?;
                Value::from(f64::from_bits(u64::from_be_bytes(bs))).wrap()
            }
            Tag::Annotation => {
                if read_annotations {
                    let mut annotations = vec![self.demand_next(read_annotations)?];
                    while Tag::try_from(self.peek()?)? == Tag::Annotation {
                        self.skip()?;
                        annotations.push(self.demand_next(read_annotations)?);
                    }
                    let (existing_annotations, v) = self.demand_next(read_annotations)?.pieces();
                    annotations.extend_from_slice(existing_annotations.slice());
                    IOValue::wrap(Annotations::new(Some(annotations)), v)
                } else {
                    self.skip_value()?;
                    while Tag::try_from(self.peek()?)? == Tag::Annotation {
                        self.skip()?;
                        self.skip_value()?;
                    }
                    self.demand_next(read_annotations)?
                }
            }
            Tag::Embedded => {
                let v = self.demand_next(read_annotations)?;
                Value::Embedded(v).wrap()
            }
            Tag::SmallInteger(v) => {
                // TODO: prebuild these in value.rs
                Value::from(v).wrap()
            }
            Tag::MediumInteger(count) => {
                let n = self.read_signed_integer(count.into())?;
                Value::SignedInteger(n).wrap()
            }
            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 iter = DelimitedStream { reader: self.configured(read_annotations) };
                let vs = iter.collect::<IOResult<Vec<IOValue>>>()?;
                if vs.is_empty() {
                    return Err(io_syntax_error("Too few elements in encoded record"))
                }
                Value::Record(Record(vs)).wrap()
            }
            Tag::Sequence => {
                let iter = DelimitedStream { reader: self.configured(read_annotations) };
                let vs = iter.collect::<IOResult<Vec<IOValue>>>()?;
                Value::Sequence(vs).wrap()
            }
            Tag::Set => {
                let iter = DelimitedStream { reader: self.configured(read_annotations) };
                let mut s = Set::new();
                for res in iter { s.insert(res?); }
                Value::Set(s).wrap()
            }
            Tag::Dictionary => {
                let mut iter = DelimitedStream { reader: self.configured(read_annotations) };
                let mut d = Map::new();
                while let Some(kres) = iter.next() {
                    let k = kres?;
                    match iter.next() {
                        Some(vres) => {
                            let v = vres?;
                            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)));
            }
        }))
    }

    fn open_record(&mut self, arity: Option<usize>) -> ReaderResult<()> {
        self.next_compound(Tag::Record, ExpectedKind::Record(arity))?;
        self.ensure_more_expected()
    }

    fn open_sequence_or_set(&mut self) -> ReaderResult<()> {
        match self.peek_next_nonannotation_tag()? {
            Tag::Sequence | Tag::Set => {
                self.skip()?;
                Ok(())
            }
            _ => Err(self.expected(ExpectedKind::SequenceOrSet)),
        }
    }

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

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

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

    fn close_compound(&mut self) -> ReaderResult<bool> {
        Ok(self.peekend()?)
    }

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

    fn close_embedded(&mut self) -> ReaderResult<()> {
        Ok(())
    }

    fn next_boolean(&mut self) -> ReaderResult<bool> {
        match self.peek_next_nonannotation_tag()? {
            Tag::False => { self.skip()?; Ok(false) }
            Tag::True => { self.skip()?; Ok(true) }
            _ => Err(self.expected(ExpectedKind::Boolean)),
        }
    }

    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_f32(&mut self) -> ReaderResult<f32> {
        match self.peek_next_nonannotation_tag()? {
            Tag::Float => {
                self.skip()?;
                let mut bs = [0; 4];
                self.readbytes_into(&mut bs)?;
                Ok(f32::from_bits(u32::from_be_bytes(bs)))
            },
            Tag::Double => {
                self.skip()?;
                let mut bs = [0; 8];
                self.readbytes_into(&mut bs)?;
                Ok(f64::from_bits(u64::from_be_bytes(bs)) as f32)
            },
            _ => Err(self.expected(ExpectedKind::Float)),
        }
    }

    fn next_f64(&mut self) -> ReaderResult<f64> {
        match self.peek_next_nonannotation_tag()? {
            Tag::Float => {
                self.skip()?;
                let mut bs = [0; 4];
                self.readbytes_into(&mut bs)?;
                Ok(f32::from_bits(u32::from_be_bytes(bs)) as f64)
            },
            Tag::Double => {
                self.skip()?;
                let mut bs = [0; 8];
                self.readbytes_into(&mut bs)?;
                Ok(f64::from_bits(u64::from_be_bytes(bs)))
            },
            _ => Err(self.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)?)?)
    }
}

struct DelimitedStream<'a, 'de, S: BinarySource<'de>> {
    reader: ConfiguredReader<'de, &'a mut PackedReader<'de, S>>,
}

impl<'a, 'de, S: BinarySource<'de>> Iterator for DelimitedStream<'a, 'de, S>
{
    type Item = IOResult<IOValue>;
    fn next(&mut self) -> Option<Self::Item> {
        match self.reader.reader.peekend() {
            Err(e) => Some(Err(e)),
            Ok(true) => None,
            Ok(false) => Some(self.reader.reader.demand_next(self.reader.read_annotations)),
        }
    }
}

fn decodestr(cow: Cow<'_, [u8]>) -> IOResult<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"))?)),
    }
}