use std::io;

use crate::buffer::data_source::{IteratorDataSource, ReadDataSource};
use crate::buffer::{
    Buffer, DataSource, FixedSizeBuffer, InputBuf, RWDataSource, Stream, StreamError,
};
use crate::primitives::IntoInner;
use crate::types::{Input, ParseResult};

bitflags! {
    #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
    struct ParserState: u64 {
        /// The parser which was last run on the buffer did not manage to complete with the data
        /// available in the buffer.
        const INCOMPLETE     = 1;
        /// The buffer did not manage to read any more data from the underlying `Read`
        /// implementation.
        const END_OF_INPUT   = 2;
        /// `parse()` should attempt to read more data whenever the `INCOMPLETE` flag is set.
        const AUTOMATIC_FILL = 4;
    }
}

/// Manages a buffer and data source pair, enabling efficient parsing from a
/// streaming source.
#[derive(Debug)]
pub struct Source<S: DataSource, B: Buffer<S::Item>> {
    /// Source reader
    source: S,
    /// Temporary source
    buffer: B,
    /// The requested amount of bytes to be available for reading from the
    /// buffer
    request: usize,
    /// Input state, if end has been reached
    state: ParserState,
}

impl<R: io::Read> Source<ReadDataSource<R>, FixedSizeBuffer<u8>> {
    /// Creates a new `Source` from a `Read` instance with the default
    /// `FixedSizeBuffer` settings.
    #[inline]
    pub fn new(source: R) -> Self {
        Self::with_buffer(ReadDataSource::new(source), FixedSizeBuffer::new())
    }
}

impl<R: io::Read, B: Buffer<u8>> Source<ReadDataSource<R>, B> {
    /// Creates a new `Source` from `Read` and buffer instances.
    #[inline]
    pub fn from_read(source: R, buffer: B) -> Self {
        Self::with_buffer(ReadDataSource::new(source), buffer)
    }
}

impl<RW: io::Read + io::Write> Source<RWDataSource<RW>, FixedSizeBuffer<u8>> {
    /// Creates a new `Source` from `Read`+`Write` with the default
    /// `FixedSizeBuffer` settings.
    #[inline]
    pub fn new_rw(rwsource: RW) -> Self {
        Self::with_buffer(RWDataSource::new(rwsource), FixedSizeBuffer::new())
    }
}

impl<RW: io::Read + io::Write, B: Buffer<u8>> Source<RWDataSource<RW>, B> {
    /// Creates a new `Source` from `Read`+`Write` and buffer instances.
    #[inline]
    pub fn from_read_write(source: RW, buffer: B) -> Self {
        Self::with_buffer(RWDataSource::new(source), buffer)
    }
}

impl<I: Iterator, B: Buffer<I::Item>> Source<IteratorDataSource<I>, B>
where
    I::Item: Copy + PartialEq,
{
    /// Creates a new `Source` from `Iterator` and `Buffer` instances.
    #[inline]
    pub fn from_iter(source: I, buffer: B) -> Self {
        Self::with_buffer(IteratorDataSource::new(source), buffer)
    }
}

impl<S: DataSource, B: Buffer<S::Item>> Source<S, B> {
    /// Creates a new `Source` from `DataSource` and `Buffer` instances.
    #[inline]
    pub fn with_buffer(source: S, buffer: B) -> Self {
        Source {
            source,
            buffer,
            request: 0,
            state: ParserState::INCOMPLETE | ParserState::AUTOMATIC_FILL,
        }
    }

    /// Attempts to fill this source so it contains at least ``request`` bytes.
    #[inline]
    fn fill_requested(&mut self, request: usize) -> io::Result<usize> {
        let mut read = 0;

        let buffer = &mut self.buffer;
        let source = &mut self.source;

        if buffer.len() < request {
            let diff = request - buffer.len();

            buffer.request_space(diff);

            while buffer.len() < request {
                match buffer.fill(source)? {
                    0 => break,
                    n => read += n,
                }
            }
        }

        Ok(read)
    }

    /// Attempts to fill the buffer to satisfy the last call to `parse()`.
    #[inline]
    pub fn fill(&mut self) -> io::Result<usize> {
        let req = self.buffer.len() + 1;

        self.fill_requested(req).map(|n| {
            self.state.remove(ParserState::INCOMPLETE);

            if n > 0 {
                self.state.remove(ParserState::END_OF_INPUT);
            } else {
                self.state.insert(ParserState::END_OF_INPUT);
            }

            n
        })
    }

    /// Returns the number of bytes left in the buffer which have not yet been
    /// parsed.
    #[inline]
    pub fn len(&self) -> usize {
        self.buffer.len()
    }

    /// If the buffer is empty and the reader has reached the end.
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.state.contains(ParserState::END_OF_INPUT) && self.len() == 0
    }

    /// Returns the capacity of the underlying buffer.
    ///
    /// This is the maximum number of input items the buffer can store.
    #[inline]
    pub fn capacity(&self) -> usize {
        self.buffer.capacity()
    }

    /// Borrows the remainder of the buffer.
    #[inline]
    pub fn buffer(&self) -> &[S::Item] {
        &self.buffer
    }

    /// Resets the buffer state, keeping the current buffer contents and cursor
    /// position.
    ///
    /// This is useful when streaming data and more data has been made available
    /// on a socket/stream.
    #[inline]
    pub fn reset(&mut self) {
        self.state = ParserState::empty();
    }

    /// Changes the setting automatic fill feature, `true` will make the buffer
    /// automatically call `fill()` on the next call to `parse()` after a
    /// `Retry` was encountered.
    // TODO: Make a part of the constructor/builder
    #[inline]
    pub fn set_autofill(&mut self, value: bool) {
        if value {
            self.state.insert(ParserState::AUTOMATIC_FILL)
        } else {
            self.state.remove(ParserState::AUTOMATIC_FILL)
        }
    }
}

impl<S: DataSource<Item = u8>, B: Buffer<u8>> io::Read for Source<S, B> {
    #[inline]
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        if buf.len() > self.len() {
            self.fill_requested(buf.len())?;
        }

        (&self.buffer[..]).read(buf).map(|n| {
            self.buffer.consume(n);

            n
        })
    }
}

impl<S: DataSource<Item = u8>, B: Buffer<u8>> io::BufRead for Source<S, B> {
    #[inline]
    fn fill_buf(&mut self) -> io::Result<&[u8]> {
        let cap = self.buffer.capacity();

        self.fill_requested(cap)?;

        Ok(self.buffer())
    }

    #[inline]
    fn consume(&mut self, num: usize) {
        self.buffer.consume(num)
    }
}

impl<RW: io::Read + io::Write, B: Buffer<u8>> io::Write for Source<RWDataSource<RW>, B> {
    #[inline]
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.source.write(buf)
    }

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

impl<'a, S: DataSource, B: Buffer<S::Item>> Stream<'a, 'a> for Source<S, B>
where
    S::Item: 'a,
{
    type Input = InputBuf<'a, S::Item>;

    #[inline]
    fn parse<F, T, E>(
        &'a mut self,
        f: F,
    ) -> Result<T, StreamError<<Self::Input as Input>::Buffer, E>>
    where
        F: FnOnce(Self::Input) -> ParseResult<Self::Input, T, E>,
        T: 'a,
        E: 'a,
    {
        use crate::primitives::Primitives;

        if self
            .state
            .contains(ParserState::INCOMPLETE | ParserState::AUTOMATIC_FILL)
        {
            self.fill().map_err(StreamError::IoError)?;
        }

        if self.is_empty() {
            return Err(StreamError::EndOfInput);
        }

        match f(InputBuf::new(&self.buffer)).into_inner() {
            (remainder, Ok(data)) => {
                if remainder.is_incomplete() && !self.state.contains(ParserState::END_OF_INPUT) {
                    // We can't accept this since we might have hit a premature end
                    self.state.insert(ParserState::INCOMPLETE);

                    Err(StreamError::Retry)
                } else {
                    // TODO: Do something neater with the remainder
                    self.buffer.consume(self.buffer.len() - remainder.len());

                    Ok(data)
                }
            }
            (mut remainder, Err(err)) => {
                match (
                    remainder.is_incomplete(),
                    self.state.contains(ParserState::END_OF_INPUT),
                ) {
                    (true, true) => Err(StreamError::Incomplete),
                    (true, false) => {
                        self.state.insert(ParserState::INCOMPLETE);

                        Err(StreamError::Retry)
                    }
                    _ => {
                        // TODO: Do something neater with the remainder
                        // TODO: Detail this behaviour, maybe make it configurable
                        self.buffer.consume(self.buffer.len() - remainder.len());

                        Err(StreamError::ParseError(remainder.consume_remaining(), err))
                    }
                }
            }
        }
    }
}

#[cfg(test)]
mod test {
    use std::io;

    use super::*;
    use crate::buffer::data_source::ReadDataSource;
    use crate::buffer::{FixedSizeBuffer, Stream, StreamError};
    use crate::parsers::{any, take, take_while, Error};
    use crate::types::Input;

    fn buf(
        source: &[u8],
        buffer_length: usize,
    ) -> Source<ReadDataSource<io::Cursor<&[u8]>>, FixedSizeBuffer<u8>> {
        Source::with_buffer(
            ReadDataSource::new(io::Cursor::new(source)),
            FixedSizeBuffer::with_size(buffer_length),
        )
    }

    #[test]
    #[should_panic]
    fn bufsize_zero() {
        let _ = buf(&b"this is a test"[..], 0);
    }

    #[test]
    fn default_bufsize() {
        let b: Source<_, FixedSizeBuffer<_>> = Source::new(io::Cursor::new(&b"test"[..]));

        assert!(b.capacity() > 0);
    }

    #[test]
    fn empty_buf() {
        let mut n = 0;
        let mut b = Source::new(io::Cursor::new(&b""[..]));

        let r = b.parse(|i| {
            n += 1;

            take(i, 1).bind(|i, _| i.ret::<_, Error<_>>(true))
        });

        assert_eq!(r, Err(StreamError::EndOfInput));
        assert_eq!(n, 0);
    }

    #[test]
    fn fill() {
        let mut n = 0; // Times it has entered the parsing function
        let mut m = 0; // Times it has managed to get past the request for data
        let mut b = buf(&b"test"[..], 1);

        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Ok(b't')
        );
        assert_eq!(n, 1);
        assert_eq!(m, 1);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Err(StreamError::Retry)
        );
        assert_eq!(n, 2);
        assert_eq!(m, 1);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Ok(b'e')
        );
        assert_eq!(n, 3);
        assert_eq!(m, 2);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Err(StreamError::Retry)
        );
        assert_eq!(n, 4);
        assert_eq!(m, 2);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Ok(b's')
        );
        assert_eq!(n, 5);
        assert_eq!(m, 3);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Err(StreamError::Retry)
        );
        assert_eq!(n, 6);
        assert_eq!(m, 3);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Ok(b't')
        );
        assert_eq!(n, 7);
        assert_eq!(m, 4);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Err(StreamError::Retry)
        );
        assert_eq!(n, 8);
        assert_eq!(m, 4);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Err(StreamError::EndOfInput)
        );
        assert_eq!(n, 8);
        assert_eq!(m, 4);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Err(StreamError::EndOfInput)
        );
        assert_eq!(n, 8);
        assert_eq!(m, 4);
    }

    #[test]
    fn fill2() {
        let mut n = 0; // Times it has entered the parsing function
        let mut m = 0; // Times it has managed to get past the request for data
        let mut b = buf(&b"test"[..], 2);

        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Ok(b't')
        );
        assert_eq!(n, 1);
        assert_eq!(m, 1);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Ok(b'e')
        );
        assert_eq!(n, 2);
        assert_eq!(m, 2);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Err(StreamError::Retry)
        );
        assert_eq!(n, 3);
        assert_eq!(m, 2);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Ok(b's')
        );
        assert_eq!(n, 4);
        assert_eq!(m, 3);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Ok(b't')
        );
        assert_eq!(n, 5);
        assert_eq!(m, 4);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Err(StreamError::Retry)
        );
        assert_eq!(n, 6);
        assert_eq!(m, 4);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Err(StreamError::EndOfInput)
        );
        assert_eq!(n, 6);
        assert_eq!(m, 4);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Err(StreamError::EndOfInput)
        );
        assert_eq!(n, 6);
        assert_eq!(m, 4);
    }

    #[test]
    fn fill3() {
        let mut n = 0; // Times it has entered the parsing function
        let mut m = 0; // Times it has managed to get past the request for data
        let mut b = buf(&b"test"[..], 3);

        assert_eq!(
            b.parse(|i| {
                n += 1;
                take(i, 2).inspect(|_| m += 1)
            }),
            Ok(&b"te"[..])
        );
        assert_eq!(n, 1);
        assert_eq!(m, 1);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                take(i, 2).inspect(|_| m += 1)
            }),
            Err(StreamError::Retry)
        );
        assert_eq!(n, 2);
        assert_eq!(m, 1);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                take(i, 2).inspect(|_| m += 1)
            }),
            Ok(&b"st"[..])
        );
        assert_eq!(n, 3);
        assert_eq!(m, 2);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                take(i, 2).inspect(|_| m += 1)
            }),
            Err(StreamError::Retry)
        );
        assert_eq!(n, 4);
        assert_eq!(m, 2);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                take(i, 2).inspect(|_| m += 1)
            }),
            Err(StreamError::EndOfInput)
        );
        assert_eq!(n, 4);
        assert_eq!(m, 2);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                take(i, 2).inspect(|_| m += 1)
            }),
            Err(StreamError::EndOfInput)
        );
        assert_eq!(n, 4);
        assert_eq!(m, 2);
    }

    #[test]
    fn incomplete() {
        let mut n = 0; // Times it has entered the parsing function
        let mut m = 0; // Times it has managed to get past the request for data
        let mut b = buf(&b"tes"[..], 2);

        assert_eq!(
            b.parse(|i| {
                n += 1;
                take(i, 2).inspect(|_| m += 1)
            }),
            Ok(&b"te"[..])
        );
        assert_eq!(n, 1);
        assert_eq!(m, 1);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                take(i, 2).inspect(|_| m += 1)
            }),
            Err(StreamError::Retry)
        );
        assert_eq!(n, 2);
        assert_eq!(m, 1);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                take(i, 2).inspect(|_| m += 1)
            }),
            Err(StreamError::Retry)
        );
        assert_eq!(n, 3);
        assert_eq!(m, 1);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                take(i, 2).inspect(|_| m += 1)
            }),
            Err(StreamError::Incomplete)
        );
        assert_eq!(n, 4);
        assert_eq!(m, 1);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                take(i, 2).inspect(|_| m += 1)
            }),
            Err(StreamError::Incomplete)
        );
        assert_eq!(n, 5);
        assert_eq!(m, 1);
    }

    #[test]
    fn incomplete2() {
        let mut o = 0;
        let mut n = 0; // Times it has entered the parsing function
        let mut m = 0; // Times it has managed to get past the request for data
        let mut b = buf(&b"tes"[..], 2);

        assert_eq!(
            b.parse(|i| {
                n += 1;
                take_while(i, |_| {
                    o += 1;
                    o < 2
                })
                .inspect(|_| m += 1)
            }),
            Ok(&b"t"[..])
        );
        assert_eq!(n, 1);
        assert_eq!(m, 1);
        o = 0;
        assert_eq!(
            b.parse(|i| {
                n += 1;
                take_while(i, |_| {
                    o += 1;
                    o < 2
                })
                .inspect(|_| m += 1)
            }),
            Err(StreamError::Retry)
        );
        assert_eq!(n, 2);
        assert_eq!(m, 2);
        o = 0;
        assert_eq!(
            b.parse(|i| {
                n += 1;
                take_while(i, |_| {
                    o += 1;
                    o < 2
                })
                .inspect(|_| m += 1)
            }),
            Ok(&b"e"[..])
        );
        assert_eq!(n, 3);
        assert_eq!(m, 3);
        o = 0;
        assert_eq!(
            b.parse(|i| {
                n += 1;
                take_while(i, |_| {
                    o += 1;
                    o < 2
                })
                .inspect(|_| m += 1)
            }),
            Err(StreamError::Retry)
        );
        assert_eq!(n, 4);
        assert_eq!(m, 4);
        o = 0;
        assert_eq!(
            b.parse(|i| {
                n += 1;
                take_while(i, |_| {
                    o += 1;
                    o < 2
                })
                .inspect(|_| m += 1)
            }),
            Ok(&b"s"[..])
        );
        assert_eq!(n, 5);
        assert_eq!(m, 5);
        o = 0;
        assert_eq!(
            b.parse(|i| {
                n += 1;
                take_while(i, |_| {
                    o += 1;
                    o < 2
                })
                .inspect(|_| m += 1)
            }),
            Err(StreamError::EndOfInput)
        );
        assert_eq!(n, 5);
        assert_eq!(m, 5);
    }

    #[test]
    fn no_autofill() {
        let mut n = 0; // Times it has entered the parsing function
        let mut m = 0; // Times it has managed to get past the request for data
        let mut b = buf(&b"test"[..], 2);

        b.set_autofill(false);

        assert_eq!(
            b.parse(|i| {
                n += 1;
                take(i, 2).inspect(|_| m += 1)
            }),
            Err(StreamError::Retry)
        );
        assert_eq!(n, 1);
        assert_eq!(m, 0);

        assert_eq!(b.fill().unwrap(), 2);

        assert_eq!(
            b.parse(|i| {
                n += 1;
                take(i, 2).inspect(|_| m += 1)
            }),
            Ok(&b"te"[..])
        );
        assert_eq!(n, 2);
        assert_eq!(m, 1);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                take(i, 2).inspect(|_| m += 1)
            }),
            Err(StreamError::Retry)
        );
        assert_eq!(n, 3);
        assert_eq!(m, 1);

        assert_eq!(b.fill().unwrap(), 2);

        assert_eq!(
            b.parse(|i| {
                n += 1;
                take(i, 2).inspect(|_| m += 1)
            }),
            Ok(&b"st"[..])
        );
        assert_eq!(n, 4);
        assert_eq!(m, 2);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                take(i, 2).inspect(|_| m += 1)
            }),
            Err(StreamError::Retry)
        );
        assert_eq!(n, 5);
        assert_eq!(m, 2);

        assert_eq!(b.fill().unwrap(), 0);

        assert_eq!(
            b.parse(|i| {
                n += 1;
                take(i, 2).inspect(|_| m += 1)
            }),
            Err(StreamError::EndOfInput)
        );
        assert_eq!(n, 5);
        assert_eq!(m, 2);
    }

    #[test]
    fn no_autofill_first() {
        let mut n = 0; // Times it has entered the parsing function
        let mut m = 0; // Times it has managed to get past the request for data
        let mut b = buf(&b"ab"[..], 1);

        b.set_autofill(false);

        assert_eq!(b.fill().unwrap(), 1);

        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Ok(b'a')
        );
        assert_eq!(n, 1);
        assert_eq!(m, 1);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Err(StreamError::Retry)
        );
        assert_eq!(n, 2);
        assert_eq!(m, 1);

        assert_eq!(b.fill().unwrap(), 1);

        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Ok(b'b')
        );
        assert_eq!(n, 3);
        assert_eq!(m, 2);
        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Err(StreamError::Retry)
        );
        assert_eq!(n, 4);
        assert_eq!(m, 2);

        assert_eq!(b.fill().unwrap(), 0);

        assert_eq!(
            b.parse(|i| {
                n += 1;
                any(i).inspect(|_| m += 1)
            }),
            Err(StreamError::EndOfInput)
        );
        assert_eq!(n, 4);
        assert_eq!(m, 2);
    }
}