use std::{fmt, cmp};
use std::rc::{Rc, Weak};
use std::cell::RefCell;
use std::collections::VecDeque;
use std::error::Error;
use std::io::Error as IoError;
use bytes::{Bytes, BytesMut};
use futures::{Async, Poll, Stream};
use futures::task::{Task, current as current_task};

const MAX_PAYLOAD_SIZE: usize = 65_536; // max buffer size 64k

/// Just Bytes object
pub type PayloadItem = Result<Bytes, PayloadError>;

#[derive(Debug)]
/// A set of error that can occur during payload parsing.
pub enum PayloadError {
    /// A payload reached EOF, but is not complete.
    Incomplete,
    /// Parse error
    ParseError(IoError),
}

impl fmt::Display for PayloadError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            PayloadError::ParseError(ref e) => fmt::Display::fmt(e, f),
            ref e => f.write_str(e.description()),
        }
    }
}

impl Error for PayloadError {
    fn description(&self) -> &str {
        match *self {
            PayloadError::Incomplete => "A payload reached EOF, but is not complete.",
            PayloadError::ParseError(ref e) => e.description(),
        }
    }

    fn cause(&self) -> Option<&Error> {
        match *self {
            PayloadError::ParseError(ref error) => Some(error),
            _ => None,
        }
    }
}

impl From<IoError> for PayloadError {
    fn from(err: IoError) -> PayloadError {
        PayloadError::ParseError(err)
    }
}

/// Stream of byte chunks
///
/// Payload stores chunks in vector. First chunk can be received with `.readany()` method.
#[derive(Debug)]
pub struct Payload {
    inner: Rc<RefCell<Inner>>,
}

impl Payload {

    pub(crate) fn new(eof: bool) -> (PayloadSender, Payload) {
        let shared = Rc::new(RefCell::new(Inner::new(eof)));

        (PayloadSender{inner: Rc::downgrade(&shared)}, Payload{inner: shared})
    }

    /// Indicates paused state of the payload. If payload data is not consumed
    /// it get paused. Max size of not consumed data is 64k
    pub fn paused(&self) -> bool {
        self.inner.borrow().paused()
    }

    /// Indicates EOF of payload
    pub fn eof(&self) -> bool {
        self.inner.borrow().eof()
    }

    /// Length of the data in this payload
    pub fn len(&self) -> usize {
        self.inner.borrow().len()
    }

    /// Is payload empty
    pub fn is_empty(&self) -> bool {
        self.inner.borrow().len() == 0
    }

    /// Get first available chunk of data.
    /// Returns Some(PayloadItem) as chunk, `None` indicates eof.
    pub fn readany(&mut self) -> Async<Option<PayloadItem>> {
        self.inner.borrow_mut().readany()
    }

    /// Get exactly number of bytes
    /// Returns Some(PayloadItem) as chunk, `None` indicates eof.
    pub fn readexactly(&mut self, size: usize) -> Result<Async<Bytes>, PayloadError> {
        self.inner.borrow_mut().readexactly(size)
    }

    /// Read until `\n`
    /// Returns Some(PayloadItem) as line, `None` indicates eof.
    pub fn readline(&mut self) -> Result<Async<Bytes>, PayloadError> {
        self.inner.borrow_mut().readline()
    }

    /// Read until match line
    /// Returns Some(PayloadItem) as line, `None` indicates eof.
    pub fn readuntil(&mut self, line: &[u8]) -> Result<Async<Bytes>, PayloadError> {
        self.inner.borrow_mut().readuntil(line)
    }

    #[doc(hidden)]
    pub fn readall(&mut self) -> Option<Bytes> {
        self.inner.borrow_mut().readall()
    }

    /// Put unused data back to payload
    pub fn unread_data(&mut self, data: Bytes) {
        self.inner.borrow_mut().unread_data(data);
    }
}


impl Stream for Payload {
    type Item = PayloadItem;
    type Error = ();

    fn poll(&mut self) -> Poll<Option<PayloadItem>, ()> {
        Ok(self.readany())
    }
}

pub(crate) struct PayloadSender {
    inner: Weak<RefCell<Inner>>,
}

impl PayloadSender {
    pub(crate) fn set_error(&mut self, err: PayloadError) {
        if let Some(shared) = self.inner.upgrade() {
            shared.borrow_mut().set_error(err)
        }
    }

    pub(crate) fn feed_eof(&mut self) {
        if let Some(shared) = self.inner.upgrade() {
            shared.borrow_mut().feed_eof()
        }
    }

    pub(crate) fn feed_data(&mut self, data: Bytes) {
        if let Some(shared) = self.inner.upgrade() {
            shared.borrow_mut().feed_data(data)
        }
    }

    pub(crate) fn maybe_paused(&self) -> bool {
        match self.inner.upgrade() {
            Some(shared) => {
                let inner = shared.borrow();
                if inner.paused() && inner.len() < MAX_PAYLOAD_SIZE {
                    drop(inner);
                    shared.borrow_mut().resume();
                    false
                } else if !inner.paused() && inner.len() > MAX_PAYLOAD_SIZE {
                    drop(inner);
                    shared.borrow_mut().pause();
                    true
                } else {
                    inner.paused()
                }
            }
            None => false,
        }
    }
}

#[derive(Debug)]
struct Inner {
    len: usize,
    eof: bool,
    paused: bool,
    err: Option<PayloadError>,
    task: Option<Task>,
    items: VecDeque<Bytes>,
}

impl Inner {

    fn new(eof: bool) -> Self {
        Inner {
            len: 0,
            eof: eof,
            paused: false,
            err: None,
            task: None,
            items: VecDeque::new(),
        }
    }

    fn paused(&self) -> bool {
        self.paused
    }

    fn pause(&mut self) {
        self.paused = true;
    }

    fn resume(&mut self) {
        self.paused = false;
    }

    fn set_error(&mut self, err: PayloadError) {
        self.err = Some(err);
        if let Some(task) = self.task.take() {
            task.notify()
        }
    }

    fn feed_eof(&mut self) {
        self.eof = true;
        if let Some(task) = self.task.take() {
            task.notify()
        }
    }

    fn feed_data(&mut self, data: Bytes) {
        self.len += data.len();
        self.items.push_back(data);
        if let Some(task) = self.task.take() {
            task.notify()
        }
    }

    fn eof(&self) -> bool {
        self.items.is_empty() && self.eof
    }

    fn len(&self) -> usize {
        self.len
    }

    fn readany(&mut self) -> Async<Option<PayloadItem>> {
        if let Some(data) = self.items.pop_front() {
            self.len -= data.len();
            Async::Ready(Some(Ok(data)))
        } else if self.eof {
            Async::Ready(None)
        } else if let Some(err) = self.err.take() {
            Async::Ready(Some(Err(err)))
        } else {
            self.task = Some(current_task());
            Async::NotReady
        }
    }

    fn readexactly(&mut self, size: usize) -> Result<Async<Bytes>, PayloadError> {
        if size <= self.len {
            let mut buf = BytesMut::with_capacity(size);
            while buf.len() < size {
                let mut chunk = self.items.pop_front().unwrap();
                let rem = cmp::min(size - buf.len(), chunk.len());
                self.len -= rem;
                buf.extend(&chunk.split_to(rem));
                if !chunk.is_empty() {
                    self.items.push_front(chunk);
                    return Ok(Async::Ready(buf.freeze()))
                }
            }
        }

        if let Some(err) = self.err.take() {
            Err(err)
        } else {
            self.task = Some(current_task());
            Ok(Async::NotReady)
        }
    }

    fn readuntil(&mut self, line: &[u8]) -> Result<Async<Bytes>, PayloadError> {
        let mut idx = 0;
        let mut num = 0;
        let mut offset = 0;
        let mut found = false;
        let mut length = 0;

        for no in 0..self.items.len() {
            {
                let chunk = &self.items[no];
                for (pos, ch) in chunk.iter().enumerate() {
                    if *ch == line[idx] {
                        idx += 1;
                        if idx == line.len() {
                            num = no;
                            offset = pos+1;
                            length += pos+1;
                            found = true;
                            break;
                        }
                    } else {
                        idx = 0
                    }
                }
                if !found {
                    length += chunk.len()
                }
            }

            if found {
                let mut buf = BytesMut::with_capacity(length);
                if num > 0 {
                    for _ in 0..num {
                        buf.extend(self.items.pop_front().unwrap());
                    }
                }
                if offset > 0 {
                    let mut chunk = self.items.pop_front().unwrap();
                    buf.extend(chunk.split_to(offset));
                    if !chunk.is_empty() {
                        self.items.push_front(chunk)
                    }
                }
                self.len -= length;
                return Ok(Async::Ready(buf.freeze()))
            }
        }
        if let Some(err) = self.err.take() {
            Err(err)
        } else {
            self.task = Some(current_task());
            Ok(Async::NotReady)
        }
    }

    fn readline(&mut self) -> Result<Async<Bytes>, PayloadError> {
        self.readuntil(b"\n")
    }

    #[doc(hidden)]
    pub fn readall(&mut self) -> Option<Bytes> {
        let len = self.items.iter().fold(0, |cur, item| cur + item.len());
        if len > 0 {
            let mut buf = BytesMut::with_capacity(len);
            for item in &self.items {
                buf.extend(item);
            }
            self.items = VecDeque::new();
            self.len = 0;
            Some(buf.take().freeze())
        } else {
            None
        }
    }

    pub fn unread_data(&mut self, data: Bytes) {
        self.len += data.len();
        self.items.push_front(data)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::io;
    use futures::future::{lazy, result};
    use tokio_core::reactor::Core;

    #[test]
    fn test_error() {
        let err: PayloadError = IoError::new(io::ErrorKind::Other, "ParseError").into();
        assert_eq!(err.description(), "ParseError");
        assert_eq!(err.cause().unwrap().description(), "ParseError");
        assert_eq!(format!("{}", err), "ParseError");

        let err = PayloadError::Incomplete;
        assert_eq!(err.description(), "A payload reached EOF, but is not complete.");
        assert_eq!(format!("{}", err), "A payload reached EOF, but is not complete.");
    }

    #[test]
    fn test_basic() {
        Core::new().unwrap().run(lazy(|| {
            let (_, mut payload) = Payload::new(false);

            assert!(!payload.eof());
            assert!(payload.is_empty());
            assert_eq!(payload.len(), 0);

            match payload.readany() {
                Async::NotReady => (),
                _ => panic!("error"),
            }

            let res: Result<(), ()> = Ok(());
            result(res)
        })).unwrap();
    }

    #[test]
    fn test_eof() {
        Core::new().unwrap().run(lazy(|| {
            let (mut sender, mut payload) = Payload::new(false);

            match payload.readany() {
                Async::NotReady => (),
                _ => panic!("error"),
            }

            assert!(!payload.eof());

            sender.feed_data(Bytes::from("data"));
            sender.feed_eof();

            assert!(!payload.eof());

            match payload.readany() {
                Async::Ready(Some(data)) => assert_eq!(&data.unwrap(), "data"),
                _ => panic!("error"),
            }
            assert!(payload.is_empty());
            assert!(payload.eof());
            assert_eq!(payload.len(), 0);

            match payload.readany() {
                Async::Ready(None) => (),
                _ => panic!("error"),
            }
            let res: Result<(), ()> = Ok(());
            result(res)
        })).unwrap();
    }

    #[test]
    fn test_err() {
        Core::new().unwrap().run(lazy(|| {
            let (mut sender, mut payload) = Payload::new(false);

            match payload.readany() {
                Async::NotReady => (),
                _ => panic!("error"),
            }

            sender.set_error(PayloadError::Incomplete);
            match payload.readany() {
                Async::Ready(Some(data)) => assert!(data.is_err()),
                _ => panic!("error"),
            }
            let res: Result<(), ()> = Ok(());
            result(res)
        })).unwrap();
    }

    #[test]
    fn test_readany() {
        Core::new().unwrap().run(lazy(|| {
            let (mut sender, mut payload) = Payload::new(false);

            sender.feed_data(Bytes::from("line1"));

            assert!(!payload.is_empty());
            assert_eq!(payload.len(), 5);

            sender.feed_data(Bytes::from("line2"));
            assert!(!payload.is_empty());
            assert_eq!(payload.len(), 10);

            match payload.readany() {
                Async::Ready(Some(data)) => assert_eq!(&data.unwrap(), "line1"),
                _ => panic!("error"),
            }
            assert!(!payload.is_empty());
            assert_eq!(payload.len(), 5);

            let res: Result<(), ()> = Ok(());
            result(res)
        })).unwrap();
    }

    #[test]
    fn test_readexactly() {
        Core::new().unwrap().run(lazy(|| {
            let (mut sender, mut payload) = Payload::new(false);

            match payload.readexactly(2) {
                Ok(Async::NotReady) => (),
                _ => panic!("error"),
            }

            sender.feed_data(Bytes::from("line1"));
            sender.feed_data(Bytes::from("line2"));
            assert_eq!(payload.len(), 10);

            match payload.readexactly(2) {
                Ok(Async::Ready(data)) => assert_eq!(&data, "li"),
                _ => panic!("error"),
            }
            assert_eq!(payload.len(), 8);

            match payload.readexactly(4) {
                Ok(Async::Ready(data)) => assert_eq!(&data, "ne1l"),
                _ => panic!("error"),
            }
            assert_eq!(payload.len(), 4);

            sender.set_error(PayloadError::Incomplete);
            match payload.readexactly(10) {
                Err(_) => (),
                _ => panic!("error"),
            }

            let res: Result<(), ()> = Ok(());
            result(res)
        })).unwrap();
    }

    #[test]
    fn test_readuntil() {
        Core::new().unwrap().run(lazy(|| {
            let (mut sender, mut payload) = Payload::new(false);

            match payload.readuntil(b"ne") {
                Ok(Async::NotReady) => (),
                _ => panic!("error"),
            }

            sender.feed_data(Bytes::from("line1"));
            sender.feed_data(Bytes::from("line2"));
            assert_eq!(payload.len(), 10);

            match payload.readuntil(b"ne") {
                Ok(Async::Ready(data)) => assert_eq!(&data, "line"),
                _ => panic!("error"),
            }
            assert_eq!(payload.len(), 6);

            match payload.readuntil(b"2") {
                Ok(Async::Ready(data)) => assert_eq!(&data, "1line2"),
                _ => panic!("error"),
            }
            assert_eq!(payload.len(), 0);

            sender.set_error(PayloadError::Incomplete);
            match payload.readuntil(b"b") {
                Err(_) => (),
                _ => panic!("error"),
            }

            let res: Result<(), ()> = Ok(());
            result(res)
        })).unwrap();
    }

    #[test]
    fn test_pause() {
        Core::new().unwrap().run(lazy(|| {
            let (mut sender, mut payload) = Payload::new(false);

            assert!(!payload.paused());
            assert!(!sender.maybe_paused());

            for _ in 0..MAX_PAYLOAD_SIZE+1 {
                sender.feed_data(Bytes::from("1"));
            }
            assert!(sender.maybe_paused());
            assert!(payload.paused());

            payload.readexactly(10).unwrap();
            assert!(!sender.maybe_paused());
            assert!(!payload.paused());

            let res: Result<(), ()> = Ok(());
            result(res)
        })).unwrap();
    }

    #[test]
    fn test_unread_data() {
        Core::new().unwrap().run(lazy(|| {
            let (_, mut payload) = Payload::new(false);

            payload.unread_data(Bytes::from("data"));
            assert!(!payload.is_empty());
            assert_eq!(payload.len(), 4);

            match payload.readany() {
                Async::Ready(Some(data)) => assert_eq!(&data.unwrap(), "data"),
                _ => panic!("error"),
            }

            let res: Result<(), ()> = Ok(());
            result(res)
        })).unwrap();
    }
}