use http;
use super::*;
use codec::{RecvError, UserError};
use codec::UserError::*;
use frame::{self, Reason};

use bytes::Buf;

use std::{cmp, io};

/// Manages state transitions related to outbound frames.
#[derive(Debug)]
pub(super) struct Send {
    /// Stream identifier to use for next initialized stream.
    next_stream_id: Result<StreamId, StreamIdOverflow>,

    /// Initial window size of locally initiated streams
    init_window_sz: WindowSize,

    /// Prioritization layer
    prioritize: Prioritize,
}

impl Send {
    /// Create a new `Send`
    pub fn new(config: &Config) -> Self {
        Send {
            init_window_sz: config.local_init_window_sz,
            next_stream_id: Ok(config.local_next_stream_id),
            prioritize: Prioritize::new(config),
        }
    }

    /// Returns the initial send window size
    pub fn init_window_sz(&self) -> WindowSize {
        self.init_window_sz
    }

    pub fn open(&mut self) -> Result<StreamId, UserError> {
        let stream_id = self.ensure_next_stream_id()?;
        self.next_stream_id = stream_id.next_id();
        Ok(stream_id)
    }

    pub fn send_headers<B>(
        &mut self,
        frame: frame::Headers,
        buffer: &mut Buffer<Frame<B>>,
        stream: &mut store::Ptr,
        counts: &mut Counts,
        task: &mut Option<Task>,
    ) -> Result<(), UserError> {
        trace!(
            "send_headers; frame={:?}; init_window={:?}",
            frame,
            self.init_window_sz
        );

        // 8.1.2.2. Connection-Specific Header Fields
        if frame.fields().contains_key(http::header::CONNECTION)
            || frame.fields().contains_key(http::header::TRANSFER_ENCODING)
            || frame.fields().contains_key(http::header::UPGRADE)
            || frame.fields().contains_key("keep-alive")
            || frame.fields().contains_key("proxy-connection")
        {
            debug!("illegal connection-specific headers found");
            return Err(UserError::MalformedHeaders);
        } else if let Some(te) = frame.fields().get(http::header::TE) {
            if te != "trailers" {
                debug!("illegal connection-specific headers found");
                return Err(UserError::MalformedHeaders);

            }
        }

        let end_stream = frame.is_end_stream();

        // Update the state
        stream.state.send_open(end_stream)?;

        if counts.peer().is_local_init(frame.stream_id()) {
            if counts.can_inc_num_send_streams() {
                counts.inc_num_send_streams();
            } else {
                self.prioritize.queue_open(stream);
            }
        }

        // Queue the frame for sending
        self.prioritize.queue_frame(frame.into(), buffer, stream, task);

        Ok(())
    }

    /// Send an explicit RST_STREAM frame
    ///
    /// # Arguments
    /// + `reason`: the error code for the RST_STREAM frame
    /// + `clear_queue`: if true, all pending outbound frames will be cleared,
    ///    if false, the RST_STREAM frame will be appended to the end of the
    ///    send queue.
    pub fn send_reset<B>(
        &mut self,
        reason: Reason,
        buffer: &mut Buffer<Frame<B>>,
        stream: &mut store::Ptr,
        task: &mut Option<Task>,
    ) {
        let is_reset = stream.state.is_reset();
        let is_closed = stream.state.is_closed();
        let is_empty = stream.pending_send.is_empty();

        trace!(
            "send_reset(..., reason={:?}, stream={:?}, ..., \
             is_reset={:?}; is_closed={:?}; pending_send.is_empty={:?}; \
             state={:?} \
            ",
            stream.id,
            reason,
            is_reset,
            is_closed,
            is_empty,
            stream.state
        );

        if is_reset {
            // Don't double reset
            trace!(
                " -> not sending RST_STREAM ({:?} is already reset)",
                stream.id
            );
            return;
        }

        // If closed AND the send queue is flushed, then the stream cannot be
        // reset explicitly, either. Implicit resets can still be queued.
        if is_closed && is_empty {
            trace!(
                " -> not sending explicit RST_STREAM ({:?} was closed \
                     and send queue was flushed)",
                stream.id
            );
            return;
        }

        // Transition the state
        stream.state.set_reset(reason);

        self.recv_err(buffer, stream);

        let frame = frame::Reset::new(stream.id, reason);

        trace!("send_reset -- queueing; frame={:?}", frame);
        self.prioritize.queue_frame(frame.into(), buffer, stream, task);
    }

    pub fn schedule_cancel(&mut self, stream: &mut store::Ptr, task: &mut Option<Task>) {
        trace!("schedule_cancel; {:?}", stream.id);
        if stream.state.is_closed() {
            // Stream is already closed, nothing more to do
            return;
        }

        stream.state.set_canceled();

        self.prioritize.reclaim_reserved_capacity(stream);
        self.prioritize.schedule_send(stream, task);
    }

    pub fn send_data<B>(
        &mut self,
        frame: frame::Data<B>,
        buffer: &mut Buffer<Frame<B>>,
        stream: &mut store::Ptr,
        task: &mut Option<Task>,
    ) -> Result<(), UserError>
        where B: Buf,
    {
        self.prioritize.send_data(frame, buffer, stream, task)
    }

    pub fn send_trailers<B>(
        &mut self,
        frame: frame::Headers,
        buffer: &mut Buffer<Frame<B>>,
        stream: &mut store::Ptr,
        task: &mut Option<Task>,
    ) -> Result<(), UserError> {
        // TODO: Should this logic be moved into state.rs?
        if !stream.state.is_send_streaming() {
            return Err(UnexpectedFrameType.into());
        }

        stream.state.send_close();

        trace!("send_trailers -- queuing; frame={:?}", frame);
        self.prioritize.queue_frame(frame.into(), buffer, stream, task);

        // Release any excess capacity
        self.prioritize.reserve_capacity(0, stream);

        Ok(())
    }

    pub fn poll_complete<T, B>(
        &mut self,
        buffer: &mut Buffer<Frame<B>>,
        store: &mut Store,
        counts: &mut Counts,
        dst: &mut Codec<T, Prioritized<B>>,
    ) -> Poll<(), io::Error>
    where T: AsyncWrite,
          B: Buf,
    {
        self.prioritize.poll_complete(buffer, store, counts, dst)
    }

    /// Request capacity to send data
    pub fn reserve_capacity(&mut self, capacity: WindowSize, stream: &mut store::Ptr) {
        self.prioritize.reserve_capacity(capacity, stream)
    }

    pub fn poll_capacity(
        &mut self,
        stream: &mut store::Ptr,
    ) -> Poll<Option<WindowSize>, UserError> {
        if !stream.state.is_send_streaming() {
            return Ok(Async::Ready(None));
        }

        if !stream.send_capacity_inc {
            stream.wait_send();
            return Ok(Async::NotReady);
        }

        stream.send_capacity_inc = false;

        Ok(Async::Ready(Some(self.capacity(stream))))
    }

    /// Current available stream send capacity
    pub fn capacity(&self, stream: &mut store::Ptr) -> WindowSize {
        let available = stream.send_flow.available().as_size();
        let buffered = stream.buffered_send_data;

        if available <= buffered {
            0
        } else {
            available - buffered
        }
    }

    pub fn recv_connection_window_update(
        &mut self,
        frame: frame::WindowUpdate,
        store: &mut Store,
    ) -> Result<(), Reason> {
        self.prioritize
            .recv_connection_window_update(frame.size_increment(), store)
    }

    pub fn recv_stream_window_update<B>(
        &mut self,
        sz: WindowSize,
        buffer: &mut Buffer<Frame<B>>,
        stream: &mut store::Ptr,
        task: &mut Option<Task>,
    ) -> Result<(), Reason> {
        if let Err(e) = self.prioritize.recv_stream_window_update(sz, stream) {
            debug!("recv_stream_window_update !!; err={:?}", e);

            self.send_reset(
                Reason::FLOW_CONTROL_ERROR.into(),
                buffer, stream, task);

            return Err(e);
        }

        Ok(())
    }

    pub fn recv_err<B>(
        &mut self,
        buffer: &mut Buffer<Frame<B>>,
        stream: &mut store::Ptr
    ) {
        // Clear all pending outbound frames
        self.prioritize.clear_queue(buffer, stream);
        self.prioritize.reclaim_all_capacity(stream);
    }

    pub fn apply_remote_settings<B>(
        &mut self,
        settings: &frame::Settings,
        buffer: &mut Buffer<Frame<B>>,
        store: &mut Store,
        task: &mut Option<Task>,
    ) -> Result<(), RecvError> {
        // Applies an update to the remote endpoint's initial window size.
        //
        // Per RFC 7540 §6.9.2:
        //
        // In addition to changing the flow-control window for streams that are
        // not yet active, a SETTINGS frame can alter the initial flow-control
        // window size for streams with active flow-control windows (that is,
        // streams in the "open" or "half-closed (remote)" state). When the
        // value of SETTINGS_INITIAL_WINDOW_SIZE changes, a receiver MUST adjust
        // the size of all stream flow-control windows that it maintains by the
        // difference between the new value and the old value.
        //
        // A change to `SETTINGS_INITIAL_WINDOW_SIZE` can cause the available
        // space in a flow-control window to become negative. A sender MUST
        // track the negative flow-control window and MUST NOT send new
        // flow-controlled frames until it receives WINDOW_UPDATE frames that
        // cause the flow-control window to become positive.
        if let Some(val) = settings.initial_window_size() {
            let old_val = self.init_window_sz;
            self.init_window_sz = val;

            if val < old_val {
                let dec = old_val - val;

                trace!("decrementing all windows; dec={}", dec);

                let mut total_reclaimed = 0;
                store.for_each(|mut stream| {
                    let stream = &mut *stream;

                    stream.send_flow.dec_window(dec);

                    let available = stream.send_flow.available().as_size();
                    let reclaim = cmp::min(dec, available);
                    stream.send_flow.claim_capacity(reclaim);
                    total_reclaimed += reclaim;

                    trace!(
                        "decremented stream window; id={:?}; decr={}; flow={:?}",
                        stream.id,
                        dec,
                        stream.send_flow
                    );

                    // TODO: Should this notify the producer when the capacity
                    // of a stream is reduced? Maybe it should if the capacity
                    // is reduced to zero, allowing the producer to stop work.

                    Ok::<_, RecvError>(())
                })?;

                self.prioritize
                    .assign_connection_capacity(total_reclaimed, store);
            } else if val > old_val {
                let inc = val - old_val;

                store.for_each(|mut stream| {
                    self.recv_stream_window_update(inc, buffer, &mut stream, task)
                        .map_err(RecvError::Connection)
                })?;
            }
        }

        Ok(())
    }

    pub fn ensure_not_idle(&self, id: StreamId) -> Result<(), Reason> {
        if let Ok(next) = self.next_stream_id {
            if id >= next {
                return Err(Reason::PROTOCOL_ERROR);
            }
        }
        // if next_stream_id is overflowed, that's ok.

        Ok(())
    }

    pub fn ensure_next_stream_id(&self) -> Result<StreamId, UserError> {
        self.next_stream_id.map_err(|_| OverflowedStreamId)
    }
}