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// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package http2

import "math"

// NewRandomWriteScheduler constructs a WriteScheduler that ignores HTTP/2
// priorities. Control frames like SETTINGS and PING are written before DATA
// frames, but if no control frames are queued and multiple streams have queued
// HEADERS or DATA frames, Pop selects a ready stream arbitrarily.
func NewRandomWriteScheduler() WriteScheduler {
    return &randomWriteScheduler{sq: make(map[uint32]*writeQueue)}
}

type randomWriteScheduler struct {
    // zero are frames not associated with a specific stream.
    zero writeQueue

    // sq contains the stream-specific queues, keyed by stream ID.
    // When a stream is idle or closed, it's deleted from the map.
    sq map[uint32]*writeQueue

    // pool of empty queues for reuse.
    queuePool writeQueuePool
}

func (ws *randomWriteScheduler) OpenStream(streamID uint32, options OpenStreamOptions) {
    // no-op: idle streams are not tracked
}

func (ws *randomWriteScheduler) CloseStream(streamID uint32) {
    q, ok := ws.sq[streamID]
    if !ok {
        return
    }
    delete(ws.sq, streamID)
    ws.queuePool.put(q)
}

func (ws *randomWriteScheduler) AdjustStream(streamID uint32, priority PriorityParam) {
    // no-op: priorities are ignored
}

func (ws *randomWriteScheduler) Push(wr FrameWriteRequest) {
    id := wr.StreamID()
    if id == 0 {
        ws.zero.push(wr)
        return
    }
    q, ok := ws.sq[id]
    if !ok {
        q = ws.queuePool.get()
        ws.sq[id] = q
    }
    q.push(wr)
}

func (ws *randomWriteScheduler) Pop() (FrameWriteRequest, bool) {
    // Control frames first.
    if !ws.zero.empty() {
        return ws.zero.shift(), true
    }
    // Iterate over all non-idle streams until finding one that can be consumed.
    for _, q := range ws.sq {
        if wr, ok := q.consume(math.MaxInt32); ok {
            return wr, true
        }
    }
    return FrameWriteRequest{}, false
}