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// Copyright 2015 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

// Package flowcontrol implements a client side flow control mechanism
package flowcontrol

import (
    "sync"
    "time"
)

const rcConst = 1000000

type cmNode struct {
    node                       *ClientNode
    lastUpdate                 int64
    reqAccepted                int64
    serving, recharging        bool
    rcWeight                   uint64
    rcValue, rcDelta           int64
    finishRecharge, startValue int64
}

func (node *cmNode) update(time int64) {
    dt := time - node.lastUpdate
    node.rcValue += node.rcDelta * dt / rcConst
    node.lastUpdate = time
    if node.recharging && time >= node.finishRecharge {
        node.recharging = false
        node.rcDelta = 0
        node.rcValue = 0
    }
}

func (node *cmNode) set(serving bool, simReqCnt, sumWeight uint64) {
    if node.serving && !serving {
        node.recharging = true
        sumWeight += node.rcWeight
    }
    node.serving = serving
    if node.recharging && serving {
        node.recharging = false
        sumWeight -= node.rcWeight
    }

    node.rcDelta = 0
    if serving {
        node.rcDelta = int64(rcConst / simReqCnt)
    }
    if node.recharging {
        node.rcDelta = -int64(node.node.cm.rcRecharge * node.rcWeight / sumWeight)
        node.finishRecharge = node.lastUpdate + node.rcValue*rcConst/(-node.rcDelta)
    }
}

type ClientManager struct {
    lock                             sync.Mutex
    nodes                            map[*cmNode]struct{}
    simReqCnt, sumWeight, rcSumValue uint64
    maxSimReq, maxRcSum              uint64
    rcRecharge                       uint64
    resumeQueue                      chan chan bool
    time                             int64
}

func NewClientManager(rcTarget, maxSimReq, maxRcSum uint64) *ClientManager {
    cm := &ClientManager{
        nodes:       make(map[*cmNode]struct{}),
        resumeQueue: make(chan chan bool),
        rcRecharge:  rcConst * rcConst / (100*rcConst/rcTarget - rcConst),
        maxSimReq:   maxSimReq,
        maxRcSum:    maxRcSum,
    }
    go cm.queueProc()
    return cm
}

func (self *ClientManager) Stop() {
    self.lock.Lock()
    defer self.lock.Unlock()

    // signal any waiting accept routines to return false
    self.nodes = make(map[*cmNode]struct{})
    close(self.resumeQueue)
}

func (self *ClientManager) addNode(cnode *ClientNode) *cmNode {
    time := getTime()
    node := &cmNode{
        node:           cnode,
        lastUpdate:     time,
        finishRecharge: time,
        rcWeight:       1,
    }
    self.lock.Lock()
    defer self.lock.Unlock()

    self.nodes[node] = struct{}{}
    self.update(getTime())
    return node
}

func (self *ClientManager) removeNode(node *cmNode) {
    self.lock.Lock()
    defer self.lock.Unlock()

    time := getTime()
    self.stop(node, time)
    delete(self.nodes, node)
    self.update(time)
}

// recalc sumWeight
func (self *ClientManager) updateNodes(time int64) (rce bool) {
    var sumWeight, rcSum uint64
    for node, _ := range self.nodes {
        rc := node.recharging
        node.update(time)
        if rc && !node.recharging {
            rce = true
        }
        if node.recharging {
            sumWeight += node.rcWeight
        }
        rcSum += uint64(node.rcValue)
    }
    self.sumWeight = sumWeight
    self.rcSumValue = rcSum
    return
}

func (self *ClientManager) update(time int64) {
    for {
        firstTime := time
        for node, _ := range self.nodes {
            if node.recharging && node.finishRecharge < firstTime {
                firstTime = node.finishRecharge
            }
        }
        if self.updateNodes(firstTime) {
            for node, _ := range self.nodes {
                if node.recharging {
                    node.set(node.serving, self.simReqCnt, self.sumWeight)
                }
            }
        } else {
            self.time = time
            return
        }
    }
}

func (self *ClientManager) canStartReq() bool {
    return self.simReqCnt < self.maxSimReq && self.rcSumValue < self.maxRcSum
}

func (self *ClientManager) queueProc() {
    for rc := range self.resumeQueue {
        for {
            time.Sleep(time.Millisecond * 10)
            self.lock.Lock()
            self.update(getTime())
            cs := self.canStartReq()
            self.lock.Unlock()
            if cs {
                break
            }
        }
        close(rc)
    }
}

func (self *ClientManager) accept(node *cmNode, time int64) bool {
    self.lock.Lock()
    defer self.lock.Unlock()

    self.update(time)
    if !self.canStartReq() {
        resume := make(chan bool)
        self.lock.Unlock()
        self.resumeQueue <- resume
        <-resume
        self.lock.Lock()
        if _, ok := self.nodes[node]; !ok {
            return false // reject if node has been removed or manager has been stopped
        }
    }
    self.simReqCnt++
    node.set(true, self.simReqCnt, self.sumWeight)
    node.startValue = node.rcValue
    self.update(self.time)
    return true
}

func (self *ClientManager) stop(node *cmNode, time int64) {
    if node.serving {
        self.update(time)
        self.simReqCnt--
        node.set(false, self.simReqCnt, self.sumWeight)
        self.update(time)
    }
}

func (self *ClientManager) processed(node *cmNode, time int64) (rcValue, rcCost uint64) {
    self.lock.Lock()
    defer self.lock.Unlock()

    self.stop(node, time)
    return uint64(node.rcValue), uint64(node.rcValue - node.startValue)
}