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// Copyright 2018 The dexon-consensus Authors
// This file is part of the dexon-consensus library.
//
// The dexon-consensus 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 dexon-consensus 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 dexon-consensus library. If not, see
// <http://www.gnu.org/licenses/>.

package core

import (
    "sort"
    "sync"

    "github.com/dexon-foundation/dexon-consensus/common"
    "github.com/dexon-foundation/dexon-consensus/core/types"
)

type totalOrderingSyncer struct {
    lock sync.RWMutex

    numChains          uint32
    syncHeight         map[uint32]uint64
    syncDeliverySetIdx int
    pendingBlocks      []*types.Block
    inPendingBlocks    map[common.Hash]struct{}

    bootstrapChain map[uint32]struct{}

    // Data to restore delivery set.
    pendingDeliveryBlocks []*types.Block
    deliverySet           map[int][]*types.Block
    mapToDeliverySet      map[common.Hash]int
}

func newTotalOrderingSyncer(numChains uint32) *totalOrderingSyncer {
    return &totalOrderingSyncer{
        numChains:          numChains,
        syncHeight:         make(map[uint32]uint64),
        syncDeliverySetIdx: -1,
        inPendingBlocks:    make(map[common.Hash]struct{}),
        bootstrapChain:     make(map[uint32]struct{}),
        deliverySet:        make(map[int][]*types.Block),
        mapToDeliverySet:   make(map[common.Hash]int),
    }
}

func (tos *totalOrderingSyncer) synced() bool {
    tos.lock.RLock()
    defer tos.lock.RUnlock()
    return tos.syncDeliverySetIdx != -1
}

func (tos *totalOrderingSyncer) processBlock(
    block *types.Block) (delivered []*types.Block) {
    if tos.synced() {
        if tos.syncHeight[block.Position.ChainID] >= block.Position.Height {
            return
        }
        delivered = append(delivered, block)
        return
    }
    tos.lock.Lock()
    defer tos.lock.Unlock()
    tos.inPendingBlocks[block.Hash] = struct{}{}
    tos.pendingBlocks = append(tos.pendingBlocks, block)
    if block.Position.Height == 0 {
        tos.bootstrapChain[block.Position.ChainID] = struct{}{}
    }
    if uint32(len(tos.bootstrapChain)) == tos.numChains {
        // Bootstrap mode.
        delivered = tos.pendingBlocks
        tos.syncDeliverySetIdx = 0
        for i := uint32(0); i < tos.numChains; i++ {
            tos.syncHeight[i] = uint64(0)
        }
    } else {
        maxDeliverySetIdx := -1
        // TODO(jimmy-dexon): below for loop can be optimized.
    PendingBlockLoop:
        for i, block := range tos.pendingBlocks {
            idx, exist := tos.mapToDeliverySet[block.Hash]
            if !exist {
                continue
            }
            deliverySet := tos.deliverySet[idx]
            // Check if all the blocks in deliverySet are in the pendingBlocks.
            for _, dBlock := range deliverySet {
                if _, exist := tos.inPendingBlocks[dBlock.Hash]; !exist {
                    continue PendingBlockLoop
                }
            }
            if idx > maxDeliverySetIdx {
                maxDeliverySetIdx = idx
            }
            // Check if all of the chains have delivered.
            for _, dBlock := range deliverySet {
                if h, exist := tos.syncHeight[dBlock.Position.ChainID]; exist {
                    if dBlock.Position.Height < h {
                        continue
                    }
                }
                tos.syncHeight[dBlock.Position.ChainID] = dBlock.Position.Height
            }
            if uint32(len(tos.syncHeight)) != tos.numChains {
                continue
            }
            // Core is fully synced, it can start delivering blocks from idx.
            tos.syncDeliverySetIdx = maxDeliverySetIdx
            delivered = make([]*types.Block, 0, i)
            break
        }
        if tos.syncDeliverySetIdx == -1 {
            return
        }
        // Generating delivering blocks.
        for i := maxDeliverySetIdx; i < len(tos.deliverySet); i++ {
            deliverySet := tos.deliverySet[i]
            sort.Sort(types.ByHash(deliverySet))
            for _, block := range deliverySet {
                if block.Position.Height > tos.syncHeight[block.Position.ChainID] {
                    tos.syncHeight[block.Position.ChainID] = block.Position.Height
                }
                delivered = append(delivered, block)
            }
        }
        // Flush remaining blocks.
        for _, block := range tos.pendingBlocks {
            if _, exist := tos.mapToDeliverySet[block.Hash]; exist {
                continue
            }
            if block.Position.Height > tos.syncHeight[block.Position.ChainID] {
                tos.syncHeight[block.Position.ChainID] = block.Position.Height
            }
            delivered = append(delivered, block)
        }
    }
    // Clean internal data model to save memory.
    tos.pendingBlocks = nil
    tos.inPendingBlocks = nil
    tos.bootstrapChain = nil
    tos.pendingDeliveryBlocks = nil
    tos.deliverySet = nil
    tos.mapToDeliverySet = nil
    return
}

// The finalized block should be passed by the order of consensus height.
func (tos *totalOrderingSyncer) processFinalizedBlock(block *types.Block) {
    if tos.synced() {
        return
    }
    tos.lock.Lock()
    defer tos.lock.Unlock()
    if len(tos.pendingDeliveryBlocks) > 0 {
        if block.Hash.Less(
            tos.pendingDeliveryBlocks[len(tos.pendingDeliveryBlocks)-1].Hash) {
            // pendingDeliveryBlocks forms a deliverySet.
            idx := len(tos.deliverySet)
            tos.deliverySet[idx] = tos.pendingDeliveryBlocks
            for _, block := range tos.pendingDeliveryBlocks {
                tos.mapToDeliverySet[block.Hash] = idx
            }
            tos.pendingDeliveryBlocks = []*types.Block{}
        }
    }
    tos.pendingDeliveryBlocks = append(tos.pendingDeliveryBlocks, block)
}