package shell

import (
	"context"
	"flag"
	"fmt"
	"io"
	"sort"
	"sync"

	"github.com/chrislusf/seaweedfs/weed/operation"
	"github.com/chrislusf/seaweedfs/weed/pb/master_pb"
	"github.com/chrislusf/seaweedfs/weed/pb/volume_server_pb"
	"github.com/chrislusf/seaweedfs/weed/storage/erasure_coding"
	"github.com/chrislusf/seaweedfs/weed/storage/needle"
	"github.com/chrislusf/seaweedfs/weed/wdclient"
	"google.golang.org/grpc"
)

func init() {
	commands = append(commands, &commandEcEncode{})
}

type commandEcEncode struct {
}

func (c *commandEcEncode) Name() string {
	return "ec.encode"
}

func (c *commandEcEncode) Help() string {
	return `apply erasure coding to a volume

	This command will:
	1. freeze one volume
	2. apply erasure coding to the volume
	3. move the encoded shards to multiple volume servers

	The erasure coding is 10.4. So ideally you have more than 14 volume servers, and you can afford
	to lose 4 volume servers.

	If the number of volumes are not high, the worst case is that you only have 4 volume servers,
	and the shards are spread as 4,4,3,3, respectively. You can afford to lose one volume server.

	If you only have less than 4 volume servers, with erasure coding, at least you can afford to
	have 4 corrupted shard files.

`
}

func (c *commandEcEncode) Do(args []string, commandEnv *commandEnv, writer io.Writer) (err error) {

	encodeCommand := flag.NewFlagSet(c.Name(), flag.ContinueOnError)
	volumeId := encodeCommand.Int("vid", 0, "the volume id")
	if err = encodeCommand.Parse(args); err != nil {
		return nil
	}

	ctx := context.Background()

	// find volume location
	locations := commandEnv.masterClient.GetLocations(uint32(*volumeId))
	if len(locations) == 0 {
		return fmt.Errorf("volume %d not found", *volumeId)
	}

	// generate ec shards
	err = generateEcShards(ctx, commandEnv.option.GrpcDialOption, needle.VolumeId(*volumeId), locations[0].Url)
	if err != nil {
		return fmt.Errorf("generate ec shards for volume %d on %s: %v", *volumeId, locations[0].Url, err)
	}

	// balance the ec shards to current cluster
	err = balanceEcShards(ctx, commandEnv, needle.VolumeId(*volumeId), locations[0])
	if err != nil {
		return fmt.Errorf("balance ec shards for volume %d on %s: %v", *volumeId, locations[0].Url, err)
	}

	return err
}

func generateEcShards(ctx context.Context, grpcDialOption grpc.DialOption, volumeId needle.VolumeId, sourceVolumeServer string) error {

	err := operation.WithVolumeServerClient(sourceVolumeServer, grpcDialOption, func(volumeServerClient volume_server_pb.VolumeServerClient) error {
		_, genErr := volumeServerClient.VolumeEcGenerateSlices(ctx, &volume_server_pb.VolumeEcGenerateSlicesRequest{
			VolumeId: uint32(volumeId),
		})
		return genErr
	})

	return err

}

func balanceEcShards(ctx context.Context, commandEnv *commandEnv, volumeId needle.VolumeId, existingLocation wdclient.Location) (err error) {

	// list all possible locations
	var resp *master_pb.VolumeListResponse
	err = commandEnv.masterClient.WithClient(ctx, func(client master_pb.SeaweedClient) error {
		resp, err = client.VolumeList(ctx, &master_pb.VolumeListRequest{})
		return err
	})
	if err != nil {
		return err
	}

	// find out all volume servers with one volume slot left.
	var allDataNodes []*master_pb.DataNodeInfo
	var totalFreeEcSlots int
	eachDataNode(resp.TopologyInfo, func(dn *master_pb.DataNodeInfo) {
		if freeEcSlots := countFreeShardSlots(dn); freeEcSlots > 0 {
			allDataNodes = append(allDataNodes, dn)
			totalFreeEcSlots += freeEcSlots
		}
	})
	if totalFreeEcSlots < erasure_coding.TotalShardsCount {
		return fmt.Errorf("not enough free ec shard slots. only %d left", totalFreeEcSlots)
	}
	sort.Slice(allDataNodes, func(i, j int) bool {
		return countFreeShardSlots(allDataNodes[j]) < countFreeShardSlots(allDataNodes[i])
	})
	if len(allDataNodes) > erasure_coding.TotalShardsCount {
		allDataNodes = allDataNodes[:erasure_coding.TotalShardsCount]
	}

	// calculate how many shards to allocate for these servers
	allocated := balancedEcDistribution(allDataNodes)

	// ask the data nodes to copy from the source volume server
	err = parallelCopyEcShardsFromSource(ctx, commandEnv.option.GrpcDialOption, allDataNodes, allocated, volumeId, existingLocation)
	if err != nil {
		return nil
	}

	// ask the source volume server to clean up copied ec shards

	// ask the source volume server to delete the original volume

	return err

}

func parallelCopyEcShardsFromSource(ctx context.Context, grpcDialOption grpc.DialOption,
	targetServers []*master_pb.DataNodeInfo, allocated []int,
	volumeId needle.VolumeId, existingLocation wdclient.Location) (err error) {

	// parallelize
	var wg sync.WaitGroup
	startFromShardId := 0
	for i, server := range targetServers {
		if allocated[i] <= 0 {
			continue
		}

		wg.Add(1)
		go func(server *master_pb.DataNodeInfo, startFromShardId int, shardCount int) {
			defer wg.Done()
			copyErr := oneServerCopyEcShardsFromSource(ctx, grpcDialOption, server, startFromShardId, shardCount, volumeId, existingLocation)
			if copyErr != nil {
				err = copyErr
			}
		}(server, startFromShardId, allocated[i])
		startFromShardId += allocated[i]
	}
	wg.Wait()

	return err
}

func oneServerCopyEcShardsFromSource(ctx context.Context, grpcDialOption grpc.DialOption,
	targetServer *master_pb.DataNodeInfo, startFromShardId int, shardCount int,
	volumeId needle.VolumeId, existingLocation wdclient.Location) (err error) {

	if targetServer.Id == existingLocation.Url {
		return nil
	}

	for shardId := startFromShardId; shardId < startFromShardId+shardCount; shardId++ {
		fmt.Printf("copy %d.%d %s => %s\n", volumeId, shardId, existingLocation.Url, targetServer.Id)
	}

	return nil
}
func balancedEcDistribution(servers []*master_pb.DataNodeInfo) (allocated []int) {
	freeSlots := make([]int, len(servers))
	allocated = make([]int, len(servers))
	for i, server := range servers {
		freeSlots[i] = countFreeShardSlots(server)
	}
	allocatedCount := 0
	for allocatedCount < erasure_coding.TotalShardsCount {
		for i, _ := range servers {
			if freeSlots[i]-allocated[i] > 0 {
				allocated[i] += 1
				allocatedCount += 1
			}
			if allocatedCount >= erasure_coding.TotalShardsCount {
				break
			}
		}
	}

	return allocated
}

func eachDataNode(topo *master_pb.TopologyInfo, fn func(*master_pb.DataNodeInfo)) {
	for _, dc := range topo.DataCenterInfos {
		for _, rack := range dc.RackInfos {
			for _, dn := range rack.DataNodeInfos {
				fn(dn)
			}
		}
	}
}

func countShards(ecShardInfos []*master_pb.VolumeEcShardInformationMessage) (count int) {
	for _, ecShardInfo := range ecShardInfos {
		shardBits := erasure_coding.ShardBits(ecShardInfo.EcIndexBits)
		count += shardBits.ShardIdCount()
	}
	return
}

func countFreeShardSlots(dn *master_pb.DataNodeInfo) (count int) {
	return int(dn.FreeVolumeCount)*10 - countShards(dn.EcShardInfos)
}