package ec

import (
	"context"
	"fmt"
	"regexp"
	"strings"

	"github.com/seaweedfs/seaweedfs/weed/glog"
	"github.com/seaweedfs/seaweedfs/weed/operation"
	"github.com/seaweedfs/seaweedfs/weed/pb"
	"github.com/seaweedfs/seaweedfs/weed/pb/master_pb"
	"github.com/seaweedfs/seaweedfs/weed/pb/volume_server_pb"
	"github.com/seaweedfs/seaweedfs/weed/storage/erasure_coding"
	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
	"github.com/seaweedfs/seaweedfs/weed/storage/types"
	"github.com/seaweedfs/seaweedfs/weed/util"
	"google.golang.org/grpc"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/status"
)

func DoEcDecode(env *Env, topoInfo *master_pb.TopologyInfo, collection string, vid needle.VolumeId, diskType types.DiskType, checkMinFreeSpace bool, diskUsageState *DecodeDiskUsageState) (err error) {

	if !env.isLocked() {
		return fmt.Errorf("lock is lost")
	}

	// find volume location
	nodeToEcShardsInfo, dataShards := collectEcNodeShardsInfo(topoInfo, vid)

	fmt.Printf("ec volume %d shard locations: %+v\n", vid, nodeToEcShardsInfo)

	if len(nodeToEcShardsInfo) == 0 {
		return fmt.Errorf("no EC shards found for volume %d", vid)
	}

	// A decode interrupted while deleting the shards leaves the regenerated
	// volume in place with the set half gone, so a re-run finds both and fails
	// re-collecting the first shard the interrupted run removed.
	//
	// Finding a volume beside the shards is not enough to act on: an encode
	// interrupted before it deleted the original leaves the same shape, as does
	// a decode killed while generating, whose volume may be half written. Both
	// of those leave the shard set COMPLETE. Only the deletion phase can remove
	// a data shard, so require one to be gone -- that is also exactly the state
	// no decode can recover from, which makes finishing the cleanup the only
	// move left rather than a choice between two.
	if _, found := missingDataShard(nodeToEcShardsInfo, dataShards); found {
		holder, hasVolume := regularVolumeHolder(topoInfo, vid)
		if !hasVolume {
			return fmt.Errorf("volume %d cannot be decoded: data shards are missing and no decoded volume exists to finish", vid)
		}
		if err := verifyDecodedVolumeBeforeDelete(env.GrpcDialOption, holder, vid); err != nil {
			return fmt.Errorf("volume %d is already decoded on %s but did not verify, keeping its ec shards: %v", vid, holder, err)
		}
		fmt.Printf("volume %d is already decoded on %s; deleting the ec shards the interrupted run left behind\n", vid, holder)
		return unmountAndDeleteEcShardsWithPrefix("deleteDecodedEcShards", env.GrpcDialOption, collection, nodeToEcShardsInfo, vid)
	}

	var originalShardCounts map[pb.ServerAddress]int
	if diskUsageState != nil {
		originalShardCounts = make(map[pb.ServerAddress]int, len(nodeToEcShardsInfo))
		for location, si := range nodeToEcShardsInfo {
			originalShardCounts[location] = si.Count()
		}
	}

	var eligibleTargets map[pb.ServerAddress]struct{}
	if checkMinFreeSpace {
		if diskUsageState == nil {
			return fmt.Errorf("min free space checking requires disk usage state")
		}
		eligibleTargets = make(map[pb.ServerAddress]struct{})
		for location := range nodeToEcShardsInfo {
			if freeCount, found := diskUsageState.freeVolumeCount(location); found && freeCount > 0 {
				eligibleTargets[location] = struct{}{}
			}
		}
		if len(eligibleTargets) == 0 {
			return fmt.Errorf("no eligible target datanodes with free volume slots for volume %d (diskType %s); use -checkMinFreeSpace=false to override", vid, diskType.ReadableString())
		}
	}

	// collect ec shards to the server with most space
	targetNodeLocation, err := collectEcShards(env, nodeToEcShardsInfo, collection, vid, eligibleTargets, dataShards)
	if err != nil {
		return fmt.Errorf("collectEcShards for volume %d: %v", vid, err)
	}

	// generate a normal volume
	err = generateNormalVolume(env.GrpcDialOption, vid, collection, targetNodeLocation)
	if err != nil {
		// Special case: if the EC index has no live entries, decoding is a no-op.
		// Just purge EC shards and return success without generating/mounting an empty volume.
		if isEcDecodeEmptyVolumeErr(err) {
			if err := unmountAndDeleteEcShards(env.GrpcDialOption, collection, nodeToEcShardsInfo, vid); err != nil {
				return err
			}
			if diskUsageState != nil {
				diskUsageState.applyDecode(targetNodeLocation, originalShardCounts, false)
			}
			return nil
		}
		return fmt.Errorf("generate normal volume %d on %s: %v", vid, targetNodeLocation, err)
	}

	// mount the decoded volume after server-side offline compaction succeeded
	err = mountDecodedVolume(env.GrpcDialOption, targetNodeLocation, vid)
	if err != nil {
		return fmt.Errorf("mount decoded volume %d on %s: %v", vid, targetNodeLocation, err)
	}

	// Confirm the regenerated .dat is present and non-empty before destroying
	// the shards. Without this gate, a silent failure in generate/mount could
	// leave the cluster with neither shards nor volume.
	if err := verifyDecodedVolumeBeforeDelete(env.GrpcDialOption, targetNodeLocation, vid); err != nil {
		return fmt.Errorf("verify decoded volume %d on %s before deleting shards: %w", vid, targetNodeLocation, err)
	}

	// delete the previous ec shards
	err = unmountAndDeleteEcShardsWithPrefix("deleteDecodedEcShards", env.GrpcDialOption, collection, nodeToEcShardsInfo, vid)
	if err != nil {
		return fmt.Errorf("delete ec shards for volume %d: %v", vid, err)
	}
	if diskUsageState != nil {
		diskUsageState.applyDecode(targetNodeLocation, originalShardCounts, true)
	}

	return nil
}

func isEcDecodeEmptyVolumeErr(err error) bool {
	st, ok := status.FromError(err)
	if !ok {
		return false
	}
	if st.Code() != codes.FailedPrecondition {
		return false
	}
	// Keep this robust against wording tweaks while still being specific.
	return strings.Contains(st.Message(), erasure_coding.EcNoLiveEntriesSubstring)
}

func unmountAndDeleteEcShards(grpcDialOption grpc.DialOption, collection string, nodeToShardsInfo map[pb.ServerAddress]*erasure_coding.ShardsInfo, vid needle.VolumeId) error {
	return unmountAndDeleteEcShardsWithPrefix("unmountAndDeleteEcShards", grpcDialOption, collection, nodeToShardsInfo, vid)
}

func unmountAndDeleteEcShardsWithPrefix(prefix string, grpcDialOption grpc.DialOption, collection string, nodeToShardsInfo map[pb.ServerAddress]*erasure_coding.ShardsInfo, vid needle.VolumeId) error {
	ewg := util.NewErrorWaitGroup(len(nodeToShardsInfo))

	// unmount and delete ec shards in parallel (one goroutine per location)
	for location, si := range nodeToShardsInfo {
		location, si := location, si // capture loop variables for goroutine
		ewg.Add(func() error {
			fmt.Printf("unmount ec volume %d on %s has shards: %+v\n", vid, location, si.Ids())
			if err := UnmountEcShards(grpcDialOption, vid, location, si.Ids()); err != nil {
				return fmt.Errorf("%s unmount ec volume %d on %s: %w", prefix, vid, location, err)
			}

			fmt.Printf("delete ec volume %d on %s has shards: %+v\n", vid, location, si.Ids())
			if err := SourceServerDeleteEcShards(grpcDialOption, collection, vid, location, si.Ids()); err != nil {
				return fmt.Errorf("%s delete ec volume %d on %s: %w", prefix, vid, location, err)
			}
			return nil
		})
	}
	return ewg.Wait()
}

// missingDataShard reports the first data shard absent from every holder.
// Parity shards are not enough to answer this: the decode rebuilds the volume
// from the data shards, so one of those going missing is what makes a re-run
// impossible.
func missingDataShard(nodeToShardsInfo map[pb.ServerAddress]*erasure_coding.ShardsInfo, dataShards int) (erasure_coding.ShardId, bool) {
	var present erasure_coding.ShardBits
	for _, si := range nodeToShardsInfo {
		for _, id := range si.Ids() {
			present = present.Set(id)
		}
	}
	for id := 0; id < dataShards; id++ {
		if !present.Has(erasure_coding.ShardId(id)) {
			return erasure_coding.ShardId(id), true
		}
	}
	return 0, false
}

// regularVolumeHolder returns a server already serving vid as a regular
// volume. A decode only finds one when an earlier run was interrupted between
// regenerating the volume and deleting the shards it came from.
func regularVolumeHolder(topoInfo *master_pb.TopologyInfo, vid needle.VolumeId) (pb.ServerAddress, bool) {
	var holder pb.ServerAddress
	found := false
	EachDataNode(topoInfo, func(dc DataCenterId, rack RackId, dn *master_pb.DataNodeInfo) {
		if found {
			return
		}
		for _, diskInfo := range dn.DiskInfos {
			for _, vi := range diskInfo.VolumeInfos {
				if needle.VolumeId(vi.Id) == vid {
					holder = pb.NewServerAddressFromDataNode(dn)
					found = true
					return
				}
			}
		}
	})
	return holder, found
}

func verifyDecodedVolumeBeforeDelete(grpcDialOption grpc.DialOption, target pb.ServerAddress, vid needle.VolumeId) error {
	var resp *volume_server_pb.ReadVolumeFileStatusResponse
	if err := operation.WithVolumeServerClient(false, target, grpcDialOption, func(client volume_server_pb.VolumeServerClient) error {
		r, e := client.ReadVolumeFileStatus(context.Background(), &volume_server_pb.ReadVolumeFileStatusRequest{
			VolumeId: uint32(vid),
		})
		if e != nil {
			return e
		}
		resp = r
		return nil
	}); err != nil {
		return fmt.Errorf("read volume file status: %w", err)
	}
	if resp.DatFileSize == 0 {
		return fmt.Errorf("decoded .dat is 0 bytes")
	}
	if resp.IdxFileSize == 0 {
		return fmt.Errorf("decoded .idx is 0 bytes")
	}
	glog.V(0).Infof("ec decode verification ok for volume %d on %s: dat=%d idx=%d", vid, target, resp.DatFileSize, resp.IdxFileSize)
	return nil
}

func mountDecodedVolume(grpcDialOption grpc.DialOption, targetNodeLocation pb.ServerAddress, vid needle.VolumeId) error {
	return operation.WithVolumeServerClient(false, targetNodeLocation, grpcDialOption, func(volumeServerClient volume_server_pb.VolumeServerClient) error {
		_, mountErr := volumeServerClient.VolumeMount(context.Background(), &volume_server_pb.VolumeMountRequest{
			VolumeId: uint32(vid),
		})
		return mountErr
	})
}

func generateNormalVolume(grpcDialOption grpc.DialOption, vid needle.VolumeId, collection string, sourceVolumeServer pb.ServerAddress) error {
	fmt.Printf("generateNormalVolume from ec volume %d on %s\n", vid, sourceVolumeServer)

	err := operation.WithVolumeServerClient(false, sourceVolumeServer, grpcDialOption, func(volumeServerClient volume_server_pb.VolumeServerClient) error {
		_, genErr := volumeServerClient.VolumeEcShardsToVolume(context.Background(), &volume_server_pb.VolumeEcShardsToVolumeRequest{
			VolumeId:   uint32(vid),
			Collection: collection,
		})
		return genErr
	})

	return err

}

func collectEcShards(env *Env, nodeToShardsInfo map[pb.ServerAddress]*erasure_coding.ShardsInfo, collection string, vid needle.VolumeId, eligibleTargets map[pb.ServerAddress]struct{}, dataShards int) (targetNodeLocation pb.ServerAddress, err error) {

	maxShardCount := -1
	existingShardsInfo := erasure_coding.NewShardsInfo()
	for loc, si := range nodeToShardsInfo {
		if eligibleTargets != nil {
			if _, ok := eligibleTargets[loc]; !ok {
				continue
			}
		}
		toBeCopiedShardCount := si.MinusParityShards(dataShards).Count()
		if toBeCopiedShardCount > maxShardCount {
			maxShardCount = toBeCopiedShardCount
			targetNodeLocation = loc
			existingShardsInfo = si
		}
	}
	if targetNodeLocation == "" {
		return "", fmt.Errorf("no eligible target datanodes available to decode volume %d", vid)
	}

	// Trust only shards the target can actually serve: an interrupted earlier
	// decode or balance can leave the master believing the target holds a
	// shard whose file never landed. A phantom entry here would exclude the
	// shard from the copy set and the decode would then fail with "missing
	// shard"; probing the target's live inventory makes the re-run re-copy it.
	if present, probeErr := erasure_coding.CollectShardsOnServer(context.Background(), collection, uint32(vid), string(targetNodeLocation), env.GrpcDialOption); probeErr == nil {
		confirmed := erasure_coding.NewShardsInfo()
		for _, sid := range existingShardsInfo.Ids() {
			if present.Has(sid) {
				confirmed.Set(erasure_coding.NewShardInfo(sid, 0))
			}
		}
		existingShardsInfo = confirmed
	} else {
		fmt.Printf("collectEcShards: probe %s inventory for volume %d: %v (keeping the topology's view)\n", targetNodeLocation, vid, probeErr)
	}

	fmt.Printf("collectEcShards: ec volume %d collect shards to %s from: %+v\n", vid, targetNodeLocation, nodeToShardsInfo)

	copiedShardsInfo := erasure_coding.NewShardsInfo()
	for loc, si := range nodeToShardsInfo {
		if loc == targetNodeLocation {
			continue
		}

		needToCopyShardsInfo := si.Minus(existingShardsInfo).MinusParityShards(dataShards)

		err = operation.WithVolumeServerClient(false, targetNodeLocation, env.GrpcDialOption, func(volumeServerClient volume_server_pb.VolumeServerClient) error {

			// Always collect .ecj from every shard location. Each server's .ecj
			// only contains deletions for needles whose data resides in shards
			// held by that server. Without merging all .ecj files, deletions
			// recorded on other servers would be lost during decode.
			if needToCopyShardsInfo.Count() > 0 {
				fmt.Printf("copy %d.%v %s => %s\n", vid, needToCopyShardsInfo.Ids(), loc, targetNodeLocation)
			} else {
				fmt.Printf("collect ecj %d %s => %s\n", vid, loc, targetNodeLocation)
			}

			_, copyErr := volumeServerClient.VolumeEcShardsCopy(context.Background(), &volume_server_pb.VolumeEcShardsCopyRequest{
				VolumeId:       uint32(vid),
				Collection:     collection,
				ShardIds:       needToCopyShardsInfo.IdsUint32(),
				CopyEcxFile:    false,
				CopyEcjFile:    true,
				CopyVifFile:    needToCopyShardsInfo.Count() > 0,
				SourceDataNode: string(loc),
			})
			if copyErr != nil {
				return fmt.Errorf("copy %d.%v %s => %s: %v", vid, needToCopyShardsInfo.Ids(), loc, targetNodeLocation, copyErr)
			}

			if needToCopyShardsInfo.Count() > 0 {
				fmt.Printf("mount %d.%v on %s\n", vid, needToCopyShardsInfo.Ids(), targetNodeLocation)
				_, mountErr := volumeServerClient.VolumeEcShardsMount(context.Background(), &volume_server_pb.VolumeEcShardsMountRequest{
					VolumeId:   uint32(vid),
					Collection: collection,
					ShardIds:   needToCopyShardsInfo.IdsUint32(),
				})
				if mountErr != nil {
					return fmt.Errorf("mount %d.%v on %s: %v", vid, needToCopyShardsInfo.Ids(), targetNodeLocation, mountErr)
				}
			}

			return nil
		})

		if err != nil {
			break
		}

		copiedShardsInfo.Add(needToCopyShardsInfo)
	}

	nodeToShardsInfo[targetNodeLocation] = existingShardsInfo.Plus(copiedShardsInfo)

	return targetNodeLocation, err
}
func CollectEcShardIds(topoInfo *master_pb.TopologyInfo, collectionRegex *regexp.Regexp, diskType types.DiskType) (vids []needle.VolumeId) {
	vidMap := make(map[uint32]bool)
	EachDataNode(topoInfo, func(dc DataCenterId, rack RackId, dn *master_pb.DataNodeInfo) {
		if diskInfo, found := dn.DiskInfos[string(diskType)]; found {
			for _, v := range diskInfo.EcShardInfos {
				if collectionRegex.MatchString(v.Collection) {
					vidMap[v.Id] = true
				}
			}
		}
	})

	for vid := range vidMap {
		vids = append(vids, needle.VolumeId(vid))
	}

	return
}

func collectEcNodeShardsInfo(topoInfo *master_pb.TopologyInfo, vid needle.VolumeId) (map[pb.ServerAddress]*erasure_coding.ShardsInfo, int) {
	res := make(map[pb.ServerAddress]*erasure_coding.ShardsInfo)
	EachDataNode(topoInfo, func(dc DataCenterId, rack RackId, dn *master_pb.DataNodeInfo) {
		// Union across ALL disk-type buckets and, within a node, across its
		// physical disks. Shards sit wherever encode generation and balance
		// left them — a cross-tier encode leaves them in the source bucket, a
		// partial migration straddles buckets — and a decode that only looks
		// at one bucket reports a decodable volume as having no shards at all.
		// (Same rationale as the encode's shard verification.)
		for _, diskInfo := range dn.DiskInfos {
			if diskInfo == nil {
				continue
			}
			for _, v := range diskInfo.EcShardInfos {
				if v.Id == uint32(vid) {
					addr := pb.NewServerAddressFromDataNode(dn)
					si := erasure_coding.ShardsInfoFromVolumeEcShardInformationMessage(v)
					if existing, ok := res[addr]; ok {
						existing.Add(si)
					} else {
						res[addr] = si
					}
				}
			}
		}
	})

	// OSS is always 10+4; the per-volume ratio override lives in the enterprise build.
	return res, erasure_coding.DataShardsCount
}

type DecodeDiskUsageState struct {
	byNode map[pb.ServerAddress]*decodeDiskUsageCounts
}

type decodeDiskUsageCounts struct {
	maxVolumeCount    int64
	volumeCount       int64
	remoteVolumeCount int64
	ecShardCount      int64
}

func NewDecodeDiskUsageState(topoInfo *master_pb.TopologyInfo, diskType types.DiskType) *DecodeDiskUsageState {
	state := &DecodeDiskUsageState{byNode: make(map[pb.ServerAddress]*decodeDiskUsageCounts)}
	EachDataNode(topoInfo, func(dc DataCenterId, rack RackId, dn *master_pb.DataNodeInfo) {
		if diskInfo, found := dn.DiskInfos[string(diskType)]; found {
			state.byNode[pb.NewServerAddressFromDataNode(dn)] = &decodeDiskUsageCounts{
				maxVolumeCount:    diskInfo.MaxVolumeCount,
				volumeCount:       diskInfo.VolumeCount,
				remoteVolumeCount: diskInfo.RemoteVolumeCount,
				ecShardCount:      int64(CountShards(diskInfo.EcShardInfos)),
			}
		}
	})
	return state
}

func (state *DecodeDiskUsageState) freeVolumeCount(location pb.ServerAddress) (int64, bool) {
	if state == nil {
		return 0, false
	}
	usage, found := state.byNode[location]
	if !found {
		return 0, false
	}
	free := usage.maxVolumeCount - (usage.volumeCount - usage.remoteVolumeCount)
	free -= (usage.ecShardCount + int64(erasure_coding.DataShardsCount) - 1) / int64(erasure_coding.DataShardsCount)
	return free, true
}

func (state *DecodeDiskUsageState) applyDecode(targetNodeLocation pb.ServerAddress, shardCounts map[pb.ServerAddress]int, createdVolume bool) {
	if state == nil {
		return
	}
	for location, shardCount := range shardCounts {
		if usage, found := state.byNode[location]; found {
			usage.ecShardCount -= int64(shardCount)
		}
	}
	if createdVolume {
		if usage, found := state.byNode[targetNodeLocation]; found {
			usage.volumeCount++
		}
	}
}