package engine

import (
	"errors"
	"fmt"

	meta "github.com/TrueCloudLab/frostfs-node/pkg/local_object_storage/metabase"
	"github.com/TrueCloudLab/frostfs-node/pkg/local_object_storage/shard"
	"github.com/TrueCloudLab/frostfs-node/pkg/util"
	objectSDK "github.com/TrueCloudLab/frostfs-sdk-go/object"
	oid "github.com/TrueCloudLab/frostfs-sdk-go/object/id"
	"github.com/TrueCloudLab/hrw"
	"go.uber.org/zap"
)

// EvacuateShardPrm represents parameters for the EvacuateShard operation.
type EvacuateShardPrm struct {
	shardID      []*shard.ID
	handler      func(oid.Address, *objectSDK.Object) error
	ignoreErrors bool
}

// EvacuateShardRes represents result of the EvacuateShard operation.
type EvacuateShardRes struct {
	count int
}

// WithShardIDList sets shard ID.
func (p *EvacuateShardPrm) WithShardIDList(id []*shard.ID) {
	p.shardID = id
}

// WithIgnoreErrors sets flag to ignore errors.
func (p *EvacuateShardPrm) WithIgnoreErrors(ignore bool) {
	p.ignoreErrors = ignore
}

// WithFaultHandler sets handler to call for objects which cannot be saved on other shards.
func (p *EvacuateShardPrm) WithFaultHandler(f func(oid.Address, *objectSDK.Object) error) {
	p.handler = f
}

// Count returns amount of evacuated objects.
// Objects for which handler returned no error are also assumed evacuated.
func (p EvacuateShardRes) Count() int {
	return p.count
}

const defaultEvacuateBatchSize = 100

type pooledShard struct {
	hashedShard
	pool util.WorkerPool
}

var errMustHaveTwoShards = errors.New("must have at least 1 spare shard")

// Evacuate moves data from one shard to the others.
// The shard being moved must be in read-only mode.
func (e *StorageEngine) Evacuate(prm EvacuateShardPrm) (EvacuateShardRes, error) {
	sidList := make([]string, len(prm.shardID))
	for i := range prm.shardID {
		sidList[i] = prm.shardID[i].String()
	}

	e.mtx.RLock()
	for i := range sidList {
		sh, ok := e.shards[sidList[i]]
		if !ok {
			e.mtx.RUnlock()
			return EvacuateShardRes{}, errShardNotFound
		}

		if !sh.GetMode().ReadOnly() {
			e.mtx.RUnlock()
			return EvacuateShardRes{}, shard.ErrMustBeReadOnly
		}
	}

	if len(e.shards)-len(sidList) < 1 && prm.handler == nil {
		e.mtx.RUnlock()
		return EvacuateShardRes{}, errMustHaveTwoShards
	}

	e.log.Info("started shards evacuation", zap.Strings("shard_ids", sidList))

	// We must have all shards, to have correct information about their
	// indexes in a sorted slice and set appropriate marks in the metabase.
	// Evacuated shard is skipped during put.
	shards := make([]pooledShard, 0, len(e.shards))
	for id := range e.shards {
		shards = append(shards, pooledShard{
			hashedShard: hashedShard(e.shards[id]),
			pool:        e.shardPools[id],
		})
	}
	e.mtx.RUnlock()

	weights := make([]float64, 0, len(shards))
	for i := range shards {
		weights = append(weights, e.shardWeight(shards[i].Shard))
	}

	shardMap := make(map[string]*shard.Shard)
	for i := range sidList {
		for j := range shards {
			if shards[j].ID().String() == sidList[i] {
				shardMap[sidList[i]] = shards[j].Shard
			}
		}
	}

	var listPrm shard.ListWithCursorPrm
	listPrm.WithCount(defaultEvacuateBatchSize)

	var res EvacuateShardRes

mainLoop:
	for n := range sidList {
		sh := shardMap[sidList[n]]

		var c *meta.Cursor
		for {
			listPrm.WithCursor(c)

			// TODO (@fyrchik): #1731 this approach doesn't work in degraded modes
			//  because ListWithCursor works only with the metabase.
			listRes, err := sh.ListWithCursor(listPrm)
			if err != nil {
				if errors.Is(err, meta.ErrEndOfListing) || errors.Is(err, shard.ErrDegradedMode) {
					continue mainLoop
				}
				return res, err
			}

			// TODO (@fyrchik): #1731 parallelize the loop
			lst := listRes.AddressList()

		loop:
			for i := range lst {
				addr := lst[i].Address

				var getPrm shard.GetPrm
				getPrm.SetAddress(addr)

				getRes, err := sh.Get(getPrm)
				if err != nil {
					if prm.ignoreErrors {
						continue
					}
					return res, err
				}

				hrw.SortHasherSliceByWeightValue(shards, weights, hrw.Hash([]byte(addr.EncodeToString())))
				for j := range shards {
					if _, ok := shardMap[shards[j].ID().String()]; ok {
						continue
					}
					putDone, exists := e.putToShard(shards[j].hashedShard, j, shards[j].pool, addr, getRes.Object())
					if putDone || exists {
						if putDone {
							e.log.Debug("object is moved to another shard",
								zap.String("from", sidList[n]),
								zap.Stringer("to", shards[j].ID()),
								zap.Stringer("addr", addr))

							res.count++
						}
						continue loop
					}
				}

				if prm.handler == nil {
					// Do not check ignoreErrors flag here because
					// ignoring errors on put make this command kinda useless.
					return res, fmt.Errorf("%w: %s", errPutShard, lst[i])
				}

				err = prm.handler(addr, getRes.Object())
				if err != nil {
					return res, err
				}
				res.count++
			}

			c = listRes.Cursor()
		}
	}

	e.log.Info("finished shards evacuation",
		zap.Strings("shard_ids", sidList))
	return res, nil
}