package shard

import (
	"context"
	"errors"
	"sync"

	"git.frostfs.info/TrueCloudLab/frostfs-node/internal/logs"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/blobstor"
	meta "git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/metabase"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/util/logger"
	"git.frostfs.info/TrueCloudLab/frostfs-observability/tracing"
	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/trace"
	"go.uber.org/zap"
)

var ErrRebuildInProgress = errors.New("shard rebuild in progress")

type RebuildWorkerLimiter interface {
	AcquireWorkSlot(ctx context.Context) error
	ReleaseWorkSlot()
}

type rebuildLimiter struct {
	semaphore chan struct{}
}

func NewRebuildLimiter(workersCount uint32) RebuildWorkerLimiter {
	return &rebuildLimiter{
		semaphore: make(chan struct{}, workersCount),
	}
}

func (l *rebuildLimiter) AcquireWorkSlot(ctx context.Context) error {
	select {
	case l.semaphore <- struct{}{}:
		return nil
	case <-ctx.Done():
		return ctx.Err()
	}
}

func (l *rebuildLimiter) ReleaseWorkSlot() {
	<-l.semaphore
}

type rebuildTask struct {
	limiter     RebuildWorkerLimiter
	fillPercent int
}

type rebuilder struct {
	mtx    *sync.Mutex
	wg     *sync.WaitGroup
	cancel func()
	done   chan struct{}
	tasks  chan rebuildTask
}

func newRebuilder() *rebuilder {
	return &rebuilder{
		mtx:   &sync.Mutex{},
		wg:    &sync.WaitGroup{},
		tasks: make(chan rebuildTask),
	}
}

func (r *rebuilder) Start(ctx context.Context, bs *blobstor.BlobStor, mb *meta.DB, log *logger.Logger) {
	r.mtx.Lock()
	defer r.mtx.Unlock()

	if r.done != nil {
		return // already started
	}
	ctx, cancel := context.WithCancel(ctx)
	r.cancel = cancel
	r.done = make(chan struct{})
	r.wg.Add(1)
	go func() {
		defer r.wg.Done()
		for {
			select {
			case <-r.done:
				return
			case t, ok := <-r.tasks:
				if !ok {
					continue
				}
				runRebuild(ctx, bs, mb, log, t.fillPercent, t.limiter)
			}
		}
	}()
}

func runRebuild(ctx context.Context, bs *blobstor.BlobStor, mb *meta.DB, log *logger.Logger,
	fillPercent int, limiter RebuildWorkerLimiter,
) {
	select {
	case <-ctx.Done():
		return
	default:
	}
	log.Info(ctx, logs.BlobstoreRebuildStarted)
	if err := bs.Rebuild(ctx, &mbStorageIDUpdate{mb: mb}, limiter, fillPercent); err != nil {
		log.Warn(ctx, logs.FailedToRebuildBlobstore, zap.Error(err))
	} else {
		log.Info(ctx, logs.BlobstoreRebuildCompletedSuccessfully)
	}
}

func (r *rebuilder) ScheduleRebuild(ctx context.Context, limiter RebuildWorkerLimiter, fillPercent int,
) error {
	select {
	case <-ctx.Done():
		return ctx.Err()
	case r.tasks <- rebuildTask{
		limiter:     limiter,
		fillPercent: fillPercent,
	}:
		return nil
	default:
		return ErrRebuildInProgress
	}
}

func (r *rebuilder) Stop(ctx context.Context, log *logger.Logger) {
	r.mtx.Lock()
	defer r.mtx.Unlock()

	if r.done != nil {
		close(r.done)
	}
	if r.cancel != nil {
		r.cancel()
	}
	r.wg.Wait()
	r.cancel = nil
	r.done = nil
	log.Info(ctx, logs.BlobstoreRebuildStopped)
}

var errMBIsNotAvailable = errors.New("metabase is not available")

type mbStorageIDUpdate struct {
	mb *meta.DB
}

func (u *mbStorageIDUpdate) UpdateStorageID(ctx context.Context, addr oid.Address, storageID []byte) error {
	select {
	case <-ctx.Done():
		return ctx.Err()
	default:
	}

	if u.mb == nil {
		return errMBIsNotAvailable
	}

	var prm meta.UpdateStorageIDPrm
	prm.SetAddress(addr)
	prm.SetStorageID(storageID)
	_, err := u.mb.UpdateStorageID(ctx, prm)
	return err
}

type RebuildPrm struct {
	ConcurrencyLimiter RebuildWorkerLimiter
	TargetFillPercent  uint32
}

func (s *Shard) ScheduleRebuild(ctx context.Context, p RebuildPrm) error {
	ctx, span := tracing.StartSpanFromContext(ctx, "Shard.ScheduleRebuild",
		trace.WithAttributes(
			attribute.String("shard_id", s.ID().String()),
			attribute.Int64("target_fill_percent", int64(p.TargetFillPercent)),
		))
	defer span.End()

	s.m.RLock()
	defer s.m.RUnlock()

	if s.info.Mode.ReadOnly() {
		return ErrReadOnlyMode
	}
	if s.info.Mode.NoMetabase() {
		return ErrDegradedMode
	}

	return s.rb.ScheduleRebuild(ctx, p.ConcurrencyLimiter, int(p.TargetFillPercent))
}