package meta

import (
	"bytes"
	"context"
	"errors"
	"strconv"
	"time"

	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/internal/metaerr"
	"git.frostfs.info/TrueCloudLab/frostfs-observability/tracing"
	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
	"github.com/cockroachdb/pebble"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/trace"
)

// FilterExpired return expired items from addresses.
// Address considered expired if metabase does contain information about expiration and
// expiration epoch is less than epoch.
func (db *DB) FilterExpired(ctx context.Context, epoch uint64, addresses []oid.Address) ([]oid.Address, error) {
	var (
		startedAt = time.Now()
		success   = true
	)
	defer func() {
		db.metrics.AddMethodDuration("FilterExpired", time.Since(startedAt), success)
	}()

	_, span := tracing.StartSpanFromContext(ctx, "metabase.FilterExpired",
		trace.WithAttributes(
			attribute.String("epoch", strconv.FormatUint(epoch, 10)),
			attribute.Int("addr_count", len(addresses)),
		))
	defer span.End()

	db.modeMtx.RLock()
	defer db.modeMtx.RUnlock()

	if db.mode.NoMetabase() {
		return nil, ErrDegradedMode
	}

	result := make([]oid.Address, 0, len(addresses))
	err := db.snapshot(func(s *pebble.Snapshot) error {
		var e error
		result, e = selectExpiredObjects(ctx, s, epoch, addresses)
		return e
	})
	if err != nil {
		return nil, metaerr.Wrap(err)
	}
	success = true
	return result, nil
}

func isExpired(ctx context.Context, r pebble.Reader, addr oid.Address, currEpoch uint64) (bool, error) {
	prefix := []byte{expiredPrefix}
	it, err := r.NewIter(&pebble.IterOptions{
		LowerBound:                prefix,
		OnlyReadGuaranteedDurable: true,
	})
	if err != nil {
		return false, err
	}

	// iteration does in ascending order by expiration epoch.
	// gc does expired objects collect every epoch, so here should be not so much items.
	for v := it.First(); v && bytes.HasPrefix(it.Key(), prefix); v = it.Next() {
		select {
		case <-ctx.Done():
			return false, errors.Join(ctx.Err(), it.Close())
		default:
		}

		expEpoch, err := expirationEpochFromExpiredKey(it.Key())
		if err != nil {
			return false, errors.Join(err, it.Close())
		}

		if expEpoch >= currEpoch {
			return false, it.Close() // keys are ordered by epoch, so next items will be discarded anyway.
		}

		curAddr, err := addressFromExpiredKey(it.Key())
		if err != nil {
			return false, errors.Join(err, it.Close())
		}
		if curAddr == addr {
			return true, it.Close()
		}
	}
	return false, it.Close()
}

func selectExpiredObjects(ctx context.Context, r pebble.Reader, epoch uint64, objects []oid.Address) ([]oid.Address, error) {
	result := make([]oid.Address, 0)
	objMap := make(map[oid.Address]struct{})
	for _, obj := range objects {
		objMap[obj] = struct{}{}
	}

	prefix := []byte{expiredPrefix}
	it, err := r.NewIter(&pebble.IterOptions{
		LowerBound:                prefix,
		OnlyReadGuaranteedDurable: true,
	})
	if err != nil {
		return nil, err
	}

	// iteration does in ascending order by expiration epoch.
	// gc does expired objects collect every epoch, so here should be not so much items.
	for v := it.First(); v && bytes.HasPrefix(it.Key(), prefix); v = it.Next() {
		select {
		case <-ctx.Done():
			return nil, errors.Join(ctx.Err(), it.Close())
		default:
		}

		expEpoch, err := expirationEpochFromExpiredKey(it.Key())
		if err != nil {
			return nil, errors.Join(err, it.Close())
		}

		if expEpoch >= epoch {
			return result, it.Close() // keys are ordered by epoch, so next items will be discarded anyway.
		}

		addr, err := addressFromExpiredKey(it.Key())
		if err != nil {
			return nil, errors.Join(err, it.Close())
		}
		if _, ok := objMap[addr]; ok {
			result = append(result, addr)
		}
	}
	return result, it.Close()
}

// IterateExpired iterates over all objects in DB which are out of date
// relative to epoch. Locked objects are not included (do not confuse
// with objects of type LOCK).
//
// If h returns ErrInterruptIterator, nil returns immediately.
// Returns other errors of h directly.
func (db *DB) IterateExpired(ctx context.Context, epoch uint64, h ExpiredObjectHandler) error {
	var (
		startedAt = time.Now()
		success   = false
	)
	defer func() {
		db.metrics.AddMethodDuration("IterateExpired", time.Since(startedAt), success)
	}()
	_, span := tracing.StartSpanFromContext(ctx, "metabase.IterateExpired",
		trace.WithAttributes(
			attribute.String("epoch", strconv.FormatUint(epoch, 10)),
		))
	defer span.End()

	db.modeMtx.RLock()
	defer db.modeMtx.RUnlock()

	if db.mode.NoMetabase() {
		return ErrDegradedMode
	}

	err := metaerr.Wrap(db.snapshot(func(s *pebble.Snapshot) error {
		return iterateExpired(ctx, s, epoch, h)
	}))
	success = err == nil
	return err
}

func iterateExpired(ctx context.Context, r pebble.Reader, epoch uint64, h ExpiredObjectHandler) error {
	prefix := []byte{expiredPrefix}
	it, err := r.NewIter(&pebble.IterOptions{
		LowerBound:                prefix,
		OnlyReadGuaranteedDurable: true,
	})
	if err != nil {
		return err
	}

	// iteration does in ascending order by expiration epoch.
	for v := it.First(); v && bytes.HasPrefix(it.Key(), prefix); v = it.Next() {
		select {
		case <-ctx.Done():
			return errors.Join(ctx.Err(), it.Close())
		default:
		}

		expEpoch, err := expirationEpochFromExpiredKey(it.Key())
		if err != nil {
			return errors.Join(err, it.Close())
		}

		if expEpoch >= epoch {
			return it.Close() // keys are ordered by epoch, so next items will be discarded anyway.
		}

		addr, err := addressFromExpiredKey(it.Key())
		if err != nil {
			return errors.Join(err, it.Close())
		}

		// Ignore locked objects.
		//
		// To slightly optimize performance we can check only REGULAR objects
		// (only they can be locked), but it's more reliable.
		isLocked, err := objectLocked(ctx, r, addr.Container(), addr.Object())
		if err != nil {
			return errors.Join(err, it.Close())
		}
		if isLocked {
			continue
		}

		objType, err := firstIrregularObjectType(r, addr.Container(), addr.Object())
		if err != nil {
			return errors.Join(err, it.Close())
		}

		if err := h(&ExpiredObject{
			typ:  objType,
			addr: addr,
		}); err != nil {
			if errors.Is(err, ErrInterruptIterator) {
				return it.Close()
			}
			return errors.Join(err, it.Close())
		}
	}
	return it.Close()
}