package shard

import (
	"context"
	"errors"

	"git.frostfs.info/TrueCloudLab/frostfs-node/internal/logs"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/writecache"
	"git.frostfs.info/TrueCloudLab/frostfs-observability/tracing"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/trace"
	"go.uber.org/zap"
)

var (
	dummyCancel          = &writecacheSealCanceler{cancel: func() {}}
	notInitializedCancel = &writecacheSealCanceler{cancel: func() {}}
	errWriteCacheSealing = errors.New("writecache is already sealing or shard is not initialized")
)

type writecacheSealCanceler struct {
	cancel context.CancelFunc
}

// FlushWriteCachePrm represents parameters of a `FlushWriteCache` operation.
type FlushWriteCachePrm struct {
	ignoreErrors bool
	seal         bool
}

// SetIgnoreErrors sets the flag to ignore read-errors during flush.
func (p *FlushWriteCachePrm) SetIgnoreErrors(ignore bool) {
	p.ignoreErrors = ignore
}

// SetSeal sets the flag to left writecache in read-only mode after flush.
func (p *FlushWriteCachePrm) SetSeal(v bool) {
	p.seal = v
}

// errWriteCacheDisabled is returned when an operation on write-cache is performed,
// but write-cache is disabled.
var errWriteCacheDisabled = errors.New("write-cache is disabled")

// FlushWriteCache flushes all data from the write-cache.
func (s *Shard) FlushWriteCache(ctx context.Context, p FlushWriteCachePrm) error {
	ctx, span := tracing.StartSpanFromContext(ctx, "Shard.FlushWriteCache",
		trace.WithAttributes(
			attribute.String("shard_id", s.ID().String()),
			attribute.Bool("ignore_errors", p.ignoreErrors),
			attribute.Bool("seal", p.seal),
		))
	defer span.End()

	if !s.hasWriteCache() {
		return errWriteCacheDisabled
	}

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

	// To write data to the blobstor we need to write to the blobstor and the metabase.
	if s.info.Mode.ReadOnly() {
		return ErrReadOnlyMode
	}
	if s.info.Mode.NoMetabase() {
		return ErrDegradedMode
	}

	return s.writeCache.Flush(ctx, p.ignoreErrors, p.seal)
}

type SealWriteCachePrm struct {
	IgnoreErrors bool
	Async        bool
	RestoreMode  bool
	Shrink       bool
}

// SealWriteCache flushes all data from the write-cache and moves it to degraded read only mode.
func (s *Shard) SealWriteCache(ctx context.Context, p SealWriteCachePrm) error {
	ctx, span := tracing.StartSpanFromContext(ctx, "Shard.SealWriteCache",
		trace.WithAttributes(
			attribute.String("shard_id", s.ID().String()),
			attribute.Bool("ignore_errors", p.IgnoreErrors),
			attribute.Bool("restore_mode", p.RestoreMode),
		))
	defer span.End()

	if !s.hasWriteCache() {
		return errWriteCacheDisabled
	}

	if p.Async {
		ctx = context.WithoutCancel(ctx)
	}
	ctx, cancel := context.WithCancel(ctx)
	canceler := &writecacheSealCanceler{cancel: cancel}
	if !s.writecacheSealCancel.CompareAndSwap(dummyCancel, canceler) {
		return errWriteCacheSealing
	}
	s.m.RLock()
	cleanup := func() {
		s.m.RUnlock()
		s.writecacheSealCancel.Store(dummyCancel)
	}

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

	if !p.Async {
		defer cleanup()
	}
	prm := writecache.SealPrm{IgnoreErrors: p.IgnoreErrors, RestoreMode: p.RestoreMode, Shrink: p.Shrink}
	if p.Async {
		started := make(chan struct{})
		go func() {
			close(started)
			defer cleanup()

			s.log.Info(ctx, logs.StartedWritecacheSealAsync)
			if err := s.writeCache.Seal(ctx, prm); err != nil {
				s.log.Warn(ctx, logs.FailedToSealWritecacheAsync, zap.Error(err))
				return
			}
			s.log.Info(ctx, logs.WritecacheSealCompletedAsync)
		}()
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-started:
			return nil
		}
	}
	return s.writeCache.Seal(ctx, prm)
}