package writecache

import (
	"context"
	"fmt"
	"sync"
	"sync/atomic"

	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/blobstor/fstree"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/internal/metaerr"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/shard/mode"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/util/logger"
	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
	"go.etcd.io/bbolt"
	"go.uber.org/zap"
)

type cache struct {
	options

	mode    mode.Mode
	modeMtx sync.RWMutex

	// flushCh is a channel with objects to flush.
	flushCh chan objectInfo
	// cancel is cancel function, protected by modeMtx in Close.
	cancel atomic.Value
	// wg is a wait group for flush workers.
	wg sync.WaitGroup
	// fsTree contains big files stored directly on file-system.
	fsTree *fstree.FSTree
	// counter contains atomic counters for the number of objects stored in cache.
	counter *fstree.SimpleCounter
}

// wcStorageType is used for write-cache operations logging.
const wcStorageType = "write-cache"

type objectInfo struct {
	addr oid.Address
	size uint64
}

const (
	defaultMaxObjectSize   = 64 * 1024 * 1024 // 64 MiB
	defaultSmallObjectSize = 32 * 1024        // 32 KiB
	defaultMaxCacheSize    = 1 << 30          // 1 GiB
)

var (
	defaultBucket                    = []byte{0}
	dummyCanceler context.CancelFunc = func() {}
)

// New creates new writecache instance.
func New(opts ...Option) Cache {
	c := &cache{
		flushCh: make(chan objectInfo),
		mode:    mode.Disabled,
		counter: fstree.NewSimpleCounter(),

		options: options{
			log:             &logger.Logger{Logger: zap.NewNop()},
			maxObjectSize:   defaultMaxObjectSize,
			smallObjectSize: defaultSmallObjectSize,
			workersCount:    defaultFlushWorkersCount,
			maxCacheSize:    defaultMaxCacheSize,
			maxBatchSize:    bbolt.DefaultMaxBatchSize,
			maxBatchDelay:   bbolt.DefaultMaxBatchDelay,
			metrics:         DefaultMetrics(),
		},
	}

	for i := range opts {
		opts[i](&c.options)
	}

	return c
}

// SetLogger sets logger. It is used after the shard ID was generated to use it in logs.
func (c *cache) SetLogger(l *logger.Logger) {
	c.log = l
}

func (c *cache) DumpInfo() Info {
	return Info{
		Path: c.path,
	}
}

// Open opens and initializes database. Reads object counters from the ObjectCounters instance.
func (c *cache) Open(_ context.Context, mod mode.Mode) error {
	c.modeMtx.Lock()
	defer c.modeMtx.Unlock()
	c.mode = mod
	if mod.NoMetabase() {
		return nil
	}
	err := c.openStore(mode.ConvertToComponentModeDegraded(mod))
	if err != nil {
		return metaerr.Wrap(err)
	}
	return metaerr.Wrap(c.initCounters())
}

// Init runs necessary services.
func (c *cache) Init() error {
	c.metrics.SetMode(mode.ConvertToComponentModeDegraded(c.mode))
	if err := c.flushAndDropBBoltDB(context.Background()); err != nil {
		return fmt.Errorf("flush previous version write-cache database: %w", err)
	}
	ctx, cancel := context.WithCancel(context.Background())
	c.cancel.Store(cancel)
	c.runFlushLoop(ctx)
	return nil
}

// Close closes db connection and stops services. Executes ObjectCounters.FlushAndClose op.
func (c *cache) Close() error {
	if cancelValue := c.cancel.Swap(dummyCanceler); cancelValue != nil {
		cancelValue.(context.CancelFunc)()
	}
	// We cannot lock mutex for the whole operation duration
	// because it is taken by some background workers, so `wg.Wait()` is done without modeMtx.
	c.modeMtx.Lock()
	c.mode = mode.DegradedReadOnly // prevent new operations from being processed
	c.modeMtx.Unlock()

	c.wg.Wait()

	c.modeMtx.Lock()
	defer c.modeMtx.Unlock()

	var err error
	if c.fsTree != nil {
		err = c.fsTree.Close()
		if err != nil {
			c.fsTree = nil
		}
	}
	c.metrics.Close()
	return nil
}

func (c *cache) GetMetrics() Metrics {
	return c.metrics
}