package writecachebadger

import (
	"encoding/binary"
	"sync"

	"git.frostfs.info/TrueCloudLab/frostfs-node/internal/logs"
	"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/local_object_storage/writecache"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/util/logger"
	objectSDK "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
	"go.uber.org/zap"
)

type cache struct {
	options

	mode    mode.Mode
	modeMtx sync.RWMutex

	// flushCh is a channel with objects to flush.
	flushCh chan *objectSDK.Object
	// closeCh is close channel, protected by modeMtx.
	closeCh chan struct{}
	// wg is a wait group for flush workers.
	wg sync.WaitGroup
	// initCounterWG is necessary to wait for asynchronous initialization.
	initCounterWG sync.WaitGroup
	// store contains underlying database.
	store
}

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

type objectInfo struct {
	addr oid.Address
	data []byte
	obj  *objectSDK.Object
}

const (
	defaultMaxObjectSize   = 64 << 20 // 64 MiB
	defaultSmallObjectSize = 32 << 10 // 32 KiB
	defaultMaxCacheSize    = 1 << 30  // 1 GiB
)

// New creates new writecache instance.
func New(opts ...Option) writecache.Cache {
	c := &cache{
		flushCh: make(chan *objectSDK.Object),
		mode:    mode.ReadWrite,

		options: options{
			log:           &logger.Logger{Logger: zap.NewNop()},
			maxObjectSize: defaultMaxObjectSize,
			workersCount:  defaultFlushWorkersCount,
			maxCacheSize:  defaultMaxCacheSize,
			metrics:       writecache.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() writecache.Info {
	return writecache.Info{
		Path: c.path,
	}
}

// Open opens and initializes database. Reads object counters from the ObjectCounters instance.
func (c *cache) Open(readOnly bool) error {
	err := c.openStore(readOnly)
	if err != nil {
		return metaerr.Wrap(err)
	}

	// Opening after Close is done during maintenance mode,
	// thus we need to create a channel here.
	c.closeCh = make(chan struct{})

	return metaerr.Wrap(c.initCounters())
}

// Init runs necessary services.
func (c *cache) Init() error {
	c.log.Info(logs.WritecacheBadgerInitExperimental)
	c.metrics.SetMode(c.mode)
	c.runFlushLoop()
	c.runGCLoop()
	return nil
}

// flushKeysCount writes the keys count to db if it should be flushed down.
func (c *cache) flushKeysCount() {
	// Close may happen after resetting mode
	if c.db.IsClosed() {
		return
	}

	if c.objCounters.isReadyToFlush() {
		k := keyCountPrefix
		v := make([]byte, 8)
		binary.LittleEndian.PutUint64(v, c.objCounters.DB())
		if err := c.putRaw(k[:], v); err != nil {
			c.log.Error(logs.WritecacheBadgerCouldNotFlushKeysCount, zap.Error(err))
		}
	}
}

// Close closes db connection and stops services. Executes ObjectCounters.FlushAndClose op.
func (c *cache) Close() error {
	c.cancelInitCountByCloseAndWait()

	c.flushKeysCount()

	// 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()
	if c.closeCh != nil {
		close(c.closeCh)
	}
	c.mode = mode.DegradedReadOnly // prevent new operations from being processed
	c.modeMtx.Unlock()

	c.wg.Wait()

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

	c.closeCh = nil
	var err error
	if c.db != nil {
		err = c.db.Close()
		if err != nil {
			c.db = nil
		}
	}
	c.metrics.Close()

	return nil
}

// cancelInitCountByCloseAndWait cancels the counting process if Close is invoked
// and waits for correct finish of goroutine within initCount.
func (c *cache) cancelInitCountByCloseAndWait() {
	c.objCounters.cDB.cancelByClose()
	c.initCounterWG.Wait()
}