package writecache

import (
	"context"
	"os"
	"sync"

	"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"
	objectSDK "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
	"go.etcd.io/bbolt"
	"go.uber.org/zap"
)

type cache struct {
	options

	// mtx protects statistics, counters and compressFlags.
	mtx sync.RWMutex

	mode    mode.Mode
	modeMtx sync.RWMutex

	// compressFlags maps address of a big object to boolean value indicating
	// whether object should be compressed.
	compressFlags map[string]struct{}

	// flushCh is a channel with objects to flush.
	flushCh chan objectInfo
	// cancel is cancel function, protected by modeMtx in Close.
	cancel func()
	// wg is a wait group for flush workers.
	wg sync.WaitGroup
	// store contains underlying database.
	store
	// fsTree contains big files stored directly on file-system.
	fsTree *fstree.FSTree
}

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

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

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

var defaultBucket = []byte{0}

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

		compressFlags: make(map[string]struct{}),
		options: options{
			log:             &logger.Logger{Logger: zap.NewNop()},
			maxObjectSize:   defaultMaxObjectSize,
			smallObjectSize: defaultSmallObjectSize,
			workersCount:    defaultFlushWorkersCount,
			maxCacheSize:    defaultMaxCacheSize,
			maxBatchSize:    bbolt.DefaultMaxBatchSize,
			maxBatchDelay:   bbolt.DefaultMaxBatchDelay,
			openFile:        os.OpenFile,
			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, mode mode.Mode) error {
	c.modeMtx.Lock()
	defer c.modeMtx.Unlock()
	c.mode = mode
	if mode.NoMetabase() {
		return nil
	}
	err := c.openStore(mode.ReadOnly())
	if err != nil {
		return metaerr.Wrap(err)
	}

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

// Init runs necessary services.
func (c *cache) Init() error {
	c.metrics.SetMode(c.mode)
	ctx, cancel := context.WithCancel(context.Background())
	c.cancel = cancel
	c.runFlushLoop(ctx)
	return nil
}

// Close closes db connection and stops services. Executes ObjectCounters.FlushAndClose op.
func (c *cache) Close() error {
	// 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.cancel != nil {
		c.cancel()
		c.cancel = nil
	}
	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.db != nil {
		err = c.db.Close()
		if err != nil {
			c.db = nil
		}
	}
	c.metrics.Close()
	return nil
}

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