package blobovniczatree

import (
	"path/filepath"
	"sync"

	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/blobovnicza"
	utilSync "git.frostfs.info/TrueCloudLab/frostfs-node/pkg/util/sync"
)

type activeDB struct {
	blz  *blobovnicza.Blobovnicza
	shDB *sharedDB
}

func (db *activeDB) Blobovnicza() *blobovnicza.Blobovnicza {
	return db.blz
}

func (db *activeDB) Close() {
	db.shDB.Close()
}

func (db *activeDB) SystemPath() string {
	return db.shDB.SystemPath()
}

// activeDBManager manages active blobovnicza instances (that is, those that are being used for Put).
//
// Uses dbManager for opening/closing sharedDB instances.
// Stores a reference to an open active sharedDB, so dbManager does not close it.
// When changing the active sharedDB, releases the reference to the previous active sharedDB.
type activeDBManager struct {
	levelToActiveDBGuard *sync.RWMutex
	levelToActiveDB      map[string]*sharedDB
	levelLock            *utilSync.KeyLocker[string]
	closed               bool

	dbManager *dbManager
	leafWidth uint64
}

func newActiveDBManager(dbManager *dbManager, leafWidth uint64) *activeDBManager {
	return &activeDBManager{
		levelToActiveDBGuard: &sync.RWMutex{},
		levelToActiveDB:      make(map[string]*sharedDB),
		levelLock:            utilSync.NewKeyLocker[string](),

		dbManager: dbManager,
		leafWidth: leafWidth,
	}
}

// GetOpenedActiveDBForLevel returns active DB for level.
// DB must be closed after use.
func (m *activeDBManager) GetOpenedActiveDBForLevel(lvlPath string) (*activeDB, error) {
	activeDB, err := m.getCurrentActiveIfOk(lvlPath)
	if err != nil {
		return nil, err
	}
	if activeDB != nil {
		return activeDB, nil
	}

	return m.updateAndGetActive(lvlPath)
}

func (m *activeDBManager) Open() {
	m.levelToActiveDBGuard.Lock()
	defer m.levelToActiveDBGuard.Unlock()

	m.closed = false
}

func (m *activeDBManager) Close() {
	m.levelToActiveDBGuard.Lock()
	defer m.levelToActiveDBGuard.Unlock()

	for _, db := range m.levelToActiveDB {
		db.Close()
	}
	m.levelToActiveDB = make(map[string]*sharedDB)
	m.closed = true
}

func (m *activeDBManager) getCurrentActiveIfOk(lvlPath string) (*activeDB, error) {
	m.levelToActiveDBGuard.RLock()
	defer m.levelToActiveDBGuard.RUnlock()

	if m.closed {
		return nil, errClosed
	}

	db, ok := m.levelToActiveDB[lvlPath]
	if !ok {
		return nil, nil
	}

	blz, err := db.Open() // open db for usage, will be closed on activeDB.Close()
	if err != nil {
		return nil, err
	}

	if blz.IsFull() {
		db.Close()
		return nil, nil
	}

	return &activeDB{
		blz:  blz,
		shDB: db,
	}, nil
}

func (m *activeDBManager) updateAndGetActive(lvlPath string) (*activeDB, error) {
	m.levelLock.Lock(lvlPath)
	defer m.levelLock.Unlock(lvlPath)

	current, err := m.getCurrentActiveIfOk(lvlPath)
	if err != nil {
		return nil, err
	}
	if current != nil {
		return current, nil
	}

	nextShDB, err := m.getNextSharedDB(lvlPath)
	if err != nil {
		return nil, err
	}

	if nextShDB == nil {
		return nil, nil
	}

	blz, err := nextShDB.Open() // open db for client, client must call Close() after usage
	if err != nil {
		return nil, err
	}
	return &activeDB{
		blz:  blz,
		shDB: nextShDB,
	}, nil
}

func (m *activeDBManager) getNextSharedDB(lvlPath string) (*sharedDB, error) {
	var idx uint64
	var iterCount uint64
	hasActive, currentIdx := m.hasActiveDB(lvlPath)
	if hasActive {
		idx = (currentIdx + 1) % m.leafWidth
	}

	var next *sharedDB

	for iterCount < m.leafWidth {
		path := filepath.Join(lvlPath, u64ToHexStringExt(idx))
		shDB := m.dbManager.GetByPath(path)
		db, err := shDB.Open() // open db to hold active DB open, will be closed if db is full, after m.replace or by activeDBManager.Close()
		if err != nil {
			return nil, err
		}
		if db.IsFull() {
			shDB.Close()
		} else {
			next = shDB
			break
		}
		idx = (idx + 1) % m.leafWidth
		iterCount++
	}

	previous, updated := m.replace(lvlPath, next)
	if !updated && next != nil {
		next.Close() // manager is closed, so don't hold active DB open
	}
	if updated && previous != nil {
		previous.Close()
	}
	return next, nil
}

func (m *activeDBManager) hasActiveDB(lvlPath string) (bool, uint64) {
	m.levelToActiveDBGuard.RLock()
	defer m.levelToActiveDBGuard.RUnlock()

	if m.closed {
		return false, 0
	}

	db, ok := m.levelToActiveDB[lvlPath]
	if !ok {
		return false, 0
	}
	return true, u64FromHexString(filepath.Base(db.SystemPath()))
}

func (m *activeDBManager) replace(lvlPath string, shDB *sharedDB) (*sharedDB, bool) {
	m.levelToActiveDBGuard.Lock()
	defer m.levelToActiveDBGuard.Unlock()

	if m.closed {
		return nil, false
	}

	previous := m.levelToActiveDB[lvlPath]
	if shDB == nil {
		delete(m.levelToActiveDB, lvlPath)
	} else {
		m.levelToActiveDB[lvlPath] = shDB
	}
	return previous, true
}