package locks

import (
	"sync"
)

// Number of lock shards for reducing contention
const NumLockShards = 32

// GetShardIndex returns the shard index for a given key using FNV-1a hash
func GetShardIndex(key string) int {
	// Use FNV-1a hash for good distribution
	var h uint32 = 2166136261 // FNV offset basis
	for i := 0; i < len(key); i++ {
		h ^= uint32(key[i])
		h *= 16777619 // FNV prime
	}
	return int(h % NumLockShards)
}

// GetKeyLock returns a lock for the given key using sharding
func GetKeyLock(keyLocks []sync.Map, key string) *sync.RWMutex {
	shardIndex := GetShardIndex(key)
	shard := &keyLocks[shardIndex]

	keyLock, _ := shard.LoadOrStore(key, &sync.RWMutex{})
	return keyLock.(*sync.RWMutex)
}