sharding

type Cluster[KeyType ID, ConnType any] interface {

	// All returns all shards.
	All() []Shard[ConnType]

	// One returns Shard by key.
	One(key KeyType) Shard[ConnType]

	// Each runs fn on each shard within cluster.
	Each(fn func(s Shard[ConnType]) error) error

	// Map takes a list of identifiers and returns a map[] where the key is the corresponding
	// shard and the value is a slice of ids that belong to shard.
	Map(ids []KeyType) map[Shard[ConnType]][]KeyType

	// ByKeys executes fn on each result of Map func.
	ByKeys(ids []KeyType, fn func([]KeyType, Shard[ConnType]) error) error
}

type Config[KeyType ID, ConnType any] struct {
	Connect  ConnectFunc[ConnType]       // required. connection func
	Shards   []ShardConfig               // required. shards config.
	Context  context.Context             // optional. defaults to context.Background()
	Strategy Strategy[KeyType, ConnType] // optional. defaults to defaultStrategy.
}

type ConnectFunc[ConnType any] func(ctx context.Context, addr string) (ConnType, error)

type Hash[KeyType ID] interface {
	Sum(key KeyType) uint64
}

type ID interface {
	string | []byte | int64 | uint64
}

type Shard[ConnType any] interface {
	ID() int64
	Conn() ConnType
}

type ShardConfig struct {
	ID   int64  `json:"id"`
	Addr string `json:"dsn"`
}

type Strategy[KeyType ID, ConnType any] interface {

	// Find shard by key.
	Find(key KeyType, shards []Shard[ConnType]) Shard[ConnType]
}