package consistenthash
import (
	"hash/crc32"
	"sort"
)
// HashFunc defines function to generate hash code
type HashFunc func(data []byte) uint32
// NodeMap consistent hash hashFunc and you can pick node form NodeMap
type NodeMap struct {
	hashFUnc    HashFunc
	nodeHashs   []int          // sorted
	nodehashMap map[int]string // 通過節(jié)點 找到具體的hash 值
}
func NewNodeMap(fn HashFunc) *NodeMap {
	nodeMap := &NodeMap{
		hashFUnc:    fn,
		nodehashMap: make(map[int]string),
	}
	// default func
	if nodeMap.hashFUnc == nil {
		nodeMap.hashFUnc = crc32.ChecksumIEEE
	}
	return nodeMap
}
func (m *NodeMap) IsEmpty() bool {
	return len(m.nodeHashs) == 0
}
func (m *NodeMap) AddNode(keys ...string) {
	for _, key := range keys {
		if key == "" {
			continue
		}
		hash := int(m.hashFUnc([]byte(key)))
		m.nodeHashs = append(m.nodeHashs, hash)
		m.nodehashMap[hash] = key
	}
	sort.Ints(m.nodeHashs)
}
func (m *NodeMap) PickNode(key string) string {
	if m.IsEmpty() {
		return ""
	}
	hash := int(m.hashFUnc([]byte(key)))
	// Binary Search sorted hash
	idx := sort.Search(len(m.nodeHashs), func(i int) bool {
		return m.nodeHashs[i] >= hash
	})
	if idx == len(m.nodeHashs) {
		idx = 0
	}
	return m.nodehashMap[m.nodeHashs[idx]]
}