package mesh

import (
	"crypto/sha256"
	"encoding/binary"
	"sort"
	"sync"
)

type Rendezvous struct {
	mu    sync.RWMutex
	nodes []string // node IDs
}

func NewRendezvous() *Rendezvous { return &Rendezvous{} }

func (r *Rendezvous) Set(ids []string) {
	r.mu.Lock()
	r.nodes = append([]string(nil), ids...)
	r.mu.Unlock()
}

func (r *Rendezvous) Owners(key string, k int) []string {
	r.mu.RLock()
	ids := append([]string(nil), r.nodes...)
	r.mu.RUnlock()
	if len(ids) == 0 {
		return nil
	}
	type pair struct {
		id string
		w  uint64
	}
	ws := make([]pair, 0, len(ids))
	for _, id := range ids {
		h := sha256.Sum256([]byte(id + "|" + key))
		w := binary.LittleEndian.Uint64(h[:8])
		ws = append(ws, pair{id: id, w: w})
	}
	sort.Slice(ws, func(i, j int) bool { return ws[i].w > ws[j].w })
	if k > len(ws) {
		k = len(ws)
	}
	out := make([]string, 0, k)
	for i := 0; i < k; i++ {
		out = append(out, ws[i].id)
	}
	return out
}