Weighted Distribution across servers

weighted-distribution.go

package main

import (
	"container/heap"
	"fmt"
)

type Server struct {
	name     string
	priority int
	index    int
}

type PriorityQueue []*Server

func (pq PriorityQueue) Len() int { return len(pq) }
func (pq PriorityQueue) Less(i, j int) bool {
	return pq[i].priority > pq[j].priority
}
func (pq PriorityQueue) Swap(i, j int) {
	pq[i], pq[j] = pq[j], pq[i]
	pq[i].index = i
	pq[j].index = j
}

func (pq *PriorityQueue) Push(x interface{}) {
	n := len(*pq)
	server := x.(*Server)
	server.index = n
	*pq = append(*pq, server)
}

func (pq *PriorityQueue) Pop() interface{} {
	old := *pq
	n := len(old)
	server := old[n-1]
	server.index = -1
	*pq = old[0 : n-1]
	return server
}

func (pq *PriorityQueue) update(server *Server, name string, priority int) {
	server.name = name
	server.priority = priority
	heap.Fix(pq, server.index)
}

func main() {
	servers := map[string]int{
		"svc1": 5,
		"svc2": 2,
		"svc3": 7,
	}

	pq := make(PriorityQueue, len(servers))
	i := 0
	totalWeight := 0
	for name, priority := range servers {
		pq[i] = &Server{
			name:     name,
			priority: priority,
			index:    i,
		}
		i++
		totalWeight += priority
	}

	heap.Init(&pq)

	for i := 0; i < totalWeight; i++ {
		server := heap.Pop(&pq).(*Server)
		serverPriority := server.priority - 1
		newServer := &Server{
			name:     server.name,
			priority: serverPriority,
			index:    server.index,
		}

		heap.Push(&pq, newServer)
		fmt.Printf("Server selected: %s\n", server.name)
	}

}