// Copyright GoFrame Author(https://goframe.org). All Rights Reserved.
//
// This Source Code Form is subject to the terms of the MIT License.
// If a copy of the MIT was not distributed with this file,
// You can obtain one at https://github.com/gogf/gf.

package gsel

import (
	"context"
	"sync"

	"github.com/gogf/gf/v2/container/gtype"
)

const SelectorLeastConnection = "BalancerLeastConnection"

type selectorLeastConnection struct {
	mu    sync.RWMutex
	nodes []*leastConnectionNode
}

type leastConnectionNode struct {
	Node
	inflight *gtype.Int
}

func NewSelectorLeastConnection() Selector {
	return &selectorLeastConnection{
		nodes: make([]*leastConnectionNode, 0),
	}
}

func (s *selectorLeastConnection) Update(nodes []Node) error {
	var newNodes []*leastConnectionNode
	for _, v := range nodes {
		node := v
		newNodes = append(newNodes, &leastConnectionNode{
			Node:     node,
			inflight: gtype.NewInt(),
		})
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	s.nodes = newNodes
	return nil
}

func (s *selectorLeastConnection) Pick(ctx context.Context) (node Node, done DoneFunc, err error) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	var pickedNode *leastConnectionNode
	if len(s.nodes) == 1 {
		pickedNode = s.nodes[0]
	} else {
		for _, v := range s.nodes {
			if pickedNode == nil {
				pickedNode = v
			} else if v.inflight.Val() < pickedNode.inflight.Val() {
				pickedNode = v
			}
		}
	}
	pickedNode.inflight.Add(1)
	done = func(ctx context.Context, di DoneInfo) {
		pickedNode.inflight.Add(-1)
	}
	return pickedNode.Node, done, nil
}