package rands

import (
	"math/rand/v2"
	"time"
)

var (
	rad = rand.New(rand.NewPCG(uint64(time.Now().Unix()), uint64(time.Now().UnixNano())))
)

// Choice 一个选项包含一个泛型项以及一个权重，该权重用于控制其被选中的频率
type Choice[W int | int32 | int64, T any] struct {
	Weight W
	Item   T
}

// WeightedChoice 加权随机选择, 从所提供的选项中返回一个选项, 权重值为 0 的选项永远不会被选中
// Based on this algorithm: http://eli.thegreenplace.net/2010/01/22/weighted-random-generation-in-python/
func WeightedChoice[W int | int32 | int64, T any](choices []Choice[W, T], rd ...*rand.Rand) (ret Choice[W, T], ok bool) {
	sum := int64(0)
	for _, c := range choices {
		sum += int64(c.Weight)
	}
	crd := rad
	if len(rd) > 0 && rd[0] != nil {
		crd = rd[0]
	}
	r := crd.Int64N(sum)
	for _, c := range choices {
		r -= int64(c.Weight)
		if r < 0 {
			return c, true
		}
	}
	return
}