package accounts

import (
	"hash/fnv"

	"github.com/wangjia/pay/config"
)

// Weighted 按 Weight 加权选账户,决策源为 hash(OutTradeNo)(确定性、可复现、跨节点一致,
// 见计划 D1)。Weight<=0 记 1(对齐 model.Account gorm default:1)。retry 换号由
// Router 的 ExcludeAccounts 过滤驱动,不依赖随机。
type Weighted struct{}

func NewWeighted() *Weighted { return &Weighted{} }

func (Weighted) Pick(_ string, candidates []config.AccountConfig, hint PickHint) (config.AccountConfig, error) {
	if len(candidates) == 0 {
		return config.AccountConfig{}, ErrNoAccount
	}
	if hint.OutTradeNo == "" {
		return candidates[0], nil
	}
	var total uint32
	for _, c := range candidates {
		total += weightOf(c)
	}
	if total == 0 { // 理论不达(weightOf>=1),兜底
		return candidates[0], nil
	}
	h := fnv.New32a()
	_, _ = h.Write([]byte(hint.OutTradeNo))
	target := h.Sum32() % total
	var acc uint32
	for _, c := range candidates {
		acc += weightOf(c)
		if target < acc {
			return c, nil
		}
	}
	return candidates[len(candidates)-1], nil // 浮点无关的整数走位,兜底不达
}

func weightOf(c config.AccountConfig) uint32 {
	if c.Weight <= 0 {
		return 1
	}
	return uint32(c.Weight)
}