131 lines
3.8 KiB
Go
131 lines
3.8 KiB
Go
package lotteryengine
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import (
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crand "crypto/rand"
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"errors"
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"math/big"
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"strings"
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)
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const (
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PrizeKindCoin = "coin"
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PrizeKindGift = "gift"
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PrizeKindProp = "prop"
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PrizeKindDress = "dress"
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)
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var (
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ErrNoCandidate = errors.New("lottery candidate is empty")
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ErrInvalidWeight = errors.New("lottery candidate weight is invalid")
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)
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// Candidate 是抽奖引擎唯一关心的奖档视图。
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// 业务模块负责在进入引擎前完成资格、奖池和风控过滤；引擎只保证权重随机和 RTP 计值口径一致。
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type Candidate struct {
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ID string
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Weight int64
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PrizeKind string
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RTPValueCoins int64
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}
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// NormalizeCandidates 复制并清洗候选集，避免调用方的业务快照被引擎内部兜底权重改写。
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// 全部候选权重都为 0 时退化成等权随机，是为了兼容旧配置或脏数据；负权重直接拒绝，防止配置错误改变概率方向。
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func NormalizeCandidates(candidates []Candidate) ([]Candidate, error) {
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if len(candidates) == 0 {
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return nil, ErrNoCandidate
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}
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out := make([]Candidate, 0, len(candidates))
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var totalWeight int64
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for _, candidate := range candidates {
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if candidate.Weight < 0 {
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return nil, ErrInvalidWeight
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}
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candidate.PrizeKind = NormalizePrizeKind(candidate.PrizeKind)
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candidate.RTPValueCoins = NormalizeRTPValueCoins(candidate.PrizeKind, candidate.RTPValueCoins)
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if candidate.Weight > 0 {
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totalWeight += candidate.Weight
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out = append(out, candidate)
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}
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}
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if totalWeight > 0 {
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return out, nil
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}
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out = out[:0]
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for _, candidate := range candidates {
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candidate.PrizeKind = NormalizePrizeKind(candidate.PrizeKind)
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candidate.RTPValueCoins = NormalizeRTPValueCoins(candidate.PrizeKind, candidate.RTPValueCoins)
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candidate.Weight = 1
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out = append(out, candidate)
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}
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return out, nil
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}
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// SelectWeighted 从已经归一化的候选中按权重抽一档。
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// 随机源使用 crypto/rand，避免高价值奖档被时间种子或并发顺序预测。
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func SelectWeighted(candidates []Candidate) (Candidate, error) {
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normalized, err := NormalizeCandidates(candidates)
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if err != nil {
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return Candidate{}, err
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}
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var totalWeight int64
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for _, candidate := range normalized {
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totalWeight += candidate.Weight
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}
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if totalWeight <= 0 {
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return Candidate{}, ErrNoCandidate
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}
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index, err := secureIndex(totalWeight)
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if err != nil {
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return Candidate{}, err
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}
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for _, candidate := range normalized {
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if index < candidate.Weight {
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return candidate, nil
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}
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index -= candidate.Weight
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}
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return normalized[len(normalized)-1], nil
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}
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// NormalizePrizeKind 把后台和活动配置里的同义奖品类型收敛到引擎内部口径。
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// prop 和 dress 都表示装扮/道具类权益，后续发放可以不同，但 RTP 口径必须一致归零。
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func NormalizePrizeKind(kind string) string {
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switch strings.ToLower(strings.TrimSpace(kind)) {
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case PrizeKindCoin:
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return PrizeKindCoin
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case PrizeKindGift:
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return PrizeKindGift
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case PrizeKindProp, "item", "decoration", "resource":
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return PrizeKindProp
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case PrizeKindDress, "dress_up", "costume":
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return PrizeKindDress
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default:
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return strings.ToLower(strings.TrimSpace(kind))
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}
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}
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// NormalizeRTPValueCoins 是转盘和其它抽奖共用的 RTP 计值入口。
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// 装扮/道具无论后台配置了多少展示价值，都不能进入 RTP 返奖分子；金币和礼物保留配置值，负数按 0 处理。
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func NormalizeRTPValueCoins(kind string, value int64) int64 {
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if value < 0 {
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value = 0
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}
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switch NormalizePrizeKind(kind) {
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case PrizeKindProp, PrizeKindDress:
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return 0
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default:
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return value
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}
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}
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func secureIndex(totalWeight int64) (int64, error) {
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if totalWeight <= 0 {
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return 0, ErrNoCandidate
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}
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n, err := crand.Int(crand.Reader, big.NewInt(totalWeight))
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if err != nil {
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return 0, err
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}
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return n.Int64(), nil
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}
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