package reward

import (
	"context"
	"crypto/rand"
	"database/sql"
	"log/slog"
	"time"
)

type Granter interface {
	GrantRewardTx(ctx context.Context, tx *sql.Tx, userID int64, days int, source, auditAction, ref string) (int64, time.Time, error)
}

type Config struct{ RegDays, PaidDays, TgDays, RegMonthlyCap int }

type Service struct {
	db  *sql.DB
	st  *Store
	g   Granter
	cfg Config
	now func() time.Time
}

func NewService(db *sql.DB, st *Store, g Granter, cfg Config, now func() time.Time) *Service {
	if now == nil {
		now = func() time.Time { return time.Now().UTC() }
	}
	return &Service{db: db, st: st, g: g, cfg: cfg, now: now}
}

const inviteAlphabet = "ABCDEFGHJKLMNPQRSTUVWXYZ23456789" // 去 0/O/1/I,32 字符

// GenInviteCode 返回 8 位随机码。crypto/rand 失败时用 now 派生兜底(避免 panic)。
func GenInviteCode() string {
	b := make([]byte, 8)
	if _, err := rand.Read(b); err != nil {
		t := time.Now().UnixNano()
		for i := range b {
			b[i] = byte(t >> (8 * i))
		}
	}
	out := make([]byte, 8)
	for i, x := range b {
		out[i] = inviteAlphabet[int(x)%len(inviteAlphabet)]
	}
	return string(out)
}

func (s *Service) EnsureCode(ctx context.Context, userID int64) (string, error) {
	return s.st.EnsureInviteCode(ctx, userID, GenInviteCode)
}

// OnRegister best-effort:与建号解耦(自有事务,失败只 log,不回滚注册)。
func (s *Service) OnRegister(ctx context.Context, inviteeID int64, inviteCode, deviceUUID string) {
	if inviteCode == "" {
		return
	}
	inviterID, ok, err := s.st.ResolveInviteCode(ctx, inviteCode)
	if err != nil || !ok {
		if err != nil {
			slog.Warn("reward: resolve invite code failed", "err", err)
		}
		return // 无效码:静默,不报错(注册已成功)
	}
	if inviterID == inviteeID {
		return // 自邀请:不建关系
	}
	now := s.now()

	// 防刷判定:设备复用 or 月度封顶 → 记关系但 status=rejected、不发注册奖。
	rejected := false
	if used, e := s.st.DeviceUsedByOther(ctx, deviceUUID, inviteeID); e == nil && used {
		rejected = true
	}
	if !rejected {
		monthStart := time.Date(now.Year(), now.Month(), 1, 0, 0, 0, 0, time.UTC)
		if cnt, e := s.st.RegRewardCountThisMonth(ctx, inviterID, monthStart); e == nil && cnt >= s.cfg.RegMonthlyCap {
			rejected = true
		}
	}

	tx, err := s.db.BeginTx(ctx, &sql.TxOptions{})
	if err != nil {
		slog.Warn("reward: begin tx failed", "err", err)
		return
	}
	defer func() { _ = tx.Rollback() }()

	status := "reg_rewarded"
	var regAt *time.Time
	if rejected {
		status = "rejected"
	} else {
		regAt = &now
	}
	if err := s.st.InsertReferralTx(ctx, tx, inviterID, inviteeID, deviceUUID, status, regAt, now); err != nil {
		if err != ErrClaimExists {
			slog.Warn("reward: insert referral failed", "err", err)
		}
		return // invitee 已绑定过(唯一约束)→ 放弃
	}
	if !rejected {
		if _, _, err := s.g.GrantRewardTx(ctx, tx, inviterID, s.cfg.RegDays, "invite", "invite_reg_inviter", "ref-inviter"); err != nil {
			slog.Warn("reward: grant inviter reg failed", "err", err)
			return
		}
		if _, _, err := s.g.GrantRewardTx(ctx, tx, inviteeID, s.cfg.RegDays, "invite", "invite_reg_invitee", "ref-invitee"); err != nil {
			slog.Warn("reward: grant invitee reg failed", "err", err)
			return
		}
	}
	if err := tx.Commit(); err != nil {
		slog.Warn("reward: commit failed", "err", err)
	}
}