// Package stars 实现 Stars 本地账本应用服务：余额查询、贷记/借记、流水分页，
// 以及「惰性首读授予」起始余额（靠 stars_balances.granted 布尔幂等，新老账号都覆盖、
// 无需回填迁移）。原子性由 store 事务保证；本层只做校验 + 授予策略。
package stars

import (
	"context"
	"time"

	"telesrv/internal/domain"
	"telesrv/internal/store"
)

// Service 是 Stars 账本应用服务。
type Service struct {
	store       store.StarsStore
	giftStore   store.StarsGiftPurchaseStore
	grantAmount int64
	now         func() time.Time
}

// Option 配置 Service。
type Option func(*Service)

// WithStartingGrant 设置惰性首读授予的起始余额；amount<=0 关闭自动授予。
func WithStartingGrant(amount int64) Option {
	return func(s *Service) { s.grantAmount = amount }
}

// WithGiftPurchaseStore enables the atomic fiat Stars-gift checkout aggregate.
func WithGiftPurchaseStore(st store.StarsGiftPurchaseStore) Option {
	return func(s *Service) { s.giftStore = st }
}

// WithClock 注入时钟（测试用）。
func WithClock(now func() time.Time) Option {
	return func(s *Service) {
		if now != nil {
			s.now = now
		}
	}
}

// NewService 创建 Stars 账本服务，默认起始授予 domain.DefaultStarsStartingGrant。
func NewService(st store.StarsStore, opts ...Option) *Service {
	s := &Service{store: st, grantAmount: domain.DefaultStarsStartingGrant, now: time.Now}
	for _, opt := range opts {
		opt(s)
	}
	return s
}

// ensureGranted 惰性应用一次起始授予（幂等），返回最新余额。
func (s *Service) ensureGranted(ctx context.Context, userID int64) (domain.StarsBalance, error) {
	if s.grantAmount > 0 {
		bal, _, err := s.store.EnsureGrant(ctx, userID, s.grantAmount, int(s.now().Unix()))
		return bal, err
	}
	return s.store.GetBalance(ctx, userID)
}

// GetBalance 返回账号余额，首读时惰性授予起始余额。
func (s *Service) GetBalance(ctx context.Context, userID int64) (domain.StarsBalance, error) {
	return s.ensureGranted(ctx, userID)
}

// Credit 为账号入账（amount>0）。
func (s *Service) Credit(ctx context.Context, userID, amount int64, reason domain.StarsTransactionReason, peer domain.Peer, title, desc string) (domain.StarsBalance, error) {
	if amount <= 0 {
		return domain.StarsBalance{}, domain.ErrStarsInvalidAmount
	}
	return s.store.Credit(ctx, userID, amount, reason, peer, int(s.now().Unix()), title, desc)
}

// Debit 从账号扣款（amount>0），余额不足返回 domain.ErrStarsInsufficient。
// 先确保起始授予已应用，避免新账号在尚未首读余额前借记被误判余额不足。
func (s *Service) Debit(ctx context.Context, userID, amount int64, reason domain.StarsTransactionReason, peer domain.Peer, title, desc string) (domain.StarsBalance, error) {
	if amount <= 0 {
		return domain.StarsBalance{}, domain.ErrStarsInvalidAmount
	}
	if _, err := s.ensureGranted(ctx, userID); err != nil {
		return domain.StarsBalance{}, err
	}
	return s.store.Debit(ctx, userID, amount, reason, peer, int(s.now().Unix()), title, desc)
}

// ListTransactions 按方向与顺序做 keyset 分页，首读时惰性授予。
func (s *Service) ListTransactions(ctx context.Context, userID int64, query domain.StarsTransactionQuery) (domain.StarsTransactionPage, error) {
	query, err := domain.NormalizeStarsTransactionQuery(query)
	if err != nil {
		return domain.StarsTransactionPage{}, err
	}
	if _, err := s.ensureGranted(ctx, userID); err != nil {
		return domain.StarsTransactionPage{}, err
	}
	return s.store.ListTransactions(ctx, userID, query)
}

// IssueGiftPurchaseForm persists a short-lived, exact checkout intent.
func (s *Service) IssueGiftPurchaseForm(ctx context.Context, form domain.StarsGiftPurchaseForm) (domain.StarsGiftPurchaseForm, error) {
	if s.giftStore == nil || form.BuyerUserID <= 0 || form.RecipientUserID <= 0 ||
		form.BuyerUserID == form.RecipientUserID || form.Stars <= 0 || form.Amount <= 0 ||
		form.Currency == "" || form.IssuedAt <= 0 || form.ExpiresAt != form.IssuedAt+600 {
		return domain.StarsGiftPurchaseForm{}, domain.ErrStarsGiftFormInvalid
	}
	return s.giftStore.IssueStarsGiftPurchaseForm(ctx, form)
}

// PurchaseGift settles one exact persisted form. Package validation remains at
// the RPC boundary as well, while the store revalidates the persisted tuple
// under lock before performing any write.
func (s *Service) PurchaseGift(ctx context.Context, req domain.StarsGiftPurchaseRequest) (domain.StarsGiftPurchaseResult, error) {
	if s.giftStore == nil || req.FormID == 0 || req.BuyerUserID <= 0 || req.RecipientUserID <= 0 ||
		req.BuyerUserID == req.RecipientUserID || req.Stars <= 0 || req.Amount <= 0 ||
		req.Currency == "" || req.Date <= 0 {
		return domain.StarsGiftPurchaseResult{}, domain.ErrStarsGiftFormInvalid
	}
	return s.giftStore.PurchaseStarsGift(ctx, req)
}