feat: implement multi-user credits redeem and storage isolation

2026-09-17 02:18:49 +08:00
parent 7628390966
commit 8b31956c6d
12 changed files with 624 additions and 28 deletions
@@ -0,0 +1,138 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"strconv"
+	"time"
+
+	"gorm.io/gorm"
+)
+
+var (
+	errInsufficientCredits = errors.New("insufficient credits")
+	errReservationState    = errors.New("invalid credit reservation state")
+)
+
+// reserveCredit places one credit on hold for a task. The hold is released on
+// failure or converted into a debit after a successful new download.
+func (a *App) reserveCredit(userID, taskID uint, amount int64) (*CreditReservation, error) {
+	if amount <= 0 {
+		return nil, fmt.Errorf("invalid credit amount")
+	}
+	var reservation CreditReservation
+	err := a.db.Transaction(func(tx *gorm.DB) error {
+		var account CreditAccount
+		if err := tx.Where("user_id = ?", userID).First(&account).Error; err != nil {
+			if !errors.Is(err, gorm.ErrRecordNotFound) {
+				return err
+			}
+			account = CreditAccount{UserID: userID}
+			if err := tx.Create(&account).Error; err != nil {
+				return err
+			}
+		}
+		var existing CreditReservation
+		if err := tx.Where("task_id = ?", taskID).First(&existing).Error; err == nil {
+			reservation = existing
+			return nil
+		} else if !errors.Is(err, gorm.ErrRecordNotFound) {
+			return err
+		}
+		if account.Balance-account.Reserved < amount {
+			return errInsufficientCredits
+		}
+		account.Reserved += amount
+		if err := tx.Save(&account).Error; err != nil {
+			return err
+		}
+		reservation = CreditReservation{UserID: userID, TaskID: taskID, Amount: amount, Status: "reserved"}
+		if err := tx.Create(&reservation).Error; err != nil {
+			return err
+		}
+		return tx.Create(&CreditTransaction{UserID: userID, Type: "reserve", Amount: 0, BalanceAfter: account.Balance, ReferenceType: "task", ReferenceID: strconv.FormatUint(uint64(taskID), 10), Reason: "download reservation"}).Error
+	})
+	return &reservation, err
+}
+
+func (a *App) commitCredit(task *Task) error {
+	if task.CreditReservationID == 0 {
+		return nil
+	}
+	return a.db.Transaction(func(tx *gorm.DB) error {
+		var r CreditReservation
+		if err := tx.First(&r, task.CreditReservationID).Error; err != nil {
+			return err
+		}
+		if r.Status == "committed" {
+			return nil
+		}
+		if r.Status != "reserved" {
+			return errReservationState
+		}
+		var account CreditAccount
+		if err := tx.Where("user_id = ?", r.UserID).First(&account).Error; err != nil {
+			return err
+		}
+		account.Reserved -= r.Amount
+		account.Balance -= r.Amount
+		if account.Reserved < 0 || account.Balance < 0 {
+			return errReservationState
+		}
+		if err := tx.Save(&account).Error; err != nil {
+			return err
+		}
+		now := time.Now()
+		r.Status, r.CompletedAt = "committed", &now
+		if err := tx.Save(&r).Error; err != nil {
+			return err
+		}
+		return tx.Create(&CreditTransaction{UserID: r.UserID, Type: "debit", Amount: -r.Amount, BalanceAfter: account.Balance, ReferenceType: "task", ReferenceID: strconv.FormatUint(uint64(task.ID), 10), Reason: "successful download"}).Error
+	})
+}
+
+// refundCredit releases a reservation without debiting the user's balance.
+// It is idempotent so download failure paths can safely call fail repeatedly.
+func (a *App) refundCredit(task *Task) error {
+	if task.CreditReservationID == 0 {
+		return nil
+	}
+	return a.db.Transaction(func(tx *gorm.DB) error {
+		var r CreditReservation
+		if err := tx.First(&r, task.CreditReservationID).Error; err != nil {
+			return err
+		}
+		if r.Status == "refunded" {
+			return nil
+		}
+		if r.Status == "committed" {
+			return errReservationState
+		}
+		if r.Status != "reserved" {
+			return errReservationState
+		}
+		var account CreditAccount
+		if err := tx.Where("user_id = ?", r.UserID).First(&account).Error; err != nil {
+			return err
+		}
+		account.Reserved -= r.Amount
+		if account.Reserved < 0 {
+			return errReservationState
+		}
+		if err := tx.Save(&account).Error; err != nil {
+			return err
+		}
+		now := time.Now()
+		r.Status, r.CompletedAt = "refunded", &now
+		if err := tx.Save(&r).Error; err != nil {
+			return err
+		}
+		return tx.Create(&CreditTransaction{UserID: r.UserID, Type: "refund", Amount: 0, BalanceAfter: account.Balance, ReferenceType: "task", ReferenceID: strconv.FormatUint(uint64(task.ID), 10), Reason: "download failed"}).Error
+	})
+}
+
+func (a *App) creditBalance(userID uint) (CreditAccount, error) {
+	var account CreditAccount
+	err := a.db.Where("user_id = ?", userID).First(&account).Error
+	return account, err
+}