transaction.go

package db

import (
	"errors"
	"fmt"
	"log"
	"time"

	"gorm.io/gorm"
	"gorm.io/gorm/clause"
)

type Transaction struct {
	gorm.Model
	MemberNum int       `json:"-" gorm:"column:member"`
	Member    *Member   `json:"member,omitempty" gorm:"foreignKey:MemberNum;references:Num"`
	Date      time.Time `json:"date"`
	Total     int       `json:"total"`
	Type      string    `json:"type"`
	ProxyNum  int       `json:"-" gorm:"column:proxy"`
	Proxy     *Member   `json:"proxy,omitempty" gorm:"foreignKey:ProxyNum;references:Num"`

	Purchase      []Purchase      `json:"purchase,omitempty"`
	Topup         *Topup          `json:"topup,omitempty"`
	OrderPurchase []OrderPurchase `json:"order_purchase,omitempty" gorm:"foreignKey:TransactionID;constraint:OnDelete:CASCADE"`
	Order         *Order          `json:"order,omitempty" gorm:"constraint:OnDelete:CASCADE"`
	OrderID       *uint           `json:"-"`
	Refund        *Order          `json:"refund,omitempty" gorm:"foreignKey:TransactionID"`
}

type Topup struct {
	gorm.Model    `json:"-"`
	TransactionID uint   `json:"-" gorm:"column:transaction"`
	Comment       string `json:"comment"`
}

type Purchase struct {
	gorm.Model    `json:"-"`
	TransactionID uint    `json:"-" gorm:"column:transaction"`
	ProductCode   int     `json:"code" gorm:"column:product"`
	Product       Product `json:"product" gorm:"foreignKey:ProductCode;references:Code"`
	Price         int     `json:"price"`
	Amount        int     `json:"amount"`
}

func (d *DB) ListTransactions() (transactions []Transaction, err error) {
	err = d.transactionQuery().
		Order("date desc").
		Find(&transactions).Error
	return
}

func (d *DB) TransactionByMember(num int) (transactions []Transaction, err error) {
	err = d.transactionQuery().
		Where("member = ?", num).
		Order("date desc").
		Find(&transactions).Error
	return
}

func (d *DB) GetTransaction(id int) (transaction Transaction, err error) {
	err = d.transactionQuery().
		First(&transaction, id).Error
	if errors.Is(err, gorm.ErrRecordNotFound) {
		err = ErrorNotFound
	}
	return
}

func (d *DB) AddTopup(adminNum int, memberNum int, amount int, comment string) (transaction Transaction, err error) {
	transaction = Transaction{
		MemberNum: memberNum,
		ProxyNum:  adminNum,
		Date:      time.Now(),
		Topup: &Topup{
			Comment: comment,
		},
		Type:  "topup",
		Total: amount,
	}
	err = createTransaction(d.db, &transaction)
	return
}

func (d *DB) AddPurchase(adminNum int, memberNum int, purchase []Purchase) (transaction Transaction, err error) {
	total := 0
	for i, p := range purchase {
		var product Product
		err = d.db.Where("code = ?", p.ProductCode).First(&product).Error
		if err != nil {
			log.Printf("Can't get product %d: %v", p.ProductCode, err)
			err = ErrorNotFound
			return
		}

		total += product.Price * p.Amount
		purchase[i].Price = product.Price
	}
	if total == 0 {
		log.Printf("Empty purchase (%d)", memberNum)
		err = ErrorInvalidRequest
		return
	}

	transaction = Transaction{
		MemberNum: memberNum,
		ProxyNum:  adminNum,
		Date:      time.Now(),
		Purchase:  purchase,
		Type:      "purchase",
		Total:     -total,
	}
	err = d.db.Transaction(func(tx *gorm.DB) error {
		err := createTransaction(tx, &transaction)
		if err != nil {
			return err
		}

		for _, p := range purchase {
			err = tx.Model(&Product{}).
				Where("code = ?", p.ProductCode).
				Update("stock", gorm.Expr("stock - ?", p.Amount)).Error
			if err != nil {
				return fmt.Errorf("Can't update product stock %d-%d: %v", p.ProductCode, p.Amount, err)
			}
		}
		return nil
	})
	return
}

func (d *DB) transactionQuery() *gorm.DB {
	return d.db.Preload("Purchase.Product").
		Preload("Order.Products").
		Preload("OrderPurchase.OrderProduct.Product").
		Preload(clause.Associations)
}

func createTransaction(db *gorm.DB, transaction *Transaction) error {
	return db.Transaction(func(tx *gorm.DB) error {
		err := updateMemberBalance(tx, transaction.MemberNum, transaction.Total)
		if err != nil {
			return err
		}
		return tx.Create(&transaction).Error
	})
}

func updateMemberBalance(tx *gorm.DB, memberNum int, amount int) error {
	var member Member
	err := tx.Where("num = ?", memberNum).Find(&member).Error
	if err != nil {
		log.Printf("Can't find member for transaction %d: %v", memberNum, err)
		return ErrorNotFound
	}
	if member.Balance < -amount {
		log.Printf("Member %d don't have enough money (%d-%d)", member.Num, member.Balance, amount)
		return ErrorInvalidRequest
	}
	err = tx.Model(&Member{}).
		Where("num = ?", memberNum).
		Update("balance", gorm.Expr("balance + ?", amount)).Error
	if err != nil {
		log.Printf("Can't update update member balance %d-%d: %v", member.Num, amount, err)
	}
	return err
}