coinDB.go

package main

import (
	"context"
	_ "github.com/mattn/go-sqlite3"
	"log"
	"time"
)

func awardCoin(award *awardRequest) error {

	ctx := context.Background()

	tx, err := db.BeginTx(ctx, nil)
	if err != nil {
		log.Println(err)
		return err
	}

	// ignore rollback if the tx has been commited later in the function
	defer tx.Rollback()

	awardStatement, err := tx.Prepare("UPDATE students SET Coins = Coins + ? WHERE Rollno = ? ")
	if err != nil {
		log.Println("error while preparing award statement")

		tx.Rollback()
		return err
	}
	defer awardStatement.Close()

	_, err = awardStatement.Exec(award.Award, award.Rollno)
	if err != nil {
		log.Println("error while awarding the student")

		tx.Rollback()
		return err
	}

	// TODO : Find a way to use these function in the
	// transactions directly. Right now any such function call
	// will read values which are not updated i.e. outside transactions
	activityStatement, err := tx.Prepare("UPDATE students SET Activity = Activity + 1 WHERE Rollno = ? ")
	if err != nil {
		log.Println("error while preparing activity statement")
		tx.Rollback()
		return err
	}
	defer activityStatement.Close()

	// Roll no are unique so atmax 1 row will be updated
	_, err = activityStatement.Exec(award.Rollno)
	if err != nil {
		log.Println("error while updating student activity")
		return err
	}

	// Update award table
	recordStatement, err := tx.Prepare("INSERT INTO awards ( Time, AwardeeRollno, Amount ) VALUES(?,?,?)")
	if err != nil {
		log.Println("error while preparing award statement")

		tx.Rollback()
		return err
	}

	defer recordStatement.Close()

	_, err = recordStatement.Exec(time.Now(), award.Rollno, award.Award)
	if err != nil {
		log.Println("error while recording the award the student")

		tx.Rollback()
		return err
	}

	err = tx.Commit()
	return err
}

func transferCoin(transfer *transferRequest) error {

	ctx := context.Background()

	tx, err := db.BeginTx(ctx, nil)
	if err != nil {
		log.Println(err)
		return err
	}

	// ignore rollback if the tx has been commited later in the function
	defer tx.Rollback()

	// Update sender balance
	senderStatement, err := tx.Prepare("UPDATE students SET Coins = Coins - ? WHERE Rollno = ? ")
	if err != nil {
		log.Println("error while preparing award statement for sender")

		tx.Rollback()
		return err
	}
	defer senderStatement.Close()

	_, err = senderStatement.Exec(transfer.Amount, transfer.FromRollno)
	if err != nil {
		log.Println("error while updating sender info")

		tx.Rollback()
		return err
	}
	// update Reciever balance
	recieverStatement, err := tx.Prepare("UPDATE students SET Coins = Coins + ? WHERE Rollno = ? ")
	if err != nil {
		log.Println("error while preparing statement for reciever")

		tx.Rollback()
		return err
	}
	defer recieverStatement.Close()

	if sameBatch(transfer.FromRollno, transfer.ToRollno) {
		// A transfer between two people will lead
		// to destruction of 2% _coin involved in the form of taxes.
		transfer.Amount = (98 * transfer.Amount) / 100
	} else {
		// Across the batch transfer will cause a
		// destruction of 33% of _coin.
		transfer.Amount = (67 * transfer.Amount) / 100
	}

	_, err = recieverStatement.Exec(transfer.Amount, transfer.ToRollno)
	if err != nil {
		log.Println("error while updating reciever info")
		tx.Rollback()
		return err
	}

	// Update transfer table
	recordStatement, err := tx.Prepare("INSERT INTO transfers ( Time , SenderRollno ,RecieverRollno , Amount ) VALUES(?,?,?,?)")
	if err != nil {
		log.Println("error while preparing record statement of transfer")
		tx.Rollback()
		return err
	}
	defer recordStatement.Close()

	// TODO: The amount transferred is more than what has been
	// TODO: Recorded. A new field name Tax is required in order
	// TODO: Make this record table more accurate
	_, err = recordStatement.Exec(time.Now(), transfer.FromRollno, transfer.ToRollno, transfer.Amount)
	if err != nil {
		log.Println("error while recording the transfer")

		tx.Rollback()
		return err
	}

	err = tx.Commit()
	return err
}