Block Chain Technology and Investments Buzz for Beginners

// loan_chaincode.go

package main

import (
	"fmt"
	"github.com/hyperledger/fabric-contract-api-go/contractapi"
)

// LoanContract represents the smart contract
type LoanContract struct {
	contractapi.Contract
}

// Loan represents a loan transaction
type Loan struct {
	ID        string `json:"id"`
	Borrower  string `json:"borrower"`
	Lender    string `json:"lender"`
	Amount    int    `json:"amount"`
	Repaid    bool   `json:"repaid"`
}

// Init initializes the chaincode
func (lc *LoanContract) Init(ctx contractapi.TransactionContextInterface) error {
	fmt.Println("Chaincode initialized")
	return nil
}

// RequestLoan creates a new loan request
func (lc *LoanContract) RequestLoan(ctx contractapi.TransactionContextInterface, id string, borrower string, lender string, amount int) error {
	existing, err := ctx.GetStub().GetState(id)
	if err != nil {
		return fmt.Errorf("Failed to get loan: %v", err)
	}

	if existing != nil {
		return fmt.Errorf("Loan with ID %s already exists", id)
	}

	loan := Loan{
		ID:       id,
		Borrower: borrower,
		Lender:   lender,
		Amount:   amount,
		Repaid:   false,
	}

	loanJSON, err := serialize(loan)
	if err != nil {
		return err
	}

	err = ctx.GetStub().PutState(id, loanJSON)
	if err != nil {
		return fmt.Errorf("Failed to put loan into ledger: %v", err)
	}

	return nil
}

// RepayLoan marks the loan as repaid
func (lc *LoanContract) RepayLoan(ctx contractapi.TransactionContextInterface, id string) error {
	loanJSON, err := ctx.GetStub().GetState(id)
	if err != nil {
		return fmt.Errorf("Failed to read loan: %v", err)
	}

	if loanJSON == nil {
		return fmt.Errorf("Loan with ID %s does not exist", id)
	}

	var loan Loan
	err = deserialize(loanJSON, &loan)
	if err != nil {
		return err
	}

	loan.Repaid = true

	loanJSON, err = serialize(loan)
	if err != nil {
		return err
	}

	err = ctx.GetStub().PutState(id, loanJSON)
	if err != nil {
		return fmt.Errorf("Failed to update loan: %v", err)
	}

	return nil
}

// QueryLoan retrieves loan details by ID
func (lc *LoanContract) QueryLoan(ctx contractapi.TransactionContextInterface, id string) (*Loan, error) {
	loanJSON, err := ctx.GetStub().GetState(id)
	if err != nil {
		return nil, fmt.Errorf("Failed to read loan: %v", err)
	}

	if loanJSON == nil {
		return nil, fmt.Errorf("Loan with ID %s does not exist", id)
	}

	var loan Loan
	err = deserialize(loanJSON, &loan)
	if err != nil {
		return nil, err
	}

	return &loan, nil
}

// serialize converts struct to JSON
func serialize(data interface{}) ([]byte, error) {
	return json.Marshal(data)
}

// deserialize converts JSON to struct
func deserialize(data []byte, result interface{}) error {
	return json.Unmarshal(data, result)
}

func main() {
	loanContract := new(LoanContract)
	chaincode, err := contractapi.NewChaincode(loanContract)
	if err != nil {
		fmt.Printf("Error creating loan chaincode: %s", err.Error())
		return
	}

	if err := chaincode.Start(); err != nil {
		fmt.Printf("Error starting loan chaincode: %s", err.Error())
	}
}