Solução

Concluído

Este é o código completo que resolve os dois desafios deste módulo.

Teste de núcleo do banco: bank_test.go

//...

func TestTransfer(t *testing.T) {
    accountA := Account{
		Customer: Customer{
			Name:    "John",
			Address: "Los Angeles, California",
			Phone:   "(213) 555 0147",
		},
		Number:  1001,
		Balance: 0,
	}

	accountB := Account{
		Customer: Customer{
			Name:    "Mark",
			Address: "Irvine, California",
			Phone:   "(949) 555 0198",
		},
		Number:  1002,
		Balance: 0,
	}

	accountA.Deposit(100)
	err := accountA.Transfer(50, &accountB)

	if accountA.Balance != 50 && accountB.Balance != 50 {
		t.Error("transfer from account A to account B is not working", err)
	}
}

Núcleo do banco: bank.go

package bank

import (
	"errors"
	"fmt"
)

//...

// Transfer function
func (a *Account) Transfer(amount float64, dest *Account) error {
	if amount <= 0 {
		return errors.New("the amount to transfer should be greater than zero")
	}

	if a.Balance < amount {
		return errors.New("the amount to transfer should be greater than the account's balance")
	}

	a.Withdraw(amount)
	dest.Deposit(amount)
	return nil
}

// Bank ...
type Bank interface {
	Statement() string
}

// Statement ...
func Statement(b Bank) string {
	return b.Statement()
}

API do banco: main.go

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"strconv"

	"github.com/msft/bank"
)

var accounts = map[float64]*CustomAccount{}

func main() {
	accounts[1001] = &CustomAccount{
		Account: &bank.Account{
			Customer: bank.Customer{
				Name:    "John",
				Address: "Los Angeles, California",
				Phone:   "(213) 555 0147",
			},
			Number: 1001,
		},
	}

	accounts[1002] = &CustomAccount{
		Account: &bank.Account{
			Customer: bank.Customer{
				Name:    "Mark",
				Address: "Irvine, California",
				Phone:   "(949) 555 0198",
			},
			Number: 1002,
		},
	}

	http.HandleFunc("/statement", statement)
	http.HandleFunc("/deposit", deposit)
	http.HandleFunc("/withdraw", withdraw)
	http.HandleFunc("/transfer", transfer)
	log.Fatal(http.ListenAndServe("localhost:8000", nil))
}

//...

func transfer(w http.ResponseWriter, req *http.Request) {
	numberqs := req.URL.Query().Get("number")
	amountqs := req.URL.Query().Get("amount")
	destqs := req.URL.Query().Get("dest")

	if numberqs == "" {
		fmt.Fprintf(w, "Account number is missing!")
		return
	}

	if number, err := strconv.ParseFloat(numberqs, 64); err != nil {
		fmt.Fprintf(w, "Invalid account number!")
	} else if amount, err := strconv.ParseFloat(amountqs, 64); err != nil {
		fmt.Fprintf(w, "Invalid amount number!")
	} else if dest, err := strconv.ParseFloat(destqs, 64); err != nil {
		fmt.Fprintf(w, "Invalid account destination number!")
	} else {
		if accountA, ok := accounts[number]; !ok {
			fmt.Fprintf(w, "Account with number %v can't be found!", number)
		} else if accountB, ok := accounts[dest]; !ok {
			fmt.Fprintf(w, "Account with number %v can't be found!", dest)
		} else {
			err := accountA.Transfer(amount, accountB.Account)
			if err != nil {
				fmt.Fprintf(w, "%v", err)
			} else {
				fmt.Fprintf(w, accountA.Statement())
			}
		}
	}
}

func statement(w http.ResponseWriter, req *http.Request) {
	numberqs := req.URL.Query().Get("number")

	if numberqs == "" {
		fmt.Fprintf(w, "Account number is missing!")
		return
	}

	number, err := strconv.ParseFloat(numberqs, 64)
	if err != nil {
		fmt.Fprintf(w, "Invalid account number!")
	} else {
		account, ok := accounts[number]
		if !ok {
			fmt.Fprintf(w, "Account with number %v can't be found!", number)
		} else {
			json.NewEncoder(w).Encode(bank.Statement(account))
		}
	}
}

// CustomAccount ...
type CustomAccount struct {
	*bank.Account
}

// Statement ...
func (c *CustomAccount) Statement() string {
	json, err := json.Marshal(c)
	if err != nil {
		return err.Error()
	}

	return string(json)
}