計算機科学のブログ

package money

import "testing"

func TestTimes(t *testing.T) {
	five := NewMoneyDollar(5)
	tests := []struct {
		m int
		d Money
	}{
		{2, NewMoneyDollar(10)},
		{3, NewMoneyDollar(15)},
	}
	for _, test := range tests {
		got := five.Times(test.m)
		want := test.d
		if got != want {
			t.Errorf("%v.Times(%v) got %v, want %v", five, test.m, got, want)
		}
	}
}
func TestEq(t *testing.T) {
	tests := []struct {
		mx, my Money
		want   bool
	}{
		{NewMoneyDollar(5), NewMoneyDollar(5), true},
		{NewMoneyDollar(5), NewMoneyDollar(6), false},
		{NewMoneyFranc(5), NewMoneyDollar(5), false},
	}
	for _, test := range tests {
		got := test.mx.Eq(test.my)
		want := test.want
		if got != want {
			t.Errorf("%v.Eq(%v) got %v, want %v",
				test.mx, test.my, got, want)
		}
	}
}
func TestCurrency(t *testing.T) {
	tests := []struct {
		c string
		m Money
	}{
		{"USD", NewMoneyDollar(1)},
		{"CHF", NewMoneyFranc(1)},
	}
	for _, test := range tests {
		got := test.m.Currency()
		want := test.c
		if got != want {
			t.Errorf("%v.Currency() got %v, want %v",
				test.m, got, want)
		}
	}
}
func TestAdd(t *testing.T) {
	five := NewMoneyDollar(5)
	sum := five.Add(five)
	bank := NewBank()
	got := bank.reduce(sum, "USD")
	want := NewMoneyDollar(10)
	if got.Ne(want) {
		t.Errorf("%v.Add(%v) got %v, want %v", five, five, got, want)
	}
}
func TestMixedAdd(t *testing.T) {
	fiveBucks := NewMoneyDollar(5)
	tenFrancs := NewMoneyFranc(10)
	ten := fiveBucks.Add(tenFrancs)
	bank := NewBank()
	bank.addRate("CHF", "USD", 2)
	got := bank.reduce(ten, "USD")
	want := NewMoneyDollar(10)
	if got.Ne(want) {
		t.Errorf("%v.reduce(%v, USD) got %v, want %v", bank, ten, got, want)
	}
}
func TestAddReturnsSum(t *testing.T) {
	five := NewMoneyDollar(5)
	result := five.Add(five)
	sum := result.(Sum)
	tests := []Expression{sum.augend, sum.addend}
	for _, test := range tests {
		if test.Ne(five) {
			t.Errorf("%v.Ne(%v)", test, five)
		}
	}
}

func TestBankReduceSum(t *testing.T) {
	sum := NewSum(NewMoneyDollar(3), NewMoneyDollar(4))
	bank := NewBank()
	result := bank.reduce(sum, "USD")
	seven := NewMoneyDollar(7)
	if result.Ne(seven) {
		t.Errorf("%v.Ne(%v)", result, seven)
	}
}

func TestBankReduceMoney(t *testing.T) {
	bank := NewBank()
	result := bank.reduce(NewMoneyDollar(1), "USD")
	one := NewMoneyDollar(1)
	if result.Ne(one) {
		t.Errorf("%v.Ne(%v)", result, one)
	}
}
func TestBankReduceMoneyDifferentCurrency(t *testing.T) {
	bank := NewBank()
	bank.addRate("CHF", "USD", 2)
	twoFranc := NewMoneyFranc(2)
	got := bank.reduce(twoFranc, "USD")
	want := NewMoneyDollar(1)
	if got.Ne(want) {
		t.Errorf("%v.reduce(%v, \"USD\") got %v, want %v",
			bank, twoFranc, got, want)
	}
}
func TestBankIdentityRate(t *testing.T) {
	bank := NewBank()
	got := bank.rate("USD", "USD")
	want := 1
	if got != want {
		t.Errorf("%v.rate(USD, USD) want %v, got %v", bank, want, got)
	}
}

package money

import "fmt"

// Expression ...
type Expression interface {
	reduce(Bank, string) Money
	Ne(Expression) bool
}

// Money ...
type Money struct {
	amount   int
	currency string
}

// Sum ...
type Sum struct {
	augend, addend Expression
}

func (mx Money) String() string {
	return fmt.Sprintf("%v %v", mx.amount, mx.currency)
}

// NewMoney ...
func NewMoney(amount int, currency string) Money {
	return Money{amount, currency}
}

// reduce ...
func (mx Money) reduce(bank Bank, to string) Money {
	rate := bank.rate(mx.currency, to)
	return NewMoney(mx.amount/rate, to)
}

// Currency ...
func (mx Money) Currency() string {
	return mx.currency
}

// Eq ...
func (mx Money) Eq(my Money) bool {
	return mx.amount == my.amount && mx.currency == my.currency
}

// Ne ...
func (mx Money) Ne(e Expression) bool {
	if my, ok := e.(Money); ok {
		return !mx.Eq(my)
	}
	return false
}

// Times ...
func (mx Money) Times(m int) Expression {
	return NewMoney(mx.amount*m, mx.currency)
}

// NewMoneyDollar ...
func NewMoneyDollar(amount int) Money {
	return NewMoney(amount, "USD")
}

// NewMoneyFranc ...
func NewMoneyFranc(amount int) Money {
	return NewMoney(amount, "CHF")
}

// Add ...
func (mx Money) Add(my Money) Expression {
	return NewSum(mx, my)
}

// NewSum ...
func NewSum(augend, addend Expression) Sum {
	return Sum{augend, addend}
}

// Ne ...
func (sx Sum) Ne(sy Expression) bool {
	return false
}
func (sx Sum) reduce(bank Bank, to string) Money {
	// amount := s.augend.amount + s.addend.amount
	amount :=
		sx.augend.reduce(bank, to).amount + sx.addend.reduce(bank, to).amount
	return NewMoney(amount, to)
}

// Bank 通貨を換算する
type Bank struct {
	rates map[pair]int
}

// NewBank ...
func NewBank() Bank {
	return Bank{rates: map[pair]int{}}
}
func (b Bank) reduce(source Expression, to string) Money {
	return source.reduce(b, to)
}
func (b Bank) addRate(from, to string, rate int) {
	b.rates[newPair(from, to)] = rate
}
func (b Bank) rate(from, to string) int {
	if from == to {
		return 1
	}
	return b.rates[newPair(from, to)]
}

type pair struct {
	from, to string
}

func newPair(from, to string) pair {
	return pair{from, to}
}
func (px pair) eq(py pair) bool {
	return px.from == py.from && px.to == py.to
}
func (px pair) hashCode() int {
	return 0
}

% go test
--- FAIL: TestMixedAdd (0.00s)
    money_test.go:77: {map[{CHF USD}:2]}.reduce({{5 USD} {10 CHF}}, USD) got 15 USD, want 10 USD
FAIL
exit status 1
FAIL	money	0.293s
% go test
PASS
ok  	money	0.282s
% go test
PASS
ok  	money	0.455s
% go test
PASS
ok  	money	0.230s
% go test
PASS
ok  	money	0.283s
%