feat: add Airwallex payments and multi-currency support

backend/internal/payment/amount_test.go

@@ -126,3 +126,104 @@ func TestYuanToFenRoundTrip(t *testing.T) {
 		}
 	}
 }
+
+func TestPaymentCurrencyHelpers(t *testing.T) {
+	tests := []struct {
+		name      string
+		currency  string
+		amount    string
+		wantMinor int64
+		wantBack  float64
+	}{
+		{name: "hkd uses cents", currency: "hkd", amount: "12.34", wantMinor: 1234, wantBack: 12.34},
+		{name: "jpy has no minor unit", currency: "JPY", amount: "12", wantMinor: 12, wantBack: 12},
+		{name: "kwd uses three decimal minor units", currency: "KWD", amount: "12.345", wantMinor: 12345, wantBack: 12.345},
+		{name: "isk uses Stripe legacy two-decimal API amount", currency: "ISK", amount: "12", wantMinor: 1200, wantBack: 12},
+		{name: "ugx uses Stripe legacy two-decimal API amount", currency: "UGX", amount: "12.00", wantMinor: 1200, wantBack: 12},
+		{name: "empty currency defaults to cny", currency: "", amount: "1.23", wantMinor: 123, wantBack: 1.23},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := AmountToMinorUnit(tt.amount, tt.currency)
+			if err != nil {
+				t.Fatalf("AmountToMinorUnit(%q, %q) unexpected error: %v", tt.amount, tt.currency, err)
+			}
+			if got != tt.wantMinor {
+				t.Fatalf("AmountToMinorUnit(%q, %q) = %d, want %d", tt.amount, tt.currency, got, tt.wantMinor)
+			}
+			back := MinorUnitToAmount(got, tt.currency)
+			if math.Abs(back-tt.wantBack) > 1e-9 {
+				t.Fatalf("MinorUnitToAmount(%d, %q) = %f, want %f", got, tt.currency, back, tt.wantBack)
+			}
+		})
+	}
+}
+
+func TestFormatAmountForCurrency(t *testing.T) {
+	tests := []struct {
+		currency string
+		amount   float64
+		want     string
+	}{
+		{currency: "CNY", amount: 12.3, want: "12.30"},
+		{currency: "JPY", amount: 12, want: "12"},
+		{currency: "KWD", amount: 12.345, want: "12.345"},
+		{currency: "ISK", amount: 12, want: "12"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.currency, func(t *testing.T) {
+			if got := FormatAmountForCurrency(tt.amount, tt.currency); got != tt.want {
+				t.Fatalf("FormatAmountForCurrency(%v, %q) = %q, want %q", tt.amount, tt.currency, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestAmountToMinorUnitRejectsUnsupportedPrecision(t *testing.T) {
+	if _, err := AmountToMinorUnit("100.50", "JPY"); err == nil {
+		t.Fatal("expected fractional JPY amount to fail")
+	}
+	if _, err := AmountToMinorUnit("100.50", "ISK"); err == nil {
+		t.Fatal("expected fractional ISK amount to fail")
+	}
+	if _, err := AmountToMinorUnit("100.50", "UGX"); err == nil {
+		t.Fatal("expected fractional UGX amount to fail")
+	}
+	if _, err := AmountToMinorUnit("12.345", "HKD"); err == nil {
+		t.Fatal("expected amount with more than two decimal places to fail")
+	}
+	if _, err := AmountToMinorUnit("12.3456", "KWD"); err == nil {
+		t.Fatal("expected amount with more than three decimal places to fail")
+	}
+	if got, err := AmountToMinorUnit("100.00", "JPY"); err != nil || got != 100 {
+		t.Fatalf("AmountToMinorUnit integer-form JPY = (%d, %v), want (100, nil)", got, err)
+	}
+}
+
+func TestThreeDecimalPaymentCurrencies(t *testing.T) {
+	for _, currency := range []string{"BHD", "IQD", "JOD", "KWD", "LYD", "OMR", "TND"} {
+		t.Run(currency, func(t *testing.T) {
+			got, err := AmountToMinorUnit("12.345", currency)
+			if err != nil {
+				t.Fatalf("AmountToMinorUnit(%q, %q) unexpected error: %v", "12.345", currency, err)
+			}
+			if got != 12345 {
+				t.Fatalf("AmountToMinorUnit(%q, %q) = %d, want 12345", "12.345", currency, got)
+			}
+			if back := MinorUnitToAmount(got, currency); math.Abs(back-12.345) > 1e-9 {
+				t.Fatalf("MinorUnitToAmount(%d, %q) = %f, want 12.345", got, currency, back)
+			}
+		})
+	}
+}
+
+func TestNormalizePaymentCurrencyRejectsInvalidCodes(t *testing.T) {
+	if _, err := NormalizePaymentCurrency("HK"); err == nil {
+		t.Fatal("expected invalid two-letter currency to fail")
+	}
+	if _, err := NormalizePaymentCurrency("US1"); err == nil {
+		t.Fatal("expected non-letter currency to fail")
+	}
+}