Crussell/backend/handlers/payments/idempotency_helpers_test.go

//go:build test && dev

package payments

import (
	"context"
	"testing"

	"crussell/internal/square"
)

// TestDeriveRefundIdempotencyKey_Deterministic locks the M1 property: the
// server-side refund key derived from (payment_id, amount pence, refund type)
// is DETERMINISTIC — a retry of the same logical refund re-derives the SAME
// key, so Square's idempotency dedup returns the original refund instead of
// minting a second one.
func TestDeriveRefundIdempotencyKey_Deterministic(t *testing.T) {
	key1 := deriveRefundIdempotencyKey("pay1234567890", 5000, "manual")
	key2 := deriveRefundIdempotencyKey("pay1234567890", 5000, "manual")
	if key1 != key2 {
		t.Errorf("expected the derived refund key to be deterministic, got %q vs %q", key1, key2)
	}
}

// TestDeriveRefundIdempotencyKey_DistinguishesInputs locks the M1 discriminator
// fields: the key MUST change when the payment, the amount, or the refund type
// changes (a distinct partial refund of the same amount must never collide with
// a cancellation refund of the same size).
func TestDeriveRefundIdempotencyKey_DistinguishesInputs(t *testing.T) {
	base := deriveRefundIdempotencyKey("pay1234567890", 5000, "manual")

	otherPayment := deriveRefundIdempotencyKey("pay9999999999", 5000, "manual")
	if otherPayment == base {
		t.Errorf("expected a different payment id to produce a different refund key")
	}

	otherAmount := deriveRefundIdempotencyKey("pay1234567890", 5001, "manual")
	if otherAmount == base {
		t.Errorf("expected a different amount to produce a different refund key")
	}

	otherType := deriveRefundIdempotencyKey("pay1234567890", 5000, "cancellation")
	if otherType == base {
		t.Errorf("expected a different refund type to produce a different refund key")
	}
}

// TestDeriveRefundIdempotencyKey_RespectsSquareLimit locks the
// truncateIdempotencyKey semantics: every derived key stays within Square's
// 45-char /v2/refunds idempotency-key limit, even for an over-length candidate
// (a long payment id / large amount), and the truncation stays deterministic.
func TestDeriveRefundIdempotencyKey_RespectsSquareLimit(t *testing.T) {
	cases := []struct {
		paymentID  string
		amount     int64
		refundType string
	}{
		{"pay1234567890", 5000, "manual"},
		{"pay1234567890", 5000, "cancellation"},
		{"a-very-long-payment-id-that-exceeds-the-45-char-limit-when-combined", 999999999, "manual"},
		{"pay1234567890", 999999999, "a-refund-type-that-is-itself-quite-long"},
	}
	for _, c := range cases {
		key := deriveRefundIdempotencyKey(c.paymentID, c.amount, c.refundType)
		if len(key) > maxIdempotencyKeyLength {
			t.Errorf("derived refund key %q (%d chars) exceeds Square's %d-char limit", key, len(key), maxIdempotencyKeyLength)
		}
		if key != deriveRefundIdempotencyKey(c.paymentID, c.amount, c.refundType) {
			t.Errorf("derived refund key %q is not deterministic across calls", key)
		}
	}
}

// TestDeriveRefundIdempotencyKey_RetryAfterSweepResolution_NoSecondRefund locks
// the M1 end-to-end dedup: a refund issued with the deterministic server-side
// key, resolved by a sweep pass, and then RETRIED maps to the SAME Square refund
// (the mock's refundByKey dedup returns the original) — a second Square refund
// is never minted. This is the mechanism the refund issuance uses so a
// no-client-key retry after sweep resolution dedups onto the first refund.
func TestDeriveRefundIdempotencyKey_RetryAfterSweepResolution_NoSecondRefund(t *testing.T) {
	mock := square.NewDevClient().(*square.MockClient)
	payment, err := mock.CreatePayment(context.Background(), square.CreatePaymentReq{
		Amount:         5000,
		Currency:       "GBP",
		SourceID:       "cnon:test-card",
		IdempotencyKey: "seed-refund-dedup-payment",
	})
	if err != nil {
		t.Fatalf("failed to seed the payment at the mock: %v", err)
	}

	paymentID := "payrefund000001"
	amountPence := int64(5000)
	// The no-client-key refund issues with the deterministic server-side key.
	key := deriveRefundIdempotencyKey(paymentID, amountPence, "manual")

	first, err := mock.RefundPayment(context.Background(), square.RefundPaymentReq{
		PaymentID:      payment.SquarePayID,
		Amount:         amountPence,
		IdempotencyKey: key,
		Reason:         "test",
	})
	if err != nil {
		t.Fatalf("first refund failed: %v", err)
	}

	// After the sweep resolves the first attempt, the client retries the SAME
	// logical refund. The retry re-derives the SAME deterministic key, so the
	// mock's Square-style dedup returns the ORIGINAL refund — RefundKeyCount
	// stays 1 and no second Square refund is minted.
	retry, retryErr := mock.RefundPayment(context.Background(), square.RefundPaymentReq{
		PaymentID:      payment.SquarePayID,
		Amount:         amountPence,
		IdempotencyKey: deriveRefundIdempotencyKey(paymentID, amountPence, "manual"),
		Reason:         "test",
	})
	if retryErr != nil {
		t.Fatalf("retry after sweep resolution failed: %v", retryErr)
	}
	if first.ID != retry.ID {
		t.Errorf("expected the retry to dedup onto the original refund %s, got a different refund %s", first.ID, retry.ID)
	}
	if got := mock.RefundKeyCount(); got != 1 {
		t.Errorf("expected exactly ONE Square refund after the retry, got %d distinct refund keys", got)
	}
}