Crussell/backend/handlers/payments/dst_timezone_test.go

//go:build test && dev

package payments

// Strict timezone/DST tests for the payment refund tiers and the deposit
// protection window. All assertions use fixed time.Date instants.

import (
	"testing"
	"time"

	"crussell/clock"
)

// TestRefundTiers_TimezoneIndependent proves refund tiers depend only on the
// ELAPSED time between cancellation and start (startTime.Sub(cancellationTime)
// .Hours()), never on wall-clock days or the London calendar date. Two bookings
// in different seasons — 2026-01-20 10:00 UTC (GMT) and 2026-06-20 10:00 UTC
// (BST) — cancelled with identical notice must produce identical results for
// every tier.
func TestRefundTiers_TimezoneIndependent(t *testing.T) {
	t.Parallel()

	gmtStart := time.Date(2026, 1, 20, 10, 0, 0, 0, time.UTC)
	bstStart := time.Date(2026, 6, 20, 10, 0, 0, 0, time.UTC)

	// Precondition: the two starts are genuinely in different seasons — same
	// UTC instant-of-day but different London wall-clock zones.
	if gz, _ := gmtStart.In(clock.London).Zone(); gz != "GMT" {
		t.Fatalf("expected 2026-01-20 in London to be GMT, got %q", gz)
	}
	if bz, _ := bstStart.In(clock.London).Zone(); bz != "BST" {
		t.Fatalf("expected 2026-06-20 in London to be BST, got %q", bz)
	}

	notices := []struct {
		name  string
		hours float64
		want  string
	}{
		{"over 72h -> full refund", 72.5, FullRefundTier},
		{"at 72h -> partial (strict > boundary)", 72, PartialRefundTier},
		{"48h -> partial refund", 48, PartialRefundTier},
		{"at 24h -> partial refund", 24, PartialRefundTier},
		{"under 24h -> no refund", 23.5, NoRefundTier},
	}

	for _, tc := range notices {
		noticeDur := time.Duration(tc.hours * float64(time.Hour))
		cancellationGmt := gmtStart.Add(-noticeDur)
		cancellationBst := bstStart.Add(-noticeDur)

		gmtRes := CalculateRefundForCancellation(100, 50, cancellationGmt, gmtStart)
		bstRes := CalculateRefundForCancellation(100, 50, cancellationBst, bstStart)

		if gmtRes.Tier != tc.want || bstRes.Tier != tc.want {
			t.Errorf("%s: want tier %q, got GMT=%q BST=%q", tc.name, tc.want, gmtRes.Tier, bstRes.Tier)
		}
		// Elapsed-hours logic is DST-safe: identical inputs across seasons
		// produce byte-for-byte identical outputs.
		if gmtRes != bstRes {
			t.Errorf("%s: GMT and BST bookings with identical notice produced different refunds: GMT=%+v BST=%+v",
				tc.name, gmtRes, bstRes)
		}
		if gmtRes.HoursUntilAppointment != tc.hours {
			t.Errorf("%s: expected %.1f elapsed hours, got %.1f", tc.name, tc.hours, gmtRes.HoursUntilAppointment)
		}
	}
}

// TestDepositProtectionWindow_UTCInstant proves buildSplitRecords decides
// "after booking starts" by an ABSOLUTE UTC-instant comparison
// (clock.Now().After(info.StartTime)), never by the London calendar date. A
// booking at 2026-06-15 00:30 BST == 2026-06-14 23:30 UTC — where the UTC date
// and the London date disagree — is classified purely by its UTC instant.
func TestDepositProtectionWindow_UTCInstant(t *testing.T) {
	t.Parallel()

	// 2026-06-14 23:30 UTC = 2026-06-15 00:30 BST: the 00:00-01:00 BST window
	// where the UTC date (2026-06-14) is the day before the London date.
	boundaryUTC := time.Date(2026, 6, 14, 23, 30, 0, 0, time.UTC)
	if got := boundaryUTC.In(clock.London).Format("2006-01-02"); got != "2026-06-15" {
		t.Fatalf("test setup invariant: 2026-06-14 23:30 UTC must be London 2026-06-15 00:30 BST, got %s", got)
	}
	if got := boundaryUTC.Format("2006-01-02"); got != "2026-06-14" {
		t.Fatalf("test setup invariant: boundary must remain UTC date 2026-06-14, got %s", got)
	}

	// This instant is in the past -> the booking has started -> no deposit
	// protection window -> a single unsplit record.
	record := makeTestRecord("b-boundary-past", "full", 50)
	info := &BookingPaymentInfo{StartTime: boundaryUTC, TotalAmount: 50, TotalPaid: 0}
	records := buildSplitRecords(record, "full", info, 50)
	if len(records) != 1 {
		t.Fatalf("past BST-midnight booking: expected 1 record (no split), got %d", len(records))
	}
	if records[0].PaymentType != "full" {
		t.Errorf("past BST-midnight booking: expected single 'full' record, got %q", records[0].PaymentType)
	}

	// Mirror case with the IDENTICAL UTC-date != London-date property but in the
	// future (2099-06-14 23:30 UTC = 2099-06-15 00:30 BST): the booking has NOT
	// started, so the deposit split must happen. Only the UTC instant differs
	// from the case above — the London date plays no role.
	futureBoundary := time.Date(2099, 6, 14, 23, 30, 0, 0, time.UTC)
	if got := futureBoundary.In(clock.London).Format("2006-01-02"); got != "2099-06-15" {
		t.Fatalf("test setup invariant: 2099-06-14 23:30 UTC must be London 2099-06-15, got %s", got)
	}

	record2 := makeTestRecord("b-boundary-future", "full", 50)
	info2 := &BookingPaymentInfo{StartTime: futureBoundary, TotalAmount: 50, TotalPaid: 0}
	records2 := buildSplitRecords(record2, "full", info2, 50)
	if len(records2) != 2 {
		t.Fatalf("future BST-midnight booking: expected 2 records (deposit split), got %d", len(records2))
	}
	if records2[0].PaymentType != "deposit" || records2[0].Amount != 25 {
		t.Errorf("future BST-midnight booking: expected first record deposit £25, got %q £%.2f",
			records2[0].PaymentType, records2[0].Amount)
	}
	if records2[1].PaymentType != "balance" || records2[1].Amount != 25 {
		t.Errorf("future BST-midnight booking: expected second record balance £25, got %q £%.2f",
			records2[1].PaymentType, records2[1].Amount)
	}
}