Crussell/backend/handlers/payments/discount_preview_test.go

//go:build test && dev

package payments

import (
	"context"
	"encoding/json"
	"net/http"
	"net/http/httptest"
	"testing"
	"time"

	"crussell/clock"
	"crussell/db"
	"crussell/mw"
	"crussell/testutils"
	"crussell/testutils/fixtures"
	"crussell/testutils/jwt"

	"github.com/go-chi/chi/v5"
)

// =============================================================================
// GetDiscountPreviewHandler — GET /api/bookings/{id}/discount-preview
// =============================================================================

// setupDiscountPreviewTest creates a user, service, and booking for discount preview tests.
func setupDiscountPreviewTest(t *testing.T, ctx context.Context, q db.Querier) (string, string, string) {
	t.Helper()
	userID, err := fixtures.CreateTestUser(q)
	if err != nil {
		t.Fatalf("failed to create user: %v", err)
	}

	serviceID, err := fixtures.CreateTestService(q)
	if err != nil {
		t.Fatalf("failed to create service: %v", err)
	}

	bookingID, err := fixtures.CreateTestBookingAtTime(q, userID, serviceID, time.Date(2099, 12, 31, 10, 0, 0, 0, time.UTC))
	if err != nil {
		t.Fatalf("failed to create booking: %v", err)
	}

	_, err = q.Exec(ctx, `UPDATE bookings SET status = 'confirmed' WHERE id = $1`, bookingID)
	if err != nil {
		t.Fatalf("failed to confirm booking: %v", err)
	}

	token := jwt.GenerateUserToken(userID)
	return userID, bookingID, token
}

// serveDiscountPreviewHandler wires chi context with {id} param and serves the handler.
// Pass userID explicitly so the handler sees the correct user in context.
func serveDiscountPreviewHandler(bookingID, userID, token string, baseCtx ...context.Context) *httptest.ResponseRecorder {
	handler := http.HandlerFunc(GetDiscountPreviewHandler)

	req := httptest.NewRequest("GET", "/api/bookings/"+bookingID+"/discount-preview", nil)
	req.Header.Set("Authorization", "Bearer "+token)

	base := context.Background()
	if len(baseCtx) > 0 {
		base = baseCtx[0]
	}
	ctx := context.WithValue(base, mw.UserIDKey, userID)
	ctx = context.WithValue(ctx, mw.UserRoleKey, "verified_email")
	req = req.WithContext(ctx)

	rctx := chi.NewRouteContext()
	rctx.URLParams.Add("id", bookingID)
	req = req.WithContext(context.WithValue(req.Context(), chi.RouteCtxKey, rctx))

	w := httptest.NewRecorder()
	handler.ServeHTTP(w, req)
	return w
}

// TestDiscountPreview_NoCampaigns returns eligible=false when no active campaigns exist.
func TestDiscountPreview_NoCampaigns(t *testing.T) {
	t.Parallel()
	ctx, tx := testutils.SetupTestTx(t)

	userID, bookingID, token := setupDiscountPreviewTest(t, ctx, tx)

	w := serveDiscountPreviewHandler(bookingID, userID, token, ctx)

	if w.Code != http.StatusOK {
		t.Fatalf("expected 200, got %d. body: %s", w.Code, w.Body.String())
	}

	var resp DiscountPreviewResponse
	if err := json.NewDecoder(w.Body).Decode(&resp); err != nil {
		t.Fatalf("failed to decode response: %v", err)
	}

	if resp.Eligible {
		t.Error("expected eligible=false with no active campaigns")
	}
	if len(resp.Discounts) != 0 {
		t.Errorf("expected 0 discounts, got %d", len(resp.Discounts))
	}
	if resp.OriginalTotal <= 0 {
		t.Errorf("expected positive original_total, got %f", resp.OriginalTotal)
	}
	if resp.DiscountedTotal != resp.OriginalTotal {
		t.Errorf("expected discounted_total == original_total with no discounts, got %f vs %f",
			resp.DiscountedTotal, resp.OriginalTotal)
	}
}

// TestDiscountPreview_TimeBasedCampaign returns the correct discount for an active time-based campaign.
func TestDiscountPreview_TimeBasedCampaign(t *testing.T) {
	t.Parallel()
	ctx, tx := testutils.SetupTestTx(t)

	userID, bookingID, token := setupDiscountPreviewTest(t, ctx, tx)

	now := clock.Now()
	var campaignID string
	err := tx.QueryRow(ctx, `
		INSERT INTO discount_campaigns (name, campaign_type, discount_percent, status, start_date, end_date, times_redeemed)
		VALUES ('Test Sale', 'time_based', 15, 'active', $1, $2, 0)
		RETURNING id
	`, now.Add(-24*time.Hour), now.Add(24*time.Hour)).Scan(&campaignID)
	if err != nil {
		t.Fatalf("failed to create campaign: %v", err)
	}

	w := serveDiscountPreviewHandler(bookingID, userID, token, ctx)

	if w.Code != http.StatusOK {
		t.Fatalf("expected 200, got %d. body: %s", w.Code, w.Body.String())
	}

	var resp DiscountPreviewResponse
	if err := json.NewDecoder(w.Body).Decode(&resp); err != nil {
		t.Fatalf("failed to decode response: %v", err)
	}

	if !resp.Eligible {
		t.Fatal("expected eligible=true with active time-based campaign")
	}
	if len(resp.Discounts) != 1 {
		t.Fatalf("expected 1 discount, got %d", len(resp.Discounts))
	}

	d := resp.Discounts[0]
	if d.Source != "campaign" {
		t.Errorf("expected source 'campaign', got %q", d.Source)
	}
	if d.Percent != 15 {
		t.Errorf("expected 15 percent, got %f", d.Percent)
	}
	if d.Amount <= 0 {
		t.Errorf("expected positive discount amount, got %f", d.Amount)
	}

	expectedDiscount := resp.OriginalTotal * 15 / 100
	if d.Amount != expectedDiscount {
		t.Errorf("expected discount amount %f, got %f", expectedDiscount, d.Amount)
	}

	if resp.DiscountedTotal != resp.OriginalTotal-d.Amount {
		t.Errorf("discounted_total %f should be original %f - discount %f",
			resp.DiscountedTotal, resp.OriginalTotal, d.Amount)
	}

	// Verify preview did NOT create any actual booking_discounts or payment records
	var discountCount int
	tx.QueryRow(ctx,
		"SELECT COUNT(*) FROM booking_discounts WHERE booking_id = $1", bookingID).Scan(&discountCount)
	if discountCount != 0 {
		t.Errorf("preview should not create booking_discounts, found %d", discountCount)
	}

	var paymentCount int
	tx.QueryRow(ctx,
		"SELECT COUNT(*) FROM payments WHERE booking_id = $1 AND payment_method = 'discount'", bookingID).Scan(&paymentCount)
	if paymentCount != 0 {
		t.Errorf("preview should not create discount payment records, found %d", paymentCount)
	}

	// Verify campaign redemption count was NOT incremented
	var timesRedeemed int
	tx.QueryRow(ctx,
		"SELECT times_redeemed FROM discount_campaigns WHERE id = $1", campaignID).Scan(&timesRedeemed)
	if timesRedeemed != 0 {
		t.Errorf("preview should not increment times_redeemed, got %d", timesRedeemed)
	}
}

// TestDiscountPreview_CampaignExhausted returns not eligible when a campaign has reached max_redemptions.
func TestDiscountPreview_CampaignExhausted(t *testing.T) {
	t.Parallel()
	ctx, tx := testutils.SetupTestTx(t)

	userID, bookingID, token := setupDiscountPreviewTest(t, ctx, tx)

	now := clock.Now()
	_, err := tx.Exec(ctx, `
		INSERT INTO discount_campaigns (name, campaign_type, discount_percent, status, start_date, end_date, max_redemptions, times_redeemed)
		VALUES ('Exhausted Campaign', 'time_based', 20, 'active', $1, $2, 5, 5)
	`, now.Add(-24*time.Hour), now.Add(24*time.Hour))
	if err != nil {
		t.Fatalf("failed to create campaign: %v", err)
	}

	w := serveDiscountPreviewHandler(bookingID, userID, token, ctx)

	if w.Code != http.StatusOK {
		t.Fatalf("expected 200, got %d. body: %s", w.Code, w.Body.String())
	}

	var resp DiscountPreviewResponse
	if err := json.NewDecoder(w.Body).Decode(&resp); err != nil {
		t.Fatalf("failed to decode response: %v", err)
	}

	if resp.Eligible {
		t.Error("expected eligible=false when campaign is exhausted")
	}
}

// TestDiscountPreview_CampaignExpired returns not eligible for a past campaign.
func TestDiscountPreview_CampaignExpired(t *testing.T) {
	t.Parallel()
	ctx, tx := testutils.SetupTestTx(t)

	userID, bookingID, token := setupDiscountPreviewTest(t, ctx, tx)

	_, err := tx.Exec(ctx, `
		INSERT INTO discount_campaigns (name, campaign_type, discount_percent, status, start_date, end_date)
		VALUES ('Expired Campaign', 'time_based', 10, 'active', $1, $2)
	`, clock.Now().Add(-72*time.Hour), clock.Now().Add(-24*time.Hour))
	if err != nil {
		t.Fatalf("failed to create campaign: %v", err)
	}

	w := serveDiscountPreviewHandler(bookingID, userID, token, ctx)

	var resp DiscountPreviewResponse
	json.NewDecoder(w.Body).Decode(&resp)

	if resp.Eligible {
		t.Error("expected eligible=false when campaign has expired")
	}
}

// TestDiscountPreview_CampaignNotStarted returns not eligible for a future campaign.
func TestDiscountPreview_CampaignNotStarted(t *testing.T) {
	t.Parallel()
	ctx, tx := testutils.SetupTestTx(t)

	userID, bookingID, token := setupDiscountPreviewTest(t, ctx, tx)

	_, err := tx.Exec(ctx, `
		INSERT INTO discount_campaigns (name, campaign_type, discount_percent, status, start_date, end_date)
		VALUES ('Future Campaign', 'time_based', 10, 'active', $1, $2)
	`, clock.Now().Add(24*time.Hour), clock.Now().Add(72*time.Hour))
	if err != nil {
		t.Fatalf("failed to create campaign: %v", err)
	}

	w := serveDiscountPreviewHandler(bookingID, userID, token, ctx)

	var resp DiscountPreviewResponse
	json.NewDecoder(w.Body).Decode(&resp)

	if resp.Eligible {
		t.Error("expected eligible=false when campaign has not started")
	}
}

// TestDiscountPreview_MilestoneCampaign returns the discount for a milestone campaign the user has reached.
func TestDiscountPreview_MilestoneCampaign(t *testing.T) {
	t.Parallel()
	ctx, tx := testutils.SetupTestTx(t)

	userID, bookingID, token := setupDiscountPreviewTest(t, ctx, tx)

	// Create a completed booking so the user has a booking count of at least 1 (plus the current test booking)
	serviceID, err := fixtures.CreateTestService(tx)
	if err != nil {
		t.Fatalf("failed to create service: %v", err)
	}
	pastBookingID, err := fixtures.CreateTestBookingAtTime(tx, userID, serviceID, time.Date(2024, 1, 15, 10, 0, 0, 0, time.UTC))
	if err != nil {
		t.Fatalf("failed to create completed booking: %v", err)
	}
	// The fixture creates bookings with status 'pending' — mark as completed for milestone counting
	_, err = tx.Exec(ctx, `UPDATE bookings SET status = 'completed' WHERE id = $1`, pastBookingID)
	if err != nil {
		t.Fatalf("failed to mark booking as completed: %v", err)
	}

	// Create milestone campaign for 1st booking
	_, err = tx.Exec(ctx, `
		INSERT INTO discount_campaigns (name, campaign_type, discount_percent, status, start_date, end_date, milestone_type, milestone_value)
		VALUES ('First Booking Bonus', 'milestone', 25, 'active', $1, $2, 'per_user_booking_count', 1)
	`, clock.Now().Add(-24*time.Hour), clock.Now().Add(24*time.Hour))
	if err != nil {
		t.Fatalf("failed to create milestone campaign: %v", err)
	}

	w := serveDiscountPreviewHandler(bookingID, userID, token, ctx)

	if w.Code != http.StatusOK {
		t.Fatalf("expected 200, got %d. body: %s", w.Code, w.Body.String())
	}

	var resp DiscountPreviewResponse
	if err := json.NewDecoder(w.Body).Decode(&resp); err != nil {
		t.Fatalf("failed to decode response: %v", err)
	}

	if !resp.Eligible {
		t.Fatal("expected eligible=true for milestone campaign")
	}

	foundMilestone := false
	for _, d := range resp.Discounts {
		if d.Percent == 25 {
			foundMilestone = true
			break
		}
	}
	if !foundMilestone {
		t.Error("expected a 25% milestone discount in the preview")
	}
}

// TestDiscountPreview_AlreadyApplied excludes discounts already applied to this booking.
func TestDiscountPreview_AlreadyApplied(t *testing.T) {
	t.Parallel()
	ctx, tx := testutils.SetupTestTx(t)

	userID, bookingID, token := setupDiscountPreviewTest(t, ctx, tx)

	now := clock.Now()
	var campaignID string
	err := tx.QueryRow(ctx, `
		INSERT INTO discount_campaigns (name, campaign_type, discount_percent, status, start_date, end_date, times_redeemed)
		VALUES ('Already Applied', 'time_based', 10, 'active', $1, $2, 0)
		RETURNING id
	`, now.Add(-24*time.Hour), now.Add(24*time.Hour)).Scan(&campaignID)
	if err != nil {
		t.Fatalf("failed to create campaign: %v", err)
	}

	// Simulate the discount already being applied by inserting a booking_discounts record
	var bookingTotal float64
	tx.QueryRow(ctx, `
		SELECT COALESCE(SUM(price_val), 0) FROM (
			SELECT COALESCE(bs.override_price, s.price) AS price_val
			FROM booking_services bs JOIN services s ON bs.service_id = s.id
			WHERE bs.booking_id = $1
		) sub
	`, bookingID).Scan(&bookingTotal)
	discountAmount := bookingTotal * 10 / 100

	_, err = tx.Exec(ctx, `
		INSERT INTO booking_discounts (booking_id, user_id, discount_source, source_id, discount_percent, original_total, discount_amount)
		VALUES ($1, $2, 'campaign', $3, 10, $4, $5)
	`, bookingID, userID, campaignID, bookingTotal, discountAmount)
	if err != nil {
		t.Fatalf("failed to apply discount: %v", err)
	}

	w := serveDiscountPreviewHandler(bookingID, userID, token, ctx)

	var resp DiscountPreviewResponse
	if err := json.NewDecoder(w.Body).Decode(&resp); err != nil {
		t.Fatalf("failed to decode response: %v", err)
	}

	if resp.Eligible {
		t.Error("expected eligible=false when discount already applied to this booking")
	}
}

// TestDiscountPreview_InvalidBookingID returns 400 for invalid booking ID.
func TestDiscountPreview_InvalidBookingID(t *testing.T) {
	handler := http.HandlerFunc(GetDiscountPreviewHandler)

	req := httptest.NewRequest("GET", "/api/bookings/invalid/discount-preview", nil)
	ctx := context.WithValue(req.Context(), mw.UserIDKey, "test-user-id")
	ctx = context.WithValue(ctx, mw.UserRoleKey, "verified_email")
	req = req.WithContext(ctx)

	rctx := chi.NewRouteContext()
	rctx.URLParams.Add("id", "invalid-id")
	req = req.WithContext(context.WithValue(req.Context(), chi.RouteCtxKey, rctx))

	w := httptest.NewRecorder()
	handler.ServeHTTP(w, req)

	if w.Code != http.StatusBadRequest {
		t.Errorf("expected 400 for invalid booking ID, got %d", w.Code)
	}
}

// TestDiscountPreview_MultipleCampaigns returns all eligible discounts.
func TestDiscountPreview_MultipleCampaigns(t *testing.T) {
	t.Parallel()
	ctx, tx := testutils.SetupTestTx(t)

	userID, bookingID, token := setupDiscountPreviewTest(t, ctx, tx)

	now := clock.Now()

	// Create two active campaigns
	_, err := tx.Exec(ctx, `
		INSERT INTO discount_campaigns (name, campaign_type, discount_percent, status, start_date, end_date)
		VALUES ('Summer Sale', 'time_based', 15, 'active', $1, $2)
	`, now.Add(-48*time.Hour), now.Add(48*time.Hour))
	if err != nil {
		t.Fatalf("failed to create first campaign: %v", err)
	}

	_, err = tx.Exec(ctx, `
		INSERT INTO discount_campaigns (name, campaign_type, discount_percent, status, start_date, end_date, max_redemptions, times_redeemed)
		VALUES ('Flash Sale', 'time_based', 20, 'active', $1, $2, 100, 0)
	`, now.Add(-24*time.Hour), now.Add(24*time.Hour))
	if err != nil {
		t.Fatalf("failed to create second campaign: %v", err)
	}

	w := serveDiscountPreviewHandler(bookingID, userID, token, ctx)

	if w.Code != http.StatusOK {
		t.Fatalf("expected 200, got %d. body: %s", w.Code, w.Body.String())
	}

	var resp DiscountPreviewResponse
	if err := json.NewDecoder(w.Body).Decode(&resp); err != nil {
		t.Fatalf("failed to decode response: %v", err)
	}

	if !resp.Eligible {
		t.Fatal("expected eligible=true with multiple active campaigns")
	}
	if len(resp.Discounts) < 1 {
		t.Fatalf("expected at least 1 discount, got %d", len(resp.Discounts))
	}
}

// TestDiscountPreview_AnniversaryCampaign returns the correct discount for an anniversary milestone.
func TestDiscountPreview_AnniversaryCampaign(t *testing.T) {
	t.Parallel()
	ctx, tx := testutils.SetupTestTx(t)

	userID, bookingID, token := setupDiscountPreviewTest(t, ctx, tx)

	// Set first booking to be years ago so anniversary qualifies
	tx.Exec(ctx, `
		INSERT INTO bookings (user_id, start_time, status) VALUES ($1, $2, 'completed')
	`, userID, time.Date(2020, 1, 15, 10, 0, 0, 0, time.UTC))

	// Create anniversary milestone campaign
	_, err := tx.Exec(ctx, `
		INSERT INTO discount_campaigns (name, campaign_type, discount_percent, status, start_date, end_date, milestone_type, milestone_value, milestone_unit)
		VALUES ($1, 'milestone', 20, 'active', NOW(), NOW() + INTERVAL '1 year', 'anniversary', 1, 'years')
	`, "One Year Anniversary")
	if err != nil {
		t.Fatalf("failed to create anniversary campaign: %v", err)
	}

	w := serveDiscountPreviewHandler(bookingID, userID, token, ctx)

	if w.Code != http.StatusOK {
		t.Fatalf("expected 200, got %d. body: %s", w.Code, w.Body.String())
	}

	var resp DiscountPreviewResponse
	if err := json.NewDecoder(w.Body).Decode(&resp); err != nil {
		t.Fatalf("failed to decode response: %v", err)
	}

	if !resp.Eligible {
		t.Fatal("expected eligible=true for anniversary campaign")
	}

	foundAnniversary := false
	for _, d := range resp.Discounts {
		if d.Source == "campaign" && d.Percent == 20 {
			foundAnniversary = true
			break
		}
	}
	if !foundAnniversary {
		t.Error("expected a 20% anniversary discount in the preview")
	}
}

// TestDiscountPreview_PaymentLock prevents new discounts after a completed payment exists.
// After the first payment, the apply function applies discounts. After a second payment,
// no new discounts should be added.
func TestDiscountPreview_PaymentLock(t *testing.T) {
	t.Parallel()
	ctx, tx := testutils.SetupTestTx(t)

	userID, bookingID, _ := setupDiscountPreviewTest(t, ctx, tx)

	now := clock.Now()
	var campaignID string
	err := tx.QueryRow(ctx, `
		INSERT INTO discount_campaigns (name, campaign_type, discount_percent, status, start_date, end_date, times_redeemed)
		VALUES ($1, 'time_based', 10, 'active', $2, $3, 0)
		RETURNING id
	`, "Payment Lock Test", now.Add(-24*time.Hour), now.Add(24*time.Hour)).Scan(&campaignID)
	if err != nil {
		t.Fatalf("failed to create campaign: %v", err)
	}

	// First payment — discount should be applied. A £10 deposit on the £50
	// booking leaves enough headroom for the 10% (£5) discount to pass the F1
	// over-credit cap (a full/overpaid fixture would now correctly skip it).
	_, err = tx.Exec(ctx, `
		INSERT INTO payments (booking_id, payment_type, payment_method, amount, status, created_at, updated_at)
		VALUES ($1, 'deposit', 'online_square', 10.00, 'completed', NOW(), NOW())
	`, bookingID)
	if err != nil {
		t.Fatalf("failed to create first payment: %v", err)
	}

	applyEligibleCampaignsAtPayment(ctx, tx, bookingID, userID, nil)

	var discountCount int
	tx.QueryRow(ctx,
		"SELECT COUNT(*) FROM booking_discounts WHERE booking_id = $1", bookingID).Scan(&discountCount)
	if discountCount != 1 {
		t.Errorf("expected 1 discount after first payment, got %d", discountCount)
	}

	// Second payment — NO new discounts should be added (lock active). The £40
	// balance completes the £50 booking; the 2-completed-payment lock in
	// ComputeEligibleDiscounts is what refuses the second application.
	_, err = tx.Exec(ctx, `
		INSERT INTO payments (booking_id, payment_type, payment_method, amount, status, created_at, updated_at)
		VALUES ($1, 'full', 'online_square', 40.00, 'completed', NOW(), NOW())
	`, bookingID)
	if err != nil {
		t.Fatalf("failed to create second payment: %v", err)
	}

	applyEligibleCampaignsAtPayment(ctx, tx, bookingID, userID, nil)

	tx.QueryRow(ctx,
		"SELECT COUNT(*) FROM booking_discounts WHERE booking_id = $1", bookingID).Scan(&discountCount)
	if discountCount != 1 {
		t.Errorf("expected still 1 discount after second payment (lock active), got %d", discountCount)
	}

	// Verify campaign was only redeemed once
	var timesRedeemed int
	tx.QueryRow(ctx,
		"SELECT times_redeemed FROM discount_campaigns WHERE id = $1", campaignID).Scan(&timesRedeemed)
	if timesRedeemed != 1 {
		t.Errorf("expected 1 redemption, got %d", timesRedeemed)
	}
}

// TestDiscountPreview_BookingNoServices returns not eligible for a booking with no services.
func TestDiscountPreview_BookingNoServices(t *testing.T) {
	t.Parallel()
	ctx, tx := testutils.SetupTestTx(t)

	userID, err := fixtures.CreateTestUser(tx)
	if err != nil {
		t.Fatalf("failed to create user: %v", err)
	}

	// Create a booking without any services
	var bookingID string
	err = tx.QueryRow(ctx, `
		INSERT INTO bookings (user_id, start_time, status) VALUES ($1, NOW(), 'confirmed') RETURNING id
	`, userID).Scan(&bookingID)
	if err != nil {
		t.Fatalf("failed to create booking: %v", err)
	}

	now := clock.Now()
	_, err = tx.Exec(ctx, `
		INSERT INTO discount_campaigns (name, campaign_type, discount_percent, status, start_date, end_date)
		VALUES ('Test Sale', 'time_based', 10, 'active', $1, $2)
	`, now.Add(-24*time.Hour), now.Add(24*time.Hour))
	if err != nil {
		t.Fatalf("failed to create campaign: %v", err)
	}

	token := jwt.GenerateUserToken(userID)
	w := serveDiscountPreviewHandler(bookingID, userID, token, ctx)

	var resp DiscountPreviewResponse
	if err := json.NewDecoder(w.Body).Decode(&resp); err != nil {
		t.Fatalf("failed to decode response: %v", err)
	}

	if resp.Eligible {
		t.Error("expected eligible=false for booking with no services")
	}
	if resp.OriginalTotal != 0 {
		t.Errorf("expected original_total=0, got %f", resp.OriginalTotal)
	}
}

// TestDiscountPreview_ReturnsReadOnly confirms the preview endpoint never modifies state
// even when eligible campaigns exist.
func TestDiscountPreview_ReturnsReadOnly(t *testing.T) {
	t.Parallel()
	ctx, tx := testutils.SetupTestTx(t)
	userID, bookingID, token := setupDiscountPreviewTest(t, ctx, tx)

	now := clock.Now()

	// Create an active campaign
	var campaignID string
	err := tx.QueryRow(ctx, `
		INSERT INTO discount_campaigns (name, campaign_type, discount_percent, status, start_date, end_date, times_redeemed)
		VALUES ($1, 'time_based', 10, 'active', $2, $3, 0)
		RETURNING id
	`, "Test Sale", now.Add(-24*time.Hour), now.Add(24*time.Hour)).Scan(&campaignID)
	if err != nil {
		t.Fatalf("failed to create campaign: %v", err)
	}

	w := serveDiscountPreviewHandler(bookingID, userID, token, ctx)
	if w.Code != http.StatusOK {
		t.Fatalf("expected 200, got %d: %s", w.Code, w.Body.String())
	}

	var resp DiscountPreviewResponse
	if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
		t.Fatalf("failed to unmarshal: %v", err)
	}

	if !resp.Eligible {
		t.Error("expected eligible=true when there's an existing applied campaign discount")
	}

	if len(resp.Discounts) != 1 {
		t.Fatalf("expected 1 discount (applied at payment), got %d", len(resp.Discounts))
	}

	if len(resp.Discounts) > 0 && resp.Discounts[0].Source != "campaign" {
		t.Errorf("expected campaign discount source, got %q", resp.Discounts[0].Source)
	}
}

func TestDiscountPreview_ReferralDiscount(t *testing.T) {
	t.Parallel()
	ctx, tx := testutils.SetupTestTx(t)
	userID, bookingID, token := setupDiscountPreviewTest(t, ctx, tx)

	var refID string
	err := tx.QueryRow(ctx, `
		INSERT INTO user_referrals (referrer_id, referred_id)
		VALUES ($1, $2)
		RETURNING id
	`, userID, userID).Scan(&refID)
	if err != nil {
		t.Fatalf("failed to create referral: %v", err)
	}
	_, err = tx.Exec(ctx, `
		INSERT INTO referral_discounts (user_id, referral_id, discount_percent, used)
		VALUES ($1, $2, 10.00, false)
	`, userID, refID)
	if err != nil {
		t.Fatalf("failed to insert referral discount: %v", err)
	}

	w := serveDiscountPreviewHandler(bookingID, userID, token, ctx)
	if w.Code != http.StatusOK {
		t.Fatalf("expected 200, got %d: %s", w.Code, w.Body.String())
	}

	var resp DiscountPreviewResponse
	if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
		t.Fatalf("failed to unmarshal: %v", err)
	}

	if !resp.Eligible {
		t.Error("expected eligible=true when there's an unused referral discount")
	}

	foundReferral := false
	for _, d := range resp.Discounts {
		if d.Source == "referral" {
			foundReferral = true
			if d.Percent != 10.00 {
				t.Errorf("expected referral discount percent 10.00, got %f", d.Percent)
			}
			if d.Name != "Referral Discount (10%)" {
				t.Errorf("expected name 'Referral Discount (10%%)', got %q", d.Name)
			}

		}
	}
	if !foundReferral {
		t.Errorf("expected referral discount in discounts list, got %+v", resp.Discounts)
	}
}

func TestDiscountPreview_ReferralDiscount_AlreadyUsed(t *testing.T) {
	t.Parallel()
	ctx, tx := testutils.SetupTestTx(t)
	userID, bookingID, token := setupDiscountPreviewTest(t, ctx, tx)

	// Insert a used referral discount
	var refID string
	err := tx.QueryRow(ctx, `
		INSERT INTO user_referrals (referrer_id, referred_id)
		VALUES ($1, $2)
		RETURNING id
	`, userID, userID).Scan(&refID)
	if err != nil {
		t.Fatalf("failed to create referral: %v", err)
	}
	_, err = tx.Exec(ctx, `
		INSERT INTO referral_discounts (user_id, referral_id, discount_percent, used)
		VALUES ($1, $2, 10.00, true)
	`, userID, refID)
	if err != nil {
		t.Fatalf("failed to insert used referral discount: %v", err)
	}

	w := serveDiscountPreviewHandler(bookingID, userID, token, ctx)
	if w.Code != http.StatusOK {
		t.Fatalf("expected 200, got %d: %s", w.Code, w.Body.String())
	}

	var resp DiscountPreviewResponse
	if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
		t.Fatalf("failed to unmarshal: %v", err)
	}

	for _, d := range resp.Discounts {
		if d.Source == "referral" {
			t.Error("expected no referral discount when already used")
		}
	}
}

func TestDiscountPreview_ReferralDiscount_AlreadyApplied(t *testing.T) {
	t.Parallel()
	ctx, tx := testutils.SetupTestTx(t)
	userID, bookingID, token := setupDiscountPreviewTest(t, ctx, tx)

	var refID string
	err := tx.QueryRow(ctx, `
		INSERT INTO user_referrals (referrer_id, referred_id)
		VALUES ($1, $2)
		RETURNING id
	`, userID, userID).Scan(&refID)
	if err != nil {
		t.Fatalf("failed to create referral: %v", err)
	}
	var rdID string
	err = tx.QueryRow(ctx, `
		INSERT INTO referral_discounts (user_id, referral_id, discount_percent, used)
		VALUES ($1, $2, 10.00, false)
		RETURNING id
	`, userID, refID).Scan(&rdID)
	if err != nil {
		t.Fatalf("failed to insert referral discount: %v", err)
	}

	// Apply it to the booking already
	_, err = tx.Exec(ctx, `
		INSERT INTO booking_discounts (booking_id, user_id, discount_source, source_id, discount_percent, original_total, discount_amount)
		VALUES ($1, $2, 'referral', $3, 10.00, 100.00, 10.00)
	`, bookingID, userID, rdID)
	if err != nil {
		t.Fatalf("failed to insert booking discount: %v", err)
	}

	w := serveDiscountPreviewHandler(bookingID, userID, token, ctx)
	if w.Code != http.StatusOK {
		t.Fatalf("expected 200, got %d: %s", w.Code, w.Body.String())
	}

	var resp DiscountPreviewResponse
	if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
		t.Fatalf("failed to unmarshal: %v", err)
	}

	for _, d := range resp.Discounts {
		if d.Source == "referral" {
			t.Error("expected no referral discount when already applied to booking")
		}
	}
}