internal: add referrer classification

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: Ibcaa09bfd4767876ea1cdd5b61c53b476a6a6964

internal/normalize/referrer_test.go

@@ -0,0 +1,200 @@
+package normalize
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestExtractReferrerDomain(t *testing.T) {
+	tests := []struct {
+		name       string
+		referrer   string
+		siteDomain string
+		want       string
+	}{
+		{
+			name:       "empty referrer",
+			referrer:   "",
+			siteDomain: "example.com",
+			want:       "direct",
+		},
+		{
+			name:       "same domain",
+			referrer:   "https://example.com/page",
+			siteDomain: "example.com",
+			want:       "direct",
+		},
+		{
+			name:       "subdomain is direct",
+			referrer:   "https://blog.example.com/post",
+			siteDomain: "example.com",
+			want:       "direct",
+		},
+		{
+			name:       "google search",
+			referrer:   "https://www.google.com/search?q=test",
+			siteDomain: "example.com",
+			want:       "google.com",
+		},
+		{
+			name:       "google country domain",
+			referrer:   "https://www.google.co.uk/search",
+			siteDomain: "example.com",
+			want:       "google.co.uk",
+		},
+		{
+			name:       "hacker news",
+			referrer:   "https://news.ycombinator.com/item?id=123",
+			siteDomain: "example.com",
+			want:       "ycombinator.com",
+		},
+		{
+			name:       "twitter short link",
+			referrer:   "https://t.co/abc123",
+			siteDomain: "example.com",
+			want:       "t.co",
+		},
+		{
+			name:       "github",
+			referrer:   "https://github.com/user/repo",
+			siteDomain: "example.com",
+			want:       "github.com",
+		},
+		{
+			name:       "invalid url",
+			referrer:   "not-a-url",
+			siteDomain: "example.com",
+			want:       "",
+		},
+		{
+			name:       "case insensitive",
+			referrer:   "https://WWW.GOOGLE.COM/search",
+			siteDomain: "EXAMPLE.COM",
+			want:       "google.com",
+		},
+		{
+			name:       "trailing dot normalized",
+			referrer:   "https://example.com./page",
+			siteDomain: "test.com",
+			want:       "example.com",
+		},
+		{
+			name:       "localhost",
+			referrer:   "http://localhost:8080/page",
+			siteDomain: "example.com",
+			want:       "internal",
+		},
+		{
+			name:       "loopback IPv4",
+			referrer:   "http://127.0.0.1/page",
+			siteDomain: "example.com",
+			want:       "internal",
+		},
+		{
+			name:       "loopback IPv6",
+			referrer:   "http://[::1]/page",
+			siteDomain: "example.com",
+			want:       "internal",
+		},
+		{
+			name:       "private IP 192.168",
+			referrer:   "http://192.168.1.1/page",
+			siteDomain: "example.com",
+			want:       "internal",
+		},
+		{
+			name:       "private IP 10.x",
+			referrer:   "http://10.0.0.1/page",
+			siteDomain: "example.com",
+			want:       "internal",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := ExtractReferrerDomain(tt.referrer, tt.siteDomain)
+			if got != tt.want {
+				t.Errorf("ExtractReferrerDomain(%q, %q) = %q, want %q",
+					tt.referrer, tt.siteDomain, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestReferrerRegistry(t *testing.T) {
+	registry := NewReferrerRegistry(3)
+
+	// Add sources within limit
+	if got := registry.Add("google.com"); got != "google.com" {
+		t.Errorf("expected google.com, got %s", got)
+	}
+	if got := registry.Add("github.com"); got != "github.com" {
+		t.Errorf("expected github.com, got %s", got)
+	}
+	if got := registry.Add("reddit.com"); got != "reddit.com" {
+		t.Errorf("expected reddit.com, got %s", got)
+	}
+
+	// Adding same source again should succeed
+	if got := registry.Add("google.com"); got != "google.com" {
+		t.Errorf("expected google.com, got %s", got)
+	}
+
+	// Exceeding limit should return "other"
+	if got := registry.Add("twitter.com"); got != "other" {
+		t.Errorf("expected other, got %s", got)
+	}
+
+	// Direct always works
+	if got := registry.Add("direct"); got != "direct" {
+		t.Errorf("expected direct, got %s", got)
+	}
+
+	// Internal always works
+	if got := registry.Add("internal"); got != "internal" {
+		t.Errorf("expected internal, got %s", got)
+	}
+
+	// Overflow count should be 1
+	if registry.OverflowCount() != 1 {
+		t.Errorf("expected overflow count 1, got %d", registry.OverflowCount())
+	}
+}
+
+func TestReferrerRegistryConcurrentOverflow(t *testing.T) {
+	registry := NewReferrerRegistry(10)
+
+	// Use channels to coordinate goroutines
+	const numGoroutines = 50
+	const sourcesPerGoroutine = 5
+	done := make(chan bool, numGoroutines)
+
+	// Launch goroutines that race to add sources
+	for i := range numGoroutines {
+		go func(id int) {
+			for j := range sourcesPerGoroutine {
+				source := fmt.Sprintf("source-%d-%d.com", id, j)
+				registry.Add(source)
+			}
+			done <- true
+		}(i)
+	}
+
+	// Wait for all goroutines
+	for range numGoroutines {
+		<-done
+	}
+
+	// Registry should have exactly 10 sources (limit)
+	// Overflow should be (50 * 5) - 10 = 240 rejections
+	// But since same sources might be added multiple times,
+	// we just verify: overflow > 0 and total attempts tracked
+	if registry.OverflowCount() == 0 {
+		t.Error("expected some overflow with concurrent adds")
+	}
+
+	// Verify adding more sources still returns "other"
+	if got := registry.Add("new-source.com"); got != "other" {
+		t.Errorf("expected other after overflow, got %s", got)
+	}
+}