Add Google Consent Mode v2 to cookie banner SDK

Set GCM defaults to denied on load, then push consent
updates via gtag('consent', 'update', ...) before
activating scripts. The mapping from category slugs to
GCM consent types comes from the banner config endpoint.

Signed-off-by: Émile Ré <emile@getprobo.com>

packages/cookie-banner/src/client.ts

@@ -39,6 +39,7 @@ export interface Category {
   description: string;
   kind: string;
   cookies: CookieItem[];
+  gcm_consent_types: string[];
 }
 
 export interface BannerConfig {
@@ -108,6 +109,7 @@ export class CookieBannerClient {
     const config = await fetchJSON<BannerConfig>(configUrl);
     this.bannerConfig = config;
 
+    this.setGoogleConsentDefaults();
     this.startDetector(config);
 
     const cookie = getConsentCookie();
@@ -272,6 +274,8 @@ export class CookieBannerClient {
   }
 
   private activate(consentData: Record<string, boolean>): void {
+    this.updateGoogleConsentMode(consentData);
+
     const categoryCookies: Record<string, string[]> = {};
     const categoryLabels: Record<string, string> = {};
     for (const cat of this.config.categories) {
@@ -289,6 +293,55 @@ export class CookieBannerClient {
     this.observer = observeAndActivate(consentData, categoryLabels, texts);
   }
 
+  private hasGCMMapping(): boolean {
+    return this.config.categories.some(
+      (cat) => cat.gcm_consent_types && cat.gcm_consent_types.length > 0,
+    );
+  }
+
+  private setGoogleConsentDefaults(): void {
+    if (!this.hasGCMMapping()) return;
+
+    const w = window as unknown as Record<string, unknown>;
+    const gtag = w.gtag as ((...args: unknown[]) => void) | undefined;
+    if (typeof gtag !== "function") return;
+
+    const defaults: Record<string, string> = {};
+    for (const cat of this.config.categories) {
+      if (!cat.gcm_consent_types) continue;
+      for (const gcmType of cat.gcm_consent_types) {
+        defaults[gcmType] = "denied";
+      }
+    }
+
+    if (Object.keys(defaults).length > 0) {
+      gtag("consent", "default", defaults);
+    }
+  }
+
+  private updateGoogleConsentMode(
+    consentData: Record<string, boolean>,
+  ): void {
+    if (!this.hasGCMMapping()) return;
+
+    const w = window as unknown as Record<string, unknown>;
+    const gtag = w.gtag as ((...args: unknown[]) => void) | undefined;
+    if (typeof gtag !== "function") return;
+
+    const update: Record<string, string> = {};
+    for (const cat of this.config.categories) {
+      if (!cat.gcm_consent_types) continue;
+      const granted = !!consentData[cat.slug];
+      for (const gcmType of cat.gcm_consent_types) {
+        update[gcmType] = granted ? "granted" : "denied";
+      }
+    }
+
+    if (Object.keys(update).length > 0) {
+      gtag("consent", "update", update);
+    }
+  }
+
   private startDetector(config: BannerConfig): void {
     const knownNames = new Set<string>();
     knownNames.add(COOKIE_NAME);