♻️ [Story Ads] Move existing placement logic to algo impl (#33286)

* move existing algo

* write tests

* no new

* change to number

extensions/amp-story-auto-ads/0.1/algorithm-count-pages.js

@@ -14,24 +14,129 @@
  * limitations under the License.
  */
 
+import {InsertionState} from './story-ad-page-manager';
+import {StateProperty} from '../../amp-story/1.0/amp-story-store-service';
+import {hasOwn, map} from '../../../src/utils/object';
+
+/** @const {number} */
+const INTERVAL = 7;
+
 /**
  * Original Story Ads placement algorithm. Tries to place ad every seven pages.
  * Will not place if ad is still loading.
  * @implements {./algorithm-interface.StoryAdPlacementAlgorithm}
  */
 export class CountPagesAlgorithm {
   /** @override */
-  constructor(unusedStoreService, unusedPageManager) {}
+  constructor(storeService, pageManager) {
+    /** @private {!../../amp-story/1.0/amp-story-store-service.AmpStoryStoreService} */
+    this.storeService_ = storeService;
+
+    /** @private {!StoryAdPageManager} */
+    this.pageManager_ = pageManager;
+
+    /** @private {!Object<string, boolean>} */
+    this.uniquePageIds_ = map();
+
+    /** @private {number} */
+    this.newPagesSinceLastAd_ = 1;
+
+    /** @private {boolean} */
+    this.pendingAdView_ = false;
+
+    /** @private {boolean} */
+    this.tryingToInsert_ = false;
+  }
 
   /** @override */
-  isStoryEligible() {}
+  isStoryEligible() {
+    const numPages = this.storeService_.get(StateProperty.PAGE_IDS).length;
+    return numPages > INTERVAL;
+  }
 
   /** @override */
-  initializePages() {}
+  initializePages() {
+    return [this.pageManager_.createAdPage()];
+  }
 
   /** @override */
-  onPageChange(unusedPageId) {}
+  onPageChange(pageId) {
+    if (!hasOwn(this.uniquePageIds_, pageId)) {
+      this.uniquePageIds_[pageId] = true;
+      this.newPagesSinceLastAd_++;
+    }
+
+    if (
+      this.pendingAdView_ ||
+      this.tryingToInsert_ ||
+      !this.readyToPlaceAd_() ||
+      !this.pageManager_.hasUnusedAdPage()
+    ) {
+      return;
+    }
+
+    this.tryingToInsert_ = true;
+    this.tryToPlaceAdAfterPage_(pageId);
+  }
 
   /** @override */
-  onNewAdView(unusedPageIndex) {}
+  onNewAdView(pageIndex) {
+    this.pendingAdView_ = false;
+    this.newPagesSinceLastAd_ = 0;
+    if (this.shouldCreateNextAd_(pageIndex)) {
+      this.pageManager_.createAdPage();
+    }
+  }
+
+  /**
+   * Determine if enough pages in the story are left for ad placement to be
+   * possible.
+   *
+   * @param {number} pageIndex
+   * @return {boolean}
+   */
+  shouldCreateNextAd_(pageIndex) {
+    const numPages = this.storeService_.get(StateProperty.PAGE_IDS).length;
+    return numPages - pageIndex > INTERVAL;
+  }
+
+  /**
+   * Determine if user has seen enough pages to show an ad. We want a certain
+   * number of pages before the first ad, and then a separate interval
+   * thereafter.
+   * @return {boolean}
+   */
+  readyToPlaceAd_() {
+    return this.newPagesSinceLastAd_ >= INTERVAL;
+  }
+
+  /**
+   * Place ad based on user config.
+   * @param {string} pageBeforeAdId
+   * @private
+   */
+  tryToPlaceAdAfterPage_(pageBeforeAdId) {
+    const nextAdPage = this.pageManager_.getUnusedAdPage();
+
+    // Timeout fail, move to next ad on next navigation.
+    if (!nextAdPage.isLoaded() && nextAdPage.hasTimedOut()) {
+      this.pageManager_.discardCurrentAd();
+      return;
+    }
+
+    // Keep trying the same ad, so we just exit without changing state.
+    if (!nextAdPage.isLoaded()) {
+      return;
+    }
+
+    this.pageManager_
+      .maybeInsertPageAfter(pageBeforeAdId, nextAdPage)
+      .then((insertionState) => {
+        this.tryingToInsert_ = false;
+        if (insertionState === InsertionState.SUCCESS) {
+          // We have an ad inserted that has yet to be viewed.
+          this.pendingAdView_ = true;
+        }
+      });
+  }
 }