広告クリエイティブをローテーションで表示する

// Ad config with the URL of the content, a probability weight for rotation, and the clickthrough rate.
const DEMO_CONTENT_CONFIG = [
  {
    url: 'https://your-server.example/contents/content-1.html',
    weight: 0.7,
  },
  {
    url: 'https://your-server.example/contents/content-2.html',
    weight: 0.2,
  },
  {
    url: 'https://your-server.example/contents/content-3.html',
    weight: 0.1,
  },
];

// Set the mode to sequential and set the starting index to 0.
async function seedStorage() {
  await window.sharedStorage.set('content-rotation-mode', 'sequential', {
    ignoreIfPresent: true,
  });

  await window.sharedStorage.set('content-rotation-index', 0, {
    ignoreIfPresent: true,
  });
}

async function injectAd() {
  // Load the worklet module
  await window.sharedStorage.worklet.addModule('creative-rotation-worklet.js');

  // Initially set the storage to sequential mode for the demo
  seedStorage();

  // Run the URL selection operation to determine the next content rendered.
  const urls = DEMO_CONTENT_CONFIG.map(({ url }) => ({ url }));
  const fencedFrameConfig = await window.sharedStorage.selectURL('content-rotation', urls, {
    data: DEMO_CONTENT_CONFIG,
    resolveToConfig: true
  });

  // Render the opaque URL into a fenced frame
  document.getElementById('content-slot').config = fencedFrameConfig;
}

injectAd();

class SelectURLOperation {
  async run(urls, data) {
    // Read the rotation mode from Shared Storage
    const rotationMode = await sharedStorage.get('content-rotation-mode');

    // Generate a random number to be used for rotation
    const randomNumber = Math.random();

    let index;

    switch (rotationMode) {
      /**
       * Sequential rotation
       * - Rotates the contents in order
       * - Example: A -> B -> C -> A ...
       */
      case 'sequential':
        const currentIndex = await sharedStorage.get('creative-rotation-index');
        index = parseInt(currentIndex, 10);
        const nextIndex = (index + 1) % urls.length;

        await sharedStorage.set('content-rotation-index', nextIndex);
        break;

      /**
       * Weighted rotation
       * - Rotates the contentswith weighted probability
       * - Example: A=70% / B=20% / C=10%
       */
      case 'weighted-distribution':
        
        // Sum the weights cumulatively, and find the first URL where the
        // sum exceeds the random number. The array is sorted in
        // descending order first.
        let weightSum = 0;
        const { url } = data
          .sort((a, b) => b.weight - a.weight)
          .find(({ weight }) => {
            weightSum += weight;
            return weightSum > randomNumber;
          });

        index = urls.indexOf(url);
        break;

      default:
        index = 0;
    }
    return index;
  }
}

register('content-rotation', SelectURLOperation);