How to Build Mood-Based Discovery Into a Streaming Service

export const THEMES = {
  'scare-me': {
    label: 'Scare Me',
    vertical: 'movies',
    preferences: [
      'Theme: Scare Me',
      'genuinely frightening',
      'atmospheric dread over jump scares',
    ],
    where: (title) => title.genres.includes('horror'),
  },
  'quick-watches': {
    label: 'Quick Watches',
    vertical: 'tv-series',
    preferences: ['Theme: Quick Watches'],
    constraints: { max_runtime_minutes: 30 },
    where: (title) => title.runtimeMinutes <= 30,
  },
};

const ENDPOINT = 'https://api.tasteray.com/v1/recommend';

export async function rank(theme, items, viewer, count = 3) {
  if (items.length === 0) return []; // count must be 1 to 10
  const res = await fetch(ENDPOINT, {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'X-API-Key': process.env.TASTERAY_API_KEY,
    },
    signal: AbortSignal.timeout(60_000),
    body: JSON.stringify({
      vertical: theme.vertical,
      items,
      context: {
        preferences: theme.preferences,
        constraints: theme.constraints,
        profile: viewer.profile,
        history: viewer.rejections.slice(-50),
      },
      options: {
        count: Math.min(count, items.length),
        fast: true,
        explanation_depth: 'brief',
        language: viewer.locale,
      },
    }),
  });
  if (!res.ok) {
    const { error } = await res.json();
    throw new Error(`${res.status} ${error.code}: ${error.message}`);
  }
  const { recommendations, meta } = await res.json();
  return matchToCatalog(recommendations, items, meta.request_id);
}

// Each returned item carries the id you sent. Match on it, and
// drop what does not match. Fewer than count can come back.
function matchToCatalog(recommendations, items, requestId) {
  const byId = new Map(items.map((i) => [i.id, i]));
  return recommendations.flatMap((r) => {
    const item = byId.get(r.item.id);
    if (!item) {
      console.warn('unmatched', requestId, r.item.id);
      return [];
    }
    return [{
      id: item.id,
      // taste_match_score is 0-100, confidence 0.0-1.0
      score: r.metadata?.taste_match_score ?? r.confidence * 100,
      why: r.explanation.why_match,
      factors: r.explanation.key_factors ?? [],
      requestId,
    }];
  });
}

export function withRejections(viewer, rejectedTitles) {
  return {
    ...viewer,
    rejectedIds: new Set(rejectedTitles.map((t) => t.id)),
    rejections: rejectedTitles.map((t) => ({
      item: t.name,
      rating: 'rejected: do not suggest again',
    })),
    rejectionsVersion: rejectedTitles.length,
  };
}