Genarrative/src/components/platform-entry/platformRecommendation.ts

import {
  buildPlatformPublicGalleryCardKey,
  type PlatformPublicGalleryCard,
} from '../rpg-entry/rpgEntryWorldPresentation';

const MS_PER_DAY = 86_400_000;
const FEATURED_BONUS = 14;
const MAX_FRESHNESS_SCORE = 12;

export type PlatformRecommendationOptions = {
  nowMs?: number;
  limit?: number;
};

type RecommendationCandidate = {
  entry: PlatformPublicGalleryCard;
  key: string;
  sourceType: string;
  firstSeenIndex: number;
  isFeatured: boolean;
  timestampMs: number;
  score: number;
};

type PlatformRecommendationMetricKey =
  | 'playCount'
  | 'remixCount'
  | 'likeCount'
  | 'recentPlayCount7d';

function parseRecommendationTimestamp(value: string | null | undefined) {
  if (!value) {
    return 0;
  }

  const normalized = value.trim();
  const numericTimestamp = normalized.match(/^(-?\d+(?:\.\d+)?)(?:Z)?$/u);
  if (numericTimestamp?.[1]) {
    const rawTimestamp = Number(numericTimestamp[1]);
    if (Number.isFinite(rawTimestamp)) {
      const absoluteTimestamp = Math.abs(rawTimestamp);
      if (absoluteTimestamp >= 1_000_000_000_000_000) {
        return rawTimestamp / 1000;
      }
      if (absoluteTimestamp >= 1_000_000_000_000) {
        return rawTimestamp;
      }
      if (absoluteTimestamp >= 1_000_000_000) {
        return rawTimestamp * 1000;
      }
    }
  }

  const timestamp = new Date(normalized).getTime();
  return Number.isNaN(timestamp) ? 0 : timestamp;
}

function getRecommendationTimestamp(entry: PlatformPublicGalleryCard) {
  return parseRecommendationTimestamp(entry.publishedAt ?? entry.updatedAt);
}

function getRecommendationMetric(
  entry: PlatformPublicGalleryCard,
  key: PlatformRecommendationMetricKey,
) {
  const value = (
    entry as Partial<Record<PlatformRecommendationMetricKey, number>>
  )[key];
  return Math.max(0, Math.round(Number(value ?? 0) || 0));
}

function getRecommendationSourceType(entry: PlatformPublicGalleryCard) {
  if ('sourceType' in entry) {
    if (
      entry.sourceType === 'edutainment' &&
      'templateId' in entry &&
      entry.templateId
    ) {
      return `edutainment:${entry.templateId}`;
    }

    return entry.sourceType;
  }

  return 'rpg';
}

function getRecommendationThemeTags(entry: PlatformPublicGalleryCard) {
  return 'themeTags' in entry && Array.isArray(entry.themeTags)
    ? entry.themeTags
    : [];
}

function scoreRecommendationCandidate(
  candidate: Omit<RecommendationCandidate, 'score'>,
  nowMs: number,
) {
  const entry = candidate.entry;
  const ageDays =
    candidate.timestampMs > 0
      ? Math.max(0, (nowMs - candidate.timestampMs) / MS_PER_DAY)
      : Number.POSITIVE_INFINITY;
  const freshnessScore = Number.isFinite(ageDays)
    ? MAX_FRESHNESS_SCORE / (1 + ageDays / 7)
    : 0;
  const coverScore = entry.coverImageSrc ? 1.5 : 0;
  const tagScore = Math.min(3, getRecommendationThemeTags(entry).length) * 0.6;
  const summaryScore = entry.summaryText.trim() ? 0.8 : 0;

  return (
    (candidate.isFeatured ? FEATURED_BONUS : 0) +
    Math.log1p(getRecommendationMetric(entry, 'recentPlayCount7d')) * 8 +
    Math.log1p(getRecommendationMetric(entry, 'likeCount')) * 5 +
    Math.log1p(getRecommendationMetric(entry, 'remixCount')) * 3 +
    Math.log1p(getRecommendationMetric(entry, 'playCount')) * 2 +
    freshnessScore +
    coverScore +
    tagScore +
    summaryScore
  );
}

function compareRecommendationCandidates(
  left: RecommendationCandidate,
  right: RecommendationCandidate,
) {
  const scoreDiff = right.score - left.score;
  if (scoreDiff !== 0) {
    return scoreDiff;
  }

  const timeDiff = right.timestampMs - left.timestampMs;
  if (timeDiff !== 0) {
    return timeDiff;
  }

  if (left.firstSeenIndex !== right.firstSeenIndex) {
    return left.firstSeenIndex - right.firstSeenIndex;
  }

  return left.key.localeCompare(right.key, 'zh-CN');
}

function diversifyAdjacentSourceTypes(candidates: RecommendationCandidate[]) {
  const remaining = [...candidates];
  const result: RecommendationCandidate[] = [];

  while (remaining.length > 0) {
    const lastSourceType = result[result.length - 1]?.sourceType ?? null;
    let nextIndex = 0;

    if (lastSourceType) {
      const alternativeIndex = remaining.findIndex(
        (candidate) => candidate.sourceType !== lastSourceType,
      );
      if (alternativeIndex > 0) {
        nextIndex = alternativeIndex;
      }
    }

    const [nextCandidate] = remaining.splice(nextIndex, 1);
    if (nextCandidate) {
      result.push(nextCandidate);
    }
  }

  return result;
}

export function buildPlatformRecommendedEntries(
  params: {
    featuredEntries: PlatformPublicGalleryCard[];
    latestEntries: PlatformPublicGalleryCard[];
  },
  options: PlatformRecommendationOptions = {},
) {
  const candidateMap = new Map<
    string,
    Omit<RecommendationCandidate, 'score'>
  >();
  let firstSeenIndex = 0;

  const collectEntries = (
    entries: PlatformPublicGalleryCard[],
    source: 'featured' | 'latest',
  ) => {
    entries.forEach((entry) => {
      const key = buildPlatformPublicGalleryCardKey(entry);
      const timestampMs = getRecommendationTimestamp(entry);
      const existing = candidateMap.get(key);
      if (existing) {
        existing.isFeatured = existing.isFeatured || source === 'featured';
        if (timestampMs >= existing.timestampMs) {
          existing.entry = entry;
          existing.timestampMs = timestampMs;
        }
        return;
      }

      candidateMap.set(key, {
        entry,
        key,
        sourceType: getRecommendationSourceType(entry),
        firstSeenIndex,
        isFeatured: source === 'featured',
        timestampMs,
      });
      firstSeenIndex += 1;
    });
  };

  collectEntries(params.featuredEntries, 'featured');
  collectEntries(params.latestEntries, 'latest');

  const nowMs = options.nowMs ?? Date.now();
  const rankedCandidates = Array.from(candidateMap.values())
    .map((candidate) => ({
      ...candidate,
      score: scoreRecommendationCandidate(candidate, nowMs),
    }))
    .sort(compareRecommendationCandidates);
  const diversifiedCandidates = diversifyAdjacentSourceTypes(rankedCandidates);
  const limit =
    typeof options.limit === 'number' && options.limit > 0
      ? Math.floor(options.limit)
      : diversifiedCandidates.length;

  return diversifiedCandidates
    .slice(0, limit)
    .map((candidate) => candidate.entry);
}