import { logger } from "firebase-functions";
import { firestore } from "../firebase";
import {
  countRankedUsers,
  countUsersAboveTierPoints,
  getUser,
  listTopByTierPoints,
  type ScoreboardUserEntry,
} from "../repositories/userRepository";
import { writeScope, type Scope } from "../repositories/scoreboardCacheRepository";
import { tierOf } from "../constants/tiers";
import { computePercentile, deltaFor } from "./scoreboardHelpers";
import type { DateString } from "../types/dateString";
import { TeamCode, type RankSnapshot } from "../types/panit";
import type {
  ScoreboardEntry,
  ScoreboardScopeCache,
} from "../types/scoreboard";

/**
 * 유저 1명의 현재 `tierPoints` 기반 rank를 count aggregation으로 계산해
 * `rankSnapshot`에 기록한다. `dailyArchive`에서 `judgeDay` **이전에** 호출해
 * 스냅샷이 "직전 상태의 rank"를 담도록 한다.
 *
 * `tierPoints === 0`이면 스냅샷을 남기지 않는다.
 */
export async function computeRankSnapshot(
  uid: string,
  date: DateString
): Promise<RankSnapshot | null> {
  const user = await getUser(uid);
  if (!user) return null;
  const tierPoints = user.tierPoints ?? 0;
  if (tierPoints <= 0) return null;

  const overallAbove = await countUsersAboveTierPoints(tierPoints);
  const snapshot: RankSnapshot = {
    date,
    overall: overallAbove + 1,
  };

  if (user.favoriteTeamCode) {
    const teamAbove = await countUsersAboveTierPoints(
      tierPoints,
      user.favoriteTeamCode
    );
    snapshot.team = teamAbove + 1;
    snapshot.teamCode = user.favoriteTeamCode;
  }

  return snapshot;
}

export async function snapshotRankForUser(
  uid: string,
  date: DateString
): Promise<void> {
  const snapshot = await computeRankSnapshot(uid, date);
  if (!snapshot) return;
  await firestore
    .collection("users")
    .doc(uid)
    .set({ rankSnapshot: snapshot }, { merge: true });
}

/**
 * 여러 유저의 rank 스냅샷을 순차 기록. 한 명 실패해도 나머지는 계속.
 */
export async function snapshotRanksForUsers(
  uids: string[],
  date: DateString
): Promise<void> {
  for (const uid of uids) {
    try {
      await snapshotRankForUser(uid, date);
    } catch (err) {
      logger.error(`snapshotRank failed for uid=${uid}`, err);
    }
  }
}

/** 동점자 동일 rank ("above count + 1"). 상위가 1위임을 가정한 in-memory 계산. */
function assignRanks(entries: ScoreboardUserEntry[]): number[] {
  const ranks: number[] = [];
  for (let i = 0; i < entries.length; i++) {
    if (i === 0) {
      ranks.push(1);
      continue;
    }
    if (entries[i].tierPoints === entries[i - 1].tierPoints) {
      ranks.push(ranks[i - 1]);
    } else {
      ranks.push(i + 1);
    }
  }
  return ranks;
}

function enrichTop(
  entries: ScoreboardUserEntry[],
  totalCount: number,
  scope: Scope
): ScoreboardEntry[] {
  const ranks = assignRanks(entries);
  return entries.map((e, i) => {
    const rank = ranks[i];
    const entry: ScoreboardEntry = {
      uid: e.uid,
      displayName: e.displayName,
      tierPoints: e.tierPoints,
      tier: tierOf(e.tierPoints),
      rank,
      rankDelta: deltaFor(e.rankSnapshot, rank, scope),
      percentile: computePercentile(rank, totalCount),
    };
    if (e.photoUrl) entry.photoUrl = e.photoUrl;
    if (e.favoriteTeamCode) entry.favoriteTeamCode = e.favoriteTeamCode;
    return entry;
  });
}

async function buildScopeCache(scope: Scope): Promise<ScoreboardScopeCache> {
  const teamCode = scope.kind === "team" ? scope.teamCode : undefined;
  const [top, totalCount] = await Promise.all([
    listTopByTierPoints(10, teamCode),
    countRankedUsers(teamCode),
  ]);
  return {
    top: enrichTop(top, totalCount, scope),
    totalCount,
    generatedAt: Date.now(),
  };
}

/**
 * 크론에서 호출: overall + 10팀 각각의 top 10 / totalCount를 RTDB에 기록한다.
 * `snapshotRanksForUsers` 이후에 호출해야 rankDelta가 정확함.
 */
export async function precomputeScoreboardCache(
  date: DateString
): Promise<void> {
  const scopes: Scope[] = [
    { kind: "overall" },
    ...Object.values(TeamCode).map(
      (teamCode) => ({ kind: "team" as const, teamCode })
    ),
  ];

  for (const scope of scopes) {
    try {
      const doc = await buildScopeCache(scope);
      await writeScope(date, scope, doc);
    } catch (err) {
      const label =
        scope.kind === "overall" ? "overall" : `team/${scope.teamCode}`;
      logger.error(`precomputeScoreboardCache failed scope=${label}`, err);
    }
  }
}