src/lib/weeklyContest.ts

import type { CodingQuestion } from '../data/codingQuestions';
import { getActivityDateKey } from './activityDates';

export type WeeklyContest = {
  id: string;
  startTime: Date;
  endTime: Date;
  durationMinutes: number;
  isLive: boolean;
  canJoin: boolean;
};

export type WeeklyContestPrizeTier = {
  fromRank: number;
  toRank: number;
  label: string;
  coins: number;
};

const WEEKLY_CONTEST_DAY = 0;
const WEEKLY_CONTEST_START_HOUR = 20;
const WEEKLY_CONTEST_DURATION_MINUTES = 90;
const WEEKLY_CONTEST_JOIN_STORAGE_PREFIX = 'ryp.weeklyContest.joined';
const WEEKLY_CONTEST_CLAIM_STORAGE_PREFIX = 'ryp.weeklyContest.claimed';

export const WEEKLY_CONTEST_PRIZE_TIERS: WeeklyContestPrizeTier[] = [
  { fromRank: 1, toRank: 1, label: '1st place', coins: 5000 },
  { fromRank: 2, toRank: 2, label: '2nd place', coins: 3000 },
  { fromRank: 3, toRank: 3, label: '3rd place', coins: 1000 },
  { fromRank: 4, toRank: 10, label: '4th - 10th', coins: 100 },
] as const;

const contestPointsByDifficulty: Record<CodingQuestion['difficulty'], number> = {
  Easy: 150,
  Medium: 300,
  Hard: 550,
};

export function getWeeklyContest(now: Date) {
  const thisWeekContest = buildContestForWeek(now, 0, now);
  if (now >= thisWeekContest.endTime) {
    return buildContestForWeek(now, 1, now);
  }

  return thisWeekContest;
}

export function getLatestCompletedWeeklyContest(now: Date) {
  const thisWeekContest = buildContestForWeek(now, 0, now);
  if (now >= thisWeekContest.endTime) {
    return thisWeekContest;
  }

  return buildContestForWeek(now, -1, now);
}

export function getWeeklyContestQuestions(questions: CodingQuestion[]) {
  const buckets = {
    Easy: questions.filter((question) => question.difficulty === 'Easy'),
    Medium: questions.filter((question) => question.difficulty === 'Medium'),
    Hard: questions.filter((question) => question.difficulty === 'Hard'),
  };

  const selected = [
    buckets.Easy[0],
    buckets.Medium[0],
    buckets.Medium[1],
    buckets.Hard[0],
  ].filter(Boolean) as CodingQuestion[];

  if (selected.length >= 4) {
    return selected.slice(0, 4);
  }

  const selectedIds = new Set(selected.map((question) => question.id));
  for (const question of questions) {
    if (selectedIds.has(question.id)) {
      continue;
    }

    selected.push(question);
    selectedIds.add(question.id);

    if (selected.length === 4) {
      break;
    }
  }

  return selected;
}

export function getContestQuestionPoints(question: CodingQuestion) {
  return contestPointsByDifficulty[question.difficulty];
}

export function getContestPrizeForRank(rank: number) {
  const tier = WEEKLY_CONTEST_PRIZE_TIERS.find(
    (entry) => rank >= entry.fromRank && rank <= entry.toRank,
  );

  return tier?.coins ?? 0;
}

export function getContestPrizePool() {
  return WEEKLY_CONTEST_PRIZE_TIERS.reduce(
    (sum, tier) => sum + (tier.toRank - tier.fromRank + 1) * tier.coins,
    0,
  );
}

export function formatDurationFromNow(now: Date, target: Date) {
  const diffMs = Math.max(target.getTime() - now.getTime(), 0);
  const totalMinutes = Math.ceil(diffMs / 60000);
  const days = Math.floor(totalMinutes / (60 * 24));
  const hours = Math.floor((totalMinutes % (60 * 24)) / 60);
  const minutes = totalMinutes % 60;
  const parts: string[] = [];

  if (days > 0) {
    parts.push(`${days}d`);
  }
  if (hours > 0) {
    parts.push(`${hours}h`);
  }
  if ((days === 0 && hours === 0) || minutes > 0) {
    parts.push(`${minutes}m`);
  }

  return parts.join(' ');
}

export function readJoinedContestIds(userId: string) {
  return readStoredContestIds(getJoinedContestStorageKey(userId));
}

export function joinWeeklyContest(userId: string, contestId: string) {
  const nextIds = mergeStoredContestId(readJoinedContestIds(userId), contestId);
  writeStoredContestIds(getJoinedContestStorageKey(userId), nextIds);
  return nextIds;
}

export function readClaimedContestIds(userId: string) {
  return readStoredContestIds(getClaimedContestStorageKey(userId));
}

export function markWeeklyContestPrizeClaimed(userId: string, contestId: string) {
  const nextIds = mergeStoredContestId(readClaimedContestIds(userId), contestId);
  writeStoredContestIds(getClaimedContestStorageKey(userId), nextIds);
  return nextIds;
}

function buildContestForWeek(now: Date, weekOffset: number, referenceNow: Date): WeeklyContest {
  const startTime = getContestStartForWeek(now, weekOffset);
  const endTime = new Date(
    startTime.getTime() + WEEKLY_CONTEST_DURATION_MINUTES * 60 * 1000,
  );

  return {
    id: getActivityDateKey(startTime),
    startTime,
    endTime,
    durationMinutes: WEEKLY_CONTEST_DURATION_MINUTES,
    isLive: referenceNow >= startTime && referenceNow < endTime,
    canJoin: referenceNow < startTime,
  };
}

function getContestStartForWeek(now: Date, weekOffset: number) {
  const contestStart = new Date(now);
  const dayDelta = WEEKLY_CONTEST_DAY - contestStart.getDay() + weekOffset * 7;

  contestStart.setDate(contestStart.getDate() + dayDelta);
  contestStart.setHours(WEEKLY_CONTEST_START_HOUR, 0, 0, 0);

  return contestStart;
}

function getJoinedContestStorageKey(userId: string) {
  return `${WEEKLY_CONTEST_JOIN_STORAGE_PREFIX}.${userId}`;
}

function getClaimedContestStorageKey(userId: string) {
  return `${WEEKLY_CONTEST_CLAIM_STORAGE_PREFIX}.${userId}`;
}

function readStoredContestIds(storageKey: string) {
  if (typeof window === 'undefined') {
    return [] as string[];
  }

  try {
    const raw = window.localStorage.getItem(storageKey);
    if (!raw) {
      return [];
    }

    const parsed = JSON.parse(raw);
    if (Array.isArray(parsed)) {
      return normalizeContestIds(parsed);
    }

    if (typeof parsed === 'string') {
      return normalizeContestIds([parsed]);
    }
  } catch {
    try {
      const legacyValue = window.localStorage.getItem(storageKey);
      return legacyValue ? normalizeContestIds([legacyValue]) : [];
    } catch {
      return [];
    }
  }

  return [];
}

function writeStoredContestIds(storageKey: string, ids: string[]) {
  if (typeof window === 'undefined') {
    return;
  }

  try {
    window.localStorage.setItem(storageKey, JSON.stringify(normalizeContestIds(ids)));
  } catch {
    // Ignore storage errors so the UI still works without persistence.
  }
}

function mergeStoredContestId(ids: string[], contestId: string) {
  return normalizeContestIds([...ids, contestId]);
}

function normalizeContestIds(ids: string[]) {
  const seen = new Set<string>();
  const normalized: string[] = [];

  for (const rawId of ids) {
    const id = String(rawId).trim();
    if (!id || seen.has(id)) {
      continue;
    }

    seen.add(id);
    normalized.push(id);
  }

  return normalized;
}