// utils/BrainDataClient.ts
// Client for managing Brain study progress data with mode progression

import { kvStore } from "../modules/KvCacheStore.ts";
import {
  BrainQuestionProgress,
  BrainQueueItem,
  KvObj,
  QuizConfig,
} from "./types.ts";
import { calculateNextReview, isDue } from "./spacedRepetition.ts";
import {
  DEFAULT_QUIZ_MODE,
  getModeIndex,
  getNextMode,
  QUIZ_MODES,
} from "./quizModes.ts";

// How many days to push out review-only cards
const REVIEW_ONLY_INTERVAL_DAYS = 30;

const REVIEW_ONLY_MIN_DAYS_SINCE_LAST_REVIEW = 30;

function shuffleInPlace<T>(arr: T[]) {
  for (let i = arr.length - 1; i > 0; i--) {
    const j = Math.floor(Math.random() * (i + 1));
    [arr[i], arr[j]] = [arr[j], arr[i]];
  }
}

/**
 * Generate composite ID for brain progress record (mode-agnostic)
 */
export function generateBrainProgressId(
  userId: string,
  questionId: string,
): string {
  return `${userId}_${questionId}`;
}

/**
 * Client for managing Brain study progress with mode progression
 */
export class BrainDataClient {
  /**
   * Get all progress records for a user
   */
  async getUserProgress(userId: string): Promise<BrainQuestionProgress[]> {
    const progress: BrainQuestionProgress[] = [];

    for await (
      const entry of kvStore.list<BrainQuestionProgress>({
        prefix: ["brain_question_progress", userId],
      })
    ) {
      if (entry.value) {
        progress.push(entry.value);
      }
    }

    return progress;
  }

  /**
   * Get a specific progress record for a question (mode-agnostic)
   */
  async getProgress(
    userId: string,
    questionId: string,
  ): Promise<BrainQuestionProgress | null> {
    const id = generateBrainProgressId(userId, questionId);
    const key = ["brain_question_progress", userId, id];
    return await kvStore.get<BrainQuestionProgress>(key);
  }

  /**
   * Get all questions due for review
   */
  async getDueQuestions(userId: string): Promise<BrainQuestionProgress[]> {
    const allProgress = await this.getUserProgress(userId);
    return allProgress.filter((p) => isDue(p.next_due_at));
  }

  /**
   * Record an answer and update progress with mode progression logic
   *
   * Mode progression rules:
   * - When wasCorrectFirstTry is true and not in final mode: advance to next mode
   * - When wasCorrectFirstTry is true and in final mode: mark as review-only
   * - When wasCorrectFirstTry is false: stay in current mode, reset consecutive streak
   */
  async recordAnswer(
    userId: string,
    questionId: string,
    quizId: string,
    wasCorrectFirstTry: boolean,
  ): Promise<BrainQuestionProgress> {
    const id = generateBrainProgressId(userId, questionId);
    const key = ["brain_question_progress", userId, id];
    const now = Date.now();

    // Get existing progress or create new
    const existing = await kvStore.get<BrainQuestionProgress>(key);

    // Determine current mode and index
    let currentMode = existing?.current_mode ?? DEFAULT_QUIZ_MODE;
    let modeIndex = existing?.mode_index ?? 0;
    let consecutiveFirstTry = existing?.consecutive_first_try ?? 0;
    let isReviewOnly = existing?.is_review_only ?? false;
    let currentInterval = existing?.interval_days ?? 1;
    const currentEase = existing?.ease_factor ?? 2.5;

    // Mode progression logic
    if (wasCorrectFirstTry) {
      consecutiveFirstTry++;

      // Advance to next mode if correct on first try
      const nextMode = getNextMode(currentMode);
      if (nextMode !== null) {
        // Move to next harder mode
        currentMode = nextMode;
        modeIndex = getModeIndex(nextMode);
        // Reset interval for the new mode (card needs to be reviewed soon in new mode)
        currentInterval = 1;
      } else {
        // Already at final mode and correct on first try - mark as review-only
        isReviewOnly = true;
        // Push due date far out for review-only cards
        currentInterval = REVIEW_ONLY_INTERVAL_DAYS;
      }
    } else {
      // Incorrect: reset consecutive streak, stay in current mode
      consecutiveFirstTry = 0;
      // Don't reset mode - keep in current mode until they get it right
    }

    // Calculate new review schedule
    const { nextDueAt, newInterval, newEaseFactor } = calculateNextReview(
      wasCorrectFirstTry,
      currentInterval,
      currentEase,
    );

    // For review-only cards, use longer interval
    const finalInterval = isReviewOnly
      ? Math.max(newInterval, REVIEW_ONLY_INTERVAL_DAYS)
      : newInterval;
    const finalNextDueAt = isReviewOnly
      ? now + (finalInterval * 24 * 60 * 60 * 1000)
      : nextDueAt;

    const progress: BrainQuestionProgress = {
      id,
      user_id: userId,
      quiz_id: quizId,
      question_id: questionId,
      current_mode: currentMode,
      mode_index: modeIndex,
      attempts: (existing?.attempts ?? 0) + 1,
      first_try_successes: (existing?.first_try_successes ?? 0) +
        (wasCorrectFirstTry ? 1 : 0),
      consecutive_first_try: consecutiveFirstTry,
      last_result: wasCorrectFirstTry,
      next_due_at: finalNextDueAt,
      interval_days: finalInterval,
      ease_factor: newEaseFactor,
      is_review_only: isReviewOnly,
      created_on: existing?.created_on ?? now,
      updated_on: now,
    };

    await kvStore.set(key, progress);
    return progress;
  }

  /**
   * Build study queue from all user's quizzes
   * Returns cards sorted by mode (easier modes first), then by due status
   * Review-only cards are deprioritized unless there are too few active cards
   */
  async buildStudyQueue(
    userId: string,
    quizConfigs: KvObj<QuizConfig>[],
    _mode: string, // Deprecated - mode is now per-card based on progression
    newCardsLimit: number = 10,
    totalLimit: number = 50,
  ): Promise<BrainQueueItem[]> {
    const now = Date.now();
    // Get all existing progress for this user
    const allProgress = await this.getUserProgress(userId);
    const progressMap = new Map<string, BrainQuestionProgress>();

    for (const p of allProgress) {
      progressMap.set(p.question_id, p);
    }

    // Build queue items from all questions
    const allItems: {
      item: BrainQueueItem;
      nextDueAt: number | null;
      isNew: boolean; // Truly new (never seen)
      isInProgression: boolean; // Has started but not completed all modes
      modeIndex: number;
      isReviewOnly: boolean;
      isDue: boolean;
      isReviewLongEnough: boolean;
    }[] = [];

    for (const kvObj of quizConfigs) {
      if (!kvObj.value?.questions) continue;

      for (const question of kvObj.value.questions) {
        const progress = progressMap.get(question.id) ?? null;
        // "Truly new" = never seen before (no progress record)
        const isTrulyNew = progress === null;
        // "In progression" = has started but hasn't completed all 6 modes yet
        const isInProgression = progress !== null && !progress.is_review_only;
        // For UI: "new" means either truly new or still in active progression
        const isNew = isTrulyNew || isInProgression;

        // Determine the mode for this card
        const displayMode = progress?.current_mode ?? DEFAULT_QUIZ_MODE;
        const modeIndex = progress?.mode_index ?? 0;
        const isReviewOnly = progress?.is_review_only ?? false;
        const nextDueAt = progress?.next_due_at ?? null;
        const cardIsDue = isDue(nextDueAt);
        const lastReviewedAt = progress?.updated_on ?? progress?.created_on ??
          null;
        const isReviewLongEnough = !isReviewOnly || lastReviewedAt === null
          ? true
          : (now - lastReviewedAt) >=
            (REVIEW_ONLY_MIN_DAYS_SINCE_LAST_REVIEW * 24 * 60 * 60 * 1000);

        allItems.push({
          item: {
            question_id: question.id,
            quiz_id: kvObj.value.quiz_config_id,
            question_data: question,
            progress,
            is_new: isNew,
            display_mode: displayMode,
            mode_index: modeIndex,
            is_review_only: isReviewOnly,
          },
          nextDueAt,
          isNew: isTrulyNew, // For queue building, only count truly new cards toward newLimit
          isInProgression,
          modeIndex,
          isReviewOnly,
          isDue: cardIsDue,
          isReviewLongEnough,
        });
      }
    }

    // Separate cards into categories for the locked-set study behavior:
    // 1. Cards currently in progression (started but not finished all 6 modes) - highest priority
    //    IMPORTANT: Do NOT gate on isDue - active-learning cards should remain eligible
    //    even if next_due_at is in the future, so the user can complete all 6 modes in one session
    // 2. Truly new cards (never seen) - these fill the active set up to newLimit
    // 3. Review-only cards (completed all modes, now in spaced repetition) - only if due
    const inProgressionCards = allItems.filter(
      (item) => item.isInProgression, // No isDue check - always include in-progression cards
    );
    const trulyNewCards = allItems.filter((item) => item.isNew);
    const reviewOnlyCards = allItems.filter(
      (item) => item.isReviewOnly && item.isDue && item.isReviewLongEnough, // Review-only respects due and minimum time since last review
    );

    // Sort each category by mode index (easier modes first for learning progression)
    const sortByModeAndDue = (
      a: typeof allItems[0],
      b: typeof allItems[0],
    ) => {
      // Primary: mode index (lower = easier = first)
      if (a.modeIndex !== b.modeIndex) {
        return a.modeIndex - b.modeIndex;
      }
      // Secondary: due status (more overdue first)
      const aDue = a.nextDueAt ?? Date.now();
      const bDue = b.nextDueAt ?? Date.now();
      return aDue - bDue;
    };

    inProgressionCards.sort(sortByModeAndDue);
    trulyNewCards.sort(sortByModeAndDue);
    reviewOnlyCards.sort(sortByModeAndDue);

    // Randomize the pool of new cards so large queue requests don't return the same order
    // Keep in-progression cards sorted/stable so users can reliably finish what they've started.
    shuffleInPlace(trulyNewCards);
    shuffleInPlace(reviewOnlyCards);

    // Build final queue using locked-set behavior:
    // - First, include all cards currently in progression (they're part of the active set)
    // - Then, fill up to newCardsLimit with truly new cards
    // - Review-only cards are only added if specifically requested (not mixed into active set)
    const queue: BrainQueueItem[] = [];

    // 1. Add all cards currently in progression (these are the "active set" that must be completed)
    for (const { item } of inProgressionCards) {
      if (queue.length >= totalLimit) break;
      queue.push(item);
    }

    // 2. Calculate how many slots are available for new cards
    // The active set should be up to newCardsLimit (default 20)
    const activeSetCount = queue.length;
    const slotsForNew = Math.max(0, newCardsLimit - activeSetCount);

    // 3. Add truly new cards to fill the active set up to the limit
    let newCardsAdded = 0;
    for (const { item } of trulyNewCards) {
      if (queue.length >= totalLimit || newCardsAdded >= slotsForNew) break;
      queue.push(item);
      newCardsAdded++;
    }

    // 4. Only add review-only cards if there are no active new/progression cards
    // This ensures the user focuses on completing the active set before reviews
    if (queue.length === 0) {
      for (const { item } of reviewOnlyCards) {
        if (queue.length >= totalLimit) break;
        queue.push(item);
      }
    }

    return queue;
  }

  /**
   * Get count of questions due for review
   */
  async getDueCount(userId: string, _mode?: string): Promise<number> {
    const allProgress = await this.getUserProgress(userId);
    // Mode parameter is deprecated - count all due cards
    return allProgress.filter((p) => isDue(p.next_due_at)).length;
  }

  /**
   * Get statistics for a user
   */
  async getStats(userId: string, _mode?: string): Promise<{
    totalReviewed: number;
    totalCorrect: number;
    dueNow: number;
    accuracy: number;
    reviewOnlyCount: number;
    modeDistribution: Record<string, number>;
  }> {
    const allProgress = await this.getUserProgress(userId);

    const totalReviewed = allProgress.reduce(
      (sum, p) => sum + (p.attempts ?? 0),
      0,
    );
    const totalCorrect = allProgress.reduce(
      (sum, p) => sum + (p.first_try_successes ?? 0),
      0,
    );
    const dueNow = allProgress.filter((p) => isDue(p.next_due_at)).length;
    const accuracy = totalReviewed > 0
      ? (totalCorrect / totalReviewed) * 100
      : 0;
    const reviewOnlyCount = allProgress.filter((p) => p.is_review_only).length;

    // Count cards by current mode
    const modeDistribution: Record<string, number> = {};
    for (const mode of QUIZ_MODES) {
      modeDistribution[mode] = 0;
    }
    for (const p of allProgress) {
      const mode = p.current_mode ?? DEFAULT_QUIZ_MODE;
      modeDistribution[mode] = (modeDistribution[mode] ?? 0) + 1;
    }

    return {
      totalReviewed,
      totalCorrect,
      dueNow,
      accuracy: Math.round(accuracy * 10) / 10,
      reviewOnlyCount,
      modeDistribution,
    };
  }

  /**
   * Reset progress for a specific question
   */
  async resetQuestionProgress(
    userId: string,
    questionId: string,
  ): Promise<void> {
    const id = generateBrainProgressId(userId, questionId);
    const key = ["brain_question_progress", userId, id];
    await kvStore.delete(key);
  }

  /**
   * Reset all progress for a quiz
   */
  async resetQuizProgress(userId: string, quizId: string): Promise<void> {
    const allProgress = await this.getUserProgress(userId);
    for (const p of allProgress) {
      if (p.quiz_id === quizId) {
        const key = ["brain_question_progress", userId, p.id];
        await kvStore.delete(key);
      }
    }
  }

  /**
   * Reset all progress for a user
   */
  async resetAllProgress(userId: string): Promise<void> {
    const allProgress = await this.getUserProgress(userId);
    for (const p of allProgress) {
      const key = ["brain_question_progress", userId, p.id];
      await kvStore.delete(key);
    }
  }
}

// Export singleton instance
export const brainDataClient = new BrainDataClient();