import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
import { api, hasSessionToken } from '@/services/backend';
import { getLatestByPhase } from '@/services/assessmentService';
import { getProgramProgress } from '@/services/programService';
import { PROGRAM_SESSION_COUNT } from '@/data/program/sessions';

/** Sessions 1..(N-1) done ⇒ learner is on final session; post-test may open manually. */
const POST_TEST_UNLOCK_MIN_COMPLETED_SESSIONS = PROGRAM_SESSION_COUNT - 1;

export type LearningStep =
  | 'registered'
  | 'pre_test_done'
  | 'training_in_progress'
  | 'training_completed'
  | 'post_test_done'
  | 'completed';

export interface LearningProgress {
  user_id: string;
  current_step: LearningStep;
  pre_test_completed_at: string | null;
  training_started_at: string | null;
  training_completed_at: string | null;
  post_test_completed_at: string | null;
  updated_at?: string;
}

const getStorageKey = (userId: string) => `learning-progress:${userId}`;

const defaultProgress = (userId: string): LearningProgress => ({
  user_id: userId,
  current_step: 'registered',
  pre_test_completed_at: null,
  training_started_at: null,
  training_completed_at: null,
  post_test_completed_at: null
});

const readLocalProgress = (userId: string): LearningProgress => {
  try {
    const saved = localStorage.getItem(getStorageKey(userId));
    return saved ? (JSON.parse(saved) as LearningProgress) : defaultProgress(userId);
  } catch {
    return defaultProgress(userId);
  }
};

const writeLocalProgress = (progress: LearningProgress) => {
  localStorage.setItem(getStorageKey(progress.user_id), JSON.stringify(progress));
};

/** Mirrors backend deriveCurrentStep (timestamps are authoritative). */
const deriveStep = (progress: LearningProgress): LearningStep => {
  if (progress.post_test_completed_at) return 'completed';
  if (progress.training_completed_at) return 'training_completed';
  if (progress.training_started_at && progress.pre_test_completed_at) return 'training_in_progress';
  if (progress.pre_test_completed_at) return 'pre_test_done';
  return 'registered';
};

export function useLearningJourney(userId?: string) {
  /** Offline guest ids are `guest-…` and have no backend session. */
  const useLocalOnly = !hasSessionToken() || Boolean(userId?.startsWith('guest-'));

  const [progress, setProgress] = useState<LearningProgress | null>(null);
  const [backendPermissions, setBackendPermissions] = useState<{
    canTakePreTest: boolean;
    canOpenTraining: boolean;
    canTakePostTest: boolean;
    isCompleted: boolean;
  } | null>(null);
  const [loading, setLoading] = useState(true);
  /** Skeleton / blocking load only on first fetch — silent on reloadProgress. */
  const hasLoadedOnceRef = useRef(false);

  const mapBackendJourney = useCallback((journey: {
    currentStep: LearningStep;
    preTestCompletedAt: string | null;
    trainingStartedAt: string | null;
    trainingCompletedAt: string | null;
    postTestCompletedAt: string | null;
    lastActivityAt: string | null;
  }): LearningProgress => ({
    user_id: userId ?? '',
    current_step: journey.currentStep,
    pre_test_completed_at: journey.preTestCompletedAt,
    training_started_at: journey.trainingStartedAt,
    training_completed_at: journey.trainingCompletedAt,
    post_test_completed_at: journey.postTestCompletedAt,
    updated_at: journey.lastActivityAt ?? undefined,
  }), [userId]);

  const mergeAssessmentCompletion = useCallback(
    async (base: LearningProgress): Promise<LearningProgress> => {
      try {
        const [preAttempt, postAttempt] = await Promise.all([
          getLatestByPhase(base.user_id, 'pre'),
          getLatestByPhase(base.user_id, 'post'),
        ]);

        const merged: LearningProgress = {
          ...base,
          pre_test_completed_at: base.pre_test_completed_at ?? preAttempt?.completedAt ?? null,
          training_started_at:
            base.training_started_at ??
            base.pre_test_completed_at ??
            preAttempt?.completedAt ??
            null,
          post_test_completed_at: base.post_test_completed_at ?? postAttempt?.completedAt ?? null,
        };
        merged.current_step = deriveStep(merged);
        return merged;
      } catch {
        return base;
      }
    },
    []
  );

  const loadProgress = useCallback(async () => {
    if (!userId) {
      setProgress(null);
      setBackendPermissions(null);
      setLoading(false);
      return;
    }

    const isInitialLoad = !hasLoadedOnceRef.current;
    if (isInitialLoad) {
      setLoading(true);
    }

    if (useLocalOnly) {
      const local = await mergeAssessmentCompletion(readLocalProgress(userId));
      setProgress(local);
      setBackendPermissions(null);
      hasLoadedOnceRef.current = true;
      setLoading(false);
      return;
    }

    try {
      const journey = await api.get<{
        currentStep: LearningStep;
        preTestCompletedAt: string | null;
        trainingStartedAt: string | null;
        trainingCompletedAt: string | null;
        postTestCompletedAt: string | null;
        lastActivityAt: string | null;
        permissions: {
          canTakePreTest: boolean;
          canOpenTraining: boolean;
          canTakePostTest: boolean;
          isCompleted: boolean;
        };
      }>('/journey');
      const mapped = mapBackendJourney(journey);
      const merged = await mergeAssessmentCompletion(mapped);
      setProgress(merged);
      setBackendPermissions(journey.permissions);
    } catch (error) {
      console.error('Error loading learning progress:', error);
      const local = readLocalProgress(userId);
      const merged = await mergeAssessmentCompletion(local);
      setProgress(merged);
      setBackendPermissions(null);
    } finally {
      hasLoadedOnceRef.current = true;
      setLoading(false);
    }
  }, [mapBackendJourney, mergeAssessmentCompletion, userId, useLocalOnly]);

  useEffect(() => {
    hasLoadedOnceRef.current = false;
  }, [userId]);

  useEffect(() => {
    loadProgress();
  }, [loadProgress]);

  const saveProgress = useCallback(
    async (next: LearningProgress) => {
      // Optimistic update - فوری state را update کن
      setProgress(next);

      if (useLocalOnly) {
        writeLocalProgress(next);
        return;
      }

      // Backend is source of truth for authenticated users.
      // Do not write journey state directly from frontend.
      writeLocalProgress(next);
    },
    [useLocalOnly]
  );

  const markPreTestDone = useCallback(async (completedAt?: string) => {
    const now = completedAt ?? new Date().toISOString();
    const base = progress ?? {
      user_id: userId ?? '',
      current_step: 'registered' as const,
      pre_test_completed_at: null,
      training_started_at: null,
      training_completed_at: null,
      post_test_completed_at: null
    };
    const next = {
      ...base,
      current_step: 'training_in_progress' as const,
      pre_test_completed_at: base.pre_test_completed_at || now,
      training_started_at: base.training_started_at || now
    };
    await saveProgress(next);
    return true;
  }, [progress, saveProgress, userId]);

  const markTrainingDone = useCallback(async () => {
    if (!userId) return false;
    if (!useLocalOnly) {
      await loadProgress();
      return true;
    }
    const now = new Date().toISOString();
    const base = progress ?? defaultProgress(userId);
    if (base.training_completed_at) {
      return true;
    }
    const next = {
      ...base,
      user_id: userId,
      current_step: 'training_completed' as const,
      training_started_at: base.training_started_at || now,
      training_completed_at: now
    };
    await saveProgress(next);
    return true;
  }, [loadProgress, progress, saveProgress, useLocalOnly, userId]);

  const markPostTestDone = useCallback(async (completedAt?: string) => {
    if (!userId) return false;
    const now = completedAt ?? new Date().toISOString();
    const base = progress ?? defaultProgress(userId);
    if (base.post_test_completed_at) {
      return true;
    }
    const next = {
      ...base,
      user_id: userId,
      current_step: 'completed' as const,
      post_test_completed_at: now
    };
    await saveProgress(next);
    return true;
  }, [progress, saveProgress, userId]);

  const derivedPermissions = useMemo(() => {
    const completedSessions = userId
      ? getProgramProgress(userId).completedSessions.length
      : 0;
    const reachedFinalSession =
      Boolean(progress?.training_completed_at) ||
      completedSessions >= POST_TEST_UNLOCK_MIN_COMPLETED_SESSIONS;

    return {
      canTakePreTest: !progress?.pre_test_completed_at,
      canOpenTraining: Boolean(progress?.pre_test_completed_at),
      canTakePostTest: Boolean(
        progress?.pre_test_completed_at &&
          reachedFinalSession &&
          !progress?.post_test_completed_at
      ),
      isCompleted: Boolean(progress?.post_test_completed_at)
    };
  }, [progress, userId]);

  const permissions = backendPermissions ?? derivedPermissions;

  return {
    progress,
    loading,
    permissions,
    reloadProgress: loadProgress,
    markPreTestDone,
    markTrainingDone,
    markPostTestDone
  };
}