import { Injectable } from '@nestjs/common';
import { PrismaService } from '../../infrastructure/prisma.service';
import { LearningSessionRepository } from '../learning-session/learning-session.repository';
import { LearningActivityRepository } from '../learning-activity/learning-activity.repository';
import { LearningRecordService } from '../learning-record/learning-record.service';
import { MaterialReadingProgressService } from '../material-reading-progress/material-reading-progress.service';
import { ReadingEventErrorCode, ReadingEventWarningCode } from './reading-event-codes';

const VALID_EVENT_TYPES = new Set([
  'material_opened', 'material_closed', 'position_changed', 'heartbeat', 'marked_as_read',
]);
const VALID_TARGET_TYPES = new Set(['knowledge_source', 'temporary_file']);
const MAX_DELTA = 300;

interface ProcessResult {
  processed: number;
  duplicate: number;
  failed: number;
  warnings: Array<{ eventId?: string; code: string; message: string }>;
}

interface ValidatedEvent {
  eventId: string;
  clientSessionId: string;
  materialId: string;
  readingTargetType: string;
  eventType: string;
  position: any | null;
  activeSecondsDelta: number;
  clientTimestampMs: bigint;
  clientTimezoneOffsetMinutes: number | null;
  sequence: number;
  platform: string | null;
  appVersion: string | null;
}

@Injectable()
export class ReadingEventProcessorService {
  constructor(
    private readonly prisma: PrismaService,
    private readonly sessionRepo: LearningSessionRepository,
    private readonly progressSvc: MaterialReadingProgressService,
    private readonly activityRepo: LearningActivityRepository,
    private readonly recordSvc: LearningRecordService,
  ) {}

  async processBatch(userId: string, events: Array<Record<string, any>>): Promise<ProcessResult> {
    // Lazy cleanup: mark interrupted sessions before processing
    await this.cleanupInterruptedSessions(userId);

    const result: ProcessResult = { processed: 0, duplicate: 0, failed: 0, warnings: [] };

    for (const e of events) {
      const { outcome, warnings } = await this.processOne(userId, e);
      switch (outcome) {
        case 'processed': result.processed++; break;
        case 'duplicate': result.duplicate++; break;
        case 'failed': result.failed++; break;
      }
      result.warnings.push(...warnings);
    }

    return result;
  }

  /** Clean up interrupted sessions for a user before processing new events. */
  async cleanupInterruptedSessions(userId: string): Promise<number> {
    const cutoff = new Date(Date.now() - 30 * 60 * 1000); // 30 min ago

    const result = await this.prisma.learningSession.updateMany({
      where: {
        userId,
        status: 'active',
        lastEventAt: { lt: cutoff },
      },
      data: { status: 'interrupted', endedAt: new Date() },
    });

    return result.count;
  }

  async processOne(
    userId: string,
    e: Record<string, any>,
  ): Promise<{ outcome: 'processed' | 'duplicate' | 'failed'; warnings: Array<{ eventId?: string; code: string; message: string }> }> {
    // 1. Validate
    const validated = this.validateEvent(e);
    if (!validated) {
      return { outcome: 'failed', warnings: [{ eventId: e.eventId, code: ReadingEventErrorCode.INVALID_EVENT_TYPE, message: 'Validation failed' }] };
    }

    // 2. Dedup
    const isDuplicate = await this.checkDuplicate(userId, e.eventId);
    if (isDuplicate) {
      return { outcome: 'duplicate', warnings: [{ eventId: e.eventId, code: ReadingEventWarningCode.DUPLICATE_EVENT, message: 'Duplicate eventId' }] };
    }

    // 3. Validate access and resolve target
    const access = await this.validateReadingAccess(userId, e.readingTargetType, e.materialId);
    const eventWarnings = this.collectWarnings(e);
    const knowledgeBaseId = access.allowed ? access.knowledgeBaseId : null;
    if (!access.allowed) {
      eventWarnings.push(access.errorCode);
    }

    // 4. Insert event + aggregate + mark processed in one transaction (F6)
    await this.prisma.$transaction(async (tx) => {
      await this.insertReadingEvent(tx, userId, validated, knowledgeBaseId, eventWarnings);

      // 5a. Aggregate → LearningSession
      await this.sessionRepo.upsertFromReadingEvent(tx, {
        userId,
        clientSessionId: validated.clientSessionId,
        materialId: validated.materialId,
        readingTargetType: validated.readingTargetType,
        knowledgeBaseId: knowledgeBaseId,
        eventType: validated.eventType,
        activeSecondsDelta: validated.activeSecondsDelta,
        position: validated.position,
        timestampMs: validated.clientTimestampMs,
      });

      // 5b. Aggregate → MaterialReadingProgress
      await this.progressSvc.upsertFromReadingEvent(tx, {
        userId,
        readingTargetType: validated.readingTargetType,
        materialId: validated.materialId,
        knowledgeBaseId: knowledgeBaseId,
        eventType: validated.eventType,
        activeSecondsDelta: validated.activeSecondsDelta,
        position: validated.position,
        isNewSession: validated.eventType === 'material_opened',
      });

      // 5c. Aggregate → DailyLearningActivity
      await this.activityRepo.upsertFromReadingEvent(tx, {
        userId,
        clientTimestampMs: validated.clientTimestampMs,
        clientTimezoneOffsetMinutes: validated.clientTimezoneOffsetMinutes,
        activeSecondsDelta: validated.activeSecondsDelta,
        isNewMaterial: validated.eventType === 'material_opened',
        isMarkedRead: validated.eventType === 'marked_as_read',
      });

      // 5d. Write LearningRecord (first open / closed / marked read)
      if (['material_opened', 'material_closed', 'marked_as_read'].includes(validated.eventType)) {
        const recordTitle = validated.eventType === 'material_opened' ? 'Reading started'
          : validated.eventType === 'material_closed' ? 'Reading ended'
          : 'Marked as read';
        await this.recordSvc.createReadingRecordTx(tx, {
          userId,
          sessionId: validated.clientSessionId,
          materialId: validated.materialId,
          readingTargetType: validated.readingTargetType,
          knowledgeBaseId: knowledgeBaseId,
          title: recordTitle,
          totalActiveSeconds: validated.activeSecondsDelta,
          lastPosition: validated.position,
          occurredAt: new Date(Number(validated.clientTimestampMs)),
        });
      }

      // 6. Mark processed
      await tx.readingEvent.update({
        where: { userId_eventId: { userId, eventId: e.eventId } },
        data: { status: 'processed', processedAt: new Date() },
      });
    });

    const resultWarnings = eventWarnings.map(code => ({ eventId: e.eventId, code, message: code }));
    return { outcome: 'processed', warnings: resultWarnings };
  }

  // ── Step 1: Validate ──

  validateEvent(e: Record<string, any>): ValidatedEvent | null {
    if (!e.eventId || !e.clientSessionId || !e.materialId) return null;
    if (!VALID_TARGET_TYPES.has(e.readingTargetType)) return null;
    if (!VALID_EVENT_TYPES.has(e.eventType)) return null;

    const delta = Number(e.activeSecondsDelta ?? 0);
    if (isNaN(delta) || delta < 0) return null;

    const ts = Number(e.clientTimestampMs ?? 0);
    if (isNaN(ts) || ts <= 0) return null;

    let position = e.position ?? null;
    if (position && !this.isValidPosition(position)) {
      position = null; // save event but don't update progress
    }

    return {
      eventId: e.eventId,
      clientSessionId: e.clientSessionId,
      materialId: e.materialId,
      readingTargetType: e.readingTargetType,
      eventType: e.eventType,
      position,
      activeSecondsDelta: Math.min(delta, MAX_DELTA),
      clientTimestampMs: BigInt(ts),
      clientTimezoneOffsetMinutes: e.clientTimezoneOffsetMinutes ?? null,
      sequence: Number(e.sequence ?? 0),
      platform: e.platform ?? null,
      appVersion: e.appVersion ?? null,
    };
  }

  // ── Step 2: Dedup ──

  private async checkDuplicate(userId: string, eventId: string): Promise<boolean> {
    const existing = await this.prisma.readingEvent.findUnique({
      where: { userId_eventId: { userId, eventId } },
      select: { id: true, status: true },
    });
    // Only skip if already successfully processed (not failed/pending)
    return !!existing && existing.status === 'processed';
  }

  // ── Step 3: Resolve target (with access validation) ──

  /** Validate reading access and return knowledgeBaseId or error code. */
  async validateReadingAccess(
    userId: string,
    readingTargetType: string,
    materialId: string,
  ): Promise<{ allowed: true; knowledgeBaseId: string | null } | { allowed: false; errorCode: string }> {
    if (readingTargetType === 'knowledge_source') {
      const src = await this.prisma.knowledgeSource.findUnique({
        where: { id: materialId },
        select: { userId: true, knowledgeBaseId: true, deletedAt: true },
      });
      if (!src) return { allowed: false, errorCode: ReadingEventErrorCode.MATERIAL_NOT_FOUND };
      if (src.userId !== userId) return { allowed: false, errorCode: ReadingEventErrorCode.MATERIAL_ACCESS_DENIED };
      if (src.deletedAt) return { allowed: false, errorCode: ReadingEventWarningCode.SOURCE_DELETED };
      return { allowed: true, knowledgeBaseId: src.knowledgeBaseId };
    }

    if (readingTargetType === 'temporary_file') {
      const mat = await this.prisma.temporaryReadingMaterial.findUnique({
        where: { id: materialId },
        select: { userId: true, deletedAt: true, expiresAt: true, sourceStatus: true },
      });
      if (!mat) return { allowed: false, errorCode: ReadingEventErrorCode.TEMPORARY_MATERIAL_NOT_FOUND };
      if (mat.userId !== userId) return { allowed: false, errorCode: ReadingEventErrorCode.MATERIAL_ACCESS_DENIED };
      if (mat.deletedAt) return { allowed: false, errorCode: ReadingEventWarningCode.SOURCE_DELETED };
      if (mat.expiresAt && mat.expiresAt < new Date()) {
        return { allowed: false, errorCode: ReadingEventErrorCode.TEMPORARY_MATERIAL_EXPIRED };
      }
      if (mat.sourceStatus === 'expired') {
        return { allowed: false, errorCode: ReadingEventErrorCode.TEMPORARY_MATERIAL_EXPIRED };
      }
      return { allowed: true, knowledgeBaseId: null };
    }

    return { allowed: false, errorCode: ReadingEventErrorCode.INVALID_TARGET_TYPE };
  }

  async resolveReadingTarget(
    userId: string,
    readingTargetType: string,
    materialId: string,
  ): Promise<{ knowledgeBaseId: string | null } | null> {
    if (readingTargetType === 'knowledge_source') {
      const src = await this.prisma.knowledgeSource.findUnique({
        where: { id: materialId },
        select: { userId: true, knowledgeBaseId: true },
      });
      if (!src || src.userId !== userId) return null;
      return { knowledgeBaseId: src.knowledgeBaseId };
    }

    if (readingTargetType === 'temporary_file') {
      const mat = await this.prisma.temporaryReadingMaterial.findUnique({
        where: { id: materialId },
        select: { userId: true, deletedAt: true, expiresAt: true, sourceStatus: true },
      });
      if (!mat || mat.userId !== userId) return null;
      if (mat.deletedAt) return null;
      if (mat.expiresAt && mat.expiresAt < new Date()) return null;
      if (mat.sourceStatus === 'expired') return null;
      return { knowledgeBaseId: null };
    }

    return null;
  }

  // ── Step 4: Insert ──

  private async insertReadingEvent(
    tx: any,
    userId: string,
    e: ValidatedEvent,
    knowledgeBaseId: string | null,
    warnings: string[],
  ) {
    await tx.readingEvent.create({
      data: {
        userId,
        eventId: e.eventId,
        clientSessionId: e.clientSessionId,
        readingTargetType: e.readingTargetType,
        materialId: e.materialId,
        knowledgeBaseId,
        eventType: e.eventType,
        position: e.position ?? undefined,
        activeSecondsDelta: e.activeSecondsDelta,
        clientTimestampMs: e.clientTimestampMs,
        clientTimezoneOffsetMinutes: e.clientTimezoneOffsetMinutes,
        sequence: e.sequence,
        platform: e.platform,
        appVersion: e.appVersion,
        status: 'processing',
        warningCodes: warnings.length > 0 ? warnings : undefined,
        serverReceivedAt: new Date(),
      },
    });
  }

  // ── Helpers ──

  private isValidPosition(pos: any): boolean {
    if (!pos || typeof pos !== 'object') return false;
    return ['Markdown', 'Text', 'Pdf', 'Image', 'Epub', 'Unknown'].includes(pos.type);
  }

  private collectWarnings(e: Record<string, any>): string[] {
    const warnings: string[] = [];
    const delta = Number(e.activeSecondsDelta ?? 0);
    if (delta > MAX_DELTA) warnings.push(ReadingEventWarningCode.ACTIVE_SECONDS_CAPPED);

    const ts = Number(e.clientTimestampMs ?? 0);
    if (ts > Date.now() + 5 * 60 * 1000) warnings.push(ReadingEventWarningCode.CLIENT_TIMESTAMP_SKEWED);

    if (e.position && !this.isValidPosition(e.position)) {
      warnings.push(ReadingEventWarningCode.POSITION_IGNORED);
    }

    return warnings;
  }
}