import { Injectable, Logger } from '@nestjs/common';
import { createHmac, randomUUID } from 'crypto';
import { FabricEventEnvelope } from './event-envelope.js';

type RetryTask = {
  envelope: FabricEventEnvelope;
  attempts: number;
  nextRunAt: number;
};

@Injectable()
export class EventsService {
  private readonly logger = new Logger(EventsService.name);
  private readonly sentEventIds = new Map<string, number>();
  private readonly retryQueue: RetryTask[] = [];
  private retryTimer: NodeJS.Timeout | null = null;

  private cleanupSentCache(now: number): void {
    const ttlMs = 10 * 60 * 1000;
    for (const [eventId, ts] of this.sentEventIds.entries()) {
      if (now - ts > ttlMs) this.sentEventIds.delete(eventId);
    }
  }

  private signWebhook(payload: string, timestamp: string, nonce: string): string {
    const secret = process.env.FABRIC_WEBHOOK_SECRET;
    if (!secret) return '';
    const canonical = ['POST', '/webhook/events', timestamp, nonce, payload].join('\n');
    return createHmac('sha256', secret).update(canonical).digest('hex');
  }

  private scheduleRetryPump(): void {
    if (this.retryTimer) return;
    this.retryTimer = setInterval(() => {
      void this.processRetryQueue();
    }, 1000);
  }

  private enqueueRetry(envelope: FabricEventEnvelope, attempts: number): void {
    if (attempts >= 5) {
      this.logger.warn(`drop event after max retries: ${envelope.event_id}`);
      return;
    }

    const delayMs = Math.pow(2, attempts) * 1000; // 1s,2s,4s,8s,16s
    this.retryQueue.push({
      envelope,
      attempts: attempts + 1,
      nextRunAt: Date.now() + delayMs,
    });
    this.scheduleRetryPump();
  }

  private async deliverEnvelope(envelope: FabricEventEnvelope): Promise<boolean> {
    const webhookUrl = process.env.FABRIC_WEBHOOK_URL;
    if (!webhookUrl) {
      this.logger.log(`event(no-webhook): ${JSON.stringify(envelope)}`);
      return true;
    }

    const timestamp = new Date().toISOString();
    const nonce = randomUUID();
    const payload = JSON.stringify(envelope);
    const signature = this.signWebhook(payload, timestamp, nonce);

    const response = await fetch(webhookUrl, {
      method: 'POST',
      headers: {
        'content-type': 'application/json',
        'x-fabric-version': '1',
        'x-fabric-timestamp': timestamp,
        'x-fabric-nonce': nonce,
        'x-fabric-signature': signature,
      },
      body: payload,
    });

    if (response.status >= 200 && response.status < 300) {
      return true;
    }

    // retry only transient statuses
    if ([429, 500, 502, 503, 504].includes(response.status)) {
      return false;
    }

    // permanent failure: don't retry
    this.logger.warn(`event delivery permanent failure: ${response.status}`);
    return true;
  }

  private async processRetryQueue(): Promise<void> {
    const now = Date.now();
    const due = this.retryQueue.filter((t) => t.nextRunAt <= now);
    if (due.length === 0) return;

    for (const task of due) {
      const idx = this.retryQueue.indexOf(task);
      if (idx >= 0) this.retryQueue.splice(idx, 1);

      try {
        const delivered = await this.deliverEnvelope(task.envelope);
        if (delivered) {
          this.sentEventIds.set(task.envelope.event_id, Date.now());
        } else {
          this.enqueueRetry(task.envelope, task.attempts);
        }
      } catch (error) {
        const message = error instanceof Error ? error.message : String(error);
        this.logger.warn(`retry delivery failed: ${message}`);
        this.enqueueRetry(task.envelope, task.attempts);
      }
    }
  }

  buildEnvelope(input: {
    eventType: string;
    guildId?: string | null;
    channelId?: string | null;
    actorId?: string | null;
    data: Record<string, unknown>;
  }): FabricEventEnvelope {
    return {
      event_id: randomUUID(),
      event_type: input.eventType,
      occurred_at: new Date().toISOString(),
      guild_id: input.guildId ?? null,
      channel_id: input.channelId ?? null,
      actor_id: input.actorId ?? null,
      data: input.data,
    };
  }

  async emit(input: {
    eventType: string;
    guildId?: string | null;
    channelId?: string | null;
    actorId?: string | null;
    data: Record<string, unknown>;
  }): Promise<FabricEventEnvelope> {
    const envelope = this.buildEnvelope(input);
    const now = Date.now();
    this.cleanupSentCache(now);

    if (this.sentEventIds.has(envelope.event_id)) {
      this.logger.warn(`skip duplicate event_id: ${envelope.event_id}`);
      return envelope;
    }

    const webhookUrl = process.env.FABRIC_WEBHOOK_URL;
    try {
      const delivered = await this.deliverEnvelope(envelope);
      if (delivered) {
        this.sentEventIds.set(envelope.event_id, now);
      } else {
        this.enqueueRetry(envelope, 0);
      }
    } catch (error) {
      const message = error instanceof Error ? error.message : String(error);
      this.logger.warn(`event delivery failed: ${message}`);
      if (webhookUrl) {
        this.enqueueRetry(envelope, 0);
      }
    }

    return envelope;
  }
}