import { Injectable, Logger } from '@nestjs/common';
import { ConfigService } from '@nestjs/config';
import * as crypto from 'crypto';

export interface PaperlessPayload {
  document_id?:   number;
  id?:            number;
  title?:         string;
  document_type?: string;
  correspondent?: string;
  tags?:          string[];
  created?:       string;
  added?:         string;
  content?:       string;
  original_file_name?: string;
}

@Injectable()
export class WebhooksService {
  private readonly logger = new Logger(WebhooksService.name);
  private readonly secret: string;

  constructor(private readonly config: ConfigService) {
    this.secret = config.get('PAPERLESS_WEBHOOK_SECRET', '');
  }

  validateSignature(payload: string, signature: string): boolean {
    if (!this.secret) return true;  // secret not configured → allow (dev mode)
    const expected = 'sha256=' + crypto
      .createHmac('sha256', this.secret)
      .update(payload)
      .digest('hex');
    try {
      return crypto.timingSafeEqual(Buffer.from(expected), Buffer.from(signature));
    } catch {
      return false;
    }
  }

  buildObservation(doc: PaperlessPayload) {
    const docId = doc.document_id ?? doc.id ?? 0;
    const tags  = ['document', 'inbox', ...(doc.tags ?? [])];
    if (doc.document_type) tags.push(doc.document_type.toLowerCase().replace(/\s+/g, '-'));

    return {
      metric:      'document-received',
      value:       doc.title ?? `Document #${docId}`,
      unit:        doc.document_type ?? 'document',
      subjectType: 'document',
      confidence:  1,
      source:      doc.correspondent ?? undefined,
      observedAt:  doc.added ?? doc.created ?? new Date().toISOString(),
      metadata: {
        paperlessId:  docId,
        originalFile: doc.original_file_name,
        tags:         doc.tags,
        excerpt:      doc.content?.slice(0, 500),
      },
    };
  }

  logIncoming(type: string, payload: unknown) {
    this.logger.log(`Webhook received: ${type} — ${JSON.stringify(payload).slice(0, 200)}`);
  }
}