dmail-api/src/modules/email/services/email-headers.service.ts

import { Injectable } from "@nestjs/common";
import { v4 as uuidv4 } from "uuid";

import { EmailHeaderDto } from "../DTO/send-email.dto";
import { EmailHeaderKey, Priority } from "../enums/email-header.enum";
import {
  IGenerateAntiThreadingHeadersOptions,
  IGenerateGmailAntiThreadingHeadersOptions,
  IGenerateMarketingHeadersOptions,
  IGenerateTransactionalHeadersOptions,
  IImageDetectionResult,
} from "../interfaces/email-header.interface";

@Injectable()
export class EmailHeadersService {
  private readonly hostDomain = "danakcorp.com";
  private readonly hostDomain2 = "storage.danakcorp.com";
  //****************************************** */
  generateAntiThreadingHeaders(options: IGenerateAntiThreadingHeadersOptions): EmailHeaderDto[] {
    const headers: EmailHeaderDto[] = [];

    headers.push({
      key: EmailHeaderKey.References,
      value: `<${uuidv4()}@${options.businessDomain}>`,
    });

    headers.push({
      key: EmailHeaderKey.ThreadIndex,
      value: this.generateThreadIndex(),
    });

    headers.push({
      key: EmailHeaderKey.XMailer,
      value: `Danak Mail Service v1.0`,
    });

    headers.push({
      key: EmailHeaderKey.XPriority,
      value: this.getPriorityValue(options.priority || Priority.Normal),
    });

    headers.push({
      key: EmailHeaderKey.XMSMailPriority,
      value: options.priority || Priority.Normal,
    });

    headers.push({
      key: EmailHeaderKey.MIMEVersion,
      value: "1.0",
    });

    headers.push({
      key: EmailHeaderKey.XSpamStatus,
      value: "No",
    });

    headers.push({
      key: EmailHeaderKey.XSpamScore,
      value: "0.0",
    });

    headers.push({
      key: EmailHeaderKey.XFeedbackID,
      value: `${uuidv4()}:${options.businessDomain}`,
    });

    headers.push({
      key: EmailHeaderKey.XEntityRefID,
      value: uuidv4(),
    });

    if (options.hasHostedImages) {
      headers.push(...this.generateImageAntiSpamHeaders(options));
    }

    if (options.isTransactional) {
      headers.push({
        key: EmailHeaderKey.XAutoResponseSuppress,
        value: "All",
      });
      headers.push({
        key: EmailHeaderKey.XEntityID,
        value: "transactional",
      });
      headers.push({
        key: EmailHeaderKey.Precedence,
        value: "bulk",
      });
    }

    if (options.isMarketing) {
      headers.push({
        key: EmailHeaderKey.XEntityID,
        value: "marketing",
      });
      headers.push({
        key: EmailHeaderKey.ListUnsubscribePost,
        value: "List-Unsubscribe=One-Click",
      });

      if (options.listUnsubscribe) {
        headers.push({
          key: EmailHeaderKey.ListUnsubscribe,
          value: options.listUnsubscribe,
        });
      }
    }

    if (options.listId) {
      headers.push({
        key: EmailHeaderKey.ListId,
        value: options.listId,
      });
    }

    return headers;
  }

  //****************************************** */
  generateImageAntiSpamHeaders(options: IGenerateAntiThreadingHeadersOptions): EmailHeaderDto[] {
    const headers: EmailHeaderDto[] = [];

    if (!options.hasHostedImages) {
      return headers;
    }

    headers.push({
      key: EmailHeaderKey.XImageSource,
      value: this.hostDomain2,
    });

    headers.push({
      key: EmailHeaderKey.XContentSecurity,
      value: "verified",
    });

    headers.push({
      key: EmailHeaderKey.XImageValidation,
      value: "trusted-source",
    });

    headers.push({
      key: EmailHeaderKey.XOriginVerified,
      value: `${this.hostDomain}-${Date.now()}`,
    });

    if (options.imageCount && options.imageCount > 0) {
      headers.push({
        key: EmailHeaderKey.XImageCount,
        value: options.imageCount.toString(),
      });
    }

    if (options.trustedImageSources && options.trustedImageSources.length > 0) {
      headers.push({
        key: EmailHeaderKey.XTrustedSources,
        value: options.trustedImageSources.join(", "),
      });
    }

    return headers;
  }

  //****************************************** */
  detectImagesInContent(htmlContent: string): IImageDetectionResult {
    if (!htmlContent) {
      return {
        hasHostedImages: false,
        imageCount: 0,
        trustedImageSources: [],
        danakCorpImages: [],
      };
    }

    // Regex to find img tags with src attributes
    const imgRegex = /<img[^>]+src\s*=\s*["']([^"']+)["'][^>]*>/gi;
    const matches = [...htmlContent.matchAll(imgRegex)];

    const allImages = matches.map((match) => match[1]);
    const danakCorpImages = allImages.filter((src) => src.includes(this.hostDomain) || src.includes(this.hostDomain2));

    // Also check for CSS background images
    const cssImageRegex = /background-image\s*:\s*url\(["']?([^"')]+)["']?\)/gi;
    const cssMatches = [...htmlContent.matchAll(cssImageRegex)];
    const cssImages = cssMatches.map((match) => match[1]);
    const danakCorpCssImages = cssImages.filter((src) => src.includes(this.hostDomain) || src.includes(this.hostDomain2));

    const allDanakCorpImages = [...danakCorpImages, ...danakCorpCssImages];
    const hasHostedImages = allDanakCorpImages.length > 0;

    // Get unique domains from danakcorp images
    const trustedImageSources = [
      ...new Set(
        allDanakCorpImages
          .map((src) => {
            try {
              const url = new URL(src.startsWith("//") ? "https:" + src : src);
              return url.hostname;
            } catch {
              // If URL parsing fails, extract domain manually
              const match = src.match(/(?:https?:\/\/)?(?:www\.)?([^/]+)/);
              return match ? match[1] : src;
            }
          })
          .filter((domain) => domain.includes(this.hostDomain)),
      ),
    ];

    return {
      hasHostedImages,
      imageCount: allDanakCorpImages.length,
      trustedImageSources,
      danakCorpImages: allDanakCorpImages,
    };
  }

  //****************************************** */
  generateGmailAntiThreadingHeaders(options: IGenerateGmailAntiThreadingHeadersOptions): EmailHeaderDto[] {
    const headers: EmailHeaderDto[] = [];

    // Generate completely unique Message-ID for each email
    const uniqueMessageId = this.generateMessageId(options.businessDomain, true);
    headers.push({
      key: EmailHeaderKey.MessageId,
      value: uniqueMessageId,
    });

    // Clear any potential threading references
    headers.push({
      key: EmailHeaderKey.References,
      value: `<${uuidv4()}@${options.businessDomain}>`,
    });

    headers.push({
      key: EmailHeaderKey.InReplyTo,
      value: `<${uuidv4()}@${options.businessDomain}>`,
    });

    // Gmail-specific thread breaking
    headers.push({
      key: EmailHeaderKey.XGmailThreadBreak,
      value: options.conversationBreaker || uuidv4(),
    });

    // Additional thread prevention
    headers.push({
      key: EmailHeaderKey.ThreadTopic,
      value: uuidv4(),
    });

    return headers;
  }

  //****************************************** */
  generateTransactionalHeaders(options: IGenerateTransactionalHeadersOptions): EmailHeaderDto[] {
    const headers: EmailHeaderDto[] = [];

    // Base anti-threading headers
    headers.push(
      ...this.generateAntiThreadingHeaders({
        businessName: options.businessName,
        businessDomain: options.businessDomain,
        isTransactional: true,
      }),
    );

    // Transactional-specific headers
    headers.push({
      key: EmailHeaderKey.XTransactionID,
      value: options.transactionId || uuidv4(),
    });

    if (options.category) {
      headers.push({
        key: EmailHeaderKey.XCategory,
        value: options.category,
      });
    }

    // Mark as important transactional email
    headers.push({
      key: EmailHeaderKey.Importance,
      value: "high",
    });

    headers.push({
      key: EmailHeaderKey.XAutoResponseSuppress,
      value: "All",
    });

    return headers;
  }

  //****************************************** */
  generateMarketingHeaders(options: IGenerateMarketingHeadersOptions): EmailHeaderDto[] {
    const headers: EmailHeaderDto[] = [];

    // Base anti-threading headers
    headers.push(
      ...this.generateAntiThreadingHeaders({
        businessName: options.businessName,
        businessDomain: options.businessDomain,
        isMarketing: true,
        listId: options.listId,
        listUnsubscribe: `<${options.unsubscribeUrl}>`,
      }),
    );

    // Marketing-specific headers
    if (options.campaignId) {
      headers.push({
        key: EmailHeaderKey.XCampaignID,
        value: options.campaignId,
      });
    }

    headers.push({
      key: EmailHeaderKey.XMarketingEmail,
      value: "true",
    });

    // Required for bulk marketing emails
    headers.push({
      key: EmailHeaderKey.Precedence,
      value: "bulk",
    });

    return headers;
  }
  //****************************************** */

  private generateMessageId(domain: string, extraUnique = false): string {
    const timestamp = Date.now();
    const random = Math.random().toString(36).substring(2, 15);
    const uuid = extraUnique ? uuidv4() : "";
    return `<${timestamp}.${random}${uuid}@${domain}>`;
  }
  //****************************************** */
  private generateThreadIndex(): string {
    // Generate a unique thread index for Outlook
    const timestamp = Date.now().toString(16);
    const random = Math.random().toString(16).substring(2, 10);
    return `${timestamp}${random}`.toUpperCase();
  }
  //****************************************** */

  private getPriorityValue(priority: Priority): string {
    return priority === Priority.High ? "1" : priority === Priority.Low ? "5" : "3";
  }
}