dmail-api/src/modules/ai-assistant/services/ai-assistant.service.ts

import { BadRequestException, Injectable, NotFoundException } from "@nestjs/common";
import { firstValueFrom } from "rxjs";

import { AiService } from "./ai.service";
import { AiMessage } from "../../../common/enums/message.enum";
import { MessageDetails } from "../../mail-server/interfaces/messages-response.interface";
import { WildDuckMessagesService } from "../../mail-server/services/wildduck-messages.service";
import { SummarizeEmailDto } from "../DTO/summarize-email.dto";
import { WriteEmailAssistanceDto } from "../DTO/write-email-assistance.dto";
import { SummaryLength, SummaryTone } from "../enums/ai.enum";
import { EmailData, SummarizationOptions } from "../interfaces/ai-service.interface";

@Injectable()
export class AiAssistantService {
  constructor(
    private readonly messagesService: WildDuckMessagesService,
    private readonly aiService: AiService,
  ) {}

  //************************************************* */
  async summarizeEmail(summarizeDto: SummarizeEmailDto, userId: string) {
    const message = await firstValueFrom(this.messagesService.getMessage(userId, summarizeDto.mailbox, summarizeDto.messageId));

    if (!message) throw new NotFoundException(AiMessage.MESSAGE_NOT_FOUND_OR_ACCESS_DENIED);

    const emailData = this.extractEmailData(message);

    const summary = await this.generateEmailSummary(emailData, summarizeDto.length, summarizeDto.tone);

    return summary;
  }

  //************************************************* */
  async assistEmailWriting(writeAssistanceDto: WriteEmailAssistanceDto, userId: string) {
    const assistance = await this.generateEmailWritingAssistance(writeAssistanceDto, userId);

    return { assistance };
  }

  //************************************************* */
  private extractEmailData(message: MessageDetails) {
    return {
      subject: message.subject,
      content: this.extractTextContent(message),
      htmlContent: this.extractHtmlContent(message),
      from: this.extractSenderInfo(message),
      to: this.extractRecipientInfo(message),
      date: message.date || new Date(),
      attachments: message.attachments || [],
    };
  }

  //************************************************* */
  private extractTextContent(message: MessageDetails): string {
    if (message.text) {
      return typeof message.text === "string" ? message.text : message.text || "";
    }

    if (message.html) {
      return this.stripHtmlTags(typeof message.html === "string" ? message.html : message.html[0] || "");
    }

    return "";
  }

  //************************************************* */
  private extractHtmlContent(message: MessageDetails): string {
    if (message.html) {
      return typeof message.html === "string" ? message.html : message.html[0] || "";
    }
    return "";
  }

  //************************************************* */
  private extractSenderInfo(message: MessageDetails): string {
    if (message.from && message.from.address) {
      return message.from.name ? `${message.from.name} <${message.from.address}>` : message.from.address;
    }
    return "";
  }

  //************************************************* */
  private extractRecipientInfo(message: MessageDetails): string[] {
    const recipients: string[] = [];

    if (message.to && Array.isArray(message.to)) {
      recipients.push(...message.to.map((recipient) => (recipient.name ? `${recipient.name} <${recipient.address}>` : recipient.address)));
    }

    return recipients;
  }

  //************************************************* */
  private stripHtmlTags(html: string): string {
    return html
      .replace(/<[^>]*>/g, "")
      .replace(/&nbsp;/g, " ")
      .trim();
  }

  //************************************************* */
  private async generateEmailSummary(emailData: any, length: SummaryLength = SummaryLength.MEDIUM, _tone: SummaryTone = SummaryTone.PROFESSIONAL) {
    const content = emailData.content || emailData.htmlContent;

    if (!content.trim()) throw new BadRequestException(AiMessage.EMAIL_CONTENT_IS_EMPTY_OR_COULD_NOT_BE_EXTRACTED);

    const aiEmailData: EmailData = {
      subject: emailData.subject,
      content: emailData.content,
      htmlContent: emailData.htmlContent,
      from: emailData.from,
      to: emailData.to,
      date: emailData.date,
      attachments: emailData.attachments,
    };

    const summarizationOptions: SummarizationOptions = {
      length: length.toLowerCase() as "short" | "medium" | "detailed",
      tone: _tone.toLowerCase() as "formal" | "casual" | "professional",
    };

    const aiResponse = await this.aiService.summarizeEmail(aiEmailData, summarizationOptions);

    return {
      summary: aiResponse.summary,
      keyPoints: aiResponse.keyPoints,
      suggestedActions: aiResponse.suggestedActions,
      priority: aiResponse.priority,
      sentiment: aiResponse.sentiment,
    };
  }

  //************************************************* */
  private async generateEmailWritingAssistance(writeAssistanceDto: WriteEmailAssistanceDto, _userId: string) {
    const aiResponse = await this.aiService.assistEmailWriting(writeAssistanceDto.prompt);

    return {
      suggestion: {
        subject: aiResponse.subject,
        content: aiResponse.content,
        alternatives: aiResponse.alternatives,
      },
      tips: aiResponse.tips,
      improvements: aiResponse.improvements,
    };
  }
}