EmailGeneratorService.java

package com.email.email_write_sb;

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Service;
import org.springframework.web.reactive.function.client.WebClient;

import java.util.Map;

@Service
public class EmailGeneratorService {

    private final WebClient webClient;

    @Value("${gemini.api.url}")
    private String geminiApiUrl;

    @Value("${gemini.api.key}")
    private String geminiApiKey;

    public EmailGeneratorService(WebClient.Builder webClientBuilder) {
        this.webClient = webClientBuilder.build();
    }

    public String generateEmailReply(EmailRequest emailRequest) {
      
        String prompt = buildPrompt(emailRequest);
        if(prompt == null) return "";
        Map<String, Object> requestBody = Map.of(
                "contents", new Object[] {
                        Map.of("parts", new Object[]{
                                Map.of("text", prompt)
                        })
                }
        );

        String response;
        try {
            
             response = webClient.post()
                    .uri(geminiApiUrl + geminiApiKey)
                    .header("Content-Type", "application/json")
                    .bodyValue(requestBody)
                    .retrieve()
                    .bodyToMono(String.class)
                    .block();
        }
        catch (Exception e) {
            return e.getMessage();
        }

        
        return extractResponseContent(response);
    }

    private String extractResponseContent(String response) {
        try {
            ObjectMapper mapper = new ObjectMapper();
            JsonNode rootNode = mapper.readTree(response);
            return rootNode.path("candidates")
                    .get(0)
                    .path("content")
                    .path("parts")
                    .get(0)
                    .path("text")
                    .asText();
        } catch (Exception e) {
            return "Error processing request: " + e.getMessage();
        }
    }

    private String buildPrompt(EmailRequest emailRequest) {
        StringBuilder prompt = new StringBuilder();

        prompt.append(emailRequest.getEmailContent());
       prompt.append("Generate a professional email reply for the following email content. Start with Sender's name. Please don't generate a subject line ");
        if (emailRequest.getTone() != null && !emailRequest.getTone().isEmpty()) {
            prompt.append("Use a ").append(emailRequest.getTone()).append(" tone.");
        }
       prompt.append("\nOriginal email: \n").append(emailRequest.getEmailContent());

        return prompt.toString();
    }
}