Now that we are done defining the routes and updating the model, we will work on the logic, as discussed in the Solution design section. We are going to add a new method to CloudAIAPI class named postMessage. Open servercontrollerscloud-ai-api.ts, where we will first add the required imports and LanguageServiceClient. Before the class definition, add the following code:

// SNIPP SNIPP
const language = require('@google-cloud/language');
const nlpClient = new language.LanguageServiceClient({
    credentials: JSON.parse(process.env.GCP_SK_CREDENTIALS)
});
// SNIPP SNIPP

Using the environment variable we have set in the .env file, we are using a GCP_SK_CREDENTIALS value to initialise a new LanguageServiceClient. Next, we are going to create a new method named postMessage, which will read the request body as the base message:

// SNIPP SNIPP
postMessage = (req, res) => {
 let message = req.body;
 message.createdBy = req.user;
 message.lastUpdatedBy = req.user;
}
// SNIPP SNIPP

Then, we will pass the description to the Natural Language API and get a response:

// SNIPP
const request = {
    encodingType: 'UTF8',
    document: {
        content: message.description,
        type: 'PLAIN_TEXT'
    },
    features: {
        extractSyntax: true,
        extractEntities: true,
        extractDocumentSentiment: true,
        extractEntitySentiment: true,
        classifyText: true
    }
}
nlpClient.annotateText(request)
    .then(results => {
        // CODE BELOW
    })
    .catch(err => {
        console.error('ERROR:', err);
        return res.status(500).json(err);
    });
// SNIPP

Next, we are going to save the response to the database along with the message:

// SNIPP
results = results[0];
msg.nlpCategories = results.categories;
msg.nlpTokens = results.tokens;
msg.nlpEntities = results.entities;
msg.nlpDocumentSentiment = results.documentSentiment;
msg.nlpLanguage = results.language;
msg.nlpSentences = results.sentences;
let message = new Message(msg);

message.save((err, msg) => {
    if (err) {
        console.log(err);
        return this.respondErrorMessage(res, err);
    }
    res.status(200).json(msg);
});
// SNIPP

This wraps up our controller logic as well as our service-side logic. In the next section, we are going work on the client-side logic.