Parse resumes and score candidates in Salesforce

public class HireLayerParseResume implements Queueable, Database.AllowsCallouts {
    public class HireLayerException extends Exception {}
    private final Id contactId;
    private final Id documentId;

    public HireLayerParseResume(Id contactId, Id documentId) {
        this.contactId = contactId;
        this.documentId = documentId;
    }

    public void execute(QueueableContext context) {
        ContentVersion cv = [
            SELECT PathOnClient, VersionData FROM ContentVersion
            WHERE ContentDocumentId = :documentId AND IsLatest = true
        ];

        // multipart/form-data body with one "file" part
        String boundary = 'HireLayer' + Datetime.now().getTime();
        String head = '--' + boundary + '\r\nContent-Disposition: form-data; name="file"; filename="'
            + cv.PathOnClient + '"\r\nContent-Type: application/octet-stream\r\n\r\n';
        String tail = '\r\n--' + boundary + '--\r\n';
        Blob body = EncodingUtil.convertFromHex(
            EncodingUtil.convertToHex(Blob.valueOf(head))
            + EncodingUtil.convertToHex(cv.VersionData)
            + EncodingUtil.convertToHex(Blob.valueOf(tail)));

        HttpRequest req = new HttpRequest();
        req.setEndpoint('callout:HireLayer/api/v3/parser'); // adds X-API-Key
        req.setMethod('POST');
        req.setHeader('Content-Type', 'multipart/form-data; boundary=' + boundary);
        req.setBodyAsBlob(body);
        req.setTimeout(120000); // default is 10 s; parsing takes about 35 s
        HttpResponse res = new Http().send(req);
        if (res.getStatusCode() != 200) {
            throw new HireLayerException('HireLayer returned ' + res.getStatusCode());
        }

        Map<String, Object> parsed = (Map<String, Object>) JSON.deserializeUntyped(res.getBody());
        Map<String, Object> info = (Map<String, Object>) parsed.get('info_candidate');
        Map<String, Object> location = (Map<String, Object>) info.get('location');
        List<String> skills = new List<String>();
        for (Object item : (List<Object>) parsed.get('skills')) {
            skills.add((String) ((Map<String, Object>) item).get('skill_title'));
        }

        // DML after the callout: Apex refuses callouts after uncommitted work
        update new Contact(
            Id = contactId,
            Title = (String) info.get('job_title'),
            MobilePhone = (String) info.get('phone_number'), // E.164
            MailingCity = location == null ? null : (String) location.get('city'),
            Skills__c = String.join(skills, ', ') // custom long text field
        );
    }
}