import com.atlassian.crowd.embedded.api.User
import com.atlassian.jira.component.ComponentAccessor
import com.atlassian.jira.config.properties.APKeys
import com.atlassian.jira.config.properties.ApplicationProperties
import com.atlassian.jira.event.issue.AbstractIssueEventListener
import com.atlassian.jira.event.issue.IssueEvent
import com.atlassian.jira.issue.CustomFieldManager
import com.atlassian.jira.issue.Issue
import com.atlassian.jira.issue.fields.CustomField
import com.atlassian.jira.security.JiraAuthenticationContext
import com.atlassian.jira.user.ApplicationUser
import com.atlassian.jira.user.UserUtils
import com.atlassian.mail.Email
import com.atlassian.mail.queue.MailQueue
import com.atlassian.mail.queue.SingleMailQueueItem
import com.atlassian.plugin.PluginAccessor
import org.apache.commons.lang3.ObjectUtils
import org.apache.log4j.Logger
import org.ofbiz.core.entity.GenericValue
class TgeListener extends AbstractIssueEventListener {

    // configuration
    private static final String TGE_FIELD_NAME = "TGE";
    private static final String TRACKED_USERLIST_COLUMNS_NAME = "iassignee";
    private static final String PREVIOUS_USERLIST_COLUMNS_NAME = "previousiassignee";

    private static final Logger LOG = Logger.getLogger("com.idalko.scripts");

    private final CustomFieldManager customFieldManager;
    private final PluginAccessor pluginAccessor;
    private final JiraAuthenticationContext jiraAuthenticationContext;
    private final ApplicationProperties applicationProperties;
    private final MailQueue mailQueue;
    private final def tgeGridDataManager;

    public TgeListener() {
        customFieldManager = get(CustomFieldManager.class);
        pluginAccessor = get(PluginAccessor.class);
        jiraAuthenticationContext = get(JiraAuthenticationContext.class);
        Class dataManagerClass = pluginAccessor.getClassLoader().findClass("com.idalko.jira.plugins.igrid.api.data.TGEGridTableDataManager");
        tgeGridDataManager = get(dataManagerClass)
        applicationProperties = get(ApplicationProperties.class);
        mailQueue = get(MailQueue.class);
    }

    private <T> T get(Class<T> clazz) {
        return ObjectUtils.firstNonNull(
                ComponentAccessor.getComponent(clazz),
                ComponentAccessor.getComponentOfType(clazz),
                ComponentAccessor.getOSGiComponentInstanceOfType(clazz)
        );
    }

    @Override
    void issueUpdated(IssueEvent event) {
        Set<Long> updatedCustomFieldIds = getUpdatedCustomFieldsIds(event);
        LOG.debug("Updated custom fields IDs are: " + updatedCustomFieldIds);
        CustomField tgeCustomField = customFieldManager.getCustomFieldObjectByName(TGE_FIELD_NAME);
        Long tgeCustomFieldId = tgeCustomField.getIdAsLong();
        LOG.debug("TGE custom fields ID is: " + tgeCustomFieldId);
        if (updatedCustomFieldIds.contains(tgeCustomFieldId)) {
            Issue issue = event.getIssue()
            processTgeFieldChange(issue, tgeCustomFieldId);
        }
    }

    private Set<Long> getUpdatedCustomFieldsIds(IssueEvent event) {
        List<GenericValue> changeItems = event.getChangeLog().getRelated("ChildChangeItem");
        Set<Long> updatedCustomFields = new HashSet<Long>();
        for (GenericValue changeItem : changeItems) {
            String changeType = changeItem.getString("fieldtype");
            if (changeType.equalsIgnoreCase("custom")) {
                String customFieldName = changeItem.getString("field");
                CustomField customFieldObject = customFieldManager.getCustomFieldObjectByName(customFieldName);
                Long customFieldId = customFieldObject.getIdAsLong()
                updatedCustomFields.add(customFieldId);
            }
        }
        return updatedCustomFields;
    }

    private void processTgeFieldChange(Issue issue, long tgeCustomFieldId) {
        User user = getCurrentUser();
        Long issueId = issue.getId();
        def result = tgeGridDataManager.readGridData(issueId, tgeCustomFieldId, null, null, 0, 10, user);
        List<Map<String, Object>> gridData = result.getValues();
        for (Map<String, Object> row : gridData) {
            String selectedUserName = getSelectedUserNameFromRow(row);
            String previousUserName = getPreviousUserNameFromRow(row);
            if (selectedUserName != null && !selectedUserName.equals(previousUserName)) {
                sendEmailNotificationToUser(selectedUserName, issue);
                setPreviousUserEqualToSelected(row, issueId, tgeCustomFieldId, user);
            }
        }
    }

    private User getCurrentUser() {
        Object userObject = jiraAuthenticationContext.getLoggedInUser();
        User user = userObject instanceof ApplicationUser ? ((ApplicationUser) userObject).getDirectoryUser() : (User) userObject;
        return user;
    }

    private String getSelectedUserNameFromRow(Map<String, Object> row) {
        Map<String, String> selectedUser = (Map<String, String>) row.get(TRACKED_USERLIST_COLUMNS_NAME)
        String selectedUserName = selectedUser.get("value");
        return selectedUserName;
    }

    private String getPreviousUserNameFromRow(Map<String, Object> row) {
        return row.get(PREVIOUS_USERLIST_COLUMNS_NAME);
    }

    private void sendEmailNotificationToUser(String userName, Issue issue) {
        // prepare data
        User user = UserUtils.getUser(userName);
        String userEmail = user.getEmailAddress();
        String baseUrl = applicationProperties.getString(APKeys.JIRA_BASEURL);
        String issueKey = issue.getKey();
        String issueLink = baseUrl + "/browse/" + issueKey;
        String userDisplayName = user.getDisplayName();
        // build email
        Email email = new Email(userEmail);
        email.setSubject("TGE notification");
        email.setBody("Hi " + userDisplayName + "! A new task has been assigned to you in issue " + issueKey
                + "! Please visit <a href=\"" + issueLink + "\">" + issueKey + "</a>.");
        email.setMimeType("text/html");
        // send it
        SingleMailQueueItem mailItem = new SingleMailQueueItem(email);
        mailQueue.addItem(mailItem);
    }

    private void setPreviousUserEqualToSelected(Map<String, Object> row, Long issueId, Long tgeCustomFieldId, User user) {
        List changes = new ArrayList();
        // get row values
        Long rowId = (Long) row.get("id");
        String selectedUserName = getSelectedUserNameFromRow(row);
        // prepare new values
        Map<String, Object> newRowValues = new HashMap<String, Object>();
        newRowValues.put(PREVIOUS_USERLIST_COLUMNS_NAME, selectedUserName);
        // create changeset
        Class changeSetClass = pluginAccessor.getClassLoader().loadClass("com.idalko.jira.plugins.igrid.api.data.dto.TGEChangeSet");
        def changeSet = changeSetClass.newInstance();
        changeSet.setRowId(rowId);
        changeSet.setValues(newRowValues);
        changes.add(changeSet);
        // update row
        tgeGridDataManager.applyChanges(issueId, tgeCustomFieldId, changes, user);
    }
}

Subject: TGE notification
Body: Hi Samuel Stone! A new task has been assigned to you in issue TGE-1! Please visit http://seriouscopr.com/browse/TGE-1.