Set Priority Using an Impact-Urgent Matrix

import com.atlassian.jira.issue.IssueFieldConstants
import groovy.transform.BaseScript
import com.onresolve.jira.groovy.user.FieldBehaviours

@BaseScript FieldBehaviours fieldBehaviours

def priorityMatrix = [
    Critical: [
        Extensive  : 'Critical',
        Significant: 'Critical',
        Moderate   : 'High',
        Minor      : 'Medium'
    ],
    High    : [
        Extensive  : 'Critical',
        Significant: 'High',
        Moderate   : 'Medium',
        Minor      : 'Medium'
    ],
    Medium  : [
        Extensive  : 'High',
        Significant: 'Medium',
        Moderate   : 'Medium',
        Minor      : 'Low'
    ],
    Low     : [
        Extensive  : 'Medium',
        Significant: 'Medium',
        Moderate   : 'Low',
        Minor      : 'Low'
    ]
]
def priorityField = getFieldById(IssueFieldConstants.PRIORITY)

def impactFieldValue = getFieldByName('Impact').value as String
def urgencyFieldValue = getFieldByName('Urgency').value as String

def priority = priorityMatrix[urgencyFieldValue][impactFieldValue]
priorityField.setFormValue(priority)