/*
 * This script listiner which should be configured on the issue updated event shows how you can have a field to calculate and show the number of labels on an issue. 
 * "All right, title and interest in this code snippet shall remain the exclusive intellectual property of Adaptavist Group Ltd and its affiliates. Customers with a valid ScriptRunner 
 * license shall be granted a  non-exclusive, non-transferable, freely revocable right to use this code snippet only within their own instance of Atlassian products. This licensing notice cannot be removed
 * or amended and must be included in any circumstances where the code snippet is shared by You or a third party." 
 */

// get custom fields
def customFields = get("/rest/api/2/field")
        .asObject(List)
        .body
        .findAll { (it as Map).custom } as List<Map>

// Specify the Name of the custom type field that will out the calcuated value
def outputCfId = customFields.find { it.name == '<NumberFieldNameHere>' }?.id

// Specify the project where the calculated field will go
def projectKey = "<ProjectKeyHere>"

if (issue == null || ((Map)issue.fields.project).key != projectKey) {
    logger.info("Wrong Project \${issue.fields.project.key}")
    return
}

// store the number of labels
def NumberofLabels =  (issue.fields.labels.size)
int output = NumberofLabels.toInteger()

if (output == (issue.fields[outputCfId] as Integer)) {
    logger.info("already been updated")
    return
}

// Update the issue with the calculated value
put("/rest/api/2/issue/${issue.key}")
        .header("Content-Type", "application/json")
        .body([
        fields:[
                (outputCfId): output
        ]
])
        .asString()