Parsing multiple-part Gmail responses for Slack via JSONata

Gmail to Slack JSONata

{
    'channel': $.channel,
    'blocks': [
        {
            'type': 'section',
            'text': {
                'type':'mrkdwn',
                'text': '------------------------------\n*You have mail!*'
            }
        },
        $map($filter($.mailMessageSuccess.payload.headers, function($v, $i, $a) {
                /* Filter out all headers that aren't From, Subject, or Date for display in the Slack notification */
                $v.name = 'From' or $v.name = 'Subject' or $v.name = 'Date'
            }), function($v, $i, $a) {
                {
                    'type': 'section',
                    'text': {
                        'type': 'mrkdwn',
                        'text': '*' & $v.name & ':* ' & $v.value
                    }
                }
            }),
        $map($filter($.mailMessageSuccess.payload.parts, function($v, $i, $a) {
                /* TODO: Find the decode strategy for body parts that not base64 encoded  */
                $v.mimeType = 'text/plain'
            }), function($v, $i, $a) {
                {
                    'type': 'section',
                    'text': {
                        'type': 'mrkdwn',
                        'text': $replace($base64decode($v.body.data), '\r\n', '\n')
                    }
                }
            }),
        {
            'type': 'section',
            'text': {
                'type':'mrkdwn',
                'text': '(Sent with ❤️ from instanceId: ' & $._.instanceId & ')\n------------------------------'
            }
        }
    ]
}

Gmail to Slack JSONata v1.1 Beta

/**
 * Potential improvment that filters, not by mime-type, but by whether the body can be $base64decode()'ed
**/

{
    'channel': $.channel,
    'blocks': [
        {
            'type': 'section',
            'text': {
                'type':'mrkdwn',
                'text': '------------------------------\n*You have mail!*'
            }
        },
        $map($filter($.mailMessageSuccess.payload.headers, function($v, $i, $a) {
                $v.name = 'From' or $v.name = 'Subject' or $v.name = 'Date'
            }), function($v, $i, $a) {
                {
                    'type': 'section',
                    'text': {
                        'type': 'mrkdwn',
                        'text': '*' & $v.name & ':* ' & $v.value
                    }
                }
            }),
        $map($filter($.mailMessageSuccess.payload.parts, function($v, $i, $a) {
                $contains($v.body.data, /^([A-Za-z0-9+/]{4})*([A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{2}==)?$/)
            }), function($v, $i, $a) {
                {
                    'type': 'section',
                    'text': {
                        'type': 'mrkdwn',
                        'text': $replace($base64decode($v.body.data), '\r\n', '\n')
                    }
                }
            }),
        {
            'type': 'section',
            'text': {
                'type':'mrkdwn',
                'text': '(Sent with ❤️ from instanceId: ' & $._.instanceId & ')\n------------------------------'
            }
        }
    ]
}

Produces this in Slack: