[#enabled-expression]
= Enabled Expression

The `enabledExpression` property allows you to dynamically enable or disable action buttons based on entity properties. This is useful when you want to show context-appropriate actions - for example, only showing a "Turn Off" button when a device is already on, or only allowing a "Start" action when a service is stopped.

== Basic Usage

The `enabledExpression` is a Go template that must evaluate to a boolean value. When the expression evaluates to `true`, the action button will be enabled (clickable). When it evaluates to `false`, the button will be disabled (greyed out and not clickable).

[source,yaml]
----
actions:
  - title: Turn On Light
    shell: echo "Turning on {{ .CurrentEntity.name }}"
    icon: 💡
    entity: light
    enabledExpression: "{{ eq .CurrentEntity.powered_on false }}"

  - title: Turn Off Light
    shell: echo "Turning off {{ .CurrentEntity.name }}"
    icon: 💡
    entity: light
    enabledExpression: "{{ eq .CurrentEntity.powered_on true }}"
----

In this example:

* The "Turn On Light" button is only enabled when `powered_on` is `false`
* The "Turn Off Light" button is only enabled when `powered_on` is `true`

== How It Works

The `enabledExpression` uses the same Go template syntax used elsewhere in OliveTin. It has access to the `.CurrentEntity` variable which contains all properties of the entity the action is bound to.

=== Result Evaluation

The template result is evaluated as follows:

[cols="1,1", options="header"]
|===
| Result | Enabled?
| `true` (case insensitive) | ✓ Yes
| Non-zero integer (e.g., `1`, `42`) | ✓ Yes
| `false` (case insensitive) | ✗ No
| `0` | ✗ No
| Empty string | ✗ No
| Template error | ✗ No
|===

=== Default Behavior

If `enabledExpression` is not specified, the action is always enabled (assuming the user has permission to execute it via ACLs).

== Examples

=== Simple Boolean Check

[source,yaml]
----
actions:
  - title: Start Service
    shell: systemctl start {{ .CurrentEntity.service_name }}
    entity: service
    enabledExpression: "{{ eq .CurrentEntity.running false }}"

  - title: Stop Service  
    shell: systemctl stop {{ .CurrentEntity.service_name }}
    entity: service
    enabledExpression: "{{ eq .CurrentEntity.running true }}"
----

=== Checking Status Values

[source,yaml]
----
actions:
  - title: Resume Download
    shell: resume-download {{ .CurrentEntity.id }}
    entity: download
    enabledExpression: "{{ eq .CurrentEntity.status \"paused\" }}"
----

=== Using Integer Status Codes

If your entity has integer status values, you can use them directly:

[source,yaml]
----
actions:
  - title: Process Item
    shell: process {{ .CurrentEntity.id }}
    entity: item
    # Status 1 means "ready" - action is enabled when status is 1
    enabledExpression: "{{ .CurrentEntity.status }}"
----

=== Combining with Other Template Functions

You can use Go template functions for more complex logic:

[source,yaml]
----
actions:
  - title: Deploy to Production
    shell: deploy {{ .CurrentEntity.name }}
    entity: service
    # Only enable if status is "ready" AND environment is "staging"
    enabledExpression: "{{ and (eq .CurrentEntity.status \"ready\") (eq .CurrentEntity.environment \"staging\") }}"
----

== Complete Example

Here's a complete configuration showing `enabledExpression` with entities and dashboards:

[source,yaml]
----
entities:
  - file: /etc/OliveTin/lights.yaml
    name: light

actions:
  - title: Turn On Light
    shell: /opt/smart-home/light-control.sh on {{ .CurrentEntity.id }}
    icon: 💡
    entity: light
    enabledExpression: "{{ eq .CurrentEntity.powered_on false }}"

  - title: Turn Off Light
    shell: /opt/smart-home/light-control.sh off {{ .CurrentEntity.id }}
    icon: 🔌
    entity: light
    enabledExpression: "{{ eq .CurrentEntity.powered_on true }}"

dashboards:
  - title: Light Controls
    contents:
      - title: Lights
        type: fieldset
        entity: light
        contents:
          - type: display
            title: |
              <strong>{{ .CurrentEntity.name }}</strong>
          - title: Turn On Light
          - title: Turn Off Light
----

With an entity file like:

[source,yaml]
./etc/OliveTin/lights.yaml
----
- id: kitchen
  name: Kitchen Light
  powered_on: false

- id: living_room
  name: Living Room Light
  powered_on: true
----

In this setup:

* The Kitchen Light will have "Turn On" enabled and "Turn Off" disabled
* The Living Room Light will have "Turn Off" enabled and "Turn On" disabled

== Error Handling

If the `enabledExpression` template fails to parse or execute (e.g., due to syntax errors or missing entity properties), OliveTin will:

1. Log a warning message with details about the failure
2. Treat the action as **disabled** for safety

This ensures that misconfigured expressions don't accidentally allow unintended actions.

== Relationship with ACLs

The `enabledExpression` works in combination with xref:security/acl.adoc[Access Control Lists (ACLs)]. An action button is only enabled when **both** conditions are met:

1. The user has `exec` permission via ACLs
2. The `enabledExpression` evaluates to `true`

If either condition is not met, the action button will be disabled.

== See Also

* xref:entities/intro.adoc[Entities] - Learn about defining entities
* xref:dashboards/intro.adoc[Dashboards] - Display entity-bound actions
* xref:security/acl.adoc[Access Control Lists] - Control who can execute actions