mixin card
    - const slots = {}

    mixin slot(key)
        - slots[key] = block

    -
        block ? block() : undefined 

        let classes = {
            'o-card': true,
        }

    if attributes.href
        a(href=attributes.href class=classes)
            if slots.body
                .o-card__body
                    - slots.body()
            if slots.footer
                .o-card__footer
                    - slots.footer()
    else
        div(class=classes)
            if slots.body
                .o-card__body
                    - slots.body()
            if slots.footer
                .o-card__footer
                    - slots.footer()