import Gtk

/// SPI protocol for containers that manage an ordered list of children.
@_spi(Portico) @MainActor public protocol SequentialContainer {
    /// Appends a child widget to the end of the container.
    func appendChild(_ child: Gtk.Widget)

    /// Removes a previously added child widget.
    func removeChild(_ child: Gtk.Widget)
}

/// How a conditional slot deactivates a branch in a host.
@_spi(Portico) public enum ConditionalStrategy {
    /// Hide the branch's widgets while keeping them parented.
    case visibility
    /// Detach inactive widgets and reinsert them on activation.
    case insertion
}

/// SPI capability for containers that support indexed insertion.
@_spi(Portico) @MainActor public protocol DynamicChildHost: SequentialContainer {
    /// Inserts a child at the target position.
    func insertChild(_ child: Gtk.Widget, at index: Int, after sibling: Gtk.Widget?)

    /// Moves a child to the target position.
    func moveChild(_ child: Gtk.Widget, to index: Int, after sibling: Gtk.Widget?)

    /// Selects visibility or insertion semantics for conditional branches.
    var conditionalStrategy: ConditionalStrategy { get }

    /// Returns the widget whose visibility controls layout participation.
    func visibilityTarget(for child: Gtk.Widget) -> Gtk.Widget
}

@_spi(Portico) extension DynamicChildHost {
    /// Hides inactive branches by default.
    public var conditionalStrategy: ConditionalStrategy { .visibility }

    /// Uses the child itself as the layout visibility target by default.
    public func visibilityTarget(for child: Gtk.Widget) -> Gtk.Widget { child }

    /// Moves a child using remove-then-insert.
    @_spi(Portico) public func moveChild(_ child: Gtk.Widget, to index: Int, after sibling: Gtk.Widget?) {
        removeChild(child)
        insertChild(child, at: index, after: sibling)
    }
}