package tomo

import "image"

// Entity is a handle given to elements by the backend. Different types of
// entities may be assigned to elements that support different capabilities.
type Entity interface {
	// Invalidate marks the element's current visual as invalid. At the end
	// of every event, the backend will ask all invalid entities to redraw
	// themselves.
	Invalidate ()

	// Bounds returns the bounds of the element to be used for drawing and
	// layout.
	Bounds () image.Rectangle

	// Window returns the window that the element is in.
	Window () Window

	// SetMinimumSize reports to the system what the element's minimum size
	// can be. The minimum size of child elements should be taken into
	// account when calculating this.
	SetMinimumSize (width, height int)

	// DrawBackground asks the parent element to draw its background pattern
	// within the specified rectangle. This should be used for transparent
	// elements like text labels.
	DrawBackground (bounds image.Rectangle)
}

// ContainerEntity is given to elements that support the Container interface.
type ContainerEntity interface {
	Entity

	// Adopt adds an element as a child.
	Adopt (child Element)

	// Insert inserts an element in the child list at the specified
	// location.
	Insert (index int, child Element)

	// Disown removes the child at the specified index.
	Disown (index int)

	// IndexOf returns the index of the specified child.
	IndexOf (child Element) int

	// Child returns the child at the specified index.
	Child (index int) Element

	// CountChildren returns the amount of children the element has.
	CountChildren () int

	// PlaceChild sets the size and position of the child at the specified
	// index to a bounding rectangle.
	PlaceChild (index int, bounds image.Rectangle)

	// ChildMinimumSize returns the minimum size of the child at the
	// specified index.
	ChildMinimumSize (index int) (width, height int)
}

// FocusableEntity is given to elements that support the Focusable interface.
type FocusableEntity interface {
	Entity

	// Focused returns whether the element currently has input focus.
	Focused () bool

	// Focus sets this element as focused. If this succeeds, the element will
	// recieve a HandleFocus call.
	Focus ()

	// FocusNext causes the focus to move to the next element. If this
	// succeeds, the element will recieve a HandleUnfocus call.
	FocusNext ()

	// FocusPrevious causes the focus to move to the next element. If this
	// succeeds, the element will recieve a HandleUnfocus call.	
	FocusPrevious ()
}

// FlexibleEntity is given to elements that support the Flexible interface.
type FlexibleEntity interface {
	Entity

	// NotifyFlexibleHeightChange notifies the system that the parameters
	// affecting a child's flexible height have changed. This method is
	// expected to be called by flexible child element when their content
	// changes.
	NotifyFlexibleHeightChange (child Flexible)
}

// ScrollableEntity is given to elements that support the Scrollable interface.
type ScrollableEntity interface {
	Entity
	
	// NotifyScrollBoundsChange notifies the parent that a child's scroll
	// content bounds or viewport bounds have changed. This is expected to
	// be called by child elements when they change their supported scroll
	// axes, their scroll position (either autonomously or as a result of a
	// call to ScrollTo()), or their content size.
	NotifyScrollBoundsChange (child Scrollable)
}