requires: {#SceneElement. #DisplayTransform}.
provides: {#Morph. #Hand}.

Graphics addPrototype: #Morph derivedFrom: {DisplayedSceneElement}.
Morph addSlot: #coloredBorder.
Morph addSlot: #totalRegion.
Morph addSlot: #visibleRegion.

Graphics addSlot: #MorphDefaultState valued: Cloneable clone.

Morph addDelegate: #defaultState valued: MorphDefaultState.

Morph addProtectedSlot: #locked in: #defaultState valued: False.
Morph addProtectedSlot: #visible in: #defaultState valued: True.
Morph addProtectedSlot: #sticky in: #defaultState valued: False.

m@(Morph traits) clips
"Whether the morph clips its children."
[
  True
].

m@(Morph traits) delete
"Morph deletion should involve all clean-up tasks and responsibilities.
Perform the basic removal task by default."
[
  m treeParent ifNotNil: [m treeParent remove: m]
].

m@(Morph traits) grabTransform
[
  m treeParent
    ifNil: [IdentityTransform]
    ifNotNil: [m treeParent grabTransform]
].

m@(Morph traits) handle: e@(Event traits)
"The default handling for all events in general is to do nothing."
"TODO: turn the method into handleInput:?"
[
  m
].

Graphics addPrototype: #Sheet derivedFrom: {Morph}.
Sheet addSlot: #enabled valued: True.

sm@(Sheet traits) viewable
"Return whether the sheet will be viewable. This requires all of the parent
Sheets to be enabled."
[
  sm enabled and: [sm treeParent viewable]
].

Graphics addPrototype: #Transform derivedFrom: {Morph}.
Transform addSlot: #transform valued: IdentityTransform.

tm@(Transform traits) grabTransform
[
  m treeParent
    ifNil: [IdentityTransform]
    ifNotNil: [m treeParent grabTransform ++ m transform]
].

Graphics addPrototype: #Hand derivedFrom: {Morph}.


Graphics addPrototype: #DropEvent derivedFrom: {PointerEvent}.
DropEvent addSlot: #contents.

de@(DropEvent traits) newAt: p contents: m from: h
[| newDE |
  newDE: DropEvent clone.
  newDE position: p.
  newDE contents: m.
  newDE pointer: h.
  newDE
].

m@(Morph traits) reject: de@(DropEvent traits)
"The drop event has been rejected, and the morph must be put back somewhere."
[
  "Originally uses #formerOwner and #formerPosition, and then tries for the
  Trash."
].

h@(Hand traits) attach: m@(Morph traits)
"Position the center of the morph under the hand, and then grab it.
This grabs far away or created morphs."
[| delta |
  h releasePointerFocus.
  delta: m bounds extent // 2.
  m position: h position - delta.
  m lastPos: m position.
  h targetOffset: m position - h position.
  h addLast: m.
  h
].

h@(Hand traits) drop: m@(Morph traits) on: e@(Event)
[| event |
  event: (DropEvent newAt: h position contents: m from: h).
  "Send the event to the hand WRT the focus."
  event handled ifFalse: [m reject: e].
  m owner == h ifTrue: [m delete].
  "TODO: process the event as a mouse-over here?"
].

h@(Hand traits) dropAll
"Drop all submorphs at this position, maintaining z-order."
[
  h children reverseDo: [| :each | h drop: each on: e]
].

h@(Hand traits) grab: m@(Morph traits) from: src@(Morph traits)
[| grabbed offset targetPos grabTransform fullTransform |
  h releaseFocus.
  grabbed: m.
  grabTransform: src grabTransform.
  fullTransform: (src transformFrom: h owner).
  "the point in m's reference frame."
  targetPos: (fullTransform actOn: h position).
  "compute the offset due to using grabTransform to find the current position"
  offset: targetPos - (grabTransform actOn: h position).
  "apply the transform needed"
  grabbed: (grabbed transformedBy: grabTransform).
  "short for grabTransform isIdentity"
  grabbed == m ifFalse: ["Set FlexAtGrab On"].
  "apply the offset needed"
  grabbed position: grabbed position - offset truncated.
  "TODO: find out if targetOffset is needed."
  h targetOffset: grabbed position - h position.
  h addBack: grabbed.
  h
].

h@(Hand traits) grab: m@(Morph traits) from: src@Nil
"This is a simplified version of the general method."
"TODO: factor out the common method from both."
[
  h releaseFocus.
  h targetOffset: m position - h position.
  h addBack: grabbed.
].

h@(Hand traits) grab: m@(Morph traits)
"Grab the morph without changing its position, as distinguished from attach:
which can move the morph (to the hand)."
[| grabbed |
  h releaseFocus.
  (grabbed: (m morphForGrabbingBy: h)) ifNil: [^ h].
  grabbed: grabbed leastTopRenderer.
  h grab: grabbed from: grabbed owner
].