package system

import "image"
import "git.tebibyte.media/tomo/tomo"
import "git.tebibyte.media/tomo/tomo/input"
import "git.tebibyte.media/tomo/tomo/canvas"
import "git.tebibyte.media/tomo/backend/internal/util"

// Hierarchy is coupled to a tomo.Window implementation, and manages a tree of
// Boxes.
type Hierarchy struct {
	link   WindowLink
	system *System
	canvas canvas.Canvas
	
	root    anyBox
	focused anyBox
	hovered anyBox

	windowFocused bool
	
	modifiers     input.Modifiers
	mousePosition image.Point
	drags         [10]anyBox
	minimumSize   image.Point
	
	needMinimum  util.Set[anyBox]
	needLayout   util.Set[anyBox]
	needDraw     util.Set[anyBox]
	needRedo     bool
	minimumClean bool
}

// WindowLink allows the Hierarchy to call up into the tomo.Window
// implementation which contains it. This should be a separate entity from the
// tomo.Window.
type WindowLink interface {
	// GetWindow returns the tomo.Window containing the Hierarchy.
	GetWindow () tomo.Window
	// PushRegion pushes a region of the held canvas.Canvas to the screen.
	PushRegion (image.Rectangle)
	// PushAll pushes the entire canvas.Canvas to the screen.
	PushAll ()
	// NotifyMinimumSizeChange notifies the tomo.Window that the minimum
	// size of the Hierarchy has changed, and if necessary, a resize should
	// be requested.
	NotifyMinimumSizeChange ()
}

// NewHierarchy creates a new Hierarchy.
func (this *System) NewHierarchy (link WindowLink) *Hierarchy {
	hierarchy := &Hierarchy {
		system: this,
		link:   link,
	}
	return hierarchy
}

// SetRoot sets the root Box of the hierarchy.
func (this *Hierarchy) SetRoot (root tomo.Box) {
	if this.root != nil {
		this.root.setParent(nil)
	}
	if root == nil {
		this.root = nil
	} else {
		box := assertAnyBox(root.GetBox())
		box.setParent(this)
		box.flushActionQueue()
		this.invalidateLayout(box)
		this.root = box
	}
	this.minimumClean = false
}

// SetCanvas sets the held canvas of the Hierarchy that all boxes within it will
// draw to. The Hierarchy will use the canvas.Canvas's bounds to lay itself out.
func (this *Hierarchy) SetCanvas (can canvas.Canvas) {
	this.canvas = can
	if this.root != nil { this.root.loseCanvas() }
	this.needRedo = true
}

// MinimumSize returns the minimum size of the Hierarchy.
func (this *Hierarchy) MinimumSize () image.Point {
	return this.minimumSize
}

// AfterEvent should be called at the end of every event cycle.
func (this *Hierarchy) AfterEvent () {
	if this.canvas == nil { return }

	if this.needRedo {
		// set child bounds
		childBounds := this.canvas.Bounds()
		childBounds = childBounds.Sub(childBounds.Min)
		if this.root != nil {
			this.root.SetBounds(childBounds)	
		}

		// full relayout/redraw
		if this.root != nil {
			this.root.recursiveRedo()
		}
		this.link.PushAll()
		this.needRedo = false
		return
	}

	for len(this.needMinimum) > 0 {
		this.needMinimum.Pop().doMinimumSize()
	}
	if !this.minimumClean {
		this.doMinimumSize()
	}
	for len(this.needLayout) > 0 {
		this.needLayout.Pop().doLayout()
	}
	var toPush image.Rectangle
	for len(this.needDraw) > 0 {
		box := this.needDraw.Pop()
		box.doDraw()
		toPush = toPush.Union(box.Bounds())
	}
	if !toPush.Empty() {
		this.link.PushRegion(toPush)
	}
}

func (this *Hierarchy) getHierarchy () *Hierarchy {
	return this
}

func (this *Hierarchy) getWindow () tomo.Window {
	return this.link.GetWindow()
}

func (this *Hierarchy) getCanvas () canvas.Canvas {
	return this.canvas
}

func (this *Hierarchy) getModifiers () input.Modifiers {
	return this.modifiers
}

func (this *Hierarchy) getMousePosition () image.Point {
	return this.mousePosition
}

func (this *Hierarchy) notifyMinimumSizeChange (anyBox) {
	this.minimumClean = false
}

func (this *Hierarchy) invalidateMinimum (box anyBox) {
	this.needMinimum.Add(box)
}

func (this *Hierarchy) invalidateDraw (box anyBox) {
	this.needDraw.Add(box)
}

func (this *Hierarchy) invalidateLayout (box anyBox) {
	this.needLayout.Add(box)
	this.invalidateDraw(box)
}

func (this *Hierarchy) focus (box anyBox) {
	if this.focused == box { return }

	previous := this.focused
	this.focused = box

	if previous != nil {
		previous.handleFocusLeave()
	}
	if box != nil && box.canBeFocused() {
		box.handleFocusEnter()
	}
}

func (this *Hierarchy) isFocused (box anyBox) bool {
	return this.focused == box
}

func (this *Hierarchy) hover (box anyBox) {
	if this.hovered == box { return }

	previous := this.hovered
	this.hovered = box

	if previous != nil {
		previous.handleMouseLeave()
	}
	if box != nil {
		box.handleMouseEnter()
	}
}

func (this *Hierarchy) anyFocused () bool {
	return this.focused != nil
}

func (this *Hierarchy) boxUnder (point image.Point, category eventCategory) anyBox {
	if this.root == nil { return nil }
	return this.root.boxUnder(point, category)
}

func (this *Hierarchy) captures (eventCategory) bool {
	return false
}

func (this *Hierarchy) keyboardTarget () anyBox {
	focused := this.focused
	if focused == nil { return nil }
	parent := focused.getParent()
	for {
		parentBox, ok := parent.(anyBox)
		if !ok { break }
		if parent.captures(eventCategoryKeyboard) {
			return parentBox
		}
		parent = parentBox.getParent()
	}

	return focused
}

func (this *Hierarchy) focusNext () {
	found   := !this.anyFocused()
	focused := false
	this.propagateAlt (func (box anyBox) bool {
		if found {
			// looking for the next box to select
			if box.canBeFocused() {
				// found it
				this.focus(box)
				focused = true
				return false
			}
		} else {
			// looking for the current focused element
			if box == this.focused {
				// found it
				found = true
			}
		}
		return true
	})

	if !focused { this.focus(nil) }
}

func (this *Hierarchy) focusPrevious () {
	var behind anyBox
	this.propagate (func (box anyBox) bool {
		if box == this.focused {
			return false
		}
		if box.canBeFocused() { behind = box }
		return true
	})
	this.focus(behind)
}

func (this *Hierarchy) propagate (callback func (box anyBox) bool) {
	if this.root == nil { return }
	this.root.propagate(callback)
}

func (this *Hierarchy) propagateAlt (callback func (box anyBox) bool) {
	if this.root == nil { return }
	this.root.propagateAlt(callback)
}

func (this *Hierarchy) drawBackgroundPart (canvas.Canvas) {
	// TODO
	// no-op for now? maybe eventually windows will be able to have a
	// background
	// if so, windows should be transparent if the color has transparency
}

func (this *Hierarchy) doMinimumSize () {
	this.minimumClean = true

	this.minimumSize = image.Point { }
	if this.root != nil {
		this.minimumSize = this.root.MinimumSize()
	}

	this.link.NotifyMinimumSizeChange()
}