package basic

import "image"
import "git.tebibyte.media/sashakoshka/tomo"
import "git.tebibyte.media/sashakoshka/tomo/theme"
import "git.tebibyte.media/sashakoshka/tomo/artist"
import "git.tebibyte.media/sashakoshka/tomo/textmanip"
import "git.tebibyte.media/sashakoshka/tomo/elements/core"

// TextBox is a single-line text input.
type TextBox struct {
	*core.Core
	core core.CoreControl
	
	enabled  bool
	selected bool

	cursor int
	scroll int
	placeholder string
	text        []rune
	
	placeholderDrawer artist.TextDrawer
	valueDrawer       artist.TextDrawer
	
	onKeyDown func (key tomo.Key, modifiers tomo.Modifiers) (handled bool)
	onChange  func ()
	onSelectionRequest func () (granted bool)
	onSelectionMotionRequest func (tomo.SelectionDirection) (granted bool)
	onScrollBoundsChange func ()
}

// NewTextBox creates a new text box with the specified placeholder text, and
// a value. When the value is empty, the placeholder will be displayed in gray
// text.
func NewTextBox (placeholder, value string) (element *TextBox) {
	element = &TextBox { enabled: true }
	element.Core, element.core = core.NewCore(element)
	element.placeholderDrawer.SetFace(theme.FontFaceRegular())
	element.valueDrawer.SetFace(theme.FontFaceRegular())
	element.placeholder = placeholder
	element.placeholderDrawer.SetText([]rune(placeholder))
	element.updateMinimumSize()
	element.SetValue(value)
	return
}

func (element *TextBox) Resize (width, height int) {
	element.core.AllocateCanvas(width, height)
	element.scrollToCursor()
	element.draw()
	if element.onScrollBoundsChange != nil {
		element.onScrollBoundsChange()
	}
}

func (element *TextBox) HandleMouseDown (x, y int, button tomo.Button) {
	if !element.enabled { return }
	element.Select()
}

func (element *TextBox) HandleMouseUp (x, y int, button tomo.Button) { }
func (element *TextBox) HandleMouseMove (x, y int) { }
func (element *TextBox) HandleMouseScroll (x, y int, deltaX, deltaY float64) { }

func (element *TextBox) HandleKeyDown(key tomo.Key, modifiers tomo.Modifiers) {
	if element.onKeyDown != nil && element.onKeyDown(key, modifiers) {
		return
	}

	scrollMemory := element.scroll
	altered     := true
	textChanged := false
	switch {
	case key == tomo.KeyBackspace:
		if len(element.text) < 1 { break }
		element.text, element.cursor = textmanip.Backspace (
			element.text,
			element.cursor,
			modifiers.Control)
		textChanged = true
			
	case key == tomo.KeyDelete:
		if len(element.text) < 1 { break }
		element.text, element.cursor = textmanip.Delete (
			element.text,
			element.cursor,
			modifiers.Control)
		textChanged = true
			
	case key == tomo.KeyLeft:
		element.cursor = textmanip.MoveLeft (
			element.text,
			element.cursor,
			modifiers.Control)
			
	case key == tomo.KeyRight:
		element.cursor = textmanip.MoveRight (
			element.text,
			element.cursor,
			modifiers.Control)
		
	case key.Printable():
		element.text, element.cursor = textmanip.Type (
			element.text,
			element.cursor,
			rune(key))
		textChanged = true
			
	default:
		altered = false
	}

	if textChanged {
		element.runOnChange()
		element.valueDrawer.SetText(element.text)
	}

	if altered {
		element.scrollToCursor()
	}

	if (textChanged || scrollMemory != element.scroll) &&
		element.onScrollBoundsChange != nil {
		element.onScrollBoundsChange()
	}
	
	if altered && element.core.HasImage () {
		element.draw()
		element.core.DamageAll()
	}
}

func (element *TextBox) HandleKeyUp(key tomo.Key, modifiers tomo.Modifiers) { }

func (element *TextBox) Selected () (selected bool) {
	return element.selected
}

func (element *TextBox) Select () {
	if element.onSelectionRequest != nil {
		element.onSelectionRequest()
	}
}

func (element *TextBox) HandleSelection (
	direction tomo.SelectionDirection,
) (
	accepted bool,
) {
	direction = direction.Canon()
	if !element.enabled { return false }
	if element.selected && direction != tomo.SelectionDirectionNeutral {
		return false
	}
	
	element.selected = true
	if element.core.HasImage() {
		element.draw()
		element.core.DamageAll()
	}
	return true
}

func (element *TextBox) HandleDeselection () {
	element.selected = false
	if element.core.HasImage() {
		element.draw()
		element.core.DamageAll()
	}
}

func (element *TextBox) OnSelectionRequest (callback func () (granted bool)) {
	element.onSelectionRequest = callback
}

func (element *TextBox) OnSelectionMotionRequest (
	callback func (direction tomo.SelectionDirection) (granted bool),
) {
	element.onSelectionMotionRequest = callback
}

func (element *TextBox) SetEnabled (enabled bool) {
	if element.enabled == enabled { return }
	element.enabled = enabled
	if element.core.HasImage () {
		element.draw()
		element.core.DamageAll()
	}
}

func (element *TextBox) SetPlaceholder (placeholder string) {
	if element.placeholder == placeholder { return }
	
	element.placeholder = placeholder
	element.placeholderDrawer.SetText([]rune(placeholder))
	
	element.updateMinimumSize()
	if element.core.HasImage () {
		element.draw()
		element.core.DamageAll()
	}
}

func (element *TextBox) SetValue (text string) {
	// if element.text == text { return }

	element.text = []rune(text)
	element.runOnChange()
	element.valueDrawer.SetText(element.text)
	if element.cursor > element.valueDrawer.Length() {
		element.cursor = element.valueDrawer.Length()
	}
	element.scrollToCursor()
	
	if element.core.HasImage () {
		element.draw()
		element.core.DamageAll()
	}
}

func (element *TextBox) Value () (value string) {
	return string(element.text)
}

func (element *TextBox) Filled () (filled bool) {
	return len(element.text) > 0
}

func (element *TextBox) OnKeyDown (
	callback func (key tomo.Key, modifiers tomo.Modifiers) (handled bool),
) {
	element.onKeyDown = callback
}

func (element *TextBox) OnChange (callback func ()) {
	element.onChange = callback
}

// ScrollContentBounds returns the full content size of the element.
func (element *TextBox) ScrollContentBounds () (bounds image.Rectangle) {
	bounds = element.valueDrawer.LayoutBounds()
	return bounds.Sub(bounds.Min)
}

// ScrollViewportBounds returns the size and position of the element's viewport
// relative to ScrollBounds.
func (element *TextBox) ScrollViewportBounds () (bounds image.Rectangle) {
	return image.Rect (
		element.scroll,
		0,
		element.scroll + element.scrollViewportWidth(),
		0)
}

func (element *TextBox) scrollViewportWidth () (width int) {
	return element.Bounds().Inset(theme.Padding()).Dx()
}

// ScrollTo scrolls the viewport to the specified point relative to
// ScrollBounds.
func (element *TextBox) ScrollTo (position image.Point) {
	// constrain to minimum
	element.scroll = position.X
	if element.scroll < 0 { element.scroll = 0 }
	
	// constrain to maximum
	contentBounds := element.ScrollContentBounds()
	maxPosition   := contentBounds.Max.X - element.scrollViewportWidth()
	if element.scroll > maxPosition { element.scroll = maxPosition }

	if element.core.HasImage () {
		element.draw()
		element.core.DamageAll()
	}
	if element.onScrollBoundsChange != nil {
		element.onScrollBoundsChange()
	}
}

// ScrollAxes returns the supported axes for scrolling.
func (element *TextBox) ScrollAxes () (horizontal, vertical bool) {
	return true, false
}

func (element *TextBox) OnScrollBoundsChange (callback func ()) {
	element.onScrollBoundsChange = callback
}

func (element *TextBox) updateMinimumSize () {
	textBounds := element.placeholderDrawer.LayoutBounds()
	element.core.SetMinimumSize (
		textBounds.Dx() +
		theme.Padding() * 2,
		element.placeholderDrawer.LineHeight().Round() +
		theme.Padding() * 2)
}

func (element *TextBox) runOnChange () {
	if element.onChange != nil {
		element.onChange()
	}
}

func (element *TextBox) scrollToCursor () {
	if !element.core.HasImage() { return }

	bounds := element.core.Bounds().Inset(theme.Padding())
	bounds.Max.X -= element.valueDrawer.Em().Round()
	cursorPosition := element.valueDrawer.PositionOf(element.cursor)
	cursorPosition.X -= element.scroll
	maxX := bounds.Max.X
	minX := maxX
	if cursorPosition.X > maxX {
		element.scroll += cursorPosition.X - maxX
	} else if cursorPosition.X < minX {
		element.scroll -= minX - cursorPosition.X
		if element.scroll < 0 { element.scroll = 0 }
	}
}

func (element *TextBox) draw () {
	bounds := element.core.Bounds()

	artist.FillRectangle (
		element.core,
		theme.InputPattern (
			element.enabled,
			element.Selected()),
		bounds)

	if len(element.text) == 0 && !element.selected {
		// draw placeholder
		textBounds := element.placeholderDrawer.LayoutBounds()
		offset := image.Point {
			X: theme.Padding(),
			Y: theme.Padding(),
		}
		foreground := theme.ForegroundPattern(false)
		element.placeholderDrawer.Draw (
			element.core,
			foreground,
			offset.Sub(textBounds.Min))
	} else {
		// draw input value
		textBounds := element.valueDrawer.LayoutBounds()
		offset := image.Point {
			X: theme.Padding() - element.scroll,
			Y: theme.Padding(),
		}
		foreground := theme.ForegroundPattern(element.enabled)
		element.valueDrawer.Draw (
			element.core,
			foreground,
			offset.Sub(textBounds.Min))

		if element.selected {
			// cursor
			cursorPosition := element.valueDrawer.PositionOf (
				element.cursor)
			artist.Line (
				element.core,
				theme.ForegroundPattern(true), 1,
				cursorPosition.Add(offset),
				image.Pt (
					cursorPosition.X,
					cursorPosition.Y + element.valueDrawer.
					LineHeight().Round()).Add(offset))
		}
	}
}