// SPDX-License-Identifier: Unlicense OR MIT

package text

import (
	"image"
	"image/color"
	"math"
	"time"
	"unicode/utf8"

	"gioui.org/ui"
	"gioui.org/ui/draw"
	"gioui.org/ui/gesture"
	"gioui.org/ui/input"
	"gioui.org/ui/key"
	"gioui.org/ui/layout"
	"gioui.org/ui/pointer"

	"golang.org/x/image/math/fixed"
)

type Editor struct {
	Config     ui.Config
	Inputs     input.Queue
	Face       Face
	Alignment  Alignment
	SingleLine bool
	Submit     bool

	Material     ui.MacroOp
	Hint         string
	HintMaterial ui.MacroOp

	oldScale          int
	blinkStart        time.Time
	focused           bool
	rr                editBuffer
	maxWidth          int
	viewSize          image.Point
	valid             bool
	lines             []Line
	dims              layout.Dimens
	padTop, padBottom int
	padLeft, padRight int
	requestFocus      bool

	it lineIterator

	// carXOff is the offset to the current caret
	// position when moving between lines.
	carXOff fixed.Int26_6

	scroller  gesture.Scroll
	scrollOff image.Point

	clicker gesture.Click
}

type EditorEvent interface {
	isEditorEvent()
}

type ChangeEvent struct{}
type SubmitEvent struct{}

const (
	blinksPerSecond  = 1
	maxBlinkDuration = 10 * time.Second
)

func (s ChangeEvent) isEditorEvent() {}
func (s SubmitEvent) isEditorEvent() {}

func (e *Editor) Next() (EditorEvent, bool) {
	// Crude configuration change detection.
	if scale := e.Config.Px(ui.Sp(100)); scale != e.oldScale {
		e.invalidate()
		e.oldScale = scale
	}
	sbounds := e.scrollBounds()
	var smin, smax int
	var axis gesture.Axis
	if e.SingleLine {
		axis = gesture.Horizontal
		smin, smax = sbounds.Min.X, sbounds.Max.X
	} else {
		axis = gesture.Vertical
		smin, smax = sbounds.Min.Y, sbounds.Max.Y
	}
	sdist := e.scroller.Scroll(e.Config, e.Inputs, axis)
	var soff int
	if e.SingleLine {
		e.scrollOff.X += sdist
		soff = e.scrollOff.X
	} else {
		e.scrollOff.Y += sdist
		soff = e.scrollOff.Y
	}
	for _, evt := range e.clicker.Events(e.Inputs) {
		switch {
		case evt.Type == gesture.TypePress && evt.Source == pointer.Mouse,
			evt.Type == gesture.TypeClick && evt.Source == pointer.Touch:
			e.blinkStart = e.Config.Now()
			e.moveCoord(image.Point{
				X: int(math.Round(float64(evt.Position.X))),
				Y: int(math.Round(float64(evt.Position.Y))),
			})
			e.requestFocus = true
			if !e.scroller.Active() {
				e.scrollToCaret()
			}
		}
	}
	if (sdist > 0 && soff >= smax) || (sdist < 0 && soff <= smin) {
		e.scroller.Stop()
	}
	for _, ke := range e.Inputs.Events(e) {
		e.blinkStart = e.Config.Now()
		switch ke := ke.(type) {
		case key.FocusEvent:
			e.focused = ke.Focus
		case key.ChordEvent:
			if !e.focused {
				break
			}
			if e.Submit && (ke.Name == key.NameReturn || ke.Name == key.NameEnter) {
				if !ke.Modifiers.Contain(key.ModShift) {
					return SubmitEvent{}, true
				}
			}
			if e.command(ke) {
				e.scrollToCaret()
				e.scroller.Stop()
			}
		case key.EditEvent:
			e.scrollToCaret()
			e.scroller.Stop()
			e.append(ke.Text)
		}
		if e.rr.Changed() {
			return ChangeEvent{}, true
		}
	}
	return nil, false
}

func (e *Editor) caretWidth() fixed.Int26_6 {
	oneDp := e.Config.Px(ui.Dp(1))
	return fixed.Int26_6(oneDp * 64)
}

func (e *Editor) Focus() {
	e.requestFocus = true
}

func (e *Editor) Layout(ops *ui.Ops, cs layout.Constraints) layout.Dimens {
	for _, ok := e.Next(); ok; _, ok = e.Next() {
	}
	twoDp := e.Config.Px(ui.Dp(2))
	e.padLeft, e.padRight = twoDp, twoDp
	maxWidth := cs.Width.Max
	if e.SingleLine {
		maxWidth = ui.Inf
	}
	if maxWidth != ui.Inf {
		maxWidth -= e.padLeft + e.padRight
	}
	if maxWidth != e.maxWidth {
		e.maxWidth = maxWidth
		e.invalidate()
	}

	e.layout()
	lines, size := e.lines, e.dims.Size
	e.viewSize = cs.Constrain(size)

	carLine, _, carX, carY := e.layoutCaret()

	off := image.Point{
		X: -e.scrollOff.X + e.padLeft,
		Y: -e.scrollOff.Y + e.padTop,
	}
	clip := image.Rectangle{
		Min: image.Point{X: 0, Y: 0},
		Max: image.Point{X: e.viewSize.X, Y: e.viewSize.Y},
	}
	key.HandlerOp{Key: e, Focus: e.requestFocus}.Add(ops)
	e.requestFocus = false
	e.it = lineIterator{
		Lines:     lines,
		Clip:      clip,
		Alignment: e.Alignment,
		Width:     e.viewWidth(),
		Offset:    off,
	}
	var stack ui.StackOp
	stack.Push(ops)
	// Apply material. Set a default color in case the material is empty.
	if e.rr.len() > 0 {
		draw.ColorOp{Color: color.RGBA{A: 0xff}}.Add(ops)
		e.Material.Add(ops)
	} else {
		draw.ColorOp{Color: color.RGBA{A: 0xaa}}.Add(ops)
		e.HintMaterial.Add(ops)
	}
	for {
		str, lineOff, ok := e.it.Next()
		if !ok {
			break
		}
		var stack ui.StackOp
		stack.Push(ops)
		ui.TransformOp{Transform: ui.Offset(lineOff)}.Add(ops)
		e.Face.Path(str).Add(ops)
		draw.DrawOp{Rect: toRectF(clip).Sub(lineOff)}.Add(ops)
		stack.Pop()
	}
	if e.focused {
		now := e.Config.Now()
		dt := now.Sub(e.blinkStart)
		blinking := dt < maxBlinkDuration
		const timePerBlink = time.Second / blinksPerSecond
		nextBlink := now.Add(timePerBlink/2 - dt%(timePerBlink/2))
		on := !blinking || dt%timePerBlink < timePerBlink/2
		if on {
			carWidth := e.caretWidth()
			carX -= carWidth / 2
			carAsc, carDesc := -lines[carLine].Bounds.Min.Y, lines[carLine].Bounds.Max.Y
			carRect := image.Rectangle{
				Min: image.Point{X: carX.Ceil(), Y: carY - carAsc.Ceil()},
				Max: image.Point{X: carX.Ceil() + carWidth.Ceil(), Y: carY + carDesc.Ceil()},
			}
			carRect = carRect.Add(image.Point{
				X: -e.scrollOff.X + e.padLeft,
				Y: -e.scrollOff.Y + e.padTop,
			})
			carRect = clip.Intersect(carRect)
			if !carRect.Empty() {
				draw.ColorOp{Color: color.RGBA{A: 0xff}}.Add(ops)
				e.Material.Add(ops)
				draw.DrawOp{Rect: toRectF(carRect)}.Add(ops)
			}
		}
		if blinking {
			redraw := ui.InvalidateOp{At: nextBlink}
			redraw.Add(ops)
		}
	}
	stack.Pop()

	baseline := e.padTop + e.dims.Baseline
	pointer.RectAreaOp{Size: e.viewSize}.Add(ops)
	e.scroller.Add(ops)
	e.clicker.Add(ops)
	return layout.Dimens{Size: e.viewSize, Baseline: baseline}
}

func (e *Editor) layout() {
	e.adjustScroll()
	if e.valid {
		return
	}
	e.layoutText()
	e.valid = true
}

func (e *Editor) scrollBounds() image.Rectangle {
	var b image.Rectangle
	if e.SingleLine {
		if len(e.lines) > 0 {
			b.Min.X = align(e.Alignment, e.lines[0].Width, e.viewWidth()).Floor()
			if b.Min.X > 0 {
				b.Min.X = 0
			}
		}
		b.Max.X = e.dims.Size.X + b.Min.X - e.viewSize.X
	} else {
		b.Max.Y = e.dims.Size.Y - e.viewSize.Y
	}
	return b
}

func (e *Editor) adjustScroll() {
	b := e.scrollBounds()
	if e.scrollOff.X > b.Max.X {
		e.scrollOff.X = b.Max.X
	}
	if e.scrollOff.X < b.Min.X {
		e.scrollOff.X = b.Min.X
	}
	if e.scrollOff.Y > b.Max.Y {
		e.scrollOff.Y = b.Max.Y
	}
	if e.scrollOff.Y < b.Min.Y {
		e.scrollOff.Y = b.Min.Y
	}
}

func (e *Editor) moveCoord(pos image.Point) {
	e.layout()
	var (
		prevDesc fixed.Int26_6
		carLine  int
		y        int
	)
	for _, l := range e.lines {
		y += (prevDesc + l.Ascent).Ceil()
		prevDesc = l.Descent
		if y+prevDesc.Ceil() >= pos.Y+e.scrollOff.Y-e.padTop {
			break
		}
		carLine++
	}
	x := fixed.I(pos.X + e.scrollOff.X - e.padLeft)
	e.moveToLine(x, carLine)
}

func (e *Editor) layoutText() {
	s := e.rr.String()
	if s == "" {
		s = e.Hint
	}
	textLayout := e.Face.Layout(s, LayoutOptions{SingleLine: e.SingleLine, MaxWidth: e.maxWidth})
	lines := textLayout.Lines
	dims := linesDimens(lines)
	for i := 0; i < len(lines)-1; i++ {
		s := lines[i].Text.String
		// To avoid layout flickering while editing, assume a soft newline takes
		// up all available space.
		if len(s) > 0 {
			r, _ := utf8.DecodeLastRuneInString(s)
			if !IsNewline(r) {
				dims.Size.X = e.maxWidth
				break
			}
		}
	}
	padTop, padBottom := textPadding(lines)
	dims.Size.Y += padTop + padBottom
	dims.Size.X += e.padLeft + e.padRight
	e.padTop = padTop
	e.padBottom = padBottom
	e.lines, e.dims = lines, dims
}

func (e *Editor) viewWidth() int {
	return e.viewSize.X - e.padLeft - e.padRight
}

func (e *Editor) layoutCaret() (carLine, carCol int, x fixed.Int26_6, y int) {
	e.layout()
	var idx int
	var prevDesc fixed.Int26_6
loop:
	for carLine = 0; carLine < len(e.lines); carLine++ {
		l := e.lines[carLine]
		y += (prevDesc + l.Ascent).Ceil()
		prevDesc = l.Descent
		if carLine == len(e.lines)-1 || idx+len(l.Text.String) > e.rr.caret {
			str := l.Text.String
			for _, adv := range l.Text.Advances {
				if idx == e.rr.caret {
					break loop
				}
				x += adv
				_, s := utf8.DecodeRuneInString(str)
				idx += s
				str = str[s:]
				carCol++
			}
			break
		}
		idx += len(l.Text.String)
	}
	x += align(e.Alignment, e.lines[carLine].Width, e.viewWidth())
	return
}

func (e *Editor) invalidate() {
	e.valid = false
}

func (e *Editor) deleteRune() {
	e.rr.deleteRune()
	e.carXOff = 0
	e.invalidate()
}

func (e *Editor) deleteRuneForward() {
	e.rr.deleteRuneForward()
	e.carXOff = 0
	e.invalidate()
}

func (e *Editor) Text() string {
	return e.rr.String()
}

func (e *Editor) SetText(s string) {
	e.rr = editBuffer{}
	e.carXOff = 0
	e.prepend(s)
}

func (e *Editor) append(s string) {
	if e.SingleLine && s == "\n" {
		return
	}
	e.prepend(s)
	e.rr.caret += len(s)
}

func (e *Editor) prepend(s string) {
	e.rr.prepend(s)
	e.carXOff = 0
	e.invalidate()
}

func (e *Editor) movePages(pages int) {
	e.layout()
	_, _, carX, carY := e.layoutCaret()
	y := carY + pages*e.viewSize.Y
	var (
		prevDesc fixed.Int26_6
		carLine2 int
	)
	y2 := e.lines[0].Ascent.Ceil()
	for i := 1; i < len(e.lines); i++ {
		if y2 >= y {
			break
		}
		l := e.lines[i]
		h := (prevDesc + l.Ascent).Ceil()
		prevDesc = l.Descent
		if y2+h-y >= y-y2 {
			break
		}
		y2 += h
		carLine2++
	}
	e.carXOff = e.moveToLine(carX+e.carXOff, carLine2)
}

func (e *Editor) moveToLine(carX fixed.Int26_6, carLine2 int) fixed.Int26_6 {
	e.layout()
	carLine, carCol, _, _ := e.layoutCaret()
	if carLine2 < 0 {
		carLine2 = 0
	}
	if carLine2 >= len(e.lines) {
		carLine2 = len(e.lines) - 1
	}
	// Move to start of line.
	for i := carCol - 1; i >= 0; i-- {
		_, s := e.rr.runeBefore(e.rr.caret)
		e.rr.caret -= s
	}
	if carLine2 != carLine {
		// Move to start of line2.
		if carLine2 > carLine {
			for i := carLine; i < carLine2; i++ {
				e.rr.caret += len(e.lines[i].Text.String)
			}
		} else {
			for i := carLine - 1; i >= carLine2; i-- {
				e.rr.caret -= len(e.lines[i].Text.String)
			}
		}
	}
	l2 := e.lines[carLine2]
	carX2 := align(e.Alignment, l2.Width, e.viewWidth())
	// Only move past the end of the last line
	end := 0
	if carLine2 < len(e.lines)-1 {
		end = 1
	}
	// Move to rune closest to previous horizontal position.
	for i := 0; i < len(l2.Text.Advances)-end; i++ {
		adv := l2.Text.Advances[i]
		if carX2 >= carX {
			break
		}
		if carX2+adv-carX >= carX-carX2 {
			break
		}
		carX2 += adv
		_, s := e.rr.runeAt(e.rr.caret)
		e.rr.caret += s
	}
	return carX - carX2
}

func (e *Editor) moveLeft() {
	e.rr.moveLeft()
	e.carXOff = 0
}

func (e *Editor) moveRight() {
	e.rr.moveRight()
	e.carXOff = 0
}

func (e *Editor) moveStart() {
	carLine, carCol, x, _ := e.layoutCaret()
	advances := e.lines[carLine].Text.Advances
	for i := carCol - 1; i >= 0; i-- {
		_, s := e.rr.runeBefore(e.rr.caret)
		e.rr.caret -= s
		x -= advances[i]
	}
	e.carXOff = -x
}

func (e *Editor) moveEnd() {
	carLine, carCol, x, _ := e.layoutCaret()
	l := e.lines[carLine]
	// Only move past the end of the last line
	end := 0
	if carLine < len(e.lines)-1 {
		end = 1
	}
	for i := carCol; i < len(l.Text.Advances)-end; i++ {
		adv := l.Text.Advances[i]
		_, s := e.rr.runeAt(e.rr.caret)
		e.rr.caret += s
		x += adv
	}
	a := align(e.Alignment, l.Width, e.viewWidth())
	e.carXOff = l.Width + a - x
}

func (e *Editor) scrollToCaret() {
	carWidth := e.caretWidth()
	carLine, _, x, y := e.layoutCaret()
	l := e.lines[carLine]
	if e.SingleLine {
		minx := (x - carWidth/2).Ceil()
		if d := minx - e.scrollOff.X + e.padLeft; d < 0 {
			e.scrollOff.X += d
		}
		maxx := (x + carWidth/2).Ceil()
		if d := maxx - (e.scrollOff.X + e.viewSize.X - e.padRight); d > 0 {
			e.scrollOff.X += d
		}
	} else {
		miny := y + l.Bounds.Min.Y.Floor()
		if d := miny - e.scrollOff.Y + e.padTop; d < 0 {
			e.scrollOff.Y += d
		}
		maxy := y + l.Bounds.Max.Y.Ceil()
		if d := maxy - (e.scrollOff.Y + e.viewSize.Y - e.padBottom); d > 0 {
			e.scrollOff.Y += d
		}
	}
}

func (e *Editor) command(k key.ChordEvent) bool {
	switch k.Name {
	case key.NameReturn, key.NameEnter:
		e.append("\n")
	case key.NameDeleteBackward:
		e.deleteRune()
	case key.NameDeleteForward:
		e.deleteRuneForward()
	case key.NameUpArrow:
		line, _, carX, _ := e.layoutCaret()
		e.carXOff = e.moveToLine(carX+e.carXOff, line-1)
	case key.NameDownArrow:
		line, _, carX, _ := e.layoutCaret()
		e.carXOff = e.moveToLine(carX+e.carXOff, line+1)
	case key.NameLeftArrow:
		e.moveLeft()
	case key.NameRightArrow:
		e.moveRight()
	case key.NamePageUp:
		e.movePages(-1)
	case key.NamePageDown:
		e.movePages(+1)
	case key.NameHome:
		e.moveStart()
	case key.NameEnd:
		e.moveEnd()
	default:
		return false
	}
	return true
}