// Copyright (c) 2024, Přemysl Eric Janouch <p@janouch.name>
// SPDX-License-Identifier: 0BSD

package main

import (
	"bufio"
	"bytes"
	"context"
	_ "embed"
	"encoding/binary"
	"errors"
	"flag"
	"fmt"
	"image/color"
	"io"
	"log"
	"net"
	"net/url"
	"os"
	"regexp"
	"slices"
	"strings"
	"sync"
	"time"

	"github.com/ebitengine/oto/v3"

	"fyne.io/fyne/v2"
	"fyne.io/fyne/v2/app"
	"fyne.io/fyne/v2/container"
	"fyne.io/fyne/v2/dialog"
	"fyne.io/fyne/v2/driver/desktop"
	"fyne.io/fyne/v2/driver/mobile"
	"fyne.io/fyne/v2/theme"
	"fyne.io/fyne/v2/widget"
)

var (
	debug          = flag.Bool("debug", false, "enable debug output")
	projectName    = "xA"
	projectVersion = "?"

	//go:embed xA.png
	iconNormal []byte
	//go:embed xA-highlighted.png
	iconHighlighted []byte
	//go:embed beep.raw
	beepSample []byte

	resourceIconNormal = fyne.NewStaticResource(
		"xA.png", iconNormal)
	resourceIconHighlighted = fyne.NewStaticResource(
		"xA-highlighted.png", iconHighlighted)
)

// --- Theme -------------------------------------------------------------------

type customTheme struct{}

const (
	colorNameRenditionError  fyne.ThemeColorName = "renditionError"
	colorNameRenditionJoin   fyne.ThemeColorName = "renditionJoin"
	colorNameRenditionPart   fyne.ThemeColorName = "renditionPart"
	colorNameRenditionAction fyne.ThemeColorName = "renditionAction"

	colorNameBufferTimestamp fyne.ThemeColorName = "bufferTimestamp"
	colorNameBufferLeaked    fyne.ThemeColorName = "bufferLeaked"
)

func convertColor(c int) color.Color {
	base16 := []uint16{
		0x000, 0x800, 0x080, 0x880, 0x008, 0x808, 0x088, 0xccc,
		0x888, 0xf00, 0x0f0, 0xff0, 0x00f, 0xf0f, 0x0ff, 0xfff,
	}
	if c < 16 {
		r := 0xf & uint8(base16[c]>>8)
		g := 0xf & uint8(base16[c]>>4)
		b := 0xf & uint8(base16[c])
		return color.RGBA{r * 0x11, g * 0x11, b * 0x11, 0xff}
	}
	if c >= 216 {
		return color.Gray{8 + uint8(c-216)*10}
	}

	var (
		i = uint8(c - 16)
		r = i / 36 >> 0
		g = (i / 6 >> 0) % 6
		b = i % 6
	)
	if r != 0 {
		r = 55 + 40*r
	}
	if g != 0 {
		g = 55 + 40*g
	}
	if b != 0 {
		b = 55 + 40*b
	}
	return color.RGBA{r, g, b, 0xff}
}

var ircColors = make(map[fyne.ThemeColorName]color.Color)

func ircColorName(color int) fyne.ThemeColorName {
	return fyne.ThemeColorName(fmt.Sprintf("irc%02x", color))
}

func init() {
	for color := 0; color < 256; color++ {
		ircColors[ircColorName(color)] = convertColor(color)
	}
}

func (t *customTheme) Color(
	name fyne.ThemeColorName, variant fyne.ThemeVariant) color.Color {
	/*
	   // Fyne may use a dark background with the Light variant,
	   // which makes the UI unusable.
	   if runtime.GOOS == "android" {
	       variant = theme.VariantDark
	   }
	*/

	// Fuck this low contrast shit, text must be black.
	if name == theme.ColorNameForeground &&
		variant == theme.VariantLight {
		return color.Black
	}

	switch name {
	case colorNameRenditionError:
		return color.RGBA{0xff, 0x00, 0x00, 0xff}
	case colorNameRenditionJoin:
		return color.RGBA{0x00, 0x88, 0x00, 0xff}
	case colorNameRenditionPart:
		return color.RGBA{0x88, 0x00, 0x00, 0xff}
	case colorNameRenditionAction:
		return color.RGBA{0x88, 0x00, 0x00, 0xff}

	case colorNameBufferTimestamp, colorNameBufferLeaked:
		return color.RGBA{0x88, 0x88, 0x88, 0xff}
	}

	if c, ok := ircColors[name]; ok {
		return c
	}
	return theme.DefaultTheme().Color(name, variant)
}

func (t *customTheme) Font(style fyne.TextStyle) fyne.Resource {
	return theme.DefaultTheme().Font(style)
}

func (t *customTheme) Icon(i fyne.ThemeIconName) fyne.Resource {
	return theme.DefaultTheme().Icon(i)
}

func (t *customTheme) Size(s fyne.ThemeSizeName) float32 {
	switch s {
	case theme.SizeNameInnerPadding:
		return 2
	default:
		return theme.DefaultTheme().Size(s)
	}
}

// --- Relay state -------------------------------------------------------------

type server struct {
	state     RelayServerState
	user      string
	userModes string
}

type bufferLineItem struct {
	format fyne.TextStyle
	// For RichTextStyle.ColorName.
	color fyne.ThemeColorName
	// XXX: Fyne's RichText doesn't support background colours.
	background fyne.ThemeColorName
	text       string
	link       *url.URL
}

type bufferLine struct {
	/// Leaked from another buffer, but temporarily staying in another one.
	leaked bool

	isUnimportant bool
	isHighlight   bool
	rendition     RelayRendition
	when          time.Time
	items         []bufferLineItem
}

type buffer struct {
	bufferName      string
	hideUnimportant bool
	kind            RelayBufferKind
	serverName      string
	lines           []bufferLine

	// Channel:

	topic []bufferLineItem
	modes string

	// Stats:

	newMessages            int
	newUnimportantMessages int
	highlighted            bool

	// Input:

	input                 string
	inputRow, inputColumn int
	history               []string
	historyAt             int
}

type callback func(err string, response *RelayResponseData)

const (
	preferenceAddress = "address"
)

var (
	backendAddress string
	backendContext context.Context
	backendCancel  context.CancelFunc
	backendConn    net.Conn

	backendLock sync.Mutex

	// Connection state:

	commandSeq       uint32
	commandCallbacks = make(map[uint32]callback)

	buffers       []buffer
	bufferCurrent string
	bufferLast    string

	servers = make(map[string]*server)

	// Sound:

	otoContext *oto.Context
	otoReady   chan struct{}

	// Widgets:

	inForeground = true

	wConnect *dialog.FormDialog

	wWindow     fyne.Window
	wTopic      *widget.RichText
	wBufferList *widget.List
	wRichText   *widget.RichText
	wRichScroll *container.Scroll
	wLog        *logEntry
	wPrompt     *widget.Label
	wDown       *widget.Icon
	wStatus     *widget.Label
	wEntry      *inputEntry
)

// -----------------------------------------------------------------------------

func showErrorMessage(text string) {
	dialog.ShowError(errors.New(text), wWindow)
}

func beep() {
	if otoContext == nil {
		return
	}
	go func() {
		<-otoReady
		otoContext.NewPlayer(bytes.NewReader(beepSample)).Play()
	}()
}

// --- Networking --------------------------------------------------------------

func relayReadMessage(r io.Reader) (m RelayEventMessage, ok bool) {
	var length uint32
	if err := binary.Read(r, binary.BigEndian, &length); err != nil {
		log.Println("Event receive failed: " + err.Error())
		return
	}
	b := make([]byte, length)
	if _, err := io.ReadFull(r, b); err != nil {
		log.Println("Event receive failed: " + err.Error())
		return
	}

	if after, ok2 := m.ConsumeFrom(b); !ok2 {
		log.Println("Event deserialization failed")
		return
	} else if len(after) != 0 {
		log.Println("Event deserialization failed: trailing data")
		return
	}

	if *debug {
		log.Printf("<? %v\n", b)

		j, err := m.MarshalJSON()
		if err != nil {
			log.Println("Event marshalling failed: " + err.Error())
			return
		}

		log.Printf("<- %s\n", j)
	}
	return m, true
}

func relaySend(data RelayCommandData, callback callback) bool {
	backendLock.Lock()
	defer backendLock.Unlock()

	m := RelayCommandMessage{
		CommandSeq: commandSeq,
		Data:       data,
	}
	if callback != nil {
		commandCallbacks[m.CommandSeq] = callback
	}
	commandSeq++

	// TODO(p): Handle errors better.
	b, ok := m.AppendTo(make([]byte, 4))
	if !ok {
		log.Println("Command serialization failed")
		return false
	}
	binary.BigEndian.PutUint32(b[:4], uint32(len(b)-4))
	if _, err := backendConn.Write(b); err != nil {
		log.Println("Command send failed: " + err.Error())
		return false
	}

	if *debug {
		log.Printf("-> %v\n", b)
	}
	return true
}

// --- Buffers -----------------------------------------------------------------

func bufferByName(name string) *buffer {
	for i := range buffers {
		if buffers[i].bufferName == name {
			return &buffers[i]
		}
	}
	return nil
}

func bufferActivate(name string) {
	relaySend(RelayCommandData{
		Variant: &RelayCommandDataBufferActivate{BufferName: name},
	}, nil)
}

func bufferToggleUnimportant(name string) {
	relaySend(RelayCommandData{
		Variant: &RelayCommandDataBufferToggleUnimportant{BufferName: name},
	}, nil)
}

func bufferPushLine(b *buffer, line bufferLine) {
	b.lines = append(b.lines, line)

	// Fyne's text layouting is extremely slow.
	// The limit could be made configurable,
	// and we could use a ring buffer approach to storing the lines.
	if len(b.lines) > 100 {
		b.lines = slices.Delete(b.lines, 0, 1)
	}
}

// --- Current buffer ----------------------------------------------------------

func bufferToggleLogFinish(err string, response *RelayResponseDataBufferLog) {
	if response == nil {
		showErrorMessage(err)
		return
	}

	wLog.SetText(string(response.Log))
	wLog.Show()
	wRichScroll.Hide()
}

func bufferToggleLog() {
	if wLog.Visible() {
		wRichScroll.Show()
		wLog.Hide()
		wLog.SetText("")
		return
	}

	name := bufferCurrent
	relaySend(RelayCommandData{Variant: &RelayCommandDataBufferLog{
		BufferName: name,
	}}, func(err string, response *RelayResponseData) {
		if bufferCurrent == name {
			bufferToggleLogFinish(
				err, response.Variant.(*RelayResponseDataBufferLog))
		}
	})
}

func bufferAtBottom() bool {
	return wRichScroll.Offset.Y >=
		wRichScroll.Content.Size().Height-wRichScroll.Size().Height
}

func bufferScrollToBottom() {
	// XXX: Doing it once is not reliable, something's amiss.
	// (In particular, nothing happens when we switch from an empty buffer
	// to a buffer than needs scrolling.)
	wRichScroll.ScrollToBottom()
	wRichScroll.ScrollToBottom()
	refreshStatus()
}

// --- UI state refresh --------------------------------------------------------

func refreshIcon() {
	highlighted := false
	for _, b := range buffers {
		if b.highlighted {
			highlighted = true
			break
		}
	}

	if highlighted {
		wWindow.SetIcon(resourceIconHighlighted)
	} else {
		wWindow.SetIcon(resourceIconNormal)
	}
}

func refreshTopic(topic []bufferLineItem) {
	wTopic.Segments = nil
	for _, item := range topic {
		if item.link != nil {
			wTopic.Segments = append(wTopic.Segments,
				&widget.HyperlinkSegment{Text: item.text, URL: item.link})
			continue
		}
		wTopic.Segments = append(wTopic.Segments, &widget.TextSegment{
			Text: item.text,
			Style: widget.RichTextStyle{
				Alignment: fyne.TextAlignLeading,
				ColorName: item.color,
				Inline:    true,
				SizeName:  theme.SizeNameText,
				TextStyle: item.format,
			},
		})
	}
	wTopic.Refresh()
}

func refreshBufferList() {
	// This seems to be enough, even for removals.
	for i := range buffers {
		wBufferList.RefreshItem(widget.ListItemID(i))
	}
}

func refreshPrompt() {
	var prompt string
	if b := bufferByName(bufferCurrent); b == nil {
		prompt = "Synchronizing..."
	} else if server, ok := servers[b.serverName]; ok {
		prompt = server.user
		if server.userModes != "" {
			prompt += "(" + server.userModes + ")"
		}
		if prompt == "" {
			prompt = "(" + server.state.String() + ")"
		}
	}
	wPrompt.SetText(prompt)
}

func refreshStatus() {
	if bufferAtBottom() {
		wDown.Hide()
	} else {
		wDown.Show()
	}

	status := bufferCurrent
	if b := bufferByName(bufferCurrent); b != nil {
		if b.modes != "" {
			status += "(+" + b.modes + ")"
		}
		if b.hideUnimportant {
			status += "<H>"
		}
	}

	wStatus.SetText(status)
}

// --- RichText formatting -----------------------------------------------------

func defaultBufferLineItem() bufferLineItem { return bufferLineItem{} }

func convertItemFormatting(
	item RelayItemData, cf *bufferLineItem, inverse *bool) {
	switch data := item.Variant.(type) {
	case *RelayItemDataReset:
		*cf = defaultBufferLineItem()
	case *RelayItemDataFlipBold:
		cf.format.Bold = !cf.format.Bold
	case *RelayItemDataFlipItalic:
		cf.format.Italic = !cf.format.Italic
	case *RelayItemDataFlipUnderline:
		cf.format.Underline = !cf.format.Underline
	case *RelayItemDataFlipCrossedOut:
		// https://github.com/fyne-io/fyne/issues/1084
	case *RelayItemDataFlipInverse:
		*inverse = !*inverse
	case *RelayItemDataFlipMonospace:
		cf.format.Monospace = !cf.format.Monospace
	case *RelayItemDataFgColor:
		if data.Color < 0 {
			cf.color = ""
		} else {
			cf.color = ircColorName(int(data.Color))
		}
	case *RelayItemDataBgColor:
		if data.Color < 0 {
			cf.background = ""
		} else {
			cf.background = ircColorName(int(data.Color))
		}
	}
}

var linkRE = regexp.MustCompile(`https?://` +
	`(?:[^\[\](){}<>"'\s]|\([^\[\](){}<>"'\s]*\))+` +
	`(?:[^\[\](){}<>"'\s,.:]|\([^\[\](){}<>"'\s]*\))`)

func convertLinks(
	item bufferLineItem, items []bufferLineItem) []bufferLineItem {
	end, matches := 0, linkRE.FindAllStringIndex(item.text, -1)
	for _, m := range matches {
		url, _ := url.Parse(item.text[m[0]:m[1]])
		if url == nil {
			continue
		}
		if end < m[0] {
			subitem := item
			subitem.text = item.text[end:m[0]]
			items = append(items, subitem)
		}

		subitem := item
		subitem.text = item.text[m[0]:m[1]]
		subitem.link = url
		items = append(items, subitem)

		end = m[1]
	}
	if end < len(item.text) {
		subitem := item
		subitem.text = item.text[end:]
		items = append(items, subitem)
	}
	return items
}

func convertItems(items []RelayItemData) []bufferLineItem {
	result := []bufferLineItem{}
	cf, inverse := defaultBufferLineItem(), false
	for _, it := range items {
		text, ok := it.Variant.(*RelayItemDataText)
		if !ok {
			convertItemFormatting(it, &cf, &inverse)
			continue
		}

		item := cf
		item.text = text.Text
		if inverse {
			item.color, item.background = item.background, item.color
		}
		result = convertLinks(item, result)
	}
	return result
}

// --- Buffer output -----------------------------------------------------------

func convertBufferLine(m *RelayEventDataBufferLine) bufferLine {
	return bufferLine{
		items:         convertItems(m.Items),
		isUnimportant: m.IsUnimportant,
		isHighlight:   m.IsHighlight,
		rendition:     m.Rendition,
		when:          time.UnixMilli(int64(m.When)),
	}
}

func bufferPrintDateChange(last, current time.Time) {
	last, current = last.Local(), current.Local()
	if last.Year() == current.Year() &&
		last.Month() == current.Month() &&
		last.Day() == current.Day() {
		return
	}

	wRichText.Segments = append(wRichText.Segments, &widget.TextSegment{
		Style: widget.RichTextStyle{
			Alignment: fyne.TextAlignLeading,
			ColorName: "",
			Inline:    false,
			SizeName:  theme.SizeNameText,
			TextStyle: fyne.TextStyle{Bold: true},
		},
		Text: current.Format(time.DateOnly),
	})
}

func bufferPrintAndWatchTrailingDateChanges() {
	current := time.Now()
	b := bufferByName(bufferCurrent)
	if b != nil && len(b.lines) != 0 {
		last := b.lines[len(b.lines)-1].when
		bufferPrintDateChange(last, current)
	}

	// TODO(p): The watching part.
}

func bufferPrintLine(lines []bufferLine, index int) {
	line := &lines[index]

	last, current := time.Time{}, line.when
	if index == 0 {
		last = time.Now()
	} else {
		last = lines[index-1].when
	}

	bufferPrintDateChange(last, current)

	texts := []widget.RichTextSegment{&widget.TextSegment{
		Text: line.when.Format("15:04:05 "),
		Style: widget.RichTextStyle{
			Alignment: fyne.TextAlignLeading,
			ColorName: colorNameBufferTimestamp,
			Inline:    true,
			SizeName:  theme.SizeNameText,
			TextStyle: fyne.TextStyle{},
		}}}

	// Tabstops won't quite help us here, since we need it centred.
	prefix := ""
	pcf := widget.RichTextStyle{
		Alignment: fyne.TextAlignLeading,
		Inline:    true,
		SizeName:  theme.SizeNameText,
		TextStyle: fyne.TextStyle{Monospace: true},
	}
	switch line.rendition {
	case RelayRenditionBare:
	case RelayRenditionIndent:
		prefix = "    "
	case RelayRenditionStatus:
		prefix = " -  "
	case RelayRenditionError:
		prefix = "=!= "
		pcf.ColorName = colorNameRenditionError
	case RelayRenditionJoin:
		prefix = "--> "
		pcf.ColorName = colorNameRenditionJoin
	case RelayRenditionPart:
		prefix = "<-- "
		pcf.ColorName = colorNameRenditionPart
	case RelayRenditionAction:
		prefix = " *  "
		pcf.ColorName = colorNameRenditionAction
	}

	if prefix != "" {
		style := pcf
		if line.leaked {
			style.ColorName = colorNameBufferLeaked
		}
		texts = append(texts, &widget.TextSegment{
			Text:  prefix,
			Style: style,
		})
	}
	for _, item := range line.items {
		if item.link != nil {
			texts = append(texts,
				&widget.HyperlinkSegment{Text: item.text, URL: item.link})
			continue
		}
		style := widget.RichTextStyle{
			Alignment: fyne.TextAlignLeading,
			ColorName: item.color,
			Inline:    true,
			SizeName:  theme.SizeNameText,
			TextStyle: item.format,
		}
		if line.leaked {
			style.ColorName = colorNameBufferLeaked
		}
		texts = append(texts, &widget.TextSegment{
			Text:  item.text,
			Style: style,
		})
	}

	wRichText.Segments = append(wRichText.Segments,
		&widget.ParagraphSegment{Texts: texts},
		&widget.TextSegment{Style: widget.RichTextStyleParagraph})
}

func bufferPrintSeparator() {
	// TODO(p): Implement our own, so that it can use the primary colour.
	wRichText.Segments = append(wRichText.Segments,
		&widget.SeparatorSegment{})
}

func refreshBuffer(b *buffer) {
	wRichText.Segments = nil

	markBefore := len(b.lines) - b.newMessages - b.newUnimportantMessages
	for i, line := range b.lines {
		if i == markBefore {
			bufferPrintSeparator()
		}
		if !line.isUnimportant || !b.hideUnimportant {
			bufferPrintLine(b.lines, i)
		}
	}

	bufferPrintAndWatchTrailingDateChanges()
	wRichText.Refresh()
	bufferScrollToBottom()
}

// --- Event processing --------------------------------------------------------

func relayProcessBufferLine(b *buffer, m *RelayEventDataBufferLine) {
	line := convertBufferLine(m)

	// Initial sync: skip all other processing, let highlights be.
	bc := bufferByName(bufferCurrent)
	if bc == nil {
		bufferPushLine(b, line)
		return
	}

	// Retained mode is complicated.
	display := (!m.IsUnimportant || !bc.hideUnimportant) &&
		(b.bufferName == bufferCurrent || m.LeakToActive)
	toBottom := display && bufferAtBottom()
	visible := display && toBottom && inForeground && !wLog.Visible()
	separate := display &&
		!visible && bc.newMessages == 0 && bc.newUnimportantMessages == 0

	bufferPushLine(b, line)
	if !(visible || m.LeakToActive) ||
		b.newMessages != 0 || b.newUnimportantMessages != 0 {
		if line.isUnimportant || m.LeakToActive {
			b.newUnimportantMessages++
		} else {
			b.newMessages++
		}
	}

	if m.LeakToActive {
		leakedLine := line
		leakedLine.leaked = true
		bufferPushLine(bc, leakedLine)

		if !visible || bc.newMessages != 0 || bc.newUnimportantMessages != 0 {
			if line.isUnimportant {
				bc.newUnimportantMessages++
			} else {
				bc.newMessages++
			}
		}
	}

	if separate {
		bufferPrintSeparator()
	}
	if display {
		bufferPrintLine(bc.lines, len(bc.lines)-1)
		wRichText.Refresh()
	}
	if toBottom {
		bufferScrollToBottom()
	}

	// TODO(p): On mobile, we should probably send notifications.
	// Though we probably can't run in the background.
	if line.isHighlight || (!visible && !line.isUnimportant &&
		b.kind == RelayBufferKindPrivateMessage) {
		beep()

		if !visible {
			b.highlighted = true
			refreshIcon()
		}
	}

	refreshBufferList()
}

func relayProcessCallbacks(
	commandSeq uint32, err string, response *RelayResponseData) {
	if handler, ok := commandCallbacks[commandSeq]; !ok {
		if *debug {
			log.Printf("Unawaited response: %+v\n", *response)
		}
	} else {
		delete(commandCallbacks, commandSeq)
		if handler != nil {
			handler(err, response)
		}
	}

	// We don't particularly care about wraparound issues.
	for cs, handler := range commandCallbacks {
		if cs <= commandSeq {
			delete(commandCallbacks, cs)
			if handler != nil {
				handler("No response", nil)
			}
		}
	}
}

func relayProcessMessage(m *RelayEventMessage) {
	switch data := m.Data.Variant.(type) {
	case *RelayEventDataError:
		relayProcessCallbacks(data.CommandSeq, data.Error, nil)
	case *RelayEventDataResponse:
		relayProcessCallbacks(data.CommandSeq, "", &data.Data)

	case *RelayEventDataPing:
		relaySend(RelayCommandData{
			Variant: &RelayCommandDataPingResponse{EventSeq: m.EventSeq},
		}, nil)

	case *RelayEventDataBufferLine:
		b := bufferByName(data.BufferName)
		if b == nil {
			return
		}

		relayProcessBufferLine(b, data)
	case *RelayEventDataBufferUpdate:
		b := bufferByName(data.BufferName)
		if b == nil {
			buffers = append(buffers, buffer{bufferName: data.BufferName})
			b = &buffers[len(buffers)-1]
			refreshBufferList()
		}

		hidingToggled := b.hideUnimportant != data.HideUnimportant
		b.hideUnimportant = data.HideUnimportant
		b.kind = data.Context.Variant.Kind()
		b.serverName = ""
		switch context := data.Context.Variant.(type) {
		case *RelayBufferContextServer:
			b.serverName = context.ServerName
		case *RelayBufferContextChannel:
			b.serverName = context.ServerName
			b.modes = context.Modes
			b.topic = convertItems(context.Topic)
		case *RelayBufferContextPrivateMessage:
			b.serverName = context.ServerName
		}

		if b.bufferName == bufferCurrent {
			refreshTopic(b.topic)
			refreshStatus()

			if hidingToggled {
				refreshBuffer(b)
			}
		}
	case *RelayEventDataBufferStats:
		b := bufferByName(data.BufferName)
		if b == nil {
			return
		}

		b.newMessages = int(data.NewMessages)
		b.newUnimportantMessages = int(data.NewUnimportantMessages)
		b.highlighted = data.Highlighted

		refreshIcon()
	case *RelayEventDataBufferRename:
		b := bufferByName(data.BufferName)
		if b == nil {
			return
		}

		b.bufferName = data.New

		refreshBufferList()
		if data.BufferName == bufferCurrent {
			bufferCurrent = data.New
			refreshStatus()
		}
		if data.BufferName == bufferLast {
			bufferLast = data.New
		}
	case *RelayEventDataBufferRemove:
		buffers = slices.DeleteFunc(buffers, func(b buffer) bool {
			return b.bufferName == data.BufferName
		})

		refreshBufferList()
		refreshIcon()
	case *RelayEventDataBufferActivate:
		old := bufferByName(bufferCurrent)
		bufferLast = bufferCurrent
		bufferCurrent = data.BufferName
		b := bufferByName(data.BufferName)
		if b == nil {
			return
		}

		if old != nil {
			old.newMessages = 0
			old.newUnimportantMessages = 0
			old.highlighted = false

			old.input = wEntry.Text
			old.inputRow = wEntry.CursorRow
			old.inputColumn = wEntry.CursorColumn

			// Note that we effectively overwrite the newest line
			// with the current textarea contents, and jump there.
			old.historyAt = len(old.history)
		}

		if wLog.Visible() {
			bufferToggleLog()
		}
		if inForeground {
			b.highlighted = false
		}

		for i := range buffers {
			if buffers[i].bufferName == bufferCurrent {
				wBufferList.Select(widget.ListItemID(i))
				break
			}
		}

		refreshIcon()
		refreshTopic(b.topic)
		refreshBufferList()
		refreshBuffer(b)
		refreshPrompt()
		refreshStatus()

		wEntry.SetText(b.input)
		wEntry.CursorRow = b.inputRow
		wEntry.CursorColumn = b.inputColumn
		wEntry.Refresh()
		wWindow.Canvas().Focus(wEntry)
	case *RelayEventDataBufferInput:
		b := bufferByName(data.BufferName)
		if b == nil {
			return
		}

		if b.historyAt == len(b.history) {
			b.historyAt++
		}
		b.history = append(b.history, data.Text)
	case *RelayEventDataBufferClear:
		b := bufferByName(data.BufferName)
		if b == nil {
			return
		}

		b.lines = nil
		if b.bufferName == bufferCurrent {
			refreshBuffer(b)
		}

	case *RelayEventDataServerUpdate:
		s, existed := servers[data.ServerName]
		if !existed {
			s = &server{}
			servers[data.ServerName] = s
		}

		s.state = data.Data.Variant.State()
		switch state := data.Data.Variant.(type) {
		case *RelayServerDataRegistered:
			s.user = state.User
			s.userModes = state.UserModes
		default:
			s.user = ""
			s.userModes = ""
		}

		refreshPrompt()
	case *RelayEventDataServerRename:
		servers[data.New] = servers[data.ServerName]
		delete(servers, data.ServerName)
	case *RelayEventDataServerRemove:
		delete(servers, data.ServerName)
	}
}

// --- Networking --------------------------------------------------------------

func relayMakeReceiver(
	ctx context.Context, conn net.Conn) <-chan RelayEventMessage {
	// The usual event message rarely gets above 1 kilobyte,
	// thus this is set to buffer up at most 1 megabyte or so.
	p := make(chan RelayEventMessage, 1000)
	r := bufio.NewReaderSize(conn, 65536)
	go func() {
		defer close(p)
		for {
			m, ok := relayReadMessage(r)
			if !ok {
				return
			}
			select {
			case p <- m:
			case <-ctx.Done():
				return
			}
		}
	}()
	return p
}

func relayResetState() {
	commandSeq = 0
	commandCallbacks = make(map[uint32]callback)

	buffers = nil
	bufferCurrent = ""
	bufferLast = ""
	servers = make(map[string]*server)

	refreshIcon()
	refreshTopic(nil)
	refreshBufferList()
	wRichText.ParseMarkdown("")
	refreshPrompt()
	refreshStatus()
}

func relayRun() {
	fyne.CurrentApp().Preferences().SetString(preferenceAddress, backendAddress)
	backendLock.Lock()

	relayResetState()
	backendContext, backendCancel = context.WithCancel(context.Background())
	defer backendCancel()
	var err error
	backendConn, err = net.Dial("tcp", backendAddress)

	backendLock.Unlock()
	if err != nil {
		wConnect.Show()
		showErrorMessage("Connection failed: " + err.Error())
		return
	}
	defer backendConn.Close()

	// TODO(p): Figure out locking.
	//  - Messages are currently sent (semi-)synchronously, directly.
	//  - Is the net.Conn actually async-safe?
	relaySend(RelayCommandData{
		Variant: &RelayCommandDataHello{Version: RelayVersion},
	}, nil)

	relayMessages := relayMakeReceiver(backendContext, backendConn)
Loop:
	for {
		select {
		case m, ok := <-relayMessages:
			if !ok {
				break Loop
			}
			relayProcessMessage(&m)
		}
	}

	wConnect.Show()
	showErrorMessage("Disconnected")
}

// --- Input line --------------------------------------------------------------

func inputSetContents(input string) {
	wEntry.SetText(input)
}

func inputSubmit(text string) bool {
	b := bufferByName(bufferCurrent)
	if b == nil {
		return false
	}

	b.history = append(b.history, text)
	b.historyAt = len(b.history)
	inputSetContents("")

	relaySend(RelayCommandData{Variant: &RelayCommandDataBufferInput{
		BufferName: b.bufferName,
		Text:       text,
	}}, nil)
	return true
}

type inputStamp struct {
	cursorRow, cursorColumn int
	input                   string
}

func inputGetStamp() inputStamp {
	return inputStamp{
		cursorRow:    wEntry.CursorRow,
		cursorColumn: wEntry.CursorColumn,
		input:        wEntry.Text,
	}
}

func inputCompleteFinish(state inputStamp,
	err string, response *RelayResponseDataBufferComplete) {
	if response == nil {
		showErrorMessage(err)
		return
	}

	if len(response.Completions) > 0 {
		insert := response.Completions[0]
		if len(response.Completions) == 1 {
			insert += " "
		}
		inputSetContents(state.input[:response.Start] + insert)

	}
	if len(response.Completions) != 1 {
		beep()
	}

	// TODO(p): Show all completion options.
}

func inputComplete() bool {
	if wEntry.SelectedText() != "" {
		return false
	}

	// XXX: Fyne's Entry widget makes it impossible to handle this properly.
	state := inputGetStamp()
	relaySend(RelayCommandData{Variant: &RelayCommandDataBufferComplete{
		BufferName: bufferCurrent,
		Text:       state.input,
		Position:   uint32(len(state.input)),
	}}, func(err string, response *RelayResponseData) {
		if stamp := inputGetStamp(); state == stamp {
			inputCompleteFinish(state,
				err, response.Variant.(*RelayResponseDataBufferComplete))
		}
	})
	return true
}

func inputUp() bool {
	b := bufferByName(bufferCurrent)
	if b == nil || b.historyAt < 1 {
		return false
	}

	if b.historyAt == len(b.history) {
		b.input = wEntry.Text
	}
	b.historyAt--
	inputSetContents(b.history[b.historyAt])
	return true
}

func inputDown() bool {
	b := bufferByName(bufferCurrent)
	if b == nil || b.historyAt >= len(b.history) {
		return false
	}

	b.historyAt++
	if b.historyAt == len(b.history) {
		inputSetContents(b.input)
	} else {
		inputSetContents(b.history[b.historyAt])
	}
	return true
}

// --- General UI --------------------------------------------------------------

type inputEntry struct {
	widget.Entry

	// selectKeyDown is a hack to exactly invert widget.Entry's behaviour,
	// which groups both Shift keys together.
	selectKeyDown bool
}

func newInputEntry() *inputEntry {
	e := &inputEntry{}
	e.MultiLine = true
	e.Wrapping = fyne.TextWrap(fyne.TextTruncateClip)
	e.ExtendBaseWidget(e)
	return e
}

func (e *inputEntry) FocusLost() {
	e.selectKeyDown = false
	e.Entry.FocusLost()
}

func (e *inputEntry) KeyDown(key *fyne.KeyEvent) {
	// TODO(p): And perhaps on other actions, too.
	relaySend(RelayCommandData{Variant: &RelayCommandDataActive{}}, nil)

	// Modified events are eaten somewhere, not reaching TypedKey or Shortcuts.
	if dd, ok := fyne.CurrentApp().Driver().(desktop.Driver); ok {
		modifiedKey := desktop.CustomShortcut{
			KeyName: key.Name, Modifier: dd.CurrentKeyModifiers()}
		if handler := shortcuts[modifiedKey]; handler != nil {
			handler()
			return
		}

		switch {
		case modifiedKey.Modifier == fyne.KeyModifierControl &&
			modifiedKey.KeyName == fyne.KeyP:
			inputUp()
			return
		case modifiedKey.Modifier == fyne.KeyModifierControl &&
			modifiedKey.KeyName == fyne.KeyN:
			inputDown()
			return
		}
	}

	if key.Name == desktop.KeyShiftLeft || key.Name == desktop.KeyShiftRight {
		e.selectKeyDown = true
	}
	e.Entry.KeyDown(key)
}

func (e *inputEntry) KeyUp(key *fyne.KeyEvent) {
	if key.Name == desktop.KeyShiftLeft || key.Name == desktop.KeyShiftRight {
		e.selectKeyDown = false
	}
	e.Entry.KeyUp(key)
}

func (e *inputEntry) TypedKey(key *fyne.KeyEvent) {
	if e.Disabled() {
		return
	}

	// Invert the Shift key behaviour here.
	// Notice that this will never work on mobile.
	shift := &fyne.KeyEvent{Name: desktop.KeyShiftLeft}
	switch key.Name {
	case fyne.KeyReturn, fyne.KeyEnter:
		if e.selectKeyDown {
			e.Entry.KeyUp(shift)
			e.Entry.TypedKey(key)
			e.Entry.KeyDown(shift)
		} else if e.OnSubmitted != nil {
			e.OnSubmitted(e.Text)
		}
	case fyne.KeyTab:
		if e.selectKeyDown {
			// This could also go through completion lists.
			wWindow.Canvas().FocusPrevious()
		} else {
			inputComplete()
		}
	default:
		e.Entry.TypedKey(key)
	}
}

func (e *inputEntry) SetText(text string) {
	e.Entry.SetText(text)
	if text != "" {
		e.Entry.TypedKey(&fyne.KeyEvent{Name: fyne.KeyPageDown})
	}
}

// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

type logEntry struct {
	// XXX: Sadly, we can't seem to make it actually read-only.
	// https://github.com/fyne-io/fyne/issues/5263
	widget.Entry
}

func newLogEntry() *logEntry {
	e := &logEntry{}
	e.MultiLine = true
	e.Wrapping = fyne.TextWrapWord
	e.ExtendBaseWidget(e)
	return e
}

func (e *logEntry) SetText(text string) {
	e.OnChanged = nil
	e.Entry.SetText(text)
	e.OnChanged = func(string) { e.Entry.SetText(text) }
}

func (e *logEntry) AcceptsTab() bool {
	return false
}

// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

type customLayout struct{}

func (l *customLayout) MinSize(objects []fyne.CanvasObject) fyne.Size {
	var w, h float32 = 0, 0
	for _, o := range objects {
		size := o.MinSize()
		if w < size.Width {
			w = size.Width
		}
		if h < size.Height {
			h = size.Height
		}
	}
	return fyne.NewSize(w, h)
}

func (l *customLayout) Layout(objects []fyne.CanvasObject, size fyne.Size) {
	// It is not otherwise possible to be notified of resizes.
	// Embedding container.Scroll either directly or as a pointer
	// to override its Resize method results in brokenness.
	toBottom := bufferAtBottom()
	for _, o := range objects {
		o.Move(fyne.NewPos(0, 0))
		o.Resize(size)
	}
	if toBottom {
		bufferScrollToBottom()
	}
}

// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

// rotatedBuffers returns buffer indexes starting with the current buffer.
func rotatedBuffers() []int {
	r, start := make([]int, len(buffers)), 0
	for i := range buffers {
		if buffers[i].bufferName == bufferCurrent {
			start = i
			break
		}
	}
	for i := range r {
		start++
		r[i] = start % len(r)
	}
	return r
}

var shortcuts = map[desktop.CustomShortcut]func(){
	{
		KeyName:  fyne.KeyPageUp,
		Modifier: fyne.KeyModifierControl,
	}: func() {
		if r := rotatedBuffers(); len(r) <= 0 {
		} else if i := r[len(r)-1]; i == 0 {
			bufferActivate(buffers[len(buffers)-1].bufferName)
		} else {
			bufferActivate(buffers[i-1].bufferName)
		}
	},
	{
		KeyName:  fyne.KeyPageDown,
		Modifier: fyne.KeyModifierControl,
	}: func() {
		if r := rotatedBuffers(); len(r) <= 0 {
		} else {
			bufferActivate(buffers[r[0]].bufferName)
		}
	},
	{
		KeyName:  fyne.KeyTab,
		Modifier: fyne.KeyModifierAlt,
	}: func() {
		if bufferLast != "" {
			bufferActivate(bufferLast)
		}
	},
	{
		// XXX: This makes an assumption on the keyboard layout (we want '!').
		KeyName:  fyne.Key1,
		Modifier: fyne.KeyModifierAlt | fyne.KeyModifierShift,
	}: func() {
		for _, i := range rotatedBuffers() {
			if buffers[i].highlighted {
				bufferActivate(buffers[i].bufferName)
				break
			}
		}
	},
	{
		KeyName:  fyne.KeyA,
		Modifier: fyne.KeyModifierAlt,
	}: func() {
		for _, i := range rotatedBuffers() {
			if buffers[i].newMessages != 0 {
				bufferActivate(buffers[i].bufferName)
				break
			}
		}
	},
	{
		KeyName:  fyne.KeyH,
		Modifier: fyne.KeyModifierAlt | fyne.KeyModifierShift,
	}: func() {
		if b := bufferByName(bufferCurrent); b != nil {
			bufferToggleUnimportant(b.bufferName)
		}
	},
	{
		KeyName:  fyne.KeyH,
		Modifier: fyne.KeyModifierAlt,
	}: func() {
		if b := bufferByName(bufferCurrent); b != nil {
			bufferToggleLog()
		}
	},
}

func main() {
	flag.Usage = func() {
		fmt.Fprintf(flag.CommandLine.Output(),
			"Usage: %s [OPTION...] [CONNECT]\n\n", os.Args[0])
		flag.PrintDefaults()
	}

	flag.Parse()
	if flag.NArg() > 1 {
		flag.Usage()
		os.Exit(1)
	}

	var err error
	otoContext, otoReady, err = oto.NewContext(&oto.NewContextOptions{
		SampleRate:   44100,
		ChannelCount: 1,
		Format:       oto.FormatSignedInt16LE,
	})
	if err != nil {
		log.Println(err)
	}

	a := app.New()
	a.Settings().SetTheme(&customTheme{})
	wWindow = a.NewWindow(projectName)
	wWindow.Resize(fyne.NewSize(640, 480))

	a.Lifecycle().SetOnEnteredForeground(func() {
		// TODO(p): Does this need locking?
		inForeground = true
		if b := bufferByName(bufferCurrent); b != nil {
			b.highlighted = false
			refreshIcon()
		}
	})
	a.Lifecycle().SetOnExitedForeground(func() {
		inForeground = false
	})

	// TODO(p): Consider using data bindings.
	wBufferList = widget.NewList(func() int { return len(buffers) },
		func() fyne.CanvasObject {
			return widget.NewLabel(strings.Repeat(" ", 16))
		},
		func(id widget.ListItemID, item fyne.CanvasObject) {
			label, b := item.(*widget.Label), &buffers[int(id)]
			label.TextStyle.Italic = b.bufferName == bufferCurrent
			label.TextStyle.Bold = false
			text := b.bufferName
			if b.bufferName != bufferCurrent && b.newMessages != 0 {
				label.TextStyle.Bold = true
				text += fmt.Sprintf(" (%d)", b.newMessages)
			}
			label.Importance = widget.MediumImportance
			if b.highlighted {
				label.Importance = widget.HighImportance
			}
			label.SetText(text)
		})
	wBufferList.HideSeparators = true
	wBufferList.OnSelected = func(id widget.ListItemID) {
		// TODO(p): See if we can deselect it now without consequences.
		request := buffers[int(id)].bufferName
		if request != bufferCurrent {
			bufferActivate(request)
		}
	}

	wTopic = widget.NewRichText()
	wTopic.Truncation = fyne.TextTruncateEllipsis

	wRichText = widget.NewRichText()
	wRichText.Wrapping = fyne.TextWrapWord
	wRichScroll = container.NewVScroll(wRichText)
	wRichScroll.OnScrolled = func(position fyne.Position) { refreshStatus() }
	wLog = newLogEntry()
	wLog.Wrapping = fyne.TextWrapWord
	wLog.Hide()

	wPrompt = widget.NewLabelWithStyle(
		"", fyne.TextAlignLeading, fyne.TextStyle{Bold: true})
	wDown = widget.NewIcon(theme.MoveDownIcon())
	wStatus = widget.NewLabelWithStyle(
		"", fyne.TextAlignTrailing, fyne.TextStyle{})
	wEntry = newInputEntry()
	wEntry.OnSubmitted = func(text string) { inputSubmit(text) }

	top := container.NewVBox(
		wTopic,
		widget.NewSeparator(),
	)
	split := container.NewHSplit(wBufferList,
		container.New(&customLayout{}, wRichScroll, wLog))
	split.SetOffset(0.25)
	bottom := container.NewVBox(
		widget.NewSeparator(),
		container.NewBorder(nil, nil,
			wPrompt, container.NewHBox(wDown, wStatus)),
		wEntry,
	)
	wWindow.SetContent(container.NewBorder(top, bottom, nil, nil, split))

	canvas := wWindow.Canvas()
	for s, handler := range shortcuts {
		canvas.AddShortcut(&s, func(fyne.Shortcut) { handler() })
	}

	// ---

	connect := false
	backendAddress = a.Preferences().String(preferenceAddress)
	if flag.NArg() >= 1 {
		backendAddress = flag.Arg(0)
		connect = true
	}

	connectAddress := widget.NewEntry()
	connectAddress.SetPlaceHolder("host:port")
	connectAddress.SetText(backendAddress)
	connectAddress.TypedKey(&fyne.KeyEvent{Name: fyne.KeyPageDown})
	connectAddress.Validator = func(text string) error {
		_, _, err := net.SplitHostPort(text)
		return err
	}

	// TODO(p): Mobile should not have the option to cancel at all.
	// The GoBack just makes us go to the background, staying useless.
	wConnect = dialog.NewForm("Connect to relay", "Connect", "Exit",
		[]*widget.FormItem{
			{Text: "Address:", Widget: connectAddress},
		}, func(ok bool) {
			if ok {
				backendAddress = connectAddress.Text
				go relayRun()
			} else if md, ok := a.Driver().(mobile.Driver); ok {
				md.GoBack()
				wConnect.Show()
			} else {
				a.Quit()
			}
		}, wWindow)
	if connect {
		go relayRun()
	} else {
		wConnect.Show()
	}

	wWindow.ShowAndRun()
}