package cli

import (
	"fmt"
	"strings"
	"time"

	"github.com/gdamore/tcell/v2"
	"github.com/rivo/tview"
)

// Buffer holds messages for a channel/DM/status window.
type Buffer struct {
	Name   string
	Lines  []string
	Unread int
}

// UI manages the terminal interface. Most of its methods wait for
// the tview event loop to run their update. Code that runs on that
// loop, such as a key handler, must not call them: it would wait
// for itself.
type UI struct {
	app       *tview.Application
	messages  *tview.TextView
	statusBar *tview.TextView
	input     *tview.InputField
	layout    *tview.Flex

	buffers       []*Buffer
	currentBuffer int

	onInput func(string)
	// inputDone is closed once the line last passed to onInput
	// has been handled. Only callOnInput, on the event loop, uses
	// it.
	inputDone chan struct{}
}

// NewUI creates the tview-based IRC-like UI.
func NewUI() *UI {
	ui := &UI{ //nolint:exhaustruct,varnamelen // fields set below; ui is idiomatic
		app: tview.NewApplication(),
		buffers: []*Buffer{
			{Name: "(status)", Lines: nil, Unread: 0},
		},
	}

	ui.initMessages()
	ui.initStatusBar()
	ui.initInput()
	ui.initKeyCapture()

	ui.layout = tview.NewFlex().
		SetDirection(tview.FlexRow).
		AddItem(ui.messages, 0, 1, false).
		AddItem(ui.statusBar, 1, 0, false).
		AddItem(ui.input, 1, 0, true)

	ui.app.SetRoot(ui.layout, true)
	ui.app.SetFocus(ui.input)

	return ui
}

// Run starts the UI event loop (blocks).
func (ui *UI) Run() error {
	err := ui.app.Run()
	if err != nil {
		return fmt.Errorf("run ui: %w", err)
	}

	return nil
}

// Stop stops the UI.
func (ui *UI) Stop() {
	ui.app.Stop()
}

// OnInput sets the callback for user input.
func (ui *UI) OnInput(fn func(string)) {
	ui.onInput = fn
}

// AddLine adds a line to the specified buffer.
func (ui *UI) AddLine(bufferName, line string) {
	ui.app.QueueUpdateDraw(func() {
		buf := ui.getOrCreateBuffer(bufferName)
		buf.Lines = append(buf.Lines, line)

		cur := ui.buffers[ui.currentBuffer]
		if cur != buf {
			buf.Unread++

			ui.refreshStatusBar()
		}

		if cur == buf {
			_, _ = fmt.Fprintln(ui.messages, line)
		}
	})
}

// AddLineAsRead adds a line to the specified buffer, as
// AddLine does, but does not mark the buffer unread.
func (ui *UI) AddLineAsRead(bufferName, line string) {
	ui.app.QueueUpdateDraw(func() {
		buf := ui.getOrCreateBuffer(bufferName)
		buf.Lines = append(buf.Lines, line)

		if ui.buffers[ui.currentBuffer] == buf {
			_, _ = fmt.Fprintln(ui.messages, line)
		}
	})
}

// AddStatus adds a line to the status buffer.
func (ui *UI) AddStatus(line string) {
	ts := time.Now().Format("15:04")
	ui.AddLine(
		"(status)",
		"[gray]"+ts+"[white] "+line,
	)
}

// SwitchBuffer switches to the buffer at index n.
func (ui *UI) SwitchBuffer(bufIndex int) {
	ui.app.QueueUpdateDraw(func() {
		if bufIndex < 0 || bufIndex >= len(ui.buffers) {
			return
		}

		ui.currentBuffer = bufIndex

		buf := ui.buffers[bufIndex]
		buf.Unread = 0

		ui.messages.Clear()

		for _, line := range buf.Lines {
			_, _ = fmt.Fprintln(ui.messages, line)
		}

		ui.messages.ScrollToEnd()
		ui.refreshStatusBar()
	})
}

// SwitchToBuffer switches to named buffer, creating if
// needed.
func (ui *UI) SwitchToBuffer(name string) {
	ui.app.QueueUpdateDraw(func() {
		buf := ui.getOrCreateBuffer(name)

		for i, b := range ui.buffers {
			if b == buf {
				ui.currentBuffer = i

				break
			}
		}

		buf.Unread = 0

		ui.messages.Clear()

		for _, line := range buf.Lines {
			_, _ = fmt.Fprintln(ui.messages, line)
		}

		ui.messages.ScrollToEnd()
		ui.refreshStatusBar()
	})
}

// SetStatus updates the status bar text.
func (ui *UI) SetStatus(
	nick, target, connStatus string,
) {
	ui.app.QueueUpdateDraw(func() {
		ui.renderStatusBar(nick, target, connStatus)
	})
}

// BufferName returns the name of the buffer at index bufIndex,
// and whether there is such a buffer.
func (ui *UI) BufferName(bufIndex int) (string, bool) {
	var (
		name  string
		found bool
	)

	ui.app.QueueUpdate(func() {
		if bufIndex < 0 || bufIndex >= len(ui.buffers) {
			return
		}

		name = ui.buffers[bufIndex].Name
		found = true
	})

	return name, found
}

// BufferIndex returns the index of a named buffer.
func (ui *UI) BufferIndex(name string) int {
	for i, buf := range ui.buffers {
		if buf.Name == name {
			return i
		}
	}

	return -1
}

func (ui *UI) initMessages() {
	ui.messages = tview.NewTextView().
		SetDynamicColors(true).
		SetScrollable(true).
		SetWordWrap(true).
		SetChangedFunc(func() {
			ui.app.Draw()
		})
	ui.messages.SetBorder(false)
}

func (ui *UI) initStatusBar() {
	ui.statusBar = tview.NewTextView().
		SetDynamicColors(true)
	ui.statusBar.SetBackgroundColor(tcell.ColorNavy)
	ui.statusBar.SetTextColor(tcell.ColorWhite)
}

func (ui *UI) initInput() {
	ui.input = tview.NewInputField().
		SetFieldBackgroundColor(tcell.ColorBlack).
		SetFieldTextColor(tcell.ColorWhite)

	ui.input.SetDoneFunc(func(key tcell.Key) {
		if key != tcell.KeyEnter {
			return
		}

		text := ui.input.GetText()
		if text == "" {
			return
		}

		ui.input.SetText("")
		ui.callOnInput(text)
	})
}

func (ui *UI) initKeyCapture() {
	ui.app.SetInputCapture(
		func(event *tcell.EventKey) *tcell.EventKey {
			if event.Modifiers()&tcell.ModAlt == 0 {
				return event
			}

			// Alt and a digit runs /window with that digit.
			// SwitchBuffer alone would leave the target as it was.
			r := event.Rune()
			if r >= '0' && r <= '9' {
				ui.callOnInput("/window " + string(r))

				return nil
			}

			return event
		},
	)
}

// callOnInput passes text to the input callback on a new
// goroutine. The key handlers call it on the event loop, and the
// callback waits for that loop to update the screen, so they must
// not wait for the callback. The goroutine first waits for the
// line before it to be handled, which keeps lines in the order
// they were typed.
func (ui *UI) callOnInput(text string) {
	if ui.onInput == nil {
		return
	}

	previous := ui.inputDone
	done := make(chan struct{})
	ui.inputDone = done

	go func() {
		if previous != nil {
			<-previous
		}

		ui.onInput(text)
		close(done)
	}()
}

func (ui *UI) refreshStatusBar() {
	// Placeholder; full refresh needs nick/target context.
}

func (ui *UI) renderStatusBar(
	nick, target, connStatus string,
) {
	var unreadParts []string

	for i, buf := range ui.buffers {
		if buf.Unread > 0 {
			unreadParts = append(unreadParts,
				fmt.Sprintf(
					"%d:%s(%d)",
					i, buf.Name, buf.Unread,
				),
			)
		}
	}

	unread := ""
	if len(unreadParts) > 0 {
		unread = " [Act: " +
			strings.Join(unreadParts, ",") + "]"
	}

	bufInfo := fmt.Sprintf(
		"[%d:%s]",
		ui.currentBuffer,
		ui.buffers[ui.currentBuffer].Name,
	)

	ui.statusBar.Clear()

	_, _ = fmt.Fprintf(ui.statusBar,
		" [%s] %s %s %s%s",
		connStatus, nick, bufInfo, target, unread,
	)
}

func (ui *UI) getOrCreateBuffer(name string) *Buffer {
	for _, buf := range ui.buffers {
		if buf.Name == name {
			return buf
		}
	}

	buf := &Buffer{Name: name, Lines: nil, Unread: 0}
	ui.buffers = append(ui.buffers, buf)

	return buf
}