package fzf

import (
	"bytes"
	"fmt"
	"os"
	"os/exec"
	"os/signal"
	"regexp"
	"sort"
	"strings"
	"sync"
	"syscall"
	"time"

	C "github.com/junegunn/fzf/src/curses"
	"github.com/junegunn/fzf/src/util"

	"github.com/junegunn/go-runewidth"
)

// Terminal represents terminal input/output
type Terminal struct {
	inlineInfo bool
	prompt     string
	reverse    bool
	hscroll    bool
	cx         int
	cy         int
	offset     int
	yanked     []rune
	input      []rune
	multi      bool
	sort       bool
	toggleSort bool
	expect     map[int]string
	keymap     map[int]actionType
	execmap    map[int]string
	pressed    string
	printQuery bool
	history    *History
	cycle      bool
	count      int
	progress   int
	reading    bool
	merger     *Merger
	selected   map[uint32]selectedItem
	reqBox     *util.EventBox
	eventBox   *util.EventBox
	mutex      sync.Mutex
	initFunc   func()
	suppress   bool
	startChan  chan bool
}

type selectedItem struct {
	at   time.Time
	text *string
}

type byTimeOrder []selectedItem

func (a byTimeOrder) Len() int {
	return len(a)
}

func (a byTimeOrder) Swap(i, j int) {
	a[i], a[j] = a[j], a[i]
}

func (a byTimeOrder) Less(i, j int) bool {
	return a[i].at.Before(a[j].at)
}

var _spinner = []string{`-`, `\`, `|`, `/`, `-`, `\`, `|`, `/`}
var _runeWidths = make(map[rune]int)

const (
	reqPrompt util.EventType = iota
	reqInfo
	reqList
	reqRefresh
	reqRedraw
	reqClose
	reqQuit
)

type actionType int

const (
	actIgnore actionType = iota
	actInvalid
	actRune
	actMouse
	actBeginningOfLine
	actAbort
	actAccept
	actBackwardChar
	actBackwardDeleteChar
	actBackwardWord
	actClearScreen
	actDeleteChar
	actEndOfLine
	actForwardChar
	actForwardWord
	actKillLine
	actKillWord
	actUnixLineDiscard
	actUnixWordRubout
	actYank
	actBackwardKillWord
	actSelectAll
	actDeselectAll
	actToggle
	actToggleAll
	actToggleDown
	actToggleUp
	actDown
	actUp
	actPageUp
	actPageDown
	actToggleSort
	actPreviousHistory
	actNextHistory
	actExecute
)

func defaultKeymap() map[int]actionType {
	keymap := make(map[int]actionType)
	keymap[C.Invalid] = actInvalid
	keymap[C.CtrlA] = actBeginningOfLine
	keymap[C.CtrlB] = actBackwardChar
	keymap[C.CtrlC] = actAbort
	keymap[C.CtrlG] = actAbort
	keymap[C.CtrlQ] = actAbort
	keymap[C.ESC] = actAbort
	keymap[C.CtrlD] = actDeleteChar
	keymap[C.CtrlE] = actEndOfLine
	keymap[C.CtrlF] = actForwardChar
	keymap[C.CtrlH] = actBackwardDeleteChar
	keymap[C.BSpace] = actBackwardDeleteChar
	keymap[C.Tab] = actToggleDown
	keymap[C.BTab] = actToggleUp
	keymap[C.CtrlJ] = actDown
	keymap[C.CtrlK] = actUp
	keymap[C.CtrlL] = actClearScreen
	keymap[C.CtrlM] = actAccept
	keymap[C.CtrlN] = actDown
	keymap[C.CtrlP] = actUp
	keymap[C.CtrlU] = actUnixLineDiscard
	keymap[C.CtrlW] = actUnixWordRubout
	keymap[C.CtrlY] = actYank

	keymap[C.AltB] = actBackwardWord
	keymap[C.SLeft] = actBackwardWord
	keymap[C.AltF] = actForwardWord
	keymap[C.SRight] = actForwardWord
	keymap[C.AltD] = actKillWord
	keymap[C.AltBS] = actBackwardKillWord

	keymap[C.Up] = actUp
	keymap[C.Down] = actDown
	keymap[C.Left] = actBackwardChar
	keymap[C.Right] = actForwardChar

	keymap[C.Home] = actBeginningOfLine
	keymap[C.End] = actEndOfLine
	keymap[C.Del] = actDeleteChar // FIXME Del vs. CTRL-D
	keymap[C.PgUp] = actPageUp
	keymap[C.PgDn] = actPageDown

	keymap[C.Rune] = actRune
	keymap[C.Mouse] = actMouse
	return keymap
}

// NewTerminal returns new Terminal object
func NewTerminal(opts *Options, eventBox *util.EventBox) *Terminal {
	input := []rune(opts.Query)
	return &Terminal{
		inlineInfo: opts.InlineInfo,
		prompt:     opts.Prompt,
		reverse:    opts.Reverse,
		hscroll:    opts.Hscroll,
		cx:         len(input),
		cy:         0,
		offset:     0,
		yanked:     []rune{},
		input:      input,
		multi:      opts.Multi,
		sort:       opts.Sort > 0,
		toggleSort: opts.ToggleSort,
		expect:     opts.Expect,
		keymap:     opts.Keymap,
		execmap:    opts.Execmap,
		pressed:    "",
		printQuery: opts.PrintQuery,
		history:    opts.History,
		cycle:      opts.Cycle,
		reading:    true,
		merger:     EmptyMerger,
		selected:   make(map[uint32]selectedItem),
		reqBox:     util.NewEventBox(),
		eventBox:   eventBox,
		mutex:      sync.Mutex{},
		suppress:   true,
		startChan:  make(chan bool, 1),
		initFunc: func() {
			C.Init(opts.Theme, opts.Black, opts.Mouse)
		}}
}

// Input returns current query string
func (t *Terminal) Input() []rune {
	t.mutex.Lock()
	defer t.mutex.Unlock()
	return copySlice(t.input)
}

// UpdateCount updates the count information
func (t *Terminal) UpdateCount(cnt int, final bool) {
	t.mutex.Lock()
	t.count = cnt
	t.reading = !final
	t.mutex.Unlock()
	t.reqBox.Set(reqInfo, nil)
	if final {
		t.reqBox.Set(reqRefresh, nil)
	}
}

// UpdateProgress updates the search progress
func (t *Terminal) UpdateProgress(progress float32) {
	t.mutex.Lock()
	newProgress := int(progress * 100)
	changed := t.progress != newProgress
	t.progress = newProgress
	t.mutex.Unlock()

	if changed {
		t.reqBox.Set(reqInfo, nil)
	}
}

// UpdateList updates Merger to display the list
func (t *Terminal) UpdateList(merger *Merger) {
	t.mutex.Lock()
	t.progress = 100
	t.merger = merger
	t.mutex.Unlock()
	t.reqBox.Set(reqInfo, nil)
	t.reqBox.Set(reqList, nil)
}

func (t *Terminal) output() {
	if t.printQuery {
		fmt.Println(string(t.input))
	}
	if len(t.expect) > 0 {
		fmt.Println(t.pressed)
	}
	if len(t.selected) == 0 {
		cnt := t.merger.Length()
		if cnt > 0 && cnt > t.cy {
			fmt.Println(t.merger.Get(t.cy).AsString())
		}
	} else {
		sels := make([]selectedItem, 0, len(t.selected))
		for _, sel := range t.selected {
			sels = append(sels, sel)
		}
		sort.Sort(byTimeOrder(sels))
		for _, sel := range sels {
			fmt.Println(*sel.text)
		}
	}
}

func runeWidth(r rune, prefixWidth int) int {
	if r == '\t' {
		return 8 - prefixWidth%8
	} else if w, found := _runeWidths[r]; found {
		return w
	} else {
		w := runewidth.RuneWidth(r)
		_runeWidths[r] = w
		return w
	}
}

func displayWidth(runes []rune) int {
	l := 0
	for _, r := range runes {
		l += runeWidth(r, l)
	}
	return l
}

func (t *Terminal) move(y int, x int, clear bool) {
	maxy := C.MaxY()
	if !t.reverse {
		y = maxy - y - 1
	}

	if clear {
		C.MoveAndClear(y, x)
	} else {
		C.Move(y, x)
	}
}

func (t *Terminal) placeCursor() {
	t.move(0, len(t.prompt)+displayWidth(t.input[:t.cx]), false)
}

func (t *Terminal) printPrompt() {
	t.move(0, 0, true)
	C.CPrint(C.ColPrompt, true, t.prompt)
	C.CPrint(C.ColNormal, true, string(t.input))
}

func (t *Terminal) printInfo() {
	if t.inlineInfo {
		t.move(0, len(t.prompt)+displayWidth(t.input)+1, true)
		if t.reading {
			C.CPrint(C.ColSpinner, true, " < ")
		} else {
			C.CPrint(C.ColPrompt, true, " < ")
		}
	} else {
		t.move(1, 0, true)
		if t.reading {
			duration := int64(spinnerDuration)
			idx := (time.Now().UnixNano() % (duration * int64(len(_spinner)))) / duration
			C.CPrint(C.ColSpinner, true, _spinner[idx])
		}
		t.move(1, 2, false)
	}

	output := fmt.Sprintf("%d/%d", t.merger.Length(), t.count)
	if t.toggleSort {
		if t.sort {
			output += "/S"
		} else {
			output += "  "
		}
	}
	if t.multi && len(t.selected) > 0 {
		output += fmt.Sprintf(" (%d)", len(t.selected))
	}
	if t.progress > 0 && t.progress < 100 {
		output += fmt.Sprintf(" (%d%%)", t.progress)
	}
	C.CPrint(C.ColInfo, false, output)
}

func (t *Terminal) printList() {
	t.constrain()

	maxy := t.maxItems()
	count := t.merger.Length() - t.offset
	for i := 0; i < maxy; i++ {
		var line int
		if t.inlineInfo {
			line = i + 1
		} else {
			line = i + 2
		}
		t.move(line, 0, true)
		if i < count {
			t.printItem(t.merger.Get(i+t.offset), i == t.cy-t.offset)
		}
	}
}

func (t *Terminal) printItem(item *Item, current bool) {
	_, selected := t.selected[item.index]
	if current {
		C.CPrint(C.ColCursor, true, ">")
		if selected {
			C.CPrint(C.ColSelected, true, ">")
		} else {
			C.CPrint(C.ColCurrent, true, " ")
		}
		t.printHighlighted(item, true, C.ColCurrent, C.ColCurrentMatch, true)
	} else {
		C.CPrint(C.ColCursor, true, " ")
		if selected {
			C.CPrint(C.ColSelected, true, ">")
		} else {
			C.Print(" ")
		}
		t.printHighlighted(item, false, 0, C.ColMatch, false)
	}
}

func trimRight(runes []rune, width int) ([]rune, int) {
	// We start from the beginning to handle tab characters
	l := 0
	for idx, r := range runes {
		l += runeWidth(r, l)
		if idx > 0 && l > width {
			return runes[:idx], len(runes) - idx
		}
	}
	return runes, 0
}

func displayWidthWithLimit(runes []rune, prefixWidth int, limit int) int {
	l := 0
	for _, r := range runes {
		l += runeWidth(r, l+prefixWidth)
		if l > limit {
			// Early exit
			return l
		}
	}
	return l
}

func trimLeft(runes []rune, width int) ([]rune, int32) {
	currentWidth := displayWidth(runes)
	var trimmed int32

	for currentWidth > width && len(runes) > 0 {
		runes = runes[1:]
		trimmed++
		currentWidth = displayWidthWithLimit(runes, 2, width)
	}
	return runes, trimmed
}

func (t *Terminal) printHighlighted(item *Item, bold bool, col1 int, col2 int, current bool) {
	var maxe int32
	for _, offset := range item.offsets {
		if offset[1] > maxe {
			maxe = offset[1]
		}
	}

	// Overflow
	text := []rune(*item.text)
	offsets := item.colorOffsets(col2, bold, current)
	maxWidth := C.MaxX() - 3
	fullWidth := displayWidth(text)
	if fullWidth > maxWidth {
		if t.hscroll {
			// Stri..
			matchEndWidth := displayWidth(text[:maxe])
			if matchEndWidth <= maxWidth-2 {
				text, _ = trimRight(text, maxWidth-2)
				text = append(text, []rune("..")...)
			} else {
				// Stri..
				if matchEndWidth < fullWidth-2 {
					text = append(text[:maxe], []rune("..")...)
				}
				// ..ri..
				var diff int32
				text, diff = trimLeft(text, maxWidth-2)

				// Transform offsets
				for idx, offset := range offsets {
					b, e := offset.offset[0], offset.offset[1]
					b += 2 - diff
					e += 2 - diff
					b = util.Max32(b, 2)
					offsets[idx].offset[0] = b
					offsets[idx].offset[1] = util.Max32(b, e)
				}
				text = append([]rune(".."), text...)
			}
		} else {
			text, _ = trimRight(text, maxWidth-2)
			text = append(text, []rune("..")...)

			for idx, offset := range offsets {
				offsets[idx].offset[0] = util.Min32(offset.offset[0], int32(maxWidth-2))
				offsets[idx].offset[1] = util.Min32(offset.offset[1], int32(maxWidth))
			}
		}
	}

	var index int32
	var substr string
	var prefixWidth int
	maxOffset := int32(len(text))
	for _, offset := range offsets {
		b := util.Constrain32(offset.offset[0], index, maxOffset)
		e := util.Constrain32(offset.offset[1], index, maxOffset)

		substr, prefixWidth = processTabs(text[index:b], prefixWidth)
		C.CPrint(col1, bold, substr)

		if b < e {
			substr, prefixWidth = processTabs(text[b:e], prefixWidth)
			C.CPrint(offset.color, offset.bold, substr)
		}

		index = e
		if index >= maxOffset {
			break
		}
	}
	if index < maxOffset {
		substr, _ = processTabs(text[index:], prefixWidth)
		C.CPrint(col1, bold, substr)
	}
}

func processTabs(runes []rune, prefixWidth int) (string, int) {
	var strbuf bytes.Buffer
	l := prefixWidth
	for _, r := range runes {
		w := runeWidth(r, l)
		l += w
		if r == '\t' {
			strbuf.WriteString(strings.Repeat(" ", w))
		} else {
			strbuf.WriteRune(r)
		}
	}
	return strbuf.String(), l
}

func (t *Terminal) printAll() {
	t.printList()
	t.printPrompt()
	t.printInfo()
}

func (t *Terminal) refresh() {
	if !t.suppress {
		C.Refresh()
	}
}

func (t *Terminal) delChar() bool {
	if len(t.input) > 0 && t.cx < len(t.input) {
		t.input = append(t.input[:t.cx], t.input[t.cx+1:]...)
		return true
	}
	return false
}

func findLastMatch(pattern string, str string) int {
	rx, err := regexp.Compile(pattern)
	if err != nil {
		return -1
	}
	locs := rx.FindAllStringIndex(str, -1)
	if locs == nil {
		return -1
	}
	return locs[len(locs)-1][0]
}

func findFirstMatch(pattern string, str string) int {
	rx, err := regexp.Compile(pattern)
	if err != nil {
		return -1
	}
	loc := rx.FindStringIndex(str)
	if loc == nil {
		return -1
	}
	return loc[0]
}

func copySlice(slice []rune) []rune {
	ret := make([]rune, len(slice))
	copy(ret, slice)
	return ret
}

func (t *Terminal) rubout(pattern string) {
	pcx := t.cx
	after := t.input[t.cx:]
	t.cx = findLastMatch(pattern, string(t.input[:t.cx])) + 1
	t.yanked = copySlice(t.input[t.cx:pcx])
	t.input = append(t.input[:t.cx], after...)
}

func keyMatch(key int, event C.Event) bool {
	return event.Type == key || event.Type == C.Rune && int(event.Char) == key-C.AltZ
}

func executeCommand(template string, current string) {
	command := strings.Replace(template, "{}", fmt.Sprintf("%q", current), -1)
	cmd := exec.Command("sh", "-c", command)
	cmd.Stdin = os.Stdin
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	C.Endwin()
	cmd.Run()
	C.Refresh()
}

// Loop is called to start Terminal I/O
func (t *Terminal) Loop() {
	<-t.startChan
	{ // Late initialization
		t.mutex.Lock()
		t.initFunc()
		t.printPrompt()
		t.placeCursor()
		C.Refresh()
		t.printInfo()
		t.mutex.Unlock()
		go func() {
			timer := time.NewTimer(initialDelay)
			<-timer.C
			t.reqBox.Set(reqRefresh, nil)
		}()

		resizeChan := make(chan os.Signal, 1)
		signal.Notify(resizeChan, syscall.SIGWINCH)
		go func() {
			for {
				<-resizeChan
				t.reqBox.Set(reqRedraw, nil)
			}
		}()

		// Keep the spinner spinning
		go func() {
			for {
				t.mutex.Lock()
				reading := t.reading
				t.mutex.Unlock()
				if !reading {
					break
				}
				time.Sleep(spinnerDuration)
				t.reqBox.Set(reqInfo, nil)
			}
		}()
	}

	exit := func(code int) {
		if code == 0 && t.history != nil {
			t.history.append(string(t.input))
		}
		os.Exit(code)
	}

	go func() {
		for {
			t.reqBox.Wait(func(events *util.Events) {
				defer events.Clear()
				t.mutex.Lock()
				for req := range *events {
					switch req {
					case reqPrompt:
						t.printPrompt()
						if t.inlineInfo {
							t.printInfo()
						}
					case reqInfo:
						t.printInfo()
					case reqList:
						t.printList()
					case reqRefresh:
						t.suppress = false
					case reqRedraw:
						C.Clear()
						C.Endwin()
						C.Refresh()
						t.printAll()
					case reqClose:
						C.Close()
						t.output()
						exit(0)
					case reqQuit:
						C.Close()
						exit(1)
					}
				}
				t.placeCursor()
				t.mutex.Unlock()
			})
			t.refresh()
		}
	}()

	looping := true
	for looping {
		event := C.GetChar()

		t.mutex.Lock()
		previousInput := t.input
		events := []util.EventType{reqPrompt}
		req := func(evts ...util.EventType) {
			for _, event := range evts {
				events = append(events, event)
				if event == reqClose || event == reqQuit {
					looping = false
				}
			}
		}
		selectItem := func(item *Item) bool {
			if _, found := t.selected[item.index]; !found {
				t.selected[item.index] = selectedItem{time.Now(), item.StringPtr()}
				return true
			}
			return false
		}
		toggleY := func(y int) {
			item := t.merger.Get(y)
			if !selectItem(item) {
				delete(t.selected, item.index)
			}
		}
		toggle := func() {
			if t.cy < t.merger.Length() {
				toggleY(t.cy)
				req(reqInfo)
			}
		}
		for key, ret := range t.expect {
			if keyMatch(key, event) {
				t.pressed = ret
				req(reqClose)
				break
			}
		}

		action := t.keymap[event.Type]
		mapkey := event.Type
		if event.Type == C.Rune {
			mapkey = int(event.Char) + int(C.AltZ)
			if act, prs := t.keymap[mapkey]; prs {
				action = act
			}
		}
		switch action {
		case actIgnore:
		case actExecute:
			if t.cy >= 0 && t.cy < t.merger.Length() {
				item := t.merger.Get(t.cy)
				executeCommand(t.execmap[mapkey], item.AsString())
			}
		case actInvalid:
			t.mutex.Unlock()
			continue
		case actToggleSort:
			t.sort = !t.sort
			t.eventBox.Set(EvtSearchNew, t.sort)
			t.mutex.Unlock()
			continue
		case actBeginningOfLine:
			t.cx = 0
		case actBackwardChar:
			if t.cx > 0 {
				t.cx--
			}
		case actAbort:
			req(reqQuit)
		case actDeleteChar:
			if !t.delChar() && t.cx == 0 {
				req(reqQuit)
			}
		case actEndOfLine:
			t.cx = len(t.input)
		case actForwardChar:
			if t.cx < len(t.input) {
				t.cx++
			}
		case actBackwardDeleteChar:
			if t.cx > 0 {
				t.input = append(t.input[:t.cx-1], t.input[t.cx:]...)
				t.cx--
			}
		case actSelectAll:
			if t.multi {
				for i := 0; i < t.merger.Length(); i++ {
					item := t.merger.Get(i)
					selectItem(item)
				}
				req(reqList, reqInfo)
			}
		case actDeselectAll:
			if t.multi {
				for i := 0; i < t.merger.Length(); i++ {
					item := t.merger.Get(i)
					delete(t.selected, item.index)
				}
				req(reqList, reqInfo)
			}
		case actToggle:
			if t.multi && t.merger.Length() > 0 {
				toggle()
				req(reqList)
			}
		case actToggleAll:
			if t.multi {
				for i := 0; i < t.merger.Length(); i++ {
					toggleY(i)
				}
				req(reqList, reqInfo)
			}
		case actToggleDown:
			if t.multi && t.merger.Length() > 0 {
				toggle()
				t.vmove(-1)
				req(reqList)
			}
		case actToggleUp:
			if t.multi && t.merger.Length() > 0 {
				toggle()
				t.vmove(1)
				req(reqList)
			}
		case actDown:
			t.vmove(-1)
			req(reqList)
		case actUp:
			t.vmove(1)
			req(reqList)
		case actAccept:
			req(reqClose)
		case actClearScreen:
			req(reqRedraw)
		case actUnixLineDiscard:
			if t.cx > 0 {
				t.yanked = copySlice(t.input[:t.cx])
				t.input = t.input[t.cx:]
				t.cx = 0
			}
		case actUnixWordRubout:
			if t.cx > 0 {
				t.rubout("\\s\\S")
			}
		case actBackwardKillWord:
			if t.cx > 0 {
				t.rubout("[^[:alnum:]][[:alnum:]]")
			}
		case actYank:
			suffix := copySlice(t.input[t.cx:])
			t.input = append(append(t.input[:t.cx], t.yanked...), suffix...)
			t.cx += len(t.yanked)
		case actPageUp:
			t.vmove(t.maxItems() - 1)
			req(reqList)
		case actPageDown:
			t.vmove(-(t.maxItems() - 1))
			req(reqList)
		case actBackwardWord:
			t.cx = findLastMatch("[^[:alnum:]][[:alnum:]]", string(t.input[:t.cx])) + 1
		case actForwardWord:
			t.cx += findFirstMatch("[[:alnum:]][^[:alnum:]]|(.$)", string(t.input[t.cx:])) + 1
		case actKillWord:
			ncx := t.cx +
				findFirstMatch("[[:alnum:]][^[:alnum:]]|(.$)", string(t.input[t.cx:])) + 1
			if ncx > t.cx {
				t.yanked = copySlice(t.input[t.cx:ncx])
				t.input = append(t.input[:t.cx], t.input[ncx:]...)
			}
		case actKillLine:
			if t.cx < len(t.input) {
				t.yanked = copySlice(t.input[t.cx:])
				t.input = t.input[:t.cx]
			}
		case actRune:
			prefix := copySlice(t.input[:t.cx])
			t.input = append(append(prefix, event.Char), t.input[t.cx:]...)
			t.cx++
		case actPreviousHistory:
			if t.history != nil {
				t.history.override(string(t.input))
				t.input = []rune(t.history.previous())
				t.cx = len(t.input)
			}
		case actNextHistory:
			if t.history != nil {
				t.history.override(string(t.input))
				t.input = []rune(t.history.next())
				t.cx = len(t.input)
			}
		case actMouse:
			me := event.MouseEvent
			mx, my := util.Constrain(me.X-len(t.prompt), 0, len(t.input)), me.Y
			if !t.reverse {
				my = C.MaxY() - my - 1
			}
			min := 2
			if t.inlineInfo {
				min = 1
			}
			if me.S != 0 {
				// Scroll
				if t.merger.Length() > 0 {
					if t.multi && me.Mod {
						toggle()
					}
					t.vmove(me.S)
					req(reqList)
				}
			} else if me.Double {
				// Double-click
				if my >= min {
					if t.vset(t.offset+my-min) && t.cy < t.merger.Length() {
						req(reqClose)
					}
				}
			} else if me.Down {
				if my == 0 && mx >= 0 {
					// Prompt
					t.cx = mx
				} else if my >= min {
					// List
					if t.vset(t.offset+my-min) && t.multi && me.Mod {
						toggle()
					}
					req(reqList)
				}
			}
		}
		changed := string(previousInput) != string(t.input)
		t.mutex.Unlock() // Must be unlocked before touching reqBox

		if changed {
			t.eventBox.Set(EvtSearchNew, t.sort)
		}
		for _, event := range events {
			t.reqBox.Set(event, nil)
		}
	}
}

func (t *Terminal) constrain() {
	count := t.merger.Length()
	height := t.maxItems()
	diffpos := t.cy - t.offset

	t.cy = util.Constrain(t.cy, 0, count-1)

	if t.cy > t.offset+(height-1) {
		// Ceil
		t.offset = t.cy - (height - 1)
	} else if t.offset > t.cy {
		// Floor
		t.offset = t.cy
	}

	// Adjustment
	if count-t.offset < height {
		t.offset = util.Max(0, count-height)
		t.cy = util.Constrain(t.offset+diffpos, 0, count-1)
	}
}

func (t *Terminal) vmove(o int) {
	if t.reverse {
		o *= -1
	}
	dest := t.cy + o
	if t.cycle {
		max := t.merger.Length() - 1
		if dest > max {
			if t.cy == max {
				dest = 0
			}
		} else if dest < 0 {
			if t.cy == 0 {
				dest = max
			}
		}
	}
	t.vset(dest)
}

func (t *Terminal) vset(o int) bool {
	t.cy = util.Constrain(o, 0, t.merger.Length()-1)
	return t.cy == o
}

func (t *Terminal) maxItems() int {
	if t.inlineInfo {
		return C.MaxY() - 1
	}
	return C.MaxY() - 2
}