peco.peco/layout.go

package peco

import (
	"errors"
	"fmt"
	"strings"
	"time"
	"unicode/utf8"

	"github.com/lestrrat-go/pdebug"
	"github.com/mattn/go-runewidth"
	"github.com/peco/peco/hub"
	"github.com/peco/peco/internal/ansi"
	linepkg "github.com/peco/peco/line"
)

// extraOffset is a platform-specific constant that adds extra vertical
// space to layout anchors. On Windows, terminals need an additional line
// reserved at the bottom. Set per-platform via layout_windows.go and
// layout_notwindows.go.

// ansiLiner is an optional interface for lines that carry ANSI color attributes.
type ansiLiner interface {
	ANSIAttrs() []ansi.AttrSpan
}

// LayoutFactory is a function that creates a BasicLayout for the given Peco state.
type LayoutFactory func(*Peco) (*BasicLayout, error)

var layoutRegistry = map[LayoutType]LayoutFactory{}

// RegisterLayout registers a layout factory under the given name.
func RegisterLayout(name LayoutType, factory LayoutFactory) {
	layoutRegistry[name] = factory
}

// NewLayout creates a layout by looking up the registry. Falls back to top-down.
func NewLayout(layoutType LayoutType, state *Peco) (*BasicLayout, error) {
	if factory, ok := layoutRegistry[layoutType]; ok {
		return factory(state)
	}
	return layoutRegistry[LayoutTypeTopDown](state)
}

// IsValidLayoutType checks if a string is a supported layout type
func IsValidLayoutType(v LayoutType) bool {
	_, ok := layoutRegistry[v]
	return ok
}

// IsValidVerticalAnchor checks if the specified anchor is supported
func IsValidVerticalAnchor(anchor VerticalAnchor) bool {
	return anchor == AnchorTop || anchor == AnchorBottom
}

// mergeAttribute merges two Attribute values (typically backgrounds).
// If either has a default color (0), the non-default color wins via OR.
// Otherwise, color bits are merged using OR on 0-based indices.
// Attribute flags (bold, underline, reverse, true color) are always OR'd.
func mergeAttribute(a, b Attribute) Attribute {
	const flagMask = AttrTrueColor | AttrBold | AttrUnderline | AttrReverse
	aColor := a &^ flagMask
	bColor := b &^ flagMask
	flags := (a | b) & flagMask

	if aColor == 0 || bColor == 0 {
		return (aColor | bColor) | flags
	}
	return (((aColor - 1) | (bColor - 1)) + 1) | flags
}

// NewAnchorSettings creates a new AnchorSetting struct.
func NewAnchorSettings(screen Screen, anchor VerticalAnchor, offset int) (*AnchorSettings, error) {
	if !IsValidVerticalAnchor(anchor) {
		return nil, fmt.Errorf("invalid vertical anchor: %d", anchor)
	}

	return &AnchorSettings{
		anchor:       anchor,
		anchorOffset: offset,
		screen:       screen,
	}, nil
}

// AnchorPosition returns the starting y-offset, based on the
// anchor type and offset
func (as AnchorSettings) AnchorPosition() int {
	switch as.anchor {
	case AnchorTop:
		return as.anchorOffset
	case AnchorBottom:
		_, h := as.screen.Size()
		return h - as.anchorOffset - 1 // -1 is required because y is 0 base, but h is 1 base
	default:
		return 0
	}
}

// NewUserPrompt creates a new UserPrompt struct
func NewUserPrompt(screen Screen, anchor VerticalAnchor, anchorOffset int, prompt string, styles *StyleSet) (*UserPrompt, error) {
	if len(prompt) <= 0 { // default
		prompt = DefaultPrompt
	}
	promptLen := runewidth.StringWidth(prompt)

	as, err := NewAnchorSettings(screen, anchor, anchorOffset)
	if err != nil {
		return nil, fmt.Errorf("failed to create user prompt: %w", err)
	}

	return &UserPrompt{
		AnchorSettings: as,
		prompt:         prompt,
		promptLen:      promptLen,
		styles:         styles,
	}, nil
}

// Draw draws the query prompt
func (u UserPrompt) Draw(state *Peco) {
	if pdebug.Enabled {
		g := pdebug.Marker("UserPrompt.Draw")
		defer g.End()
	}

	location := u.AnchorPosition()

	// print "QUERY>"
	u.screen.Print(PrintArgs{
		Y:   location,
		Fg:  u.styles.Prompt.fg,
		Bg:  u.styles.Prompt.bg,
		Msg: u.prompt,
	})

	c := state.Caret()
	if c.Pos() <= 0 { // XXX Do we really need this?
		c.SetPos(0) // sanity
	}

	q := state.Query()
	qs := q.String()
	ql := q.Len()
	if c.Pos() > ql { // XXX Do we really need this?
		c.SetPos(ql)
	}

	fg := u.styles.Query.fg
	bg := u.styles.Query.bg

	// Used to notify the screen where our cursor is
	var posX int

	switch ql {
	case 0:
		u.screen.Print(PrintArgs{
			X:    u.promptLen,
			Y:    location,
			Fg:   fg,
			Bg:   bg,
			Fill: true,
		})
		posX = u.promptLen + 1
		u.screen.Print(PrintArgs{
			X:    u.promptLen + 1,
			Y:    location,
			Bg:   bg | AttrReverse,
			Fg:   fg | AttrReverse,
			Msg:  " ",
			Fill: false,
		})
	case c.Pos():
		// the entire string + the caret after the string
		u.screen.Print(PrintArgs{
			X:    u.promptLen,
			Y:    location,
			Fg:   fg,
			Bg:   bg,
			Fill: true,
		})
		u.screen.Print(PrintArgs{
			X:    u.promptLen + 1,
			Y:    location,
			Fg:   fg,
			Bg:   bg,
			Msg:  qs,
			Fill: false,
		})
		posX = u.promptLen + 1 + runewidth.StringWidth(qs)
		u.screen.Print(PrintArgs{
			X:    posX,
			Y:    location,
			Fg:   fg | AttrReverse,
			Bg:   bg | AttrReverse,
			Msg:  " ",
			Fill: false,
		})
	default:
		posX = c.Pos() + u.promptLen + 1
		// the caret is in the middle of the string
		prev := int(0)
		for i, r := range q.RuneSlice() {
			fg := u.styles.Query.fg
			bg := u.styles.Query.bg
			if i == c.Pos() {
				fg |= AttrReverse
				bg |= AttrReverse
			}
			u.screen.SetCell(u.promptLen+1+prev, location, r, fg, bg)
			prev += runewidth.RuneWidth(r)
		}
		fg := u.styles.Query.fg
		bg := u.styles.Query.bg
		u.screen.Print(PrintArgs{
			X:    u.promptLen + prev + 1,
			Y:    location,
			Fg:   fg,
			Bg:   bg,
			Fill: true,
		})
	}

	u.screen.SetCursor(posX, location)

	width, _ := u.screen.Size()

	loc := state.Location()
	pmsg := fmt.Sprintf("%s [%d (%d/%d)]", state.Filters().Current().String(), loc.Total(), loc.Page(), loc.MaxPage())
	u.screen.Print(PrintArgs{
		X:   width - runewidth.StringWidth(pmsg),
		Y:   location,
		Fg:  u.styles.Basic.fg,
		Bg:  u.styles.Basic.bg,
		Msg: pmsg,
	})

	u.screen.Flush()
}

// newScreenStatusBar creates a new screenStatusBar struct
func newScreenStatusBar(screen Screen, anchor VerticalAnchor, anchorOffset int, styles *StyleSet) (*screenStatusBar, error) {
	as, err := NewAnchorSettings(screen, anchor, anchorOffset)
	if err != nil {
		return nil, fmt.Errorf("failed to create status bar: %w", err)
	}

	return &screenStatusBar{
		AnchorSettings: as,
		clearTimer:     nil,
		styles:         styles,
	}, nil
}

func (s *screenStatusBar) stopTimer() {
	s.timerMutex.Lock()
	defer s.timerMutex.Unlock()
	if t := s.clearTimer; t != nil {
		t.Stop()
		s.clearTimer = nil
	}
}

func (s *screenStatusBar) setClearTimer(t *time.Timer) {
	s.timerMutex.Lock()
	defer s.timerMutex.Unlock()
	s.clearTimer = t
}

// PrintStatus prints a new status message. This also resets the
// timer created by ClearStatus()
func (s *screenStatusBar) PrintStatus(msg string, clearDelay time.Duration) {
	if pdebug.Enabled {
		g := pdebug.Marker("screenStatusBar.PrintStatus")
		defer g.End()
	}

	s.stopTimer()

	location := s.AnchorPosition()

	w, _ := s.screen.Size()
	width := runewidth.StringWidth(msg)
	for width > w {
		_, rw := utf8.DecodeRuneInString(msg)
		width = width - rw
		msg = msg[rw:]
	}

	var pad []byte
	if w > width {
		pad = make([]byte, w-width)
		for i := range w - width {
			pad[i] = ' '
		}
	}

	fgAttr := s.styles.Basic.fg
	bgAttr := s.styles.Basic.bg

	if w > width {
		s.screen.Print(PrintArgs{
			Y:   location,
			Fg:  fgAttr,
			Bg:  bgAttr,
			Msg: string(pad),
		})
	}

	if width > 0 {
		s.screen.Print(PrintArgs{
			X:   w - width,
			Y:   location,
			Fg:  fgAttr | AttrBold | AttrReverse,
			Bg:  bgAttr | AttrReverse,
			Msg: msg,
		})
	}
	s.screen.Flush()

	// if everything is successful AND the clearDelay timer is specified,
	// then set a timer to clear the status
	if clearDelay != 0 {
		s.setClearTimer(time.AfterFunc(clearDelay, func() {
			s.PrintStatus("", 0)
		}))
	}
}

// PrintStatus on nullStatusBar is a no-op
func (nullStatusBar) PrintStatus(_ string, _ time.Duration) {}

// PrintStatus on BasicLayout delegates to the StatusBar
func (l *BasicLayout) PrintStatus(msg string, delay time.Duration) {
	l.statusBar.PrintStatus(msg, delay)
}

// NewListArea creates a new ListArea struct
func NewListArea(screen Screen, anchor VerticalAnchor, anchorOffset int, sortTopDown bool, styles *StyleSet) (*ListArea, error) {
	as, err := NewAnchorSettings(screen, anchor, anchorOffset)
	if err != nil {
		return nil, fmt.Errorf("failed to create list area: %w", err)
	}

	return &ListArea{
		AnchorSettings: as,
		displayCache:   []linepkg.Line{},
		dirty:          false,
		sortTopDown:    sortTopDown,
		styles:         styles,
	}, nil
}

func (l *ListArea) purgeDisplayCache() {
	l.displayCache = []linepkg.Line{}
}

func (l *ListArea) IsDirty() bool {
	return l.dirty
}

func (l *ListArea) SetDirty(dirty bool) {
	l.dirty = dirty
}

func selectionContains(state *Peco, n int) bool {
	if l, err := state.CurrentLineBuffer().LineAt(n); err == nil {
		return state.Selection().Has(l)
	}
	return false
}

// adjustPageForRunningQuery adjusts the page number during a running query
// so that the screen is never empty when the buffer shrinks below the current page.
func adjustPageForRunningQuery(loc *Location, linebuf Buffer, parent Layout, state *Peco) {
	bufsiz := linebuf.Size()
	page := loc.Page()

	for page > 1 {
		if (loc.PerPage()*(page-1) < bufsiz) &&
			(loc.PerPage()*page) >= bufsiz {
			break
		}
		page--
	}
	if loc.Page() != page {
		loc.SetPage(page)
		parent.DrawPrompt(state)
	}
}

// renderMatchedLine renders a line with match highlighting, interleaving
// matched and non-matched segments with their respective styles.
func (l *ListArea) renderMatchedLine(ml *linepkg.Matched, line string, lineANSIAttrs []ansi.AttrSpan, x, y, xOffset int, fgAttr, bgAttr Attribute) {
	matches := ml.Indices()
	prev := x
	index := 0
	runeOffset := 0

	for _, m := range matches {
		if m[0] > index {
			c := line[index:m[0]]
			runeLen := utf8.RuneCountInString(c)
			var segAttrs []ansi.AttrSpan
			if lineANSIAttrs != nil {
				segAttrs = ansi.ExtractSegment(lineANSIAttrs, runeOffset, runeOffset+runeLen)
			}
			n := l.screen.Print(PrintArgs{
				X:         prev,
				Y:         y,
				XOffset:   xOffset,
				Fg:        fgAttr,
				Bg:        bgAttr,
				Msg:       c,
				ANSIAttrs: segAttrs,
			})
			prev += n
			index += len(c)
			runeOffset += runeLen
		}
		c := line[m[0]:m[1]]
		runeLen := utf8.RuneCountInString(c)

		n := l.screen.Print(PrintArgs{
			X:       prev,
			Y:       y,
			XOffset: xOffset,
			Fg:      l.styles.Matched.fg,
			Bg:      mergeAttribute(bgAttr, l.styles.Matched.bg),
			Msg:     c,
		})
		prev += n
		index += len(c)
		runeOffset += runeLen
	}

	if index < len(line) {
		c := line[index:]
		runeLen := utf8.RuneCountInString(c)
		var segAttrs []ansi.AttrSpan
		if lineANSIAttrs != nil {
			segAttrs = ansi.ExtractSegment(lineANSIAttrs, runeOffset, runeOffset+runeLen)
		}
		l.screen.Print(PrintArgs{
			X:         prev,
			Y:         y,
			XOffset:   xOffset,
			Fg:        fgAttr,
			Bg:        bgAttr,
			Msg:       c,
			Fill:      true,
			ANSIAttrs: segAttrs,
		})
	} else {
		l.screen.Print(PrintArgs{
			X:       prev,
			Y:       y,
			XOffset: xOffset,
			Fg:      fgAttr,
			Bg:      bgAttr,
			Msg:     "",
			Fill:    true,
		})
	}
}

// Draw displays the ListArea on the screen
func (l *ListArea) Draw(state *Peco, parent Layout, perPage int, options *hub.DrawOptions) {
	if pdebug.Enabled {
		g := pdebug.Marker("ListArea.Draw pp = %d, options = %#v", perPage, options)
		defer g.End()
	}

	if perPage < 1 {
		return
	}

	loc := state.Location()
	linebuf := state.CurrentLineBuffer()

	if options != nil && options.RunningQuery {
		adjustPageForRunningQuery(loc, linebuf, parent, state)
	}

	pf := loc.PageCrop()
	if pdebug.Enabled {
		pdebug.Printf("Cropping linebuf which contains %d lines at page %d (%d entries per page)", linebuf.Size(), pf.currentPage, pf.perPage)
	}
	buf := pf.Crop(linebuf)
	bufsiz := buf.Size()

	// This protects us from losing the selected line in case our selected
	// line is greater than the buffer
	if lbufsiz := linebuf.Size(); lbufsiz > 0 && loc.LineNumber() >= lbufsiz {
		loc.SetLineNumber(lbufsiz - 1)
	}

	// The max column size is calculated by buf. we check against where the
	// loc variable thinks we should be scrolling to, and make sure that this
	// falls in range with what we got
	width, _ := state.Screen().Size()
	if maxCol := max(buf.MaxColumn()-width, 0); loc.Column() > maxCol {
		loc.SetColumn(maxCol)
	}

	// previously drawn lines are cached. first, truncate the cache
	// to current size of the drawable area
	if ldc := len(l.displayCache); ldc != perPage {
		newCache := make([]linepkg.Line, perPage)
		copy(newCache, l.displayCache)
		l.displayCache = newCache
	} else if perPage > bufsiz {
		l.displayCache = l.displayCache[:bufsiz]
	}

	var y int
	start := l.AnchorPosition()

	// If our buffer is smaller than perPage, we may need to clear some lines
	if pdebug.Enabled {
		pdebug.Printf("ListArea.Draw: buffer size is %d, our view area is %d", bufsiz, perPage)
	}

	for n := bufsiz; n < perPage; n++ {
		if l.sortTopDown {
			y = n + start
		} else {
			y = start - n
		}
		l.screen.Print(PrintArgs{
			Y:    y,
			Fg:   l.styles.Basic.fg,
			Bg:   l.styles.Basic.bg,
			Fill: true,
		})
	}

	var cached, written int
	var fgAttr, bgAttr Attribute
	selectionPrefix := state.SelectionPrefix()
	var prefix string

	var prefixCurrentSelection, prefixSavedSelection, prefixDefault string
	if plen := len(selectionPrefix); plen > 0 {
		prefixCurrentSelection = selectionPrefix + " "
		prefixSavedSelection = "*" + strings.Repeat(" ", plen)
		prefixDefault = strings.Repeat(" ", plen+1)
	}

	for n := range perPage {
		if len(selectionPrefix) > 0 {
			switch {
			case n+loc.Offset() == loc.LineNumber():
				prefix = prefixCurrentSelection
			case selectionContains(state, n+loc.Offset()):
				prefix = prefixSavedSelection
			default:
				prefix = prefixDefault
			}
		} else {
			switch {
			case n+loc.Offset() == loc.LineNumber():
				fgAttr = l.styles.Selected.fg
				bgAttr = l.styles.Selected.bg
			case selectionContains(state, n+loc.Offset()):
				fgAttr = l.styles.SavedSelection.fg
				bgAttr = l.styles.SavedSelection.bg
			default:
				fgAttr = l.styles.Basic.fg
				bgAttr = l.styles.Basic.bg
			}
		}

		if n >= bufsiz {
			break
		}

		if l.sortTopDown {
			y = n + start
		} else {
			y = start - n
		}

		target, err := buf.LineAt(n)
		if err != nil {
			break
		}

		if (options != nil && options.DisableCache) || l.IsDirty() || target.IsDirty() {
			target.SetDirty(false)
		} else if l.displayCache[n] == target {
			cached++
			continue
		}

		written++
		l.displayCache[n] = target

		// Apply Context style for non-matched surrounding lines
		if _, isCtx := target.(*ContextLine); isCtx {
			if fgAttr == l.styles.Basic.fg && bgAttr == l.styles.Basic.bg {
				fgAttr = l.styles.Context.fg
				bgAttr = l.styles.Context.bg
			}
		}

		x := -1 * loc.Column()
		xOffset := loc.Column()
		line := target.DisplayString()

		// Extract ANSI attrs if available. Only use them for
		// non-selected (basic) lines so selection/savedSelection
		// styling takes precedence.
		var lineANSIAttrs []ansi.AttrSpan
		isBasicStyle := (fgAttr == l.styles.Basic.fg && bgAttr == l.styles.Basic.bg)
		if isBasicStyle {
			if al, ok := target.(ansiLiner); ok {
				lineANSIAttrs = al.ANSIAttrs()
			}
		}

		if plen := len(prefix); plen > 0 {
			l.screen.Print(PrintArgs{
				X:       x,
				Y:       y,
				XOffset: xOffset,
				Fg:      fgAttr,
				Bg:      bgAttr,
				Msg:     prefix,
			})
			x += plen
		}
		if state.SingleKeyJump().Mode() || state.SingleKeyJump().ShowPrefix() {
			prefixes := state.SingleKeyJump().Prefixes()
			if n < len(prefixes) {
				l.screen.Print(PrintArgs{
					X:       x,
					Y:       y,
					XOffset: xOffset,
					Fg:      fgAttr | AttrBold | AttrReverse,
					Bg:      bgAttr,
					Msg:     string(prefixes[n]),
				})
				l.screen.Print(PrintArgs{
					X:       x + 1,
					Y:       y,
					XOffset: xOffset,
					Fg:      fgAttr,
					Bg:      bgAttr,
					Msg:     " ",
				})
			} else {
				l.screen.Print(PrintArgs{
					X:       x,
					Y:       y,
					XOffset: xOffset,
					Fg:      fgAttr,
					Bg:      bgAttr,
					Msg:     "  ",
				})
			}
			x += 2
		}

		ml, ok := target.(*linepkg.Matched)
		if !ok {
			l.screen.Print(PrintArgs{
				X:         x,
				Y:         y,
				XOffset:   xOffset,
				Fg:        fgAttr,
				Bg:        bgAttr,
				Msg:       line,
				Fill:      true,
				ANSIAttrs: lineANSIAttrs,
			})
			continue
		}

		l.renderMatchedLine(ml, line, lineANSIAttrs, x, y, xOffset, fgAttr, bgAttr)
	}
	l.SetDirty(false)
	if pdebug.Enabled {
		pdebug.Printf("ListArea.Draw: Written total of %d lines (%d cached)", written+cached, cached)
	}
}

// newStatusBar returns a StatusBar appropriate for the configuration.
// If SuppressStatusMsg is true, a nullStatusBar (no-op) is returned.
func newStatusBar(state *Peco) (StatusBar, error) {
	if state.SuppressStatusMsg() {
		return nullStatusBar{}, nil
	}
	return newScreenStatusBar(state.Screen(), AnchorBottom, 0+extraOffset, state.Styles())
}

// NewDefaultLayout creates a new Layout in the default format (top-down)
func NewDefaultLayout(state *Peco) (*BasicLayout, error) {
	sb, err := newStatusBar(state)
	if err != nil {
		return nil, err
	}
	prompt, err := NewUserPrompt(state.Screen(), AnchorTop, 0, state.Prompt(), state.Styles())
	if err != nil {
		return nil, err
	}
	list, err := NewListArea(state.Screen(), AnchorTop, 1, true, state.Styles())
	if err != nil {
		return nil, err
	}
	return &BasicLayout{
		statusBar: sb,
		screen:    state.Screen(),
		prompt:    prompt,
		list:      list,
	}, nil
}

// NewBottomUpLayout creates a new Layout in bottom-up format
func NewBottomUpLayout(state *Peco) (*BasicLayout, error) {
	sb, err := newStatusBar(state)
	if err != nil {
		return nil, err
	}
	prompt, err := NewUserPrompt(state.Screen(), AnchorBottom, 1+extraOffset, state.Prompt(), state.Styles())
	if err != nil {
		return nil, err
	}
	list, err := NewListArea(state.Screen(), AnchorBottom, 2+extraOffset, false, state.Styles())
	if err != nil {
		return nil, err
	}
	return &BasicLayout{
		statusBar: sb,
		screen:    state.Screen(),
		prompt:    prompt,
		list:      list,
	}, nil
}

// NewTopDownQueryBottomLayout creates a new Layout with list top-to-bottom
// and the query prompt at the bottom.
func NewTopDownQueryBottomLayout(state *Peco) (*BasicLayout, error) {
	sb, err := newStatusBar(state)
	if err != nil {
		return nil, err
	}
	prompt, err := NewUserPrompt(state.Screen(), AnchorBottom, 1+extraOffset, state.Prompt(), state.Styles())
	if err != nil {
		return nil, err
	}
	list, err := NewListArea(state.Screen(), AnchorTop, 0, true, state.Styles())
	if err != nil {
		return nil, err
	}
	return &BasicLayout{
		statusBar: sb,
		screen:    state.Screen(),
		prompt:    prompt,
		list:      list,
	}, nil
}

// SortTopDown returns whether this layout sorts lines from top to bottom.
func (l *BasicLayout) SortTopDown() bool {
	return l.list.sortTopDown
}

func init() {
	RegisterLayout(LayoutTypeTopDown, NewDefaultLayout)
	RegisterLayout(LayoutTypeBottomUp, NewBottomUpLayout)
	RegisterLayout(LayoutTypeTopDownQueryBottom, NewTopDownQueryBottomLayout)
}

func (l *BasicLayout) PurgeDisplayCache() {
	l.list.purgeDisplayCache()
}

// CalculatePage calculates which page we're displaying
func (l *BasicLayout) CalculatePage(state *Peco, perPage int) error {
	if pdebug.Enabled {
		g := pdebug.Marker("BasicLayout.Calculate %d", perPage)
		defer g.End()
	}
	buf := state.CurrentLineBuffer()
	loc := state.Location()
	loc.SetPage((loc.LineNumber() / perPage) + 1)
	loc.SetOffset((loc.Page() - 1) * perPage)
	loc.SetPerPage(perPage)
	loc.SetTotal(buf.Size())

	if loc.Total() == 0 {
		loc.SetMaxPage(1)
	} else {
		loc.SetMaxPage((loc.Total() + perPage - 1) / perPage)
	}

	if loc.MaxPage() < loc.Page() {
		if buf.Size() == 0 {
			// wait for targets
			return errors.New("no targets or query. nothing to do")
		}
		loc.SetLineNumber(loc.Offset())
	}

	return nil
}

// DrawPrompt draws the prompt to the terminal
func (l *BasicLayout) DrawPrompt(state *Peco) {
	l.prompt.Draw(state)
}

// DrawScreen draws the entire screen
func (l *BasicLayout) DrawScreen(state *Peco, options *hub.DrawOptions) {
	if pdebug.Enabled {
		g := pdebug.Marker("BasicLayout.DrawScreen")
		defer g.End()
	}

	perPage := l.linesPerPage()

	if err := l.CalculatePage(state, perPage); err != nil {
		return
	}

	l.DrawPrompt(state)
	l.list.Draw(state, l, perPage, options)

	if options != nil && options.ForceSync {
		type syncer interface{ Sync() }
		if s, ok := l.screen.(syncer); ok {
			s.Sync()
			return
		}
	}

	if err := l.screen.Flush(); err != nil {
		return
	}
}

func (l *BasicLayout) linesPerPage() int {
	_, height := l.screen.Size()

	// list area is always the display area - 2 lines for prompt and status
	reservedLines := 2 + extraOffset
	pp := height - reservedLines
	if pp < 1 {
		// This is an error condition, and while we probably should handle this
		// error more gracefully, the consumers of this method do not really
		// do anything with this error. I think it's just safe to "2", which just
		// means no space left to draw anything
		if pdebug.Enabled {
			pdebug.Printf(
				"linesPerPage is < 1 (height = %d, reservedLines = %d), forcing return value of 2",
				height,
				reservedLines,
			)
		}
		return 2
	}
	return pp
}

// MovePage scrolls the screen
func (l *BasicLayout) MovePage(state *Peco, p hub.PagingRequest) (moved bool) {
	switch p.Type() {
	case hub.ToScrollLeft, hub.ToScrollRight:
		moved = horizontalScroll(state, l, p)
	default:
		moved = verticalScroll(state, l, p)
	}
	return
}

// computeNewLineNumber calculates the new line number based on the paging
// request, layout direction, and buffer size. It handles wrapping around
// the ends of the buffer.
func computeNewLineNumber(loc *Location, p hub.PagingRequest, sortTopDown bool, lineno, lcur, lpp int) int {
	lineBefore := lineno
	if sortTopDown {
		switch p.Type() {
		case hub.ToLineAbove:
			lineno--
		case hub.ToLineBelow:
			lineno++
		case hub.ToScrollPageDown:
			lineno += lpp
			if loc.Page() == loc.MaxPage()-1 && lcur < lineno && (lcur-lineBefore) < lpp {
				lineno = lcur - 1
			}
		case hub.ToScrollPageUp:
			lineno -= lpp
		case hub.ToLineInPage:
			if jlr, ok := p.(hub.JumpToLineRequest); ok {
				lineno = loc.PerPage()*(loc.Page()-1) + jlr.Line()
			}
		case hub.ToScrollFirstItem:
			lineno = 0
		case hub.ToScrollLastItem:
			lineno = lcur - 1
		}
	} else {
		switch p.Type() {
		case hub.ToLineAbove:
			lineno++
		case hub.ToLineBelow:
			lineno--
		case hub.ToScrollPageDown:
			lineno -= lpp
		case hub.ToScrollPageUp:
			lineno += lpp
		case hub.ToLineInPage:
			if jlr, ok := p.(hub.JumpToLineRequest); ok {
				lineno = loc.PerPage()*(loc.Page()-1) - jlr.Line()
			}
		}
	}

	// Wrap around buffer boundaries
	if lineno < 0 {
		if lcur > 0 {
			lineno = lcur - 1
		} else {
			lineno = 0
		}
	} else if lcur > 0 && lineno >= lcur {
		lineno = 0
	}

	return lineno
}

// updateRangeSelection updates the selection state when moving in range mode.
// It adds lines between the range start and the current position, and removes
// lines that were previously selected but are no longer in the range.
func updateRangeSelection(state *Peco, buf Buffer, loc *Location, lineBefore, lcur int) {
	r := state.SelectionRangeStart()
	if !r.Valid() {
		return
	}

	sel := state.Selection()
	curLine := loc.LineNumber()

	if curLine < r.Value() {
		for lineno := curLine; lineno <= r.Value(); lineno++ {
			if line, err := buf.LineAt(lineno); err == nil {
				sel.Add(line)
			}
		}
		switch {
		case r.Value() <= lineBefore:
			for lineno := r.Value(); lineno <= lcur && lineno < lineBefore; lineno++ {
				if line, err := buf.LineAt(lineno); err == nil {
					sel.Remove(line)
				}
			}
		case lineBefore < curLine:
			for lineno := lineBefore; lineno < curLine; lineno++ {
				if line, err := buf.LineAt(lineno); err == nil {
					sel.Remove(line)
				}
			}
		}
	} else {
		for lineno := r.Value(); lineno <= lcur && lineno <= curLine; lineno++ {
			if line, err := buf.LineAt(lineno); err == nil {
				sel.Add(line)
			}
		}

		switch {
		case lineBefore <= r.Value():
			for lineno := lineBefore; lineno < r.Value(); lineno++ {
				if line, err := buf.LineAt(lineno); err == nil {
					sel.Remove(line)
				}
			}
		case curLine < lineBefore:
			for lineno := curLine; lineno <= lineBefore; lineno++ {
				if line, err := buf.LineAt(lineno); err == nil {
					sel.Remove(line)
				}
			}
		}
	}
}

// verticalScroll moves the cursor position vertically
func verticalScroll(state *Peco, l *BasicLayout, p hub.PagingRequest) bool {
	loc := state.Location()
	lineBefore := loc.LineNumber()

	if pdebug.Enabled {
		defer func() {
			pdebug.Printf("currentLine changed from %d -> %d", lineBefore, state.Location().LineNumber())
		}()
	}

	buf := state.CurrentLineBuffer()
	lcur := buf.Size()

	defer func() {
		for _, lno := range []int{lineBefore, loc.LineNumber()} {
			if oldLine, err := buf.LineAt(lno); err == nil {
				oldLine.SetDirty(true)
			}
		}
	}()

	lpp := l.linesPerPage()
	lineno := computeNewLineNumber(loc, p, l.list.sortTopDown, lineBefore, lcur, lpp)
	loc.SetLineNumber(lineno)

	if l.list.sortTopDown {
		updateRangeSelection(state, buf, loc, lineBefore, lcur)
	}

	return true
}

// horizontalScroll scrolls screen horizontal
func horizontalScroll(state *Peco, l *BasicLayout, p hub.PagingRequest) bool {
	width, _ := state.Screen().Size()
	loc := state.Location()
	if p.Type() == hub.ToScrollRight {
		loc.SetColumn(loc.Column() + width/2)
	} else if loc.Column() > 0 {
		loc.SetColumn(loc.Column() - width/2)
		if loc.Column() < 0 {
			loc.SetColumn(0)
		}
	} else {
		return false
	}

	l.list.SetDirty(true)

	return true
}