package app

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

	"github.com/hjbdev/patterm/internal/preset"
)

// paletteAction is what the palette returns when the user picks an item.
type paletteAction struct {
	// kind: "spawn-agent" | "spawn-process" | "spawn-process-form" |
	//       "spawn-process-submit" | "switch" | "kill" | "quit" | "cancel"
	kind string

	// For spawn-agent / spawn-process, the preset to launch.
	preset *preset.Preset

	// For "switch" and "kill", the target child id.
	childID string

	// For "spawn-process-submit": the freeform command line the user
	// typed and the relaunch-on-exit flag they ticked.
	command  string
	relaunch bool
}

type paletteItem struct {
	label  string
	hint   string
	action paletteAction
}

// paletteMode toggles the palette between its fuzzy-picker UI and the
// freeform "spawn process" form. The form lives inside the palette so
// it shares the same modal-input contract (every byte intercepted; no
// PTY forwarding) without needing a second overlay.
type paletteMode int

const (
	paletteModePicker paletteMode = iota
	paletteModeSpawnForm
)

// spawnProcessForm is the state for the "Spawn process…" two-field
// form: a command line plus a "relaunch on exit" toggle. Tab cycles
// focus; space toggles the checkbox when it owns focus; Enter submits.
type spawnProcessForm struct {
	cmd      []rune
	relaunch bool
	field    int // 0 = command, 1 = relaunch checkbox
}

// paletteState is the in-memory model for the overlay. SPEC §4: a
// single fuzzy-searchable list of commands scoped to the current focus.
type paletteState struct {
	query    []rune
	cursor   int
	children []*Child
	focused  string
	presets  preset.Set

	items []paletteItem

	mode paletteMode
	form *spawnProcessForm
}

// macroPrefixes maps the palette macro prefix (without trailing space)
// to the paletteAction.kind values that should be retained when that
// macro is active. Typing `sw <query>` filters to switch entries only,
// `k <query>` to kills, `sp <query>` to spawn entries (agents +
// processes).
var macroPrefixes = map[string][]string{
	"sw": {"switch"},
	"k":  {"kill"},
	"sp": {"spawn-agent", "spawn-process"},
}

// detectMacro returns the macro keyword and the remaining query, or
// ("", original) if no macro is active. A macro is active when the
// query starts with one of the known prefixes followed by a space.
func detectMacro(q string) (macro, rest string) {
	for k := range macroPrefixes {
		if len(q) > len(k) && q[:len(k)] == k && q[len(k)] == ' ' {
			return k, q[len(k)+1:]
		}
	}
	return "", q
}

func newPalette(children []*Child, focused string, presets preset.Set) *paletteState {
	p := &paletteState{children: children, focused: focused, presets: presets}
	p.rebuild()
	return p
}

func (p *paletteState) rebuild() {
	all := p.allItems()
	q := strings.ToLower(string(p.query))
	macro, rest := detectMacro(q)
	if macro != "" {
		kinds := macroPrefixes[macro]
		filtered := all[:0:0]
		for _, it := range all {
			for _, k := range kinds {
				if it.action.kind == k {
					filtered = append(filtered, it)
					break
				}
			}
		}
		all = filtered
		q = rest
	}
	if q == "" {
		p.items = all
	} else {
		p.items = p.items[:0]
		for _, it := range all {
			if fuzzyMatch(strings.ToLower(it.label+" "+it.hint), q) {
				p.items = append(p.items, it)
			}
		}
	}
	if p.cursor >= len(p.items) {
		p.cursor = len(p.items) - 1
	}
	if p.cursor < 0 {
		p.cursor = 0
	}
}

func (p *paletteState) allItems() []paletteItem {
	var out []paletteItem

	// Switch entries first — existing open agents/processes should
	// surface above options to spawn new ones. Hide non-running agents
	// (e.g. killed ones) so the list doesn't accumulate corpses. Command
	// processes are session-persistent, so they remain visible after
	// exit to keep restart_process in reach.
	for _, c := range p.children {
		if c.Kind == KindAgent && c.Status() != StatusRunning {
			continue
		}
		label := "Switch to " + c.DisplayName()
		hint := strings.Join(c.Argv, " ")
		if c.ID == p.focused {
			label = "• " + label + " (current)"
		}
		if c.Status() != StatusRunning {
			label = label + "  [" + string(c.Status()) + "]"
		}
		out = append(out, paletteItem{
			label:  label,
			hint:   hint,
			action: paletteAction{kind: "switch", childID: c.ID},
		})
	}

	// Preset commands — SPEC §4 calls these out as the primary way to
	// spawn anything. One entry per file under presets/.
	for _, pr := range p.presets.Agents {
		out = append(out, paletteItem{
			label:  "Spawn agent: " + pr.Name,
			hint:   strings.Join(pr.Argv, " "),
			action: paletteAction{kind: "spawn-agent", preset: pr},
		})
	}
	for _, pr := range p.presets.Processes {
		out = append(out, paletteItem{
			label:  "Run process: " + pr.Name,
			hint:   strings.Join(pr.Argv, " "),
			action: paletteAction{kind: "spawn-process", preset: pr},
		})
	}

	// Freeform "Spawn process…" entry. Opens a sub-form for typing an
	// arbitrary command line and ticking "relaunch on exit". The action
	// kind is intercepted by acceptOrEnterForm so accept switches the
	// palette into form mode instead of closing it. Placed after the
	// preset entries so quick-spawn flows keep the same ordering as
	// before this feature landed.
	out = append(out, paletteItem{
		label:  "Spawn process…",
		hint:   "freeform command · optional relaunch on exit",
		action: paletteAction{kind: "spawn-process-form"},
	})

	// Kill entries last among the action rows, before Quit. Mirror the
	// "(current)" marker from switch entries so the focused tab is
	// obvious when scanning the kill list.
	for _, c := range p.children {
		if c.Status() != StatusRunning {
			continue
		}
		label := "Kill " + c.DisplayName()
		if c.ID == p.focused {
			label = "• " + label + " (current)"
		}
		out = append(out, paletteItem{
			label:  label,
			hint:   "SIGTERM " + strings.Join(c.Argv, " "),
			action: paletteAction{kind: "kill", childID: c.ID},
		})
	}

	out = append(out, paletteItem{
		label:  "Quit",
		hint:   "exit patterm; SIGTERM every child",
		action: paletteAction{kind: "quit"},
	})
	return out
}

func fuzzyMatch(hay, needle string) bool {
	if needle == "" {
		return true
	}
	hi := 0
	for _, r := range needle {
		idx := strings.IndexRune(hay[hi:], r)
		if idx < 0 {
			return false
		}
		hi += idx + utf8.RuneLen(r)
	}
	return true
}

// kitty functional keycodes for arrows.
const (
	kittyKeyUp   = 57352
	kittyKeyDown = 57353
)

// peekArrowEvent classifies the CSI sequence at chunk[i:] as Up ('U'),
// Down ('D'), or none (0) and returns the byte length of that sequence.
// Used by the palette input loop to suppress duplicate adjacent
// arrow events some terminals emit for a single physical keypress
// (either two legacy `CSI B` in a row, or a legacy + kitty pair).
func peekArrowEvent(chunk []byte, i int) (nav byte, advance int) {
	if i >= len(chunk) || chunk[i] != 0x1b {
		return 0, 0
	}
	n := csiLen(chunk, i)
	if n == 0 {
		return 0, 0
	}
	final := chunk[i+n-1]
	switch final {
	case 'A':
		return 'U', n
	case 'B':
		return 'D', n
	case 'u':
		k, ok := decodeCSIu(string(chunk[i+2 : i+n-1]))
		if !ok || k.event != 1 {
			return 0, n
		}
		switch k.key {
		case kittyKeyUp:
			return 'U', n
		case kittyKeyDown:
			return 'D', n
		}
	}
	return 0, 0
}

// handleInput consumes one keystroke from chunk[i:] and updates palette
// state. advance is how many bytes the keystroke occupies (1 for legacy
// keys, longer for CSI sequences). Returning done=true tells the caller
// the palette is finished and action describes what to do next.
//
// Recognised input includes both legacy byte forms and the kitty
// keyboard CSI u encoding that codex/ratatui pushes onto the terminal.
// Unknown CSI sequences (including release events from kitty flag 2)
// are consumed silently so they don't fall through to the ESC branch
// and accidentally cancel the palette.
func (p *paletteState) handleInput(chunk []byte, i int) (action paletteAction, done bool, advance int) {
	if p.mode == paletteModeSpawnForm {
		return p.handleFormInput(chunk, i)
	}
	b := chunk[i]
	if b == 0x1b {
		if n := csiLen(chunk, i); n > 0 {
			return p.handleCSI(chunk[i+2:i+n-1], chunk[i+n-1], n)
		}
		// Bare ESC (no CSI follow-up): cancel.
		return paletteAction{kind: "cancel"}, true, 1
	}
	switch b {
	case '\r', '\n':
		return p.acceptOrEnterForm(1)
	case 0x7f, 0x08:
		p.backspace()
	case 0x15: // Ctrl-U
		p.clearQuery()
	case 0x0e: // Ctrl-N
		p.cursorDown()
	case 0x10: // Ctrl-P
		p.cursorUp()
	case 0x0b: // Ctrl-K inside palette is a no-op (would re-open); ignore.
	case 0x16: // Ctrl-V literal-paste — ignore in palette.
	default:
		if b >= 0x20 && b < 0x7f {
			p.query = append(p.query, rune(b))
			p.rebuild()
		}
	}
	return paletteAction{}, false, 1
}

// acceptOrEnterForm wraps accept(): if the chosen item opens the
// spawn-process form, transition into form mode instead of returning
// done=true. The advance count is what the caller already consumed for
// the Enter keystroke.
func (p *paletteState) acceptOrEnterForm(adv int) (paletteAction, bool, int) {
	a := p.accept()
	if a.kind == "spawn-process-form" {
		p.mode = paletteModeSpawnForm
		p.form = &spawnProcessForm{}
		return paletteAction{}, false, adv
	}
	return a, true, adv
}

func (p *paletteState) handleCSI(params []byte, final byte, n int) (paletteAction, bool, int) {
	switch final {
	case 'A':
		p.cursorUp()
		return paletteAction{}, false, n
	case 'B':
		p.cursorDown()
		return paletteAction{}, false, n
	case 'u':
		k, ok := decodeCSIu(string(params))
		if !ok || k.event != 1 {
			// Repeat / release events, or malformed: ignore.
			return paletteAction{}, false, n
		}
		switch k.key {
		case 13: // Enter
			return p.acceptOrEnterForm(n)
		case 27: // Escape
			return paletteAction{kind: "cancel"}, true, n
		case 127, 8: // Backspace
			p.backspace()
		case kittyKeyUp:
			p.cursorUp()
		case kittyKeyDown:
			p.cursorDown()
		default:
			// Ctrl-modified character keys.
			if k.mods == 5 {
				switch k.key {
				case 'u':
					p.clearQuery()
				case 'n':
					p.cursorDown()
				case 'p':
					p.cursorUp()
				}
				return paletteAction{}, false, n
			}
			// Unmodified printable ASCII typed via CSI u (flag 8): treat
			// as a query keystroke.
			if k.mods == 1 && k.key >= 0x20 && k.key < 0x7f {
				p.query = append(p.query, rune(k.key))
				p.rebuild()
			}
		}
		return paletteAction{}, false, n
	}
	// Anything else (~, function keys, etc.): consume silently.
	return paletteAction{}, false, n
}

// handleFormInput drives the spawn-process form. Tab cycles fields,
// space toggles the relaunch checkbox when it has focus, Enter submits,
// Esc cancels. The form supports both legacy and kitty key encodings to
// match handleInput; bare ESC cancels the entire palette (consistent
// with the picker).
func (p *paletteState) handleFormInput(chunk []byte, i int) (paletteAction, bool, int) {
	b := chunk[i]
	if b == 0x1b {
		if n := csiLen(chunk, i); n > 0 {
			return p.handleFormCSI(chunk[i+2:i+n-1], chunk[i+n-1], n)
		}
		return paletteAction{kind: "cancel"}, true, 1
	}
	switch b {
	case '\r', '\n':
		return p.submitForm(), true, 1
	case '\t':
		p.cycleFormField()
	case 0x7f, 0x08:
		p.formBackspace()
	case ' ':
		if p.form.field == 1 {
			p.form.relaunch = !p.form.relaunch
		} else if b >= 0x20 && b < 0x7f {
			p.form.cmd = append(p.form.cmd, rune(b))
		}
	default:
		if b >= 0x20 && b < 0x7f && p.form.field == 0 {
			p.form.cmd = append(p.form.cmd, rune(b))
		}
	}
	return paletteAction{}, false, 1
}

func (p *paletteState) handleFormCSI(params []byte, final byte, n int) (paletteAction, bool, int) {
	switch final {
	case 'A', 'B':
		// Arrow up/down cycles field.
		p.cycleFormField()
		return paletteAction{}, false, n
	case 'u':
		k, ok := decodeCSIu(string(params))
		if !ok || k.event != 1 {
			return paletteAction{}, false, n
		}
		switch k.key {
		case 13:
			return p.submitForm(), true, n
		case 27:
			return paletteAction{kind: "cancel"}, true, n
		case 9:
			p.cycleFormField()
		case 127, 8:
			p.formBackspace()
		case ' ':
			if p.form.field == 1 {
				p.form.relaunch = !p.form.relaunch
			}
		default:
			if k.mods == 1 && k.key >= 0x20 && k.key < 0x7f && p.form.field == 0 {
				p.form.cmd = append(p.form.cmd, rune(k.key))
			}
		}
	}
	return paletteAction{}, false, n
}

func (p *paletteState) cycleFormField() {
	p.form.field++
	if p.form.field > 1 {
		p.form.field = 0
	}
}

func (p *paletteState) formBackspace() {
	if p.form.field == 0 && len(p.form.cmd) > 0 {
		p.form.cmd = p.form.cmd[:len(p.form.cmd)-1]
	}
}

func (p *paletteState) submitForm() paletteAction {
	cmd := strings.TrimSpace(string(p.form.cmd))
	if cmd == "" {
		return paletteAction{kind: "cancel"}
	}
	return paletteAction{
		kind:     "spawn-process-submit",
		command:  cmd,
		relaunch: p.form.relaunch,
	}
}

func (p *paletteState) accept() paletteAction {
	if p.cursor >= 0 && p.cursor < len(p.items) {
		return p.items[p.cursor].action
	}
	return paletteAction{kind: "cancel"}
}

func (p *paletteState) backspace() {
	if len(p.query) > 0 {
		p.query = p.query[:len(p.query)-1]
		p.rebuild()
	}
}

func (p *paletteState) clearQuery() {
	p.query = p.query[:0]
	p.rebuild()
}

func (p *paletteState) cursorUp() {
	p.cursor--
	if p.cursor < 0 {
		p.cursor = 0
	}
}

func (p *paletteState) cursorDown() {
	p.cursor++
	if p.cursor >= len(p.items) {
		p.cursor = len(p.items) - 1
	}
}

// render draws the palette onto out. Layout is a rounded box with a
// title bar, query line, divider, item list, divider, and footer.
// The caller is responsible for the screen clear before the first
// render.
func (p *paletteState) render(out writeFlusher, cols, rows int) {
	if p.mode == paletteModeSpawnForm {
		p.renderForm(out, cols, rows)
		return
	}
	if cols < 32 {
		cols = 32
	}
	if rows < 10 {
		rows = 10
	}
	width := cols - 8
	if width > 72 {
		width = 72
	}
	if width < 40 {
		width = cols - 2
	}
	if width < 32 {
		width = 32
	}
	leftPad := (cols - width) / 2
	if leftPad < 1 {
		leftPad = 1
	}
	content := width - 4 // visible cells between the " " padding on each side

	var b strings.Builder
	b.WriteString("\x1b[?25l\x1b[H\x1b[2J\x1b[3J")

	row := 2
	titleText := "patterm"
	keyHint := "Ctrl-K"
	// ╭─ patterm ─...─ Ctrl-K ─╮ uses: 3 + len(title) + 1 + dashes + 1 + len(hint) + 3
	dashes := width - 3 - len(titleText) - 1 - 1 - len(keyHint) - 3
	if dashes < 2 {
		dashes = 2
	}
	moveTo(&b, row, leftPad)
	b.WriteString(styleBorder + "╭─ " + styleActive + titleText + styleReset + styleBorder + " " +
		strings.Repeat("─", dashes) + " " + styleHint + keyHint + styleReset + styleBorder + " ─╮" + styleReset)
	row++

	queryStr := string(p.query)
	queryRow := row
	qLen := utf8.RuneCountInString(queryStr)
	qPad := content - 2 - qLen
	if qPad < 0 {
		qPad = 0
	}
	moveTo(&b, row, leftPad)
	b.WriteString(styleBorder + "│" + styleReset + " " + styleAccent + "❯" + styleReset + " " + queryStr +
		strings.Repeat(" ", qPad) + " " + styleBorder + "│" + styleReset)
	row++

	moveTo(&b, row, leftPad)
	b.WriteString(styleBorder + "├" + strings.Repeat("─", width-2) + "┤" + styleReset)
	row++

	maxItems := rows - 6
	if maxItems > 12 {
		maxItems = 12
	}
	if maxItems < 1 {
		maxItems = 1
	}
	start := 0
	if p.cursor >= maxItems {
		start = p.cursor - maxItems + 1
	}
	end := start + maxItems
	if end > len(p.items) {
		end = len(p.items)
	}

	for i := 0; i < maxItems; i++ {
		moveTo(&b, row, leftPad)
		if start+i >= end {
			if len(p.items) == 0 && i == 0 {
				msg := styleDim + "no matches" + styleReset
				pad := content - 2 - 10
				if pad < 0 {
					pad = 0
				}
				b.WriteString(styleBorder + "│" + styleReset + "   " + msg +
					strings.Repeat(" ", pad) + " " + styleBorder + "│" + styleReset)
			} else {
				b.WriteString(styleBorder + "│" + styleReset + strings.Repeat(" ", width-2) +
					styleBorder + "│" + styleReset)
			}
			row++
			continue
		}

		it := p.items[start+i]
		isSel := (start + i) == p.cursor
		avail := content - 2 // 2 cells reserved for the selection indicator

		label := it.label
		hint := it.hint
		labelLen := utf8.RuneCountInString(label)
		hintLen := utf8.RuneCountInString(hint)

		if labelLen > avail {
			label = clipRunes(label, avail-1) + "…"
			labelLen = utf8.RuneCountInString(label)
			hint = ""
			hintLen = 0
		} else if hintLen > 0 {
			gap := avail - labelLen - hintLen
			if gap < 3 {
				budget := avail - labelLen - 3
				if budget > 1 {
					hint = clipRunes(hint, budget-1) + "…"
					hintLen = utf8.RuneCountInString(hint)
				} else {
					hint = ""
					hintLen = 0
				}
			}
		}
		gap := avail - labelLen - hintLen
		if gap < 0 {
			gap = 0
		}

		var indicator, labelStr, hintStr string
		if isSel {
			indicator = styleAccent + "▎" + styleReset + " "
			labelStr = styleBold + label + styleReset
		} else {
			indicator = "  "
			labelStr = label
		}
		if hint != "" {
			hintStr = styleHint + hint + styleReset
		}

		b.WriteString(styleBorder + "│" + styleReset + " " + indicator + labelStr +
			strings.Repeat(" ", gap) + hintStr + " " + styleBorder + "│" + styleReset)
		row++
	}

	moveTo(&b, row, leftPad)
	b.WriteString(styleBorder + "├" + strings.Repeat("─", width-2) + "┤" + styleReset)
	row++

	footer := "↵ run  ·  esc close  ·  ↑↓ navigate  ·  sw/k/sp <q> filter"
	fLen := utf8.RuneCountInString(footer)
	fPad := content - fLen
	if fPad < 0 {
		fPad = 0
	}
	moveTo(&b, row, leftPad)
	b.WriteString(styleBorder + "│" + styleReset + " " + styleHint + footer + styleReset +
		strings.Repeat(" ", fPad) + " " + styleBorder + "│" + styleReset)
	row++

	moveTo(&b, row, leftPad)
	b.WriteString(styleBorder + "╰" + strings.Repeat("─", width-2) + "╯" + styleReset)

	// Park the real terminal cursor at the end of the query so it
	// blinks naturally in place of the old underscore stub.
	moveTo(&b, queryRow, leftPad+4+qLen)
	b.WriteString("\x1b[?25h")

	_, _ = out.Write([]byte(b.String()))
	_ = out.Flush()
}

// renderForm paints the "Spawn process…" two-field form. Layout
// mirrors the picker (centered rounded box) so the user feels like
// they're still inside the palette. Cursor parks at the active field
// so it blinks where the next byte will land.
func (p *paletteState) renderForm(out writeFlusher, cols, rows int) {
	if p.form == nil {
		p.form = &spawnProcessForm{}
	}
	if cols < 32 {
		cols = 32
	}
	if rows < 10 {
		rows = 10
	}
	width := cols - 8
	if width > 72 {
		width = 72
	}
	if width < 40 {
		width = cols - 2
	}
	if width < 32 {
		width = 32
	}
	leftPad := (cols - width) / 2
	if leftPad < 1 {
		leftPad = 1
	}
	content := width - 4

	var b strings.Builder
	b.WriteString("\x1b[?25l\x1b[H\x1b[2J\x1b[3J")

	row := 2
	title := "Spawn process"
	hint := "esc cancel"
	dashes := width - 3 - len(title) - 1 - 1 - len(hint) - 3
	if dashes < 2 {
		dashes = 2
	}
	moveTo(&b, row, leftPad)
	b.WriteString(styleBorder + "╭─ " + styleActive + title + styleReset + styleBorder + " " +
		strings.Repeat("─", dashes) + " " + styleHint + hint + styleReset + styleBorder + " ─╮" + styleReset)
	row++

	cmdStr := string(p.form.cmd)
	cmdLen := utf8.RuneCountInString(cmdStr)
	pad := content - 2 - cmdLen
	if pad < 0 {
		pad = 0
		cmdStr = clipRunes(cmdStr, content-2)
		cmdLen = utf8.RuneCountInString(cmdStr)
	}
	prompt := "❯"
	if p.form.field == 0 {
		prompt = styleAccent + "❯" + styleReset
	} else {
		prompt = styleDim + "❯" + styleReset
	}
	cmdRow := row
	moveTo(&b, row, leftPad)
	b.WriteString(styleBorder + "│" + styleReset + " " + prompt + " " + cmdStr +
		strings.Repeat(" ", pad) + " " + styleBorder + "│" + styleReset)
	row++

	moveTo(&b, row, leftPad)
	b.WriteString(styleBorder + "├" + strings.Repeat("─", width-2) + "┤" + styleReset)
	row++

	box := "[ ]"
	if p.form.relaunch {
		box = "[x]"
	}
	check := "  " + box + " Relaunch on exit"
	if p.form.field == 1 {
		check = styleAccent + "▎" + styleReset + " " + styleBold + box + styleReset + " Relaunch on exit"
	}
	checkLen := visibleLen(check)
	cpad := content - checkLen
	if cpad < 0 {
		cpad = 0
	}
	moveTo(&b, row, leftPad)
	b.WriteString(styleBorder + "│" + styleReset + " " + check +
		strings.Repeat(" ", cpad) + " " + styleBorder + "│" + styleReset)
	row++

	moveTo(&b, row, leftPad)
	b.WriteString(styleBorder + "├" + strings.Repeat("─", width-2) + "┤" + styleReset)
	row++

	footer := "↵ spawn · esc cancel · tab cycle · space toggle"
	fLen := utf8.RuneCountInString(footer)
	fpad := content - fLen
	if fpad < 0 {
		fpad = 0
	}
	moveTo(&b, row, leftPad)
	b.WriteString(styleBorder + "│" + styleReset + " " + styleHint + footer + styleReset +
		strings.Repeat(" ", fpad) + " " + styleBorder + "│" + styleReset)
	row++

	moveTo(&b, row, leftPad)
	b.WriteString(styleBorder + "╰" + strings.Repeat("─", width-2) + "╯" + styleReset)

	// Park the cursor on the command line if that field is focused.
	if p.form.field == 0 {
		moveTo(&b, cmdRow, leftPad+4+cmdLen)
		b.WriteString("\x1b[?25h")
	} else {
		b.WriteString("\x1b[?25l")
	}

	_, _ = out.Write([]byte(b.String()))
	_ = out.Flush()
}

func clipRunes(s string, n int) string {
	if n <= 0 {
		return ""
	}
	count := 0
	for i := range s {
		if count == n {
			return s[:i]
		}
		count++
	}
	return s
}

type writeFlusher interface {
	Write(p []byte) (int, error)
	Flush() error
}

type writeFlusherBase interface {
	Write(p []byte) (int, error)
}

type nopFlusher struct{ io writeFlusherBase }

func wrapWriter(w writeFlusherBase) writeFlusher { return nopFlusher{io: w} }
func (n nopFlusher) Write(p []byte) (int, error) { return n.io.Write(p) }
func (n nopFlusher) Flush() error                { return nil }

func moveTo(b *strings.Builder, row, col int) {
	fmt.Fprintf(b, "\x1b[%d;%dH", row, col)
}

func padRight(s string, width int) string {
	w := width - visibleLen(s)
	if w <= 0 {
		return s
	}
	return s + strings.Repeat(" ", w)
}

func visibleLen(s string) int {
	n := 0
	in := false
	for _, r := range s {
		if r == 0x1b {
			in = true
			continue
		}
		if in {
			if r == 'm' || r == 'H' {
				in = false
			}
			continue
		}
		n++
	}
	return n
}

func countAnsi(s string) int {
	return len(s) - visibleLen(s)
}