Add initial version

.gitignore

@@ -0,0 +1 @@
+/levi

go.mod

@@ -0,0 +1,7 @@
+module tea.kareha.org/lab/levi
+
+go 1.25.0
+
+require golang.org/x/term v0.41.0
+
+require golang.org/x/sys v0.42.0 // indirect

go.sum

@@ -0,0 +1,4 @@
+golang.org/x/sys v0.42.0 h1:omrd2nAlyT5ESRdCLYdm3+fMfNFE/+Rf4bDIQImRJeo=
+golang.org/x/sys v0.42.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
+golang.org/x/term v0.41.0 h1:QCgPso/Q3RTJx2Th4bDLqML4W6iJiaXFq2/ftQF13YU=
+golang.org/x/term v0.41.0/go.mod h1:3pfBgksrReYfZ5lvYM0kSO0LIkAl4Yl2bXOkKP7Ec2A=

main.go

@@ -0,0 +1,182 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"strings"
+	"unicode/utf8"
+
+	"golang.org/x/term"
+)
+
+func enableRawMode() (*term.State, error) {
+	return term.MakeRaw(int(os.Stdin.Fd()))
+}
+
+func disableRawMode(state *term.State) {
+	term.Restore(int(os.Stdin.Fd()), state)
+}
+
+func clearScreen() {
+	fmt.Print("\x1b[2J")
+}
+
+func goHome() {
+	fmt.Print("\x1b[H")
+}
+
+func moveCursor(x, y int) {
+	fmt.Printf("\x1b[%d;%dH", y, x)
+}
+
+func hideCursor() {
+	fmt.Print("\x1b[?25l")
+}
+
+func showCursor() {
+	fmt.Print("\x1b[?25h")
+}
+
+func getScreenSize() (int, int) {
+	w, h, err := term.GetSize(int(os.Stdout.Fd()))
+	if err != nil {
+		panic(err)
+	}
+	return w, h
+}
+
+type Screen struct {
+	w, h int
+}
+
+func NewScreen() Screen {
+	w, h := getScreenSize()
+	return Screen{
+		w: w,
+		h: h,
+	}
+}
+
+func (scr *Screen) Size() (int, int) {
+	return scr.w, scr.h
+}
+
+const Esc rune = 0x1b
+
+func runeSize(b byte) int {
+	switch {
+	case b & 0x80 == 0:
+		return 1
+	case b & 0xe0 == 0xc0:
+		return 2
+	case b & 0xf0 == 0xe0:
+		return 3
+	case b & 0xf8 == 0xf0:
+		return 4
+	default:
+		return -1 // invalid
+	}
+}
+
+func readRune() rune {
+	buf := make([]byte, 1)
+	_, err := io.ReadFull(os.Stdin, buf)
+	if err != nil {
+		panic(err)
+	}
+	size := runeSize(buf[0])
+	if size == -1 {
+		panic("Invalid UTF-8")
+	}
+	full := make([]byte, size)
+	full[0] = buf[0]
+	if size > 1 {
+		_, err := io.ReadFull(os.Stdin, full[1:])
+		if err != nil {
+			panic(err)
+		}
+	}
+	r, size := utf8.DecodeRune(full)
+	if r == utf8.RuneError && size == 1 {
+		panic("Invalid UTF-8")
+	}
+	return r
+}
+
+type Keyboard struct {}
+
+func NewKeyboard() Keyboard {
+	return Keyboard{}
+}
+
+func (kb *Keyboard) ReadRune() rune {
+	return readRune()
+}
+
+type Editor struct {
+	scr *Screen
+	kb *Keyboard
+	x, y int
+	line *strings.Builder
+}
+
+func NewEditor(scr *Screen, kb *Keyboard) Editor {
+	_, h := scr.Size()
+	return Editor{
+		scr: scr,
+		x: 0,
+		y: h / 2,
+		line: new(strings.Builder),
+	}
+}
+
+func (ed *Editor) Screen() *Screen {
+	return ed.scr
+}
+
+func (ed *Editor) AddRune(r rune) {
+	ed.line.WriteRune(r)
+}
+
+func draw(ed *Editor) {
+	clearScreen()
+	goHome()
+
+	fmt.Print("Hit Esc to Exit")
+
+	moveCursor(ed.x, ed.y)
+	fmt.Print(ed.line.String())
+}
+
+func main() {
+	// init
+	oldState, err := enableRawMode()
+	if err != nil {
+		panic(err)
+	}
+	defer func() {
+		disableRawMode(oldState)
+		showCursor()
+	}()
+
+	// main
+	scr := NewScreen()
+	kb := NewKeyboard()
+	ed := NewEditor(&scr, &kb)
+	for {
+		hideCursor()
+		draw(&ed)
+		showCursor()
+
+		r := kb.ReadRune()
+		if r == Esc {
+			break
+		}
+		ed.AddRune(r)
+	}
+
+	// cleanup
+	clearScreen()
+	goHome()
+}