1 files changed, 203 insertions, 0 deletions
diff --git a/tui/draw.go b/tui/draw.go
new file mode 100644
index 0000000..671d7e1
--- /dev/null
+++ b/tui/draw.go
@@ -0,0 +1,203 @@
+package tui
+
+import (
+	"github.com/rivo/uniseg"
+	"golang.org/x/term"
+	"unicode"
+	"unicode/utf8"
+	"fmt"
+	"bufio"
+	"os"
+)
+
+type pos struct {
+	x int
+	y int
+}
+
+type char struct {
+	c string
+	style Style
+}
+
+type surface map[pos]char
+
+type screen struct {
+	front surface
+	back surface
+	prevSize Dims
+	writer *bufio.Writer
+	cursor pos
+}
+
+var scr screen
+func init() {
+	scr.writer = bufio.NewWriterSize(os.Stdout, 50000)
+	Clear()
+}
+
+type Dims struct {
+	Width int
+	Height int
+}
+
+func Size() Dims {
+	w, h, _ := term.GetSize(0)
+	return Dims {w, h}
+}
+
+func Write(x int, y int, text string, style Style) int {
+	width := 0
+	g := uniseg.NewGraphemes(text)
+	for g.Next() {
+		c := g.Str()
+		r, _ := utf8.DecodeRuneInString(c)
+		if !unicode.IsGraphic(r) {
+			continue
+		}
+		scr.front[pos {x, y}] = char {c, style}
+		w := g.Width()
+		for i := 1; i < w; i++ {
+			scr.front[pos {x + i, y}] = char {"", style}
+		}
+		x += w
+		width += w
+	}
+	return width
+}
+
+func Clear() {
+	scr.front = make(surface)
+}
+
+func MoveCursor(x int, y int) {
+	scr.cursor = pos {x, y}
+}
+
+var saved *term.State
+func Start() error {
+	if saved != nil {
+		return nil
+	}
+	var err error
+	saved, err = term.MakeRaw(0)
+	if err != nil {
+		return err
+	}
+	scr.back = make(surface)
+	_, err = os.Stdout.WriteString("\033[?47h\033[2J\033[?2004h")
+	return err
+}
+
+func End() {
+	if saved == nil {
+		return
+	}
+	if term.Restore(0, saved) != nil {
+		return
+	}
+	os.Stdout.WriteString("\033[?2004l\033[2J\033[0;0H\033[?47l")
+}
+
+func writeCursor(x int, y int) error {
+	_, err := scr.writer.WriteString(fmt.Sprintf("\033[%d;%dH", y + 1, x + 1))
+	return err
+}
+
+func writeStyle(style Style) error {
+	_, err := scr.writer.WriteString("\033[0m")
+	if err != nil {
+		return err
+	}
+	_, err = scr.writer.WriteString(fmt.Sprintf("\033[38;5;%dm", style.Fg))
+	if err != nil {
+		return err
+	}
+	_, err = scr.writer.WriteString(fmt.Sprintf("\033[48;5;%dm", style.Bg))
+	if err != nil {
+		return err
+	}
+	if style.Bold {
+		_, err = scr.writer.WriteString("\033[1m")
+		if err != nil {
+			return err
+		}
+	}
+	if style.Italic {
+		_, err = scr.writer.WriteString("\033[3m")
+		if err != nil {
+			return err
+		}
+	}
+	if style.Underline {
+		_, err = scr.writer.WriteString("\033[4m")
+		if err != nil {
+			return err
+		}
+	}
+	if style.Strikethrough {
+		_, err = scr.writer.WriteString("\033[9m")
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func Present() error {
+	s := Size()
+	reset := true
+	style := DefaultStyle
+	var p pos
+	for p.y = 0; p.y < s.Height; p.y++ {
+		for p.x = 0; p.x < s.Width; {
+			if reset {
+				err := writeCursor(p.x, p.y)
+				if err != nil {
+					return err
+				}
+			}
+			c := scr.front[p]
+			if c.c == "" {
+				c.c = " "
+			}
+			cw := uniseg.StringWidth(c.c)
+			if p.x + cw > s.Width {
+				c.c = " "
+			}
+			if c != scr.back[p] || scr.prevSize != s {
+				if style != c.style {
+					style = c.style
+					err := writeStyle(style)
+					if err != nil {
+						return err
+					}
+				}
+				_, err := scr.writer.WriteString(c.c)
+				if err != nil {
+					return err
+				}
+				// make sure that the cursor position remains synced even if
+				// the terminal mangles a wide char or grapheme
+				if cw == 1 && len([]rune(c.c)) == 1 {
+					reset = false
+				} else {
+					reset = true
+				}
+			} else {
+				reset = true
+			}
+			p.x += cw
+		}
+	}
+	err := writeCursor(scr.cursor.x, scr.cursor.y)
+	if err != nil {
+		return err
+	}
+	scr.prevSize = s
+
+	f := scr.front
+	scr.front = scr.back
+	scr.back = f
+	return scr.writer.Flush()
+}