Move ANSI stuff into its own file

ansi.go

@@ -0,0 +1,64 @@
+package tea
+
+import "fmt"
+
+// Escape sequence
+const esc = "\033["
+
+// Fullscreen switches to the altscreen and clears the terminal. The former
+// view can be restored with ExitFullscreen().
+func Fullscreen() {
+	fmt.Print(esc + "?1049h" + esc + "H")
+}
+
+// ExitFullscreen exits the altscreen and returns the former terminal view
+func ExitFullscreen() {
+	fmt.Print(esc + "?1049l")
+}
+
+// ClearScreen clears the visible portion of the terminal. Effectively, it
+// fills the terminal with blank spaces.
+func ClearScreen() {
+	fmt.Printf(esc + "2J" + esc + "3J" + esc + "1;1H")
+}
+
+// Invert inverts the foreground and background colors of a given string
+func Invert(s string) string {
+	return esc + "7m" + s + esc + "0m"
+}
+
+// Hide the cursor
+func hideCursor() {
+	fmt.Printf(esc + "?25l")
+}
+
+// Show the cursor
+func showCursor() {
+	fmt.Printf(esc + "?25h")
+}
+
+// Move the cursor down a given number of lines and place it at the beginning
+// of the line
+func cursorNextLine(n int) {
+	fmt.Printf(esc+"%dE", n)
+}
+
+// Move the cursor up a given number of lines and place it at the beginning of
+// the line
+func cursorPrevLine(n int) {
+	fmt.Printf(esc+"%dF", n)
+}
+
+// Clear the current line
+func clearLine() {
+	fmt.Printf(esc + "2K")
+}
+
+// Clear a given number of lines
+func clearLines(n int) {
+	clearLine()
+	for i := 0; i < n; i++ {
+		cursorPrevLine(1)
+		clearLine()
+	}
+}