use ESM module syntax & minor cleanups

The biggest change here is moving various element classes under
more scope-specific directories, which helps to avoid circular
dependencies and is just cleaner to navigate and expand in the
future.

Otherwise this is a largely uncritical port to ESM module syntax!
There are probably a number of changes and other cleanups that
remain much needed.

Whenever I make changes to tui-lib it's hard to believe it's
already been <INSERT COUNTING NUMBER HERE> years since the
previous time. First commits are from January 2017, and the
code originates a month earlier in KAaRMNoD!

1 files changed, 51 insertions, 0 deletions

diff --git a/ui/controls/Button.js b/ui/controls/Button.js
new file mode 100644
index 0000000..5be2b2a
--- /dev/null
+++ b/ui/controls/Button.js
@@ -0,0 +1,51 @@
+import {FocusElement} from 'tui-lib/ui/primitives'
+
+import * as ansi from 'tui-lib/util/ansi'
+import telc from 'tui-lib/util/telchars'
+
+export default class Button extends FocusElement {
+  // A button.
+
+  constructor(text) {
+    super()
+
+    this.text = text
+
+    this.cursorX = null
+    this.cursorY = null
+  }
+
+  fixLayout() {
+    this.w = ansi.measureColumns(this.text)
+    this.h = 1
+  }
+
+  drawTo(writable) {
+    if (this.isSelected) {
+      writable.write(ansi.invert())
+    }
+
+    writable.write(ansi.moveCursor(this.absTop, this.absLeft))
+    writable.write(this.text)
+
+    writable.write(ansi.resetAttributes())
+
+    super.drawTo(writable)
+  }
+
+  keyPressed(keyBuf) {
+    if (telc.isSelect(keyBuf)) {
+      this.emit('pressed')
+    }
+  }
+
+  clicked(button) {
+    if (button === 'left') {
+      if (this.isSelected) {
+        this.emit('pressed')
+      } else {
+        this.root.select(this)
+      }
+    }
+  }
+}