selection update

lib/cursor.js

@@ -0,0 +1,25 @@
+export function moveUp(buffer, cursor) {
+  if (cursor.line > 0) cursor.line--;
+  cursor.col = Math.min(cursor.col, buffer[cursor.line].length);
+}
+
+export function moveDown(buffer, cursor) {
+  if (cursor.line < buffer.length - 1) cursor.line++;
+  cursor.col = Math.min(cursor.col, buffer[cursor.line].length);
+}
+
+export function moveLeft(buffer, cursor) {
+  if (cursor.col > 0) cursor.col--;
+  else if (cursor.line > 0) {
+    cursor.line--;
+    cursor.col = buffer[cursor.line].length;
+  }
+}
+
+export function moveRight(buffer, cursor) {
+  if (cursor.col < buffer[cursor.line].length) cursor.col++;
+  else if (cursor.line < buffer.length - 1) {
+    cursor.line++;
+    cursor.col = 0;
+  }
+}