Fix bugs that exceed boundaries when selecting text. (Issue: #88)

Author: YowFung

lib/terminal/terminal.dart

@@ -558,25 +558,23 @@ class Terminal
     }
 
     final builder = StringBuffer();
+    final yStart = max(_selection.start!.y, 0);
+    final yEnd = min(_selection.end!.y, buffer.height);
 
-    for (var row = _selection.start!.y; row <= _selection.end!.y; row++) {
-      if (row >= buffer.height) {
-        break;
-      }
-
+    for (var row = yStart; row <= yEnd; row++) {
       final line = buffer.lines[row];
 
       var xStart = 0;
       var xEnd = viewWidth - 1;
 
-      if (row == _selection.start!.y) {
-        xStart = _selection.start!.x;
+      if (row == yStart) {
+        xStart = max(_selection.start!.x, 0);
       } else if (!line.isWrapped) {
         builder.write("\n");
       }
 
-      if (row == _selection.end!.y) {
-        xEnd = _selection.end!.x;
+      if (row == yEnd) {
+        xEnd = min(_selection.end!.x, terminalWidth);
       }
 
       for (var col = xStart; col <= xEnd; col++) {

test/terminal/terminal_selection_test.dart

@@ -0,0 +1,33 @@
+import 'dart:math' show max;
+import 'package:flutter_test/flutter_test.dart';
+import 'package:xterm/mouse/position.dart';
+import 'package:xterm/xterm.dart';
+
+
+void main() async {
+
+  group("Terminal selection test", () {
+
+    const text = ""
+        "Hello World!\r\n"
+        "This is beautiful plugin!";
+    final linesLength = text.split('\n').length;
+    final maxLengthInLine = text.split('\n').fold<int>(0, (pre, e) => max(pre, e.length));
+
+    test("Select in normal range", () {
+      final terminal = Terminal(maxLines: 100);
+      terminal.write(text);
+      terminal.selection!.init(Position(0, 0));
+      terminal.selection!.update(Position(maxLengthInLine, linesLength));
+      expect(terminal.getSelectedText(), text.replaceAll('\r', '') + "\n");
+    });
+
+    test("Select beyond the boundary", () {
+      final terminal = Terminal(maxLines: 100);
+      terminal.write(text);
+      terminal.selection!.init(Position(-3, -7));
+      terminal.selection!.update(Position(maxLengthInLine + 8, linesLength));
+      expect(terminal.getSelectedText(), text.replaceAll('\r', '') + "\n");
+    });
+  });
+}