terminal: cursor down respects bottom margins

src/terminal/Terminal.zig

@@ -1449,16 +1449,21 @@ pub fn cursorRight(self: *Terminal, count: usize) void {
 /// Move the cursor down amount lines. If amount is greater than the maximum
 /// move distance then it is internally adjusted to the maximum. This sequence
 /// will not scroll the screen or scroll region. If amount is 0, adjust it to 1.
-// TODO: test
-pub fn cursorDown(self: *Terminal, count: usize) void {
+pub fn cursorDown(self: *Terminal, count_req: usize) void {
     const tracy = trace(@src());
     defer tracy.end();
 
+    // Always resets pending wrap
     self.screen.cursor.pending_wrap = false;
-    self.screen.cursor.y += if (count == 0) 1 else count;
-    if (self.screen.cursor.y >= self.rows) {
-        self.screen.cursor.y = self.rows - 1;
-    }
+
+    // The max the cursor can move to depends where the cursor currently is
+    const max = if (self.screen.cursor.y <= self.scrolling_region.bottom)
+        self.scrolling_region.bottom
+    else
+        self.rows - 1;
+
+    const count = @max(count_req, 1);
+    self.screen.cursor.y = @min(max, self.screen.cursor.y +| count);
 }
 
 /// Move the cursor up amount lines. If amount is greater than the maximum
@@ -3561,3 +3566,72 @@ test "Terminal: cursorLeft extended reverse wrap is priority if both set" {
         try testing.expectEqualStrings("ABCDE\n1\n    X", str);
     }
 }
+
+test "Terminal: cursorDown basic" {
+    const alloc = testing.allocator;
+    var t = try init(alloc, 5, 5);
+    defer t.deinit(alloc);
+
+    try t.print('A');
+    t.cursorDown(10);
+    try t.print('X');
+
+    {
+        var str = try t.plainString(testing.allocator);
+        defer testing.allocator.free(str);
+        try testing.expectEqualStrings("A\n\n\n\n X", str);
+    }
+}
+
+test "Terminal: cursorDown above bottom scroll margin" {
+    const alloc = testing.allocator;
+    var t = try init(alloc, 5, 5);
+    defer t.deinit(alloc);
+
+    t.setScrollingRegion(1, 3);
+    try t.print('A');
+    t.cursorDown(10);
+    try t.print('X');
+
+    {
+        var str = try t.plainString(testing.allocator);
+        defer testing.allocator.free(str);
+        try testing.expectEqualStrings("A\n\n X", str);
+    }
+}
+
+test "Terminal: cursorDown below bottom scroll margin" {
+    const alloc = testing.allocator;
+    var t = try init(alloc, 5, 5);
+    defer t.deinit(alloc);
+
+    t.setScrollingRegion(1, 3);
+    try t.print('A');
+    t.setCursorPos(4, 1);
+    t.cursorDown(10);
+    try t.print('X');
+
+    {
+        var str = try t.plainString(testing.allocator);
+        defer testing.allocator.free(str);
+        try testing.expectEqualStrings("A\n\n\n\nX", str);
+    }
+}
+
+test "Terminal: cursorDown resets wrap" {
+    const alloc = testing.allocator;
+    var t = try init(alloc, 5, 5);
+    defer t.deinit(alloc);
+
+    for ("ABCDE") |c| try t.print(c);
+    try testing.expect(t.screen.cursor.pending_wrap);
+    t.cursorDown(1);
+    try testing.expect(!t.screen.cursor.pending_wrap);
+    try t.print('X');
+
+    {
+        var str = try t.plainString(testing.allocator);
+        defer testing.allocator.free(str);
+        try testing.expectEqualStrings("ABCDE\n    X", str);
+    }
+}