Reduce number of writes in order to avoid flickering

Author: clue

src/Stdio.php

@@ -70,17 +70,40 @@ public function handleBuffer()
 
     public function write($data)
     {
-        // clear readline prompt in order to overwrite with data
-        $this->readline->clear();
+        if ((string)$data === '') {
+            return;
+        }
+
+        $out = $data;
+
+        $lastNewline = strrpos($data, "\n");
+
+        $restoreReadline = false;
 
-        // move one line up if the last write did not end with a newline
         if ($this->incompleteLine !== '') {
-            $this->output->write("\033[A");
-            $this->output->write("\r\033[" . $this->width($this->incompleteLine) . "C");
-        }
+            // the last write did not end with a newline => append to existing row
 
-        // write actual data
-        $this->output->write($data);
+            // move one line up and move cursor to last position before writing data
+            $out = "\033[A" . "\r\033[" . $this->width($this->incompleteLine) . "C" . $out;
+
+            // data contains a newline, so this will overwrite the readline prompt
+            if ($lastNewline !== false) {
+                // move cursor to beginning of readline prompt and clear line
+                // clearing is important because $data may not overwrite the whole line
+                $out = "\r\033[K" . $out;
+
+                // make sure to restore readline after this output
+                $restoreReadline = true;
+            }
+        } else {
+            // here, we're writing to a new line => overwrite readline prompt
+
+            // move cursor to beginning of readline prompt and clear line
+            $out = "\r\033[K" . $out;
+
+            // we always overwrite the readline prompt, so restore it on next line
+            $restoreReadline = true;
+        }
 
         // following write will have have to append to this line if it does not end with a newline
         $endsWithNewline = substr($data, -1) === "\n";
@@ -90,9 +113,7 @@ public function write($data)
             $this->incompleteLine = '';
         } else {
             // always end data with newline in order to append readline on next line
-            $this->output->write("\n");
-
-            $lastNewline = strrpos($data, "\n");
+            $out .= "\n";
 
             if ($lastNewline === false) {
                 // contains no newline at all, everything is incomplete
@@ -103,8 +124,21 @@ public function write($data)
             }
         }
 
-        // restore original readline prompt and line buffer
-        $this->readline->redraw();
+        if ($restoreReadline) {
+            // write output and restore original readline prompt and line buffer
+            $this->output->write($out);
+            $this->readline->redraw();
+        } else {
+            // restore original cursor position in readline prompt
+            $pos = $this->width($this->readline->getPrompt()) + $this->readline->getCursorCell();
+            if ($pos !== 0) {
+                // we always start at beginning of line, move right by X
+                $out .= "\033[" . $pos . "C";
+            }
+
+            // write to actual output stream
+            $this->output->write($out);
+        }
     }
 
     public function writeln($line)

tests/StdioTest.php

@@ -34,6 +34,23 @@ public function testCtorArgsWillBeReturnedByGetters()
         $this->assertSame($readline, $stdio->getReadline());
     }
 
+    public function testWriteEmptyStringWillNotWriteToOutput()
+    {
+        $input = $this->getMock('React\Stream\ReadableStreamInterface');
+        $output = $this->getMock('React\Stream\WritableStreamInterface');
+
+        //$readline = $this->getMockBuilder('Clue\React\Stdio\Readline')->disableOriginalConstructor()->getMock();
+        $readline = new Readline($input, $output);
+        $readline->setPrompt('> ');
+        $readline->setInput('input');
+
+        $stdio = new Stdio($this->loop, $input, $output, $readline);
+
+        $output->expects($this->never())->method('write');
+
+        $stdio->write('');
+    }
+
     public function testWriteWillClearReadlineWriteOutputAndRestoreReadline()
     {
         $input = $this->getMock('React\Stream\ReadableStreamInterface');
@@ -56,7 +73,7 @@ public function testWriteWillClearReadlineWriteOutputAndRestoreReadline()
         $this->assertEquals("\r\033[K" . "test\n" . "\r\033[K" . "> input", $buffer);
     }
 
-    public function testWriteAgainWillClearReadlineMoveToPreviousLineWriteOutputAndRestoreReadline()
+    public function testWriteAgainWillMoveToPreviousLineWriteOutputAndRestoreReadlinePosition()
     {
         $input = $this->getMock('React\Stream\ReadableStreamInterface');
         $output = $this->getMock('React\Stream\WritableStreamInterface');
@@ -77,10 +94,10 @@ public function testWriteAgainWillClearReadlineMoveToPreviousLineWriteOutputAndR
 
         $stdio->write('world');
 
-        $this->assertEquals("\r\033[K" . "\033[A" . "\r\033[5C" . "world\n" . "\r\033[K" . "> input", $buffer);
+        $this->assertEquals("\033[A" . "\r\033[5C" . "world\n" . "\033[7C", $buffer);
     }
 
-    public function testWriteAgainWithBackspaceWillClearReadlineMoveToPreviousLineWriteOutputAndRestoreReadline()
+    public function testWriteAgainWithBackspaceWillMoveToPreviousLineWriteOutputAndRestoreReadlinePosition()
     {
         $input = $this->getMock('React\Stream\ReadableStreamInterface');
         $output = $this->getMock('React\Stream\WritableStreamInterface');
@@ -101,7 +118,7 @@ public function testWriteAgainWithBackspaceWillClearReadlineMoveToPreviousLineWr
 
         $stdio->write("\x08 world!");
 
-        $this->assertEquals("\r\033[K" . "\033[A" . "\r\033[6C" . "\x08 world!\n" . "\r\033[K" . "> input", $buffer);
+        $this->assertEquals("\033[A" . "\r\033[6C" . "\x08 world!\n" . "\033[7C", $buffer);
     }
 
     public function testWriteAgainWithNewlinesWillClearReadlineMoveToPreviousLineWriteOutputAndRestoreReadline()