From d5278bfd5b995f6cbe00420c6b9bca56ad5806c4 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Sat, 18 Jan 2014 14:16:17 +0530
Subject: [PATCH] Start work on diff view

---
 src/calibre/gui2/tweak_book/diff.py | 83 +++++++++++++++++++++++++++++
 src/calibre/utils/diff/__init__.py  |  4 +-
 2 files changed, 85 insertions(+), 2 deletions(-)
 create mode 100644 src/calibre/gui2/tweak_book/diff.py

diff --git a/src/calibre/gui2/tweak_book/diff.py b/src/calibre/gui2/tweak_book/diff.py
new file mode 100644
index 0000000000..23df2713da
--- /dev/null
+++ b/src/calibre/gui2/tweak_book/diff.py
@@ -0,0 +1,83 @@
+#!/usr/bin/env python
+# vim:fileencoding=utf-8
+from __future__ import (unicode_literals, division, absolute_import,
+                        print_function)
+
+__license__ = 'GPL v3'
+__copyright__ = '2014, Kovid Goyal <kovid at kovidgoyal.net>'
+
+import sys
+from functools import partial
+
+from PyQt4.Qt import (QSplitter, QApplication)
+
+from calibre.gui2.tweak_book.editor.text import PlainTextEdit
+from calibre.utils.diff import get_sequence_matcher
+
+class TextBrowser(PlainTextEdit):
+
+    def __init__(self, parent=None):
+        PlainTextEdit.__init__(self, parent)
+        self.setReadOnly(True)
+        self.setLineWrapMode(self.NoWrap)
+
+class DiffView(QSplitter):
+
+    def __init__(self, parent=None):
+        QSplitter.__init__(self, parent)
+
+        self.left, self.right = TextBrowser(self), TextBrowser(self)
+        self.addWidget(self.left), self.addWidget(self.right)
+
+    def __call__(self, left_text, right_text, context=None, syntax=None):
+        left_lines = left_text.splitlines()
+        right_lines = right_text.splitlines()
+        self.context = context
+
+        self.left_insert = partial(self.do_insert, self.left.textCursor(), left_lines)
+        self.right_insert = partial(self.do_insert, self.right.textCursor(), right_lines)
+        self.cruncher = get_sequence_matcher()(None, left_lines, right_lines)
+        self.do_layout(context)
+
+    def refresh(self):
+        self.do_layout(self.context)
+
+    def do_layout(self, context=None):
+        self.left.clear(), self.right.clear()
+        opcodes = self.cruncher.get_opcodes() if context is None else self.cruncher.get_grouped_opcodes(context)
+        for tag, alo, ahi, blo, bhi in opcodes:
+            getattr(self, tag)(alo, ahi, blo, bhi)
+        for v in (self.left, self.right):
+            c = v.textCursor()
+            c.movePosition(c.Start)
+            v.setTextCursor(c)
+
+    def do_insert(self, cursor, lines, lo, hi):
+        start_block = cursor.blockNumber()
+        if lo != hi:
+            cursor.insertText('\n'.join(lines[lo:hi]))
+            cursor.insertBlock()
+        return start_block, cursor.blockNumber()
+
+    def equal(self, alo, ahi, blo, bhi):
+        self.left_insert(alo, ahi), self.right_insert(blo, bhi)
+
+    def delete(self, alo, ahi, blo, bhi):
+        self.left_insert(alo, ahi)
+
+    def insert(self, alo, ahi, blo, bhi):
+        self.right_insert(blo, bhi)
+
+    def replace(self, alo, ahi, blo, bhi):
+        self.left_insert(alo, ahi)
+        self.right_insert(blo, bhi)
+
+if __name__ == '__main__':
+    app = QApplication([])
+    raw1 = open(sys.argv[-2], 'rb').read().decode('utf-8')
+    raw2 = open(sys.argv[-1], 'rb').read().decode('utf-8')
+    w = DiffView()
+    w(raw1, raw2)
+    w.show()
+    app.exec_()
+
diff --git a/src/calibre/utils/diff/__init__.py b/src/calibre/utils/diff/__init__.py
index ad765c8871..b7746fecce 100644
--- a/src/calibre/utils/diff/__init__.py
+++ b/src/calibre/utils/diff/__init__.py
@@ -10,8 +10,8 @@ from calibre.constants import plugins
 
 def load_patience_module():
     p, err = plugins['_patiencediff_c']
-    if err is not None:
-        raise ImportError('Failed to import the PatienceDiff C module with error: %s' % err)
+    if err:
+        raise ImportError('Failed to import the PatienceDiff C module with error: %r' % err)
     return p
 
 def get_sequence_matcher():