From d4703adfcbbfcd24499ee4aa7ee47703f00a1ff7 Mon Sep 17 00:00:00 2001
From: Henrik Johansson <henrik.johansson@kisel.com>
Date: Thu, 26 Sep 2013 08:23:23 +0200
Subject: [PATCH] added functionality to transform.fromstring which add a
 prefix to all ids in order to avoid id name clashes

---
 src/svgutils/transform.py | 18 ++++++++++++++++--
 src/svgutils/util.py      | 25 +++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 2 deletions(-)
 create mode 100644 src/svgutils/util.py

diff --git a/src/svgutils/transform.py b/src/svgutils/transform.py
index c1e981e..3fef4a1 100644
--- a/src/svgutils/transform.py
+++ b/src/svgutils/transform.py
@@ -6,6 +6,8 @@
 except ImportError:
     from io import StringIO
 
+import util
+
 SVG_NAMESPACE = "http://www.w3.org/2000/svg"
 SVG = "{%s}" % SVG_NAMESPACE
 NSMAP = {None : SVG_NAMESPACE}
@@ -54,6 +56,12 @@ def __init__(self, element_list):
 
 class SVGFigure(object):
     def __init__(self, width=None, height=None):
+        # create a unique id
+        if not hasattr(SVGFigure, 'maxid'):
+            SVGFigure.maxid = 0
+        self.id = SVGFigure.maxid + 1
+        SVGFigure.maxid = self.id
+
         self.root = etree.Element(SVG+"svg",nsmap=NSMAP)
         self.root.set("version", "1.1")
         if width or height:
@@ -96,13 +104,19 @@ def set_size(self, size):
         self.root.set('width', w)
         self.root.set('height', h)
 
-def fromfile(fname):
+def fromfile(fname, idprefix=None):
     fig = SVGFigure()
     fid = open(fname)
     svg_file = etree.parse(fid)
     fid.close()
+    
+    # make id's unique in order to avoid clashes
+    if idprefix is None:
+        idprefix = 'inst%d_' % fig.id
+    fig_root = util.svg_id_prepend(svg_file.getroot(), prefix=idprefix)
+
+    fig.root = fig_root
 
-    fig.root = svg_file.getroot() 
     return fig
 
 def fromstring(text):
diff --git a/src/svgutils/util.py b/src/svgutils/util.py
new file mode 100644
index 0000000..1440670
--- /dev/null
+++ b/src/svgutils/util.py
@@ -0,0 +1,25 @@
+import copy
+import re
+
+def svg_id_prepend(root, prefix):
+    """Append prefix to id attributes and url(#id) references"""
+
+    root = copy.deepcopy(root)
+
+    id_attributes = {}
+    ## Replace id attributes
+    for e in root.findall("*//*[@id]"):
+        idvalue = e.attrib['id']
+        newidvalue = prefix + idvalue
+        e.attrib['id'] = newidvalue
+        
+        id_attributes[idvalue] = newidvalue
+        
+    ## Update references
+    for e in root.xpath("//*[contains(@*, 'url(#')]"):
+        for attr, value in e.attrib.items():
+            matchobj = re.match('url\(#(.*)\)', value)
+            if matchobj and matchobj.groups()[0] in id_attributes:
+                e.attrib[attr] = 'url(#%s)' % id_attributes[matchobj.groups()[0]]
+
+    return root