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+
+"""dir_attach, a Pelican plugin to attach files from a directory named after
+restructuredText file names.
+
+If your file is named ``foobar.rst``, then the following
+restructuredText entry:
+
+    .. image:: {dir_attach}example-thumbnail.jpg
+        :alt: An example image for demonstration.
+        :target: {dir_attach}example.jpg
+
+Will automatically be pre-processed by this plugin to become:
+
+    .. image:: {attach}../images/foobar/example-thumbnail.jpg
+        :alt: An example image for demonstration.
+        :target: {attach}../images/foobar/example.jpg
+
+Using ``../images/`` directory instead of ``images/`` is mandatory. This is
+because the current Pelican implementation will simplify the path only if the
+target directory is not in the same root as the current page.
+
+If ``images/`` directory was used, then the resulting path in HTML would be:
+
+    foobar/images/foobar/example.jpg
+
+By using a directory outside of the page's source folder, the generated HTML
+path is simplified by Pelican:
+
+    foobar/example.jpg
+
+"""
+
+import os
+import tempfile
+import re
+
+from pelican import signals
+from pelican.readers import RstReader
+
+
+def dirname_from_source_path(source_path):
+    """Get the dirname to use from the .rst filename.
+
+    >>> dirname_from_source_path("/tmp/foobar.rst")
+    'foobar'
+
+    """
+    return os.path.splitext(os.path.basename(source_path))[0]
+
+
+def expand_dir_attach(content, dirname):
+    """Expand the {dir_attach} directives to image {attach} directives.
+
+    >>> src = \
+        ".. image:: {dir_attach}example.jpg\\n" \
+        "    :alt: Example illustration.\\n" \
+        "    :target: {dir_attach}example.jpg\\n"
+    >>> expand_dir_attach(src, "foobar")
+    '.. image:: {attach}../images/foobar/example.jpg\\n\
+    :alt: Example illustration.\\n\
+    :target: {attach}../images/foobar/example.jpg\\n'
+
+    """
+
+    dest = f"{{attach}}../images/{dirname}/"
+
+    # We are trying to match only restructuredText directives instead of doing
+    # a whole content.replace to avoid to replace inside of paragraphs, etc.
+    regexes = (
+        (r"^(.. \w+::) {dir_attach}(.*)$", fr"\1 {dest}\2"),
+        (r"^(.. _.*:) {dir_attach}(.*)$", fr"\1 {dest}\2"),
+        (r"^(    :\w+:) {dir_attach}(.*)$", fr"\1 {dest}\2"),
+    )
+
+    for match, replace in regexes:
+        content = re.sub(match, replace, content, flags=re.MULTILINE)
+
+    return content
+
+
+class CustomRstReader(RstReader):
+    """A custom restructuredText reader that will pre-process source first."""
+
+    enabled = True
+    file_extensions = ['rst']
+
+    def read(self, source_path):
+        """Parses restructured text."""
+        dirname = dirname_from_source_path(source_path)
+
+        # Open temporary file in "w" instead of default "w+b" in order to
+        # use utf-8 by default.
+        with tempfile.NamedTemporaryFile(mode="w") as tmp:
+            with open(source_path) as src:
+                tmp.write(expand_dir_attach(src.read(), dirname))
+
+            # Force flush to disk before docutils tries to open the file
+            # in super().read(), elsewise file may be empty.
+            tmp.flush()
+
+            return super().read(tmp.name)
+
+
+def add_reader(readers):
+    """Override the .rst reader with our custom reader."""
+    readers.reader_classes['rst'] = CustomRstReader
+
+
+def register():
+    """Register the plugin to Pelican."""
+    signals.readers_init.connect(add_reader)