methanoliver · September 14, 2016 23:19 · Sep 14, 2016 · Sep 14, 2016 · Sep 14, 2016
diff --git a/diff-critic.py b/diff-critic.py
@@ -0,0 +1,137 @@
+#!/usr/bin/python
+
+from __future__ import print_function
+
+import subprocess
+import os
+import re
+
+
+def criticize(root, from_ref, to_ref, filename, html=False):
+    # Git uses "^+" for additions, "^-" for deletions, "^~$" for newlines. It's
+    # always deletion first additions second, so when a deletion is followed by
+    # addition, it's a change {~~this~>that~~}, otherwise {--deletion--} and
+    # {++addition++}.
+
+    # There is probably a simpler way to do this, but this one works
+    # passably well.
+
+    git_args = [
+        "git", "diff", "--unified=100000", "--word-diff=porcelain",
+        "--no-color",
+        from_ref, to_ref, filename
+    ]
+
+    p = subprocess.Popen(git_args, cwd=root, stdout=subprocess.PIPE,
+                         universal_newlines=True)
+    p.wait()
+
+    if p.returncode > 0:
+        raise IOError("Git complained about something.")
+
+    raw_data = p.stdout.read()
+
+    # Now we massage this into CriticMark format.
+
+    # Cut off the unified diff header.
+    raw_data = re.sub(
+        r"^diff --git .*\nindex .*\n--- .*\n\+\+\+ .*\n@@ .* @@\n", "",
+        raw_data, flags=re.MULTILINE)
+
+    # Replace all cases of changed pairs, i.e. - followed by a +.
+
+    raw_data = re.sub(
+        r"^-(?P<from>.*)\n\+(?P<to>.*)\n",
+        r" <del>\g<from></del><ins>\g<to></ins>\n" if html
+        else r" {~~\g<from>~>\g<to>~~}\n",
+        raw_data,
+        flags=re.MULTILINE
+    )
+
+    # Replace solo deletions and additions.
+    raw_data = re.sub(
+        r"^-(?P<del>.*)\n",
+        r" <del>\g<del></del>\n" if html else r" {--\g<del>--}\n",
+        raw_data,
+        flags=re.MULTILINE
+    )
+    raw_data = re.sub(
+        r"^\+(?P<add>.*)\n",
+        r" <ins>\g<add></ins>\n" if html else r" {++\g<add>++}\n",
+        raw_data,
+        flags=re.MULTILINE
+    )
+
+    # The rest is easier to do manually:
+
+    # If a line starts with a space, cut the space off and join it to the
+    # previous one.
+
+    # If a line starts with a tilde, convert it to a straight newline.
+
+    output_data = ""
+
+    for line in raw_data.split('\n'):
+        if line.startswith('~'):
+            output_data += "\n"
+        elif line.startswith(" "):
+            output_data += line[1:]
+        else:
+            output_data += line
+
+    return output_data
+
+if __name__ == "__main__":
+
+    import argparse
+    import sys
+
+    def output_pattern(filename):
+        if any([filename.endswith(x) for x in ['.md', '.markdown']]):
+            return ".".join(filename.split('.')[:-1]) + ".critic.md"
+        return filename + ".critic.md"
+
+    parser = argparse.ArgumentParser(
+        description="Using git's word-based diff facility, produce a "
+        "diff between two versions of a given file expressed as CriticMark "
+        "markup.\nAssumes it's running in the root of a git tree.\n"
+        "Nothing will be written if the file did not change between the "
+        "given revisions."
+    )
+
+    parser.add_argument('filename', metavar='FILE', type=str, nargs='+',
+                        help='Filenames to produce a diff for.')
+
+    parser.add_argument('--output', '-o', metavar='output_filename', type=str,
+                        help="Output filename. Can "
+                        "only be used when processing files one by one, "
+                        "otherwise default pattern *.critic.md is used.")
+
+    parser.add_argument('--html', action="store_true",
+                        help="Output HTML instead of CriticMark.")
+
+    parser.add_argument('--from', '-f', dest='from_ref', metavar='from',
+                        type=str, required=True,
+                        help="The 'before' version of the file, required.")
+
+    parser.add_argument('--to', '-t', dest='to_ref', metavar='to', type=str,
+                        default='HEAD',
+                        help="The 'after' version of the file, "
+                        "defaults to HEAD.")
+
+    args = parser.parse_args()
+
+    if not os.path.isdir('.git'):
+        print("Not running in a git tree. Use -h for help.")
+        sys.exit(1)
+
+    if len(args.filename) > 1 and args.output:
+        print("Cannot write multiple output files into the same filename.")
+        sys.exit(1)
+
+    for filename in args.filename:
+        data = criticize(os.getcwd(), args.from_ref, args.to_ref,
+                         filename, html=args.html)
+        if len(data):
+            with open(args.output or output_pattern(filename), 'w+b') as f:
+                f.write(data)
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