#!/bin/bash

if [ $# -ne 1 ]; then
    echo "Invalid arguments!"
    echo "$0 <commit to revert>"
    exit 1
fi

if [ -n "$(git status -uno -s --porcelain)" ]; then
    echo "You have unstashed changes. Please stash and then revert."
    git status -uno
    exit 1
fi

COMMIT=$1

SVN_REVISION=$(git log -1 $COMMIT | grep git-svn-id | tr -s "@" " " | cut -f 4 -d " ")

if [ -z "$SVN_REVISION" ]; then
    echo "Error! Given commit is not a git-svn revision!"
    exit 1
fi

# Grab the one line message for our revert commit message.
ONE_LINE_MSG=$(git log --oneline $COMMIT -1 | cut -f2- -d " ")

# Revert the commit.
git revert --no-commit $COMMIT 2>/dev/null
if [ $? -ne 0 ]; then
    echo "Error! Failed to revert commit $COMMIT. Resetting to head."
    git reset --hard HEAD
    exit 1
fi

# Create a template in our .git directory.
TEMPLATE="`git rev-parse --git-dir`/git-svn-revert-template"
cat > $TEMPLATE <<EOF
Revert "$ONE_LINE_MSG"

This reverts commit r$SVN_REVISION.
EOF

# Begin the commit but give our user an opportunity to edit it.
git commit --file="$TEMPLATE" --edit
if [ $? -ne 0 ]; then
    echo "Error! Failed to commit reverting commit for commit $COMMIT. Reverting to head."
    git reset --hard HEAD
    rm -rf $TEMPLATE
    exit 1
fi

rm -rf $TEMPLATE