#!/bin/sh

# =============================================================================
# This is a modified version of this:
# https://help.github.com/articles/changing-author-info
# =============================================================================


FILTER_SCRIPT_TEMPLATE='
an="$GIT_AUTHOR_NAME";
am="$GIT_AUTHOR_EMAIL";
cn="$GIT_COMMITTER_NAME";
cm="$GIT_COMMITTER_EMAIL";

if [ "$GIT_COMMITTER_EMAIL" = "OLD_COMMITTER_EMAIL" ];
then
    cn="$GIT_COMMITTER_NAME";
    cm="NEW_COMMITTER_EMAIL";
fi;

if [ "$GIT_AUTHOR_EMAIL" = "OLD_AUTHOR_EMAIL" ];
then
    an="$GIT_AUTHOR_NAME";
    am="NEW_AUTHOR_EMAIL";
fi;

export GIT_AUTHOR_NAME="$an";
export GIT_AUTHOR_EMAIL="$am";
export GIT_COMMITTER_NAME="$cn";
export GIT_COMMITTER_EMAIL="$cm";
'


git_filter_branch() {
    git filter-branch -f --env-filter "$1"
}


main() {
    old_email="$1"
    new_email="$2"

    filter_script=$(\
        echo $FILTER_SCRIPT_TEMPLATE \
        | sed "s/OLD_COMMITTER_EMAIL/$old_email/g" \
        | sed "s/NEW_COMMITTER_EMAIL/$new_email/g" \
        | sed "s/OLD_AUTHOR_EMAIL/$old_email/g" \
        | sed "s/NEW_AUTHOR_EMAIL/$new_email/g" \
    )

    git_filter_branch "$filter_script"
}

main "$@"