switch_bundler_environment

#!/bin/sh

######################################################################
#
# switch_bundler_environment OLD-BRANCH NEW-BRANCH
#
# Swap out the old branch's Bundler environment, and swaps in the new
# branch's. Arguments may be branch names or SHAs.
#
# For best results, add this to .git/hooks/post-checkout:
#
#     #!/bin/sh
#     exec script/switch_bundler_environment $1 $2
#
######################################################################

branch()
{
    local branchish=$1
    if [ -f ".git/refs/heads/$branchish" ]; then
        echo "$branchish"
    else
        for f in .git/refs/heads/*; do
            if [ -f "$f" ]; then
                local name=$(basename $f)
                if [ "$(cat .git/refs/heads/$name)" = "$branchish" ]; then
                    echo "$name"
                fi
            fi
        done
    fi
}

save()
{
    local branch=$1
    if [ -n $branch ]; then
        copy_directory .bundle ".branch_bundles/$branch/bundle"
    fi
}

load()
{
    local branch=$1
    if [ -n $branch ]; then
        copy_directory ".branch_bundles/$branch/bundle" .bundle
    fi
}

copy_directory()
{
    local src=$1
    local dst=$2

    rm -rf "$dst"
    if [ -d "$src" ]; then
        mkdir -p "$(dirname $dst)"
        cp -r "$src" "$dst"
    fi
}

if [ $# -ne 2 ]; then
    echo "USAGE: #$0 FROM-BRANCHISH TO-BRANCHISH" >&2
    exit 1
fi

old_branch=$(branch $1)
new_branch=$(branch $2)

if [ -n "$old_branch" ]; then
    save $old_branch
fi

# If no bundler environment exists for the new branch, only kill the
# existing one if the Gemfile is different. This way forking a new
# branch off the current one doesn't require a "bundle install".
if [ -n "$new_branch" -a                                        \
     '('                                                        \
       -d ".branch_bundles/$new_branch/bundle" -o               \
       -n "$(git diff $old_branch:Gemfile $new_branch:Gemfile)" \
     ')'                                                        \
   ]; then
    load $new_branch
fi