#!/usr/bin/env bash

set -e

if [ $# -lt 3 ]; then
  echo "Usage: $0 <repo> <branch> <directory>" 1>&2
  exit 2
fi

REPO=$1
COMMIT=$2
DIR=$3

echo "Copy '$COMMIT' from '$REPO' to '$DIR'"
if [ -f $DIR/.git-copy ]; then
  CURRENT=$(cat $DIR/.git-copy)
  if [ $(echo -n $COMMIT | wc -c) != "40" ]; then
    # On the off chance that $COMMIT is a remote head.
    ACTUAL=$(git ls-remote $REPO $COMMIT | cut -c 1-40 -)
  else
    ACTUAL=$COMMIT
  fi
  if [ "$CURRENT" = "$ACTUAL" ]; then
    echo "Up to date."
    exit
  fi
fi

git init -q $DIR
git -C $DIR fetch -q --depth=1 $REPO $COMMIT:git-copy-tmp
git -C $DIR reset --hard git-copy-tmp
git -C $DIR rev-parse --verify HEAD > $DIR/.git-copy
rm -rf $DIR/.git