#!/bin/bash
#
# Script to remove GPG key from git-crypt
#
# It will re-initialize git-crypt for the repository and re-add all keys except
# the one requested for removal.
#
# Note: You still need to change all your secrets to fully protect yourself.
# Removing a user will prevent them from reading future changes but they will
# still have a copy of the data up to the point of their removal.
#
# Usage: see 'remove-gpg-user.sh -h'
#    remove-gpg-user.sh -l   : list GPG keys configured within git-crypt for the current directory
#    remove-gpg-user.sh -r <FULL-GPG-FINGERPRINT> :  remove specified key from git-crypt configuration
#        Ex: remove-gpg-user.sh -r 3BC18383F838C0B815B961480F8CAF5467D
#
# Typical workflow (assuming the script is placed in ~/bin/) :
#
#     cd /path/to/protected/repo
#     git checkout -b  git-crypt-remove
#     ~/bin/$(basename $0) -l           # List configured GPG keys
#     ~/bin/$(basename $0) -r <KEYID>
#
# The script will create multiple commits to your repo. Feel free to squash them
# all down to one.
#
# Based on https://github.com/AGWA/git-crypt/issues/47#issuecomment-212734882
#
# GIST source https://gist.github.com/glogiotatidis/e0ab45ed5575a9d7973390dace0552b0
# amended to work on Mac OS and with cosmetic changes for a more convenient interface in
#   https://gist.github.com/Falkor/7b29f16f5f79404fe41476be0d992783
#################
set -eo pipefail

KEY_TO_REMOVE=
KEY_FINGERPRINT=
CMD_PREFIX=

###############
print_error_and_exit() { echo -e "*** ERROR *** $*\n Usage: see '$(basename $0) -h'"; exit 1; }
really_continue() {
    echo -n -e "/!\\ WARNING: $*\n     Are you sure you want to continue? [Y|n]"
    read ans
    case $ans in
	      n*|N*) exit 1;;
    esac
}
print_usage() {
    cat <<EOF
Remove a given GPG key from a git-crypt enabled repository.

Usage:
   $(basename $0) -l : list GPG keys configured within git-crypt
   $(basename $0) [-n] -r <FULL-GPG-FINGERPRINT> : remove key from git-crypt configuration

Typical workflow:

    cd /path/to/protected/repo
    git checkout -b  git-crypt-remove
    ~/bin/$(basename $0) -l           # List configured GPG keys
    ~/bin/$(basename $0) -r <KEYID>

You can check the full, 64-bit (8-byte) key ID for a key within your keyring with
     gpg -k [email | pattern]
     gpg -k --with-colons  [email | pattern | id] |  awk -F: '/^pub:/ { print $5 }'

EOF
}

###
# Print info for a given key from your keyring
##
print_key_info() {
    [ -z "$1" ] && print_error_and_exit "[$FUNCNAME] missing text argument"
    local key=$1
    local gpgid=$(gpg --list-keys --with-colons $key |  awk -F: '/^pub:/ { print $5 }')
    local fpr=$(gpg -k --with-colons $key | awk -F: '/^fpr:/ { print $10; exit; }')  # Only first fpr
    echo "==== Key Fingerprint: ${fpr} ==="
    echo "==== Long GPG ID: ${gpgid}"
    gpg --list-key "$key" || print_error_and_exit "Couldn't find info about $key"
    export KEY_FINGERPRINT=$fpr
}

###
# List GPG keys configured for protecting this repository
##
list_git_crypt_keys() {
    for f in .git-crypt/keys/default/0/*.gpg; do
        # key="$(basename "${f}" .gpg)"
        print_key_info $(basename "${f}" .gpg)
        # gpgid=$(gpg --list-keys --with-colons $key |  awk -F: '/^pub:/ { print $5 }')
        # echo "==== Key Fingerprint: ${key} ==="
        # echo "==== Long GPG ID: ${gpgid}"
        # gpg --list-key "$key" || print_error_and_exit "Couldn't find info about $key"
    done
}

##### Let's go #####
# Check for options
while [ $# -ge 1 ]; do
    case $1 in
        -h | --help)    print_usage;  exit 0;;
        -l | --list)    list_git_crypt_keys;    exit 0;;
        -r | --remove)  shift; KEY_TO_REMOVE=$1;;
        # -n | --dry-run) CMD_PREFIX=echo ;;
    esac
    shift
done

[ -z "${KEY_TO_REMOVE}" ] && print_error_and_exit "No key to remove has been indicated"

print_key_info "${KEY_TO_REMOVE}"
[ -z "${KEY_FINGERPRINT}" ] && print_error_and_exit "Unable to retrieve key fingerprint"
really_continue "About to remove the GPG Key ID ${KEY_TO_REMOVE} from Git-crypt configuration"

# Below code adapted from @glogiotatidis - https://gist.github.com/glogiotatidis/e0ab45ed5575a9d7973390dace0552b0
TMPDIR=$(mktemp -d)
CURRENT_DIR=$(git rev-parse --show-toplevel)
BASENAME=$(basename `pwd`)
TMPFILE=list-encrypted-files.txt

cat <<EOF
TMPDIR=${TMPDIR}
CURRENT_DIR=${CURRENT_DIR}
EOF
# Unlock the directory, we need to copy encrypted versions of the files
git crypt unlock

# Work on copy.
cp -rp $(pwd) $TMPDIR || true

pushd $TMPDIR/$BASENAME
# git status

# Remove encrypted files and git-crypt
git crypt status -e > ${TMPFILE}
if [ -s "${TMPFILE}" ]; then
    awk '{print $2}' ${TMPFILE} | xargs rm
    git commit -a -m "Remove encrypted files"
fi
rm -rf .git-crypt
git commit -m "Remove git-crypt (in particular configuration related to key ${KEY_TO_REMOVE})" .git-crypt
rm -rf .git/git-crypt

# Re-initialize git crypt
git crypt init

# Add existing users, except the
for keyfilename in `ls $CURRENT_DIR/.git-crypt/keys/default/0/*gpg`; do
    basename=`basename $keyfilename`
    key=${basename%.*}
    if [[ $key == $KEY_FINGERPRINT ]]; then
        echo "ignoring key ${KEY_FINGERPRINT} to be removed"
        continue;
    fi
    git crypt add-gpg-user $key
done

cd $CURRENT_DIR
for i in `awk '{print $2}' ${TMPDIR}/${BASENAME}/${TMPFILE}`; do
    #cp -rp --parents $i $TMPDIR/$BASENAME;
    #gcp -rp --parents $i $TMPDIR/$BASENAME;
    rsync -rp -R       $i $TMPDIR/$BASENAME;
done
cd $TMPDIR/$BASENAME
for i in `awk '{print $2}' ${TMPFILE}`; do
    git add $i
done
git commit -m "New encrypted files" || true
popd

git crypt lock
git pull $TMPDIR/$BASENAME

rm -rf $TMPDIR