Add organization and documentation to hooks collection

contrib/hooks/encrypt_with_checksums/post_encrypt

@@ -0,0 +1,96 @@
+#!/usr/bin/env bash
+
+# yadm - Yet Another Dotfiles Manager
+# Copyright (C) 2015-2019 Tim Byrne and Martin Zuther
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+
+YADM_CHECKSUMS="$YADM_HOOK_DIR/files.checksums"
+WARNING_MESSAGE="No checksums were created"
+
+# unpack exported array; filenames including a newline character (\n)
+# are NOT supported
+OLD_IFS="$IFS"
+IFS=$'\n'
+YADM_ENCRYPT_INCLUDE_FILES=( $YADM_ENCRYPT_INCLUDE_FILES )
+IFS="$OLD_IFS"
+
+
+function get_checksum_command {
+    # check if "shasum" exists and supports the algorithm (which is
+    # tested by sending an empty string to "shasum")
+    if command -v "shasum" > /dev/null && printf "" | shasum --algorithm "256" &> /dev/null; then
+        printf "shasum --algorithm 256"
+    # check if "sha256sum" exists
+    elif command -v "sha256sum" > /dev/null; then
+        printf "sha256sum"
+    # check if "gsha256sum" exists
+    elif command -v "gsha256sum" > /dev/null; then
+        printf "gsha256sum"
+    else
+        # display warning in bright yellow
+        printf "\033[1;33m" >&2
+        printf "\nWARNING: \"shasum\", \"sha256sum\" and \"gsha256sum\" not found.   %s\n" "$WARNING_MESSAGE." >&2
+
+        # reset output color
+        printf "\033[0m" >&2
+
+        # signal error
+        return 1
+    fi
+}
+
+
+# get checksum command
+CHECKSUM_COMMAND=$(get_checksum_command)
+
+# no command found
+if (($?)); then
+    # return original exit status of yadm command
+    exit "$YADM_HOOK_EXIT"
+fi
+
+# empty (or create) checksum file
+true > "$YADM_CHECKSUMS"
+
+# calculate checksums for encrypted files
+for included in "${YADM_ENCRYPT_INCLUDE_FILES[@]}"; do
+    # highlight any errors in red
+    printf "\033[0;31m"
+
+    # calculate checksums
+    $CHECKSUM_COMMAND "$included" >> "$YADM_CHECKSUMS"
+    ERROR_CODE=$?
+
+    # reset output color
+    printf "\033[0m"
+
+    # handle errors
+    if (($ERROR_CODE)); then
+        # display warning in bright yellow
+        printf "\033[1;33m" >&2
+        printf "\nWARNING: an error occurred.  Please inspect the checksum file.\n" >&2
+
+        # reset output color
+        printf "\033[0m" >&2
+
+        # exit and signal error
+        exit $ERROR_CODE
+    fi
+done
+
+# announce success and return original exit status of yadm command
+printf "Wrote SHA-256 checksums: %s\n" "$YADM_CHECKSUMS"
+exit "$YADM_HOOK_EXIT"