Check an online ics file for changes

.editorconfig

@@ -1,6 +1,6 @@
 root = true
 
-[*.sh]
+[*.{sh,conf,conf.dist}]
 charset = utf-8
 indent_style = space
 indent_size = 2

icscheck.sh

@@ -0,0 +1 @@
+icscheck/icscheck.sh

icscheck/.gitignore

@@ -0,0 +1,4 @@
+/*.conf
+
+# ics storage
+/store

icscheck/icscheck.conf.dist

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+# Configuration file for icscheck.sh
+# https://winklerfamilie.eu/git/SmallThings/icsutils.git
+
+local icsconf_url="https://somethi.ng"
+local icsconf_output="${HOME}/my.ics"
+
+# icsError
+# Called if the download from ${icsconf_url} failed
+icsError() {
+  echo ICS Error
+}
+
+# icsChanged <new ics> <previous ics> <diff file>
+icsChanged() {
+  echo ICS Changed. Generate ${icsconf_output}
+  [ ! e "${2:-}" ] && printf "First "
+  printf 'change of %s -> %s\n' "${1:-}" "${2:-}"
+}
+

icscheck/icscheck.sh

@@ -0,0 +1,102 @@
+#!/usr/bin/env bash
+
+#  Author: Martin Winkler
+# License: Please refer to the repository
+#  Origin: https://winklerfamilie.eu/git/SmallThings/icsutils.git
+
+
+# Exit on error inside any functions or subshells.
+set -o errtrace
+# Do not allow use of undefined vars. Use ${VAR:-} to use an undefined VAR
+set -o nounset
+# Catch the error in case mysqldump fails (but gzip succeeds) in `mysqldump |gzip`
+set -o pipefail
+
+icsusage() {
+  cat<<USAGE_END
+Usage: ${0##/*} [OPTIONS] [ICSNAME]
+
+   Checks an online ics file for changes. A diff is created
+   excluding "DTSTAMP:" lines, which change with every download.
+
+ [OPTIONS]
+   --help,  -h  :  Displays this help
+   --           :  End of options
+
+ [ICSNAME]
+   An unique identifier for the comparisson process. Used for 
+   configuration ([ICSNAME].conf), temporary and cached files.
+     Default: icscheck
+
+USAGE_END
+}
+
+error() {
+  printf '%b%s%b\n\n' "${color_red}" "${1:-}" "${color_less}"
+  icsusage
+}
+
+# icscheck <ICSNAME>
+icscheck() {
+  readonly origin="$(cd "$(dirname -- "$(readlink -f "${BASH_SOURCE[0]}")")" && pwd)"
+
+  local arg=
+  local ics_name=
+  local ics_url=
+  local ics_output=
+  local ics_config=
+  local diff_ignore=
+  local renew=0
+
+  color_red= ; [ -t 1 ] && color_red='\033[0;31m'
+  color_less= ; [ -t 1 ] && color_less='\033[0m' # No Color
+
+  for arg in "${@}" ; do
+    case "${1:-}" in
+      --help|-h)
+        icsusage && return 0 ;; 
+      --renew|-r)
+        renew=1 && shift ;;
+      --)
+        shift && break ;;
+    esac
+  done
+
+  ics_name="${1:-"icscheck"}"
+  ics_config="${origin}/${ics_name}.conf"
+  . "${ics_config}" 2>/dev/null || { error "${ics_config} not found" && return 1; }
+
+  ics_url="${icsconf_url:?"$(error "URL to ics file must not be empty.")"}"
+  ics_output="${icsconf_output:?"$(error "Download destination must not be empty")"}"
+
+  readonly ics_temp_dir="/tmp/icscheck"
+  readonly ics_store_dir="${origin}/store"
+  readonly ics_down_file="$ics_temp_dir/${ics_name}_new.ics"
+  readonly ics_store_file="${ics_store_dir}/${ics_name}.last.ics"
+  readonly ics_diff="${ics_store_dir}/${ics_name}.diff"
+
+  mkdir -p "${ics_temp_dir}" "${ics_store_dir}"
+
+  wget -O "$ics_down_file" "$ics_url" >/dev/null 2>&1
+
+  # -s : exists and size greater zero
+  if [ ! -s "$ics_down_file" ] || [ ! -r "$ics_down_file" ]; then
+    icsError 
+    exit 1
+  fi
+
+  # Delete storage if manual renew is requested
+  (( renew )) && rm -f "${ics_store_file}"
+
+  # Find differences in download and send notification
+  diff_ignore="^DTSTAMP:.*"
+  diff <(grep -vE "$diff_ignore" "$ics_down_file") <(grep -vE "$diff_ignore" "$ics_store_file" 2>/dev/null) > "$ics_diff" 2>/dev/null
+  if [ $? -eq 1 ]; then
+    icsChanged "${ics_down_file}" "${ics_store_file}" "${ics_diff}"
+
+    # Save download for next comparison
+    cp -f "$ics_down_file" "$ics_store_file"
+  fi
+}
+
+icscheck "${@}"