From ca7b92dde2d7e7fc6f57609d99fd65012edb7eaa Mon Sep 17 00:00:00 2001
From: Martin Winkler <efelon@winklerfamilie.eu>
Date: Sun, 10 Apr 2022 17:50:24 +0200
Subject: [PATCH] gcgetics.sh - Extract cids and ics links from google embedded
 calendars

---
 .editorconfig |   6 ++
 README.md     |   4 +-
 gcgetics.sh   | 165 ++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 174 insertions(+), 1 deletion(-)
 create mode 100644 .editorconfig
 create mode 100755 gcgetics.sh

diff --git a/.editorconfig b/.editorconfig
new file mode 100644
index 0000000..270aad7
--- /dev/null
+++ b/.editorconfig
@@ -0,0 +1,6 @@
+root = true
+
+[*.sh]
+charset = utf-8
+indent_style = space
+indent_size = 2
diff --git a/README.md b/README.md
index bd4be01..a18c66b 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,5 @@
 # icsutils
 
-Tools to work with ics files in bash.
\ No newline at end of file
+Tools to work with ics files in bash.
+
+* `gcgetics.sh` : Extract google calender IDs and ICS links from given embedded google calendar
diff --git a/gcgetics.sh b/gcgetics.sh
new file mode 100755
index 0000000..510115b
--- /dev/null
+++ b/gcgetics.sh
@@ -0,0 +1,165 @@
+#!/usr/bin/env bash
+
+#  Author: Martin Winkler
+# License: Please refer to the repository
+#  Origin: https://winklerfamilie.eu/git/SmallThings/icsutils.git
+
+# Exit on error. Append "|| true" if you expect an error.
+set -o errexit
+# 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
+
+# gc = google calendar
+gc::getIcsUsage() {
+  cat <<USAGE_END
+Usage: ${0##*/} [OPTIONS] [URL/FILE]
+
+ Parses a google calendar embbeded URL content for any number
+ of containted google calendar id (cid). 
+
+ [OPTIONS]
+   --file,  -f  : Input is a file containing a previous curl
+                  of a google calendar embbeded link.
+   --help,  -h  : Show this help.
+   --           : End of Options.
+
+ [URL/FILE]
+   Such a URL usually starts with:
+     "https://calendar.google.com/calendar/../embed?"
+   Where ".." may be empty or a more specific reference.
+
+   If [URL/FILE] is empty or "-", standard input is used.
+
+USAGE_END
+}
+
+gc::makeIcsUrl() {
+  # Exclude public holiday calendar
+  local rexHoliday='group\.v\.calendar'
+  [[ "${1:?}" =~ $rexHoliday ]] && return 1
+  echo "https://calendar.google.com/calendar/ical/${1}/public/basic.ics"
+}
+
+gc::findcid() {
+  local arg=""
+  local content=""
+  local file=0
+  local cids=()
+  local title=()
+
+  local color_green= ; [ -t 1 ] && color_green='\033[1;32m'
+  local color_blue= ; [ -t 1 ] && color_blue='\033[1;34m'
+  local color_red= ; [ -t 1 ] && color_red='\033[2;31m'
+  local color_less= ; [ -t 1 ] && color_less='\033[0m'
+
+  for arg in "${@}" ; do
+    case "$1" in
+      --file|-f)
+        file=1
+        shift 1 ;;
+      --)
+        shift && break ;;
+    esac
+  done
+
+  if [[ "${1}" = "-" ]] || [ -z "${1}" ] ; then 
+    file=1
+    shift
+  fi
+  if (( file )) ; then
+    content=$(<"${1:-"/dev/stdin"}")
+  else
+    # could grep for "cids", but unsure if result is always on one line
+    content="$(curl --silent -L "${1:-}")"
+  fi
+
+  while IFS= read -r line || [[ "${line}" ]] ; do
+    cids+=("${line}")
+  done < <(grep -oP '(?<=")[^"]*@(group|group\.v)\.calendar\.google\.com(?=")' <<<"${content}")
+
+  while IFS= read -r line || [[ "${line}" ]] ; do
+    title+=("${line}")
+  done < <(grep -oP '(?<="title":")[^"]*(?=")' <<<"${content}")
+
+  for i in "${!cids[@]}" ; do
+    printf '%12s: %b%s%b\n' "Title" "${color_green}" "${title[$i]}" "${color_less}"
+    printf '%12s: %s\n' "Calendar ID" "${cids[$i]}"
+    printf '%12s: %b' "ICS Url" "${color_blue}"
+    gc::makeIcsUrl "${cids[$i]}" || printf '%b\n' "${color_red}No ics file for this calendar${color_less}"
+    printf '%b' "${color_less}"
+    echo
+  done
+}
+
+gc::getIcs() {
+  local arg=
+  local element=
+  local opt=""
+
+  readonly shortMax=80
+  local shortEnd=0
+
+  local color_yellow= ; [ -t 1 ] && color_yellow='\033[1;33m'
+  local color_less= ; [ -t 1 ] && color_less='\033[0m'
+
+  # shellcheck disable=SC2034 # arg not used
+  for arg in "${@}" ; do
+    case "$1" in
+      --help|-h)
+        gc::getIcsUsage
+        return 0 ;;
+      --file|-f)
+        opt="-f"
+        shift ;;
+      --)
+        shift && break ;;
+    esac
+  done
+
+  local args=("${@}")
+  
+  # Use standard input if no files are present
+  [ $# -eq 0 ] && args[0]="-"
+
+  for element in "${args[@]}" ; do
+    if [[ $# -gt 1 ]] ; then
+      printf "%b## CID information from: " "${color_yellow}"
+      # Shorten the URL of PATH if it is greater than $shortMax
+      if [[ ${#element} -gt ${shortMax} ]] ; then
+        shortEnd=$((${#element} - shortMax/2))
+        printf '%s[...]%s' \
+          "${element:0:$((shortMax/2))}" \
+          "${element:${shortEnd}:${#element}}"
+      else
+        printf '%s' "${element}"
+      fi
+      printf '%b\n\n' "${color_less}"
+    fi
+    gc::findcid ${opt} "${element}"
+  done
+}
+
+### Check if script is _sourced
+### https://stackoverflow.com/a/28776166
+_sourced=0
+if [ -n "${ZSH_EVAL_CONTEXT:-}" ]; then
+  case ${ZSH_EVAL_CONTEXT:-} in *:file) _sourced=1;; esac
+elif [ -n "${KSH_VERSION:-}" ]; then
+  [ "$(cd "$(dirname -- "$0")" && pwd -P)/$(basename -- "$0")" \
+    != "$(cd "$(dirname -- "${.sh.file}")" && pwd -P)/$(basename -- "${.sh.file}")" ] && _sourced=1
+elif [ -n "${BASH_VERSION:-}" ]; then
+  (return 0 2>/dev/null) && _sourced=1
+else # All other shells: examine $0 for known shell binary filenames
+  # Detects `sh` and `dash`; add additional shell filenames as needed.
+  case ${0##*/} in sh|dash) _sourced=1;; esac
+fi
+###
+
+if (( ! _sourced )); then
+  gc::getIcs "${@}"
+fi
+