#!/bin/bash
# Version: 0.1.0
# Copyright (c) 2023:
#   Darren 'Tadgy' Austin <darren (at) afterdark.org.uk>
# Licensed under the terms of the GNU General Public License version 3.
#
# A PushOver client to send alert messages.

# Configuration.
CONFIG_API_URL="https://api.pushover.net/1/messages.json"
CONFIG_SOUNDS_API_URL="https://api.pushover.net/1/sounds.json"

# Defaults.
DEFAULT_SYSTEM_DIR="/etc/pushover-client"
DEFAULT_USER_DIR="${HOME}/.pushover-client"
DEFAULT_CONFIG_FILE="default"
DEFAULT_EXPIRY="3600"
DEFAULT_RETRY="60"

# Functions.
show_help() {
  local SCRIPT="${0##*/}"

        #........1.........2.........3.........4.........5.........6.........7.........8
  cat <<-EOF
	Usage: $SCRIPT [config file] [options]
	Push notifications to your https://pushover.net registered devices.

	If [config_file] is specified it is used to read the default configuration.
	If [config_file] is not specified, a custom user or system 'default' file will be
	read to obtain the defaults.  If no 'default' custom user or system config file
	can be read, command line options are required for operation.
	Command line [options] override any config file.

	Options:
	  -a, --attachment <filename>	The picture to send with the alert.  No default.
	  -A, --api-url <url>		The API URL to use for this submission.  Default
	  				is: $CONFIG_API_URL.
	 				Quote <url> if it contains shell special chars.
	  -c, --callback <url>		A URL which is accessed by API server when the
	 				user acknowledges the alert.  This option is
	 				only used in priority 2 alerts.
	 				Quote <url> if it contains shell special chars.
	  -d, --devices <devices>	A comma seperated list of the devices to receive
	 				the alert.  Default is to send to all devices.
	  -e, --expiry <seconds>	Set the expiration time for alerts sent with
	 				priority 2.  Default is 3600 (1 hour).  The
	 				maximum expiry time is 10800 (3 hours).
	      --examples		Show extended example usage of this program.
	  -h, --help			Show this help page.
	  -m, --message <text>		The plain text message to send.
	 				Quote <text> if it contains spaces.
	 				This option or -M is required if a message is
	 				not available from a config file.
	  -M, --html-message <text>	The HTML message to send.
	 				Quote <text> if it contains spaces.
	 				This option or -m is required if a message is
	 				not available from a config file.
	      --monospace		Use a monospace font to display the message
	 				given with -m.  Default is to use regular font.
	 				This option cannot be used with -M.
	  -p, --priority <priority>	Set the priority of the message:
	 				  -2	Lowest priority - no alert/notification
	 					will be generated.  However, the app
	 					badge or number will update on devices.
	 				  -1	Low priority - no alert sound is
	 					emitted but a notification will appear.
	 					During a user's configured quiet hours,
	 					priority -1 is used for messages.
	 				   0	Normal priority (the default) - an alert
	 					sound and notification are generated.
	 				   1	High priority - bypass the user's
	 					configured quiet hours and generate an
	 					alert and notification.
	 				   2	Emergency - as priority 1, but the alert
	 					and notification is repeated (subject to
	 					the -r and -e options) until it is
	 					acknowledged by the recipient.
	  -q, --quiet			Do not print the API execution reply to stdout.
	  -r, --retry <seconds>		Set the retry interval for alerts sent with
	 				priority 2.  Default is 60 (1 minute).  The
	 				minimum retry time is 30 seconds.
	  -s, --subject <text>		The subject/title of the message.  If unset,
	 				the configured app name is used.
	 				Quote <text> if it contains spaces.
	  -S, --sound <sound>		Set the alert sound to play with message:
	 				  none		None/silent.
	 				  vibrate	Vibrate only.
	 				  pushover	Pushover (short, default).
	 				  bike		Bike (short).
	 				  bugle		Bugle (short).
	 				  cashregister	Cash Register (short).
	 				  classical	Classical (short).
	 				  cosmic	Cosmic (short).
	 				  falling	Falling (short).
	 				  gamelan	Gamelan (short).
	 				  incoming	Incoming (short).
	 				  intermission	Intermission (short).
	 				  magic		Magic (short).
	 				  mechanical	Mechanical (short).
	 				  pianobar	Piano Bar (short).
	 				  siren		Siren (short).
	 				  spacealarm	Space Alarm (short).
	 				  tugboat	Tug Boat (short).
	 				  alien		Alien Alarm (long).
	 				  climb		Climb (long).
	 				  persistent	Persistent (long).
	 				  echo		Pushover Echo (long).
	 				  updown	Up Down (long).
	 				Or a sound uploaded to the user's account.
	  -t, --token <token>		The pushover.net API token/key for the specific
	 				application.  This option is required if not
	 				available from a config file.
	  -T, --ttl <seconds>		The number of seconds the alert will live (or
	 				be displayed) on a users device before being
	 				automatically removed.  The default is no ttl.
	 				This option is ignored when alerts are sent with
	 				priority (-p) 2.
	      --timestamp <seconds>	The number of seconds since the unix epoch to
	 				use as the timestamp for the alert.
	 				The default timestamp is the time the API
	 				received the message.
	  -u, --user <user_key>		The pushover.net user key(s).  If a single user
	 				key is specified, that account's configuration
	 				will be used for the alerts.  If a comma
	 				separated list (maximum 50) of user keys is
	 				given, the alert is sent only to those users.
	 				This option is required if not available from a
	 				config file.
	  -U, --url <url>		Set the URL to send with the alert.
	 				Quote <url> if it contains shell special chars.
	      --url-title <text>	The title of the URL given with -U.  Ignored
	 				if -U is not used also.
	 				Quote <text> if it contains spaces.
	Option processing ceases with "--".

	For example usage, use: $SCRIPT --examples
	EOF
}

show_examples() {
  local SCRIPT="${0##*/}"

        #........1.........2.........3.........4.........5.........6.........7.........8
  cat <<-EOF
	Basic usage is: $SCRIPT [config file] [options]

	[config file] configuration options are overridden by command line [options].
	All or part settings may be specified in the [config file], with the addition of
	command line [options] to augment the [config file] settings.
	[options] can be seen by running: $SCRIPT --help

	Command line examples:
	  Send a plain text message to all devices, showing all required [options].
	    $SCRIPT -u <user key> -t <API token> -m "Test message"

	  Same as the above, but do not show any response from the API server (an
	  appropriate error/return code is set).
	    $SCRIPT -q -u <user key> -t <API token> -m "Test message"

	  Send a HTML message (which will be underlined) to all devices, showing all
	  required [options].
	    $SCRIPT -u <user key> -t <API token> -M "<u>Test message</u>"

	  Send a plain text message to all devices, with the addition of a subject/title
	  to the message.
	    $SCRIPT -u <user key> -t <API token> -s "Test subject" -m "..."

	  Send a message to all devices, including a picture attachment.
	    $SCRIPT -u <user key> -t <API token> -a </path/to/image> -m "..."

	  Send a message to all devices, including a supplimentary URL with a title.
	    $SCRIPT -u <user key> -t <API token> -U "https://afterdark.org.uk" \\
	      --url-title "Afterdark" -m "Check out the included URL!"

	  Send a message to all devices, selecting an alternative sound alert.
	    $SCRIPT -u <user key> -t <API token> -s "magic" -m "..."

	  Send a message to a specific list of devices.
	    $SCRIPT -u <user key> -t <API token> -d "iphone,ipad" -m "..."

	  Send an emergency alert, repeated every minute for an 2 hours until it is
	  acknowledged by the user.
	    $SCRIPT -u <user key> -t <API token> -p 2 -r 60 -e 7200 -m "..."

	Read all configuration from <config file> path and use that for sending the
	alert.  If this path does not exist, search for a file matching the the
	<config file> name in the user's private pushover directory (~/.pushover-client)
	or the system wide pushover directory (/etc/pushover-client), in that order.
	  $SCRIPT <config file>
	EOF
}

# Pick out possible config file and '--' arguments of the command line.
ARGS=( "$@" )
(( ${#ARGS[@]} >= 1 )) && FIRST_ARG="${ARGS[0]}"
(( ${#ARGS[@]} >= 2 )) && SECOND_ARG="${ARGS[1]}"

# Get the config filename if it was given on the command line, or use the default.
[[ -z "$FIRST_ARG" ]] || [[ "$FIRST_ARG" =~ -[^-] ]] && FILENAME="$DEFAULT_CONFIG_FILE" && SKIP_CUSTOM=1
[[ ! -v FILENAME ]] && [[ "$FIRST_ARG" != -* ]] && FILENAME="$FIRST_ARG" && unset "ARGS[0]"
[[ ! -v FILENAME ]] && [[ "$FIRST_ARG" == "--" ]] && [[ -n "$SECOND_ARG" ]] && FILENAME="$SECOND_ARG" && unset "ARGS[1]"

# Find and validate the correct config filename.
if (( ${SKIP_CUSTOM:-0} == 1 )) && [[ -e "$DEFAULT_USER_DIR/$FILENAME" ]] && [[ ! -d "$DEFAULT_USER_DIR/$FILENAME" ]] && \
    [[ -r "$DEFAULT_USER_DIR/$FILENAME" ]]; then
  FILENAME="$DEFAULT_USER_DIR/$FILENAME"
elif (( ${SKIP_CUSTOM:-0} == 1 )) && [[ -e "$DEFAULT_SYSTEM_DIR/$FILENAME" ]] && [[ ! -d "$DEFAULT_SYSTEM_DIR/$FILENAME" ]] && \
    [[ -r "$DEFAULT_SYSTEM_DIR/$FILENAME" ]]; then
  FILENAME="$DEFAULT_SYSTEM_DIR/$FILENAME"
elif [[ "${FILENAME:0:1}" != "/" ]] && [[ -e "$FILENAME" ]] && [[ ! -d "$FILENAME" ]] && [[ -r "$FILENAME" ]]; then
  :
elif [[ "${FILENAME:0:1}" != "/" ]] && [[ -e "$DEFAULT_USER_DIR/$FILENAME" ]] && [[ ! -d "$DEFAULT_USER_DIR/$FILENAME" ]] && \
    [[ -r "$DEFAULT_USER_DIR/$FILENAME" ]]; then
  FILENAME="$DEFAULT_USER_DIR/$FILENAME"
elif [[ "${FILENAME:0:1}" != "/" ]] && [[ -e "$DEFAULT_SYSTEM_DIR/$FILENAME" ]] && [[ ! -d "$DEFAULT_SYSTEM_DIR/$FILENAME" ]] && \
    [[ -r "$DEFAULT_SYSTEM_DIR/$FILENAME" ]]; then
  FILENAME="$DEFAULT_SYSTEM_DIR/$FILENAME"
elif [[ "${FILENAME:0:1}" == "/" ]] && [[ -e "$FILENAME" ]] && [[ ! -d "$FILENAME" ]] && [[ -r "$FILENAME" ]]; then
  :
elif [[ -n "$FILENAME" ]]; then
  printf "%s: '%s' %s\\n" "${0##*/}" "$FILENAME" "invalid config file name" >&2
  exit 1
fi

# Read the config file.
[[ -n "$FILENAME" ]] && {
  eval "$(awk '!/^(#|$|[[:blank:]]*$)/ { print "CONFIG_"$0 }' "$FILENAME")" 2>/dev/null || {
    printf "%s: %s '%s'\\n" "${0##*/}" "error in config file" "$FILENAME" >&2
    exit 1
  }
}

# Parse command line options.
set -- "${ARGS[@]}"
while [[ -n "$1" ]]; do
  case "$1" in
    -a|-attachment|--attachment)
      if [[ "$2" =~ ^[[:blank:]]*$ ]]; then
        printf "%s: %s\\n" "${0##*/}" "attachment filename cannot be an empty value" >&2
        exit 1
      else
        CONFIG_ATTACHMENT="$2"
      fi
      shift
      ;;
    -A|-api-url|--api-url)
      # Setting is validated below.
      CONFIG_API_URL="$2"
      shift
      ;;
    -c|-callback|--callback)
      if [[ "$2" =~ ^[[:blank:]]*$ ]]; then
        printf "%s: %s\\n" "${0##*/}" "callback URL address cannot be empty" >&2
        exit 1
      else
        CONFIG_CALLBACK_URL="$2"
      fi
      shift
      ;;
    -d|-devices|--devices)
      if [[ "$2" =~ ^[[:blank:]]*$ ]]; then
        printf "%s: %s\\n" "${0##*/}" "device list cannot be an empty value" >&2
        exit 1
      else
        CONFIG_DEVICES="$2"
      fi
      shift
      ;;
    -e|-expiry|--expiry)
      if [[ "$2" =~ ^[[:blank:]]*$ ]]; then
        printf "%s: %s\\n" "${0##*/}" "expiry time cannot be an empty value" >&2
        exit 1
      else
        CONFIG_EXPIRY="$2"
      fi
      shift
      ;;
    -examples|--examples)
      show_examples
      exit 0
      ;;
    -h|-help|--help)
      show_help
      exit 0
      ;;
    -m|-message|--message)
      # Setting is validated below.
      CONFIG_MESSAGE="$2"
      shift
      ;;
    -M|-html-message|--html-message)
      # Setting is validated below.
      CONFIG_HTML_MESSAGE="$2"
      shift
      ;;
    -monospace|--monospace)
      # Setting is validated below.
      CONFIG_MONOSPACE="1"
      shift
      ;;
    -p|-priority|--priority)
      if [[ "$2" =~ ^[[:blank:]]*$ ]]; then
        printf "%s: %s\\n" "${0##*/}" "priority setting cannot be an empty value" >&2
        exit 1
      else
        CONFIG_PRIORITY="$2"
      fi
      shift
      ;;
    -q|-quiet|--quiet)
      CONFIG_QUIET=1
      shift
      ;;
    -r|-retry|--retry)
      if [[ "$2" =~ ^[[:blank:]]*$ ]]; then
        printf "%s: %s\\n" "${0##*/}" "retry time cannot be an empty value" >&2
        exit 1
      else
        CONFIG_RETRY="$2"
      fi
      shift
      ;;
    -s|-subject|--subject)
      if [[ "$2" =~ ^[[:blank:]]*$ ]]; then
        printf "%s: %s\\n" "${0##*/}" "subject/title cannot be an empty value" >&2
        exit 1
      else
        CONFIG_SUBJECT="$2"
      fi
      shift
      ;;
    -S|-sound|--sound)
      if [[ "$2" =~ ^[[:blank:]]*$ ]]; then
        printf "%s: %s\\n" "${0##*/}" "sound selection cannot be empty" >&2
        exit 1
      else
        CONFIG_SOUND="$2"
      fi
      shift
      ;;
    -t|-token|--token)
      if [[ "$2" =~ ^[[:blank:]]*$ ]]; then
        printf "%s: %s\\n" "${0##*/}" "token key cannot be an empty value" >&2
        exit 1
      else
        CONFIG_TOKEN="$2"
      fi
      shift
      ;;
    -T|-ttl|--ttl)
      if [[ "$2" =~ ^[[:blank:]]*$ ]]; then
        printf "%s: %s\\n" "${0##*/}" "ttl cannot be an empty value" >&2
        exit 1
      else
        CONFIG_TTL="$2"
      fi
      shift
      ;;
    -timestamp|--timestamp)
      if [[ "$2" =~ ^[[:blank:]]*$ ]]; then
        printf "%s: %s\\n" "${0##*/}" "timestamp cannot be an empty value" >&2
        exit 1
      else
        CONFIG_TIMESTAMP="$2"
      fi
      shift
      ;;
    -u|-user|--user)
      # Setting is validated below.
      CONFIG_USER_KEYS="$2"
      shift
      ;;
    -U|-url|--url)
      if [[ "$2" =~ ^[[:blank:]]*$ ]]; then
        printf "%s: %s\\n" "${0##*/}" "URL address cannot be empty" >&2
        exit 1
      else
        CONFIG_URL="$2"
      fi
      shift
      ;;
    -url-title|--url-title)
      if [[ "$2" =~ ^[[:blank:]]*$ ]]; then
        printf "%s: %s\\n" "${0##*/}" "URL title cannot be empty" >&2
        exit 1
      else
        CONFIG_URL_TITLE="$2"
      fi
      shift
      ;;
    --)
      shift
      break
      ;;
    *)
      printf "%s: %s: %s\\n" "${0##*/}" "invalid option" "$1" >&2
      printf "%s: %s %s\\n" "Try" "${0##*/}" "--help" >&2
      exit 1
      ;;
  esac
  shift
done

# The options list should be empty if the correct syntax was used.
[[ -n "$1" ]] && {
  printf "%s: %s\\n" "${0##*/}" "options cannot come after --" >&2
  exit 1
}

# Validate all the CONFIG_* settings.
[[ "$CONFIG_API_URL" =~ ^[[:blank:]]*$ ]] && {
  printf "%s: %s\\n" "${0##*/}" "API URL (-A) cannot be an empty value" >&2
  exit 1
}

if [[ ! "$CONFIG_ATTACHMENT" =~ ^[[:blank:]]*$ ]]; then
  if [[ ! -e "$CONFIG_ATTACHMENT" ]]; then
    printf "%s: %s '%s' %s\\n" "${0##*/}" "attachment (-a)" "$CONFIG_ATTACHMENT" "does not exist" >&2
    exit 1
  elif [[ -d "$CONFIG_ATTACHMENT" ]]; then
    printf "%s: %s '%s' %s\\n" "${0##*/}" "attachment (-a)" "$CONFIG_ATTACHMENT" "is a directory, not a file" >&2
    exit 1
  elif [[ ! -r "$CONFIG_ATTACHMENT" ]]; then
    printf "%s: %s '%s' %s\\n" "${0##*/}" "attachment (-a)" "$CONFIG_ATTACHMENT" "is not readable by you" >&2
    exit 1
  elif (( $(stat --printf=%s "$CONFIG_ATTACHMENT") > 2621440 )); then
    printf "%s: %s\\n" "${0##*/}" "attachment (-a) is too large (2.5MB maximum)" >&2
    exit 1
  fi
else
  unset "CONFIG_ATTACHMENT"
fi

if [[ ! "$CONFIG_CALLBACK_URL" =~ ^[[:blank:]]*$ ]]; then
  (( ${#CONFIG_CALLBACK_URL} > 512 )) && {
    printf "%s: %s\\n" "${0##*/}" "callback URL (-c) is too long (maximum 512 characters)" >&2
    exit 1
  }
else
  unset "CONFIG_CALLBACK_URL"
fi

if [[ ! "$CONFIG_DEVICES" =~ ^[[:blank:]]*$ ]]; then
  while read -r -d , DEV; do
    [[ -z "$DEV" ]] && continue
    if (( "${#DEV}" > 25 )); then
      printf "%s: %s\\n" "${0##*/}" "device IDs (-d) are 25 characters or less in length" >&2
      exit 1
    elif [[ ! "$DEV" =~ ^[[:alnum:]_-]*$ ]]; then
      printf "%s: %s\\n" "${0##*/}" "device IDs (-d) can only be letters, numbers, _ and -" >&2
      exit 1
    else
      if [[ -z "$LIST" ]]; then
        LIST="$DEV"
      else
        LIST+=",$DEV"
      fi
    fi
  done <<<"$CONFIG_DEVICES,"		# The , on the end is required.
  CONFIG_DEVICES="$LIST"
else
  unset "CONFIG_DEVICES"
fi

if [[ ! "$CONFIG_EXPIRY" =~ ^[[:blank:]]*$ ]]; then
  if [[ ! "$CONFIG_EXPIRY" =~ [[:digit:]] ]]; then
    printf "%s: %s\\n" "${0##*/}" "expiry time (-e) must be a number" >&2
    exit 1
  elif (( CONFIG_EXPIRY < 30 )); then
    printf "%s: %s\\n" "${0##*/}" "expiry time (-e) cannot be that short (30s minimum)" >&2
    exit 1
  elif (( CONFIG_EXPIRY > 10800 )); then
    printf "%s: %s\\n" "${0##*/}" "expiry time (-e) cannot be that long (10800s/3h maximum)" >&2
    exit 1
  elif [[ -n "$CONFIG_RETRY" ]] && (( CONFIG_EXPIRY < CONFIG_RETRY )); then
    printf "%s: %s\\n" "${0##*/}" "expiry time (-e) is less than retry time" >&2
    exit 1
  fi
else
  unset "CONFIG_EXPIRY"
fi

if [[ "$CONFIG_MONOSPACE" =~ ^[[:blank:]]*$ ]] || [[ "$CONFIG_MONOSPACE" =~ ^(false|0)$ ]]; then
  CONFIG_MONOSPACE=0
elif [[ "$CONFIG_MONOSPACE" =~ ^(true|1)$ ]]; then
  CONFIG_MONOSPACE=1
else
  printf "%s: %s\\n" "${0##*/}" "monospace (--monospace) setting must be 'true', '1', 'false' or '0'" >&2
  exit 1
fi

if [[ ! "$CONFIG_MESSAGE" =~ ^[[:blank:]]*$ ]] && [[ ! "$CONFIG_HTML_MESSAGE" =~ ^[[:blank:]]*$ ]]; then
  printf "%s: %s\\n" "${0##*/}" "cannot mix a plain text (-m) and HTML (-M) message setting" >&2
  exit 1
elif [[ "$CONFIG_MESSAGE" =~ ^[[:blank:]]*$ ]] && [[ "$CONFIG_HTML_MESSAGE" =~ ^[[:blank:]]*$ ]]; then
  printf "%s: %s\\n" "${0##*/}" "must set either a plain text (-m) or HTML (-M) message" >&2
  exit 1
elif [[ ! "$CONFIG_HTML_MESSAGE" =~ ^[[:blank:]]*$ ]] && (( CONFIG_MONOSPACE == 1 )); then
  printf "%s: %s\\n" "${0##*/}" "HTML messages (-M) cannot be used with a monospace font (--monospace)" >&2
  exit 1
elif (( ${#CONFIG_MESSAGE} > 1024 )) || (( ${#CONFIG_HTML_MESSAGE} > 1024 )); then
  printf "%s: %s\\n" "${0##*/}" "message (-m/-M) length is too long (maximum 1024 characters)" >&2
  exit 1
fi

if [[ ! "$CONFIG_PRIORITY" =~ ^[[:blank:]]*$ ]]; then
  if [[ ! "$CONFIG_PRIORITY" =~ [[:digit:]] ]]; then
    printf "%s: %s\\n" "${0##*/}" "priority (-p) setting must be a number" >&2
    exit 1
  elif (( CONFIG_PRIORITY < -2 )) || (( CONFIG_PRIORITY > 2 )); then
    printf "%s: %s\\n" "${0##*/}" "priority (-p) setting must be in the range -2 - 2" >&2
    exit 1
  fi
else
  unset "CONFIG_PRIORITY"
fi

if [[ "$CONFIG_QUIET" =~ ^[[:blank:]]*$ ]] || [[ "$CONFIG_QUIET" =~ ^(false|0)$ ]]; then
  CONFIG_QUIET=0
elif [[ "$CONFIG_QUIET" =~ ^(true|1)$ ]]; then
  CONFIG_QUIET=1
else
  printf "%s: %s\\n" "${0##*/}" "quiet (-q) setting must be 'true', '1', 'false' or '0'" >&2
  exit 1
fi

if [[ ! "$CONFIG_RETRY" =~ ^[[:blank:]]*$ ]]; then
  if [[ ! "$CONFIG_RETRY" =~ [[:digit:]] ]]; then
    printf "%s: %s\\n" "${0##*/}" "retry time (-r) must be a number" >&2
    exit 1
  elif (( CONFIG_RETRY < 30 )); then
    printf "%s: %s\\n" "${0##*/}" "retry time (-r) cannot be that short (30s minimum)" >&2
    exit 1
  elif [[ -n "$CONFIG_EXPIRY" ]] && (( CONFIG_RETRY > CONFIG_EXPIRY )); then
    printf "%s: %s\\n" "${0##*/}" "retry time (-r) exceeds expiry time" >&2
    exit 1
  fi
else
  unset "CONFIG_RETRY"
fi

if [[ ! "$CONFIG_SUBJECT" =~ ^[[:blank:]]*$ ]]; then
  (( ${#CONFIG_SUBJECT} > 250 )) && {
    printf "%s: %s\\n" "${0##*/}" "subject/title (-s) is too long (maximum 250 characters)" >&2
    exit 1
  }
else
  unset "CONFIG_SUBJECT"
fi

if [[ ! "$CONFIG_TOKEN" =~ ^[[:blank:]]*$ ]]; then
  if (( "${#CONFIG_TOKEN}" != 30 )); then
    printf "%s: %s\\n" "${0##*/}" "token key (-t) must be 30 characters in length" >&2
    exit 1
  elif [[ ! "$CONFIG_TOKEN" =~ ^[[:alnum:]]*$ ]]; then
    printf "%s: %s\\n" "${0##*/}" "token key (-t) can only be letters and numbers" >&2
    exit 1
  fi
else
  printf "%s: %s\\n" "${0##*/}" "token key (-t) cannot be an empty value" >&2
  exit 1
fi

if [[ ! "$CONFIG_SOUND" =~ ^[[:blank:]]*$ ]]; then
  [[ ! "$CONFIG_SOUND" =~ ^(none|vibrate|pushover|bike|bugle|cashregister|classical|cosmic|falling|gamelan|incoming|intermission|magic|mechanical|pianobar|siren|spacealarm|tugboat|alien|climb|persistent|echo|updown)$ ]] && {
    JSON="$(curl -s "$CONFIG_SOUNDS_API_URL?token=$CONFIG_TOKEN" 2>/dev/null)"
    if [[ "$JSON" =~ \"status\":1, ]]; then
      [[ ! "$JSON" =~ \"$CONFIG_SOUND\": ]] && {
        printf "%s: %s\\n" "${0##*/}" "sound (-S) must be a built-in or user uploaded custom sound" >&2
        exit 1
      }
    else
      printf "%s: %s\\n" "${0##*/}" "failed to get list of custom sounds from API (invalid API token?)" >&2
      exit 1
    fi
  }
else
  unset "CONFIG_SOUND"
fi

if [[ ! "$CONFIG_TTL" =~ ^[[:blank:]]*$ ]]; then
  if [[ ! "$CONFIG_TTL" =~ [[:digit:]] ]]; then
    printf "%s: %s\\n" "${0##*/}" "TTL (-T) must be a number" >&2
    exit 1
  elif (( CONFIG_TTL < 0 )); then
    printf "%s: %s\\n" "${0##*/}" "TTL (-T) must be a positive number of seconds" >&2
    exit 1
  fi
else
  unset "CONFIG_TTL"
fi

if [[ ! "$CONFIG_TIMESTAMP" =~ ^[[:blank:]]*$ ]]; then
  if [[ ! "$CONFIG_TIMESTAMP" =~ [[:digit:]] ]]; then
    printf "%s: %s\\n" "${0##*/}" "timestamp (--timestamp) must be a number" >&2
    exit 1
  elif (( CONFIG_TIMESTAMP < 0 )); then
    printf "%s: %s\\n" "${0##*/}" "timestamp (--timestamp) must be a positive number of seconds" >&2
    exit 1
  fi
else
  unset "CONFIG_TIMESTAMP"
fi

if [[ ! "$CONFIG_USER_KEYS" =~ ^[[:blank:]]*$ ]]; then
  unset COUNT LIST
  while read -r -d , KEY; do
    [[ -z "$KEY" ]] && continue
    if (( "${#KEY}" != 30 )); then
      printf "%s: %s\\n" "${0##*/}" "user keys (-u) must be 30 characters in length" >&2
      exit 1
    elif [[ ! "$KEY" =~ ^[[:alnum:]]*$ ]]; then
      printf "%s: %s\\n" "${0##*/}" "user keys (-u) can only be letters and numbers" >&2
      exit 1
    else
      if [[ -z "$LIST" ]]; then
        LIST="$KEY"
        COUNT=1
      else
        LIST+=",$KEY"
        (( COUNT++ ))
      fi
    fi
  done <<<"$CONFIG_USER_KEYS,"		# The , on the end is required.
  (( COUNT > 50 )) && {
    printf "%s: %s\\n" "${0##*/}" "too many user keys (-u) (maximum 50)" >&2
    exit 1
  }
  CONFIG_USER_KEYS="$LIST"
else
  printf "%s: %s\\n" "${0##*/}" "user keys (-u) cannot be an empty value" >&2
  exit 1
fi

if [[ ! "$CONFIG_URL" =~ ^[[:blank:]]*$ ]]; then
  (( ${#CONFIG_URL} > 512 )) && {
    printf "%s: %s\\n" "${0##*/}" "URL (-U) is too long (maximum 512 characters)" >&2
    exit 1
  }
else
  unset "CONFIG_URL"
fi

if [[ ! "$CONFIG_URL_TITLE" =~ ^[[:blank:]]*$ ]]; then
  (( ${#CONFIG_URL_TITLE} > 100 )) && {
    printf "%s: %s\\n" "${0##*/}" "URL title (--url-title) is too long (maximum 100 characters)" >&2
    exit 1
  }
else
  unset "CONFIG_URL_TITLE"
fi

# Build the curl command line.
COMMAND_LINE=('-s')
# Required API elements.
COMMAND_LINE+=('--form-string' user="$CONFIG_USER_KEYS")
COMMAND_LINE+=('--form-string' token="$CONFIG_TOKEN")
if [[ -v CONFIG_MESSAGE ]]; then
  COMMAND_LINE+=('--form-string' message="$CONFIG_MESSAGE")
  (( CONFIG_MONOSPACE == 1 )) && COMMAND_LINE+=('--form-string' 'monospace=1')
else
  COMMAND_LINE+=('--form-string' message="$CONFIG_HTML_MESSAGE")
  COMMAND_LINE+=('--form-string' 'html=1')
fi
# Optional API elements.
[[ -v CONFIG_ATTACHMENT ]] && COMMAND_LINE+=('--form' attachment="@$CONFIG_ATTACHMENT")
[[ -v CONFIG_DEVICES ]] && COMMAND_LINE+=('--form-string' device="$CONFIG_DEVICES")
[[ -v CONFIG_PRIORITY ]] && {
  COMMAND_LINE+=('--form-string' priority="$CONFIG_PRIORITY")
  (( CONFIG_PRIORITY == 2 )) && {
    [[ -v CONFIG_CALLBACK_URL ]] && COMMAND_LINE+=('--form-string' callback="$CONFIG_CALLBACK_URL")
    COMMAND_LINE+=('--form-string' expire="${CONFIG_EXPIRY:-$DEFAULT_EXPIRY}")
    COMMAND_LINE+=('--form-string' retry="${CONFIG_RETRY:-$DEFAULT_RETRY}")
  }
}
[[ -v CONFIG_SUBJECT ]] && COMMAND_LINE+=('--form-string' title="$CONFIG_SUBJECT")
[[ -v CONFIG_SOUND ]] && COMMAND_LINE+=('--form-string' sound="$CONFIG_SOUND")
[[ -v CONFIG_TTL ]] && COMMAND_LINE+=('--form-string' ttl="$CONFIG_TTL")
[[ -v CONFIG_TIMESTAMP ]] && COMMAND_LINE+=('--form-string' timestamp="$CONFIG_TIMESTAMP")
[[ -v CONFIG_URL ]] && COMMAND_LINE+=('--form-string' url="$CONFIG_URL")
[[ -v CONFIG_URL_TITLE ]] && COMMAND_LINE+=('--form-string' url_title="$CONFIG_URL_TITLE")

# Make the call to the messaging API.
JSON="$(curl "${COMMAND_LINE[@]}" "$CONFIG_API_URL" 2>/dev/null)" || {
  printf "%s: %s\\n" "${0##*/}" "API call failed" >&2
  exit 3
}
if [[ "$JSON" =~ \"status\":1, ]]; then
  (( CONFIG_QUIET == 0 )) && printf "%s\\n" "$JSON"
else
  printf "%s: %s\\n" "${0##*/}" "API returned a non-success status code" >&2
  (( CONFIG_QUIET == 0 )) && printf "%s\\n" "$JSON" >&2
  exit 2
fi

# 0 = Request submitted OK.
# 1 = Usage error.
# 2 = Request status error from API
# 3 = Error accessing API
exit 0