#!/usr/bin/env bash
# shellcheck disable=SC2155
set -e

#
# Script to track waiting customer count and estimated travel time
# of a Telekom appointment.
#
# Usage:
#   ./telekom_appointment_tracker.sh <uuid>
#
# Arguments:
#   uuid    6-digit UUID sent by Telekom via https://termin.telekom.de/?<uuid>
#

readonly uuid="$1"
readonly wait_interval=60
readonly ajax_url="https://termin.telekom.de/ajax.php"
readonly web_url="https://termin.telekom.de/?${uuid}"
readonly title="Telekom appointment #${uuid}"

state_changed=false
customers_count=0
travel_time=0

RED="\033[0;31m"
GREEN="\033[0;32m"
NC="\033[0m"

#
# Generate request payload for Telekom AJAX endpoint.
#
function generate_payload() {
  echo "{\"uuid\":\"${uuid}\",\"humanInteraction\":true}" | base64
}

#
# Perform request to AJAX endpoint and parse result using jq with given query.
#
function perform_and_parse_request() {
  local query="$1"

  curl -X POST -sSL -d "$(generate_payload)" "${ajax_url}" | base64 -d | jq -r "$query"
}

#
# Count waiting customers in queue.
#
function count_customers() {
  perform_and_parse_request '.kundenauftrag.auftragszaehler // empty'
}

#
# Fetch technician's estimated travel time.
#
function get_travel_time() {
  perform_and_parse_request '.kundenauftrag.traveltime // empty'
}

#
# Check if appointment is in waiting state.
#
function is_in_waiting_state() {
  local result="$(perform_and_parse_request 'if (.kundenauftrag | has("wartegrund")) then 0 else 1 end')"

  if [ -z "$result" ]; then
    return 1
  fi

  return "$result"
}

#
# Display number of waiting customers in queue.
#
# Prints a message to the console displaying the number of waiting customers
# in queue. In addition, a notification is raised to raise attention.
#
function display_customer_count() {
  if [ "$customers_count" -le 0 ]; then
    local message="A technician is on its way."
  elif [ "$customers_count" -eq 1 ]; then
    local message="One customer left."
  else
    local message="${customers_count} customers left."
  fi

  if "$state_changed"; then
    echo -e "${GREEN}State changed:${NC} ${message}"
    osascript -e "display notification \"${message}\" with title \"${title}\" subtitle \"State changed\""
  else
    echo "$message"
    osascript -e "display notification \"${message}\" with title \"${title}\""
  fi
}

#
# Display technician's travel time.
#
# Prints a message to the console displaying the technician's estimated
# travel time. In addition, a notification is raised to raise attention.
#
function display_travel_time() {
  if [ "$travel_time" -le 0 ]; then
    local message="A technician should have arrived."
  elif [ "$travel_time" -eq 1 ]; then
    local message="A technician should arrive in less than one minute."
  else
    local message="A technician should arrive in less than ${travel_time} minutes."
  fi

  if "$state_changed"; then
    echo -e "${GREEN}State changed:${NC} ${message}"
    osascript -e "display notification \"${message}\" with title \"${title}\" subtitle \"State changed\""
  else
    echo "$message"
    osascript -e "display notification \"${message}\" with title \"${title}\""
  fi

  if [ "$travel_time" -le 0 ]; then
    exit
  fi
}

#
# Display error message.
#
function display_error() {
  local message="$1"

  echo >&2 -e "${RED}${message}${NC}"
}

# Validate jq binary
if ! which jq >/dev/null; then
  display_error "jq needs to be installed in your system."
  echo >&2 "Read more at https://jqlang.github.io/jq/download/."
  exit 1
fi

# Validate given UUID
if [ -z "$uuid" ]; then
  display_error "Please pass the 6-digit UUID you received from https://termin.telekom.de/?<uuid>."
  exit 1
fi

# Exit early if appointment is in waiting state
if is_in_waiting_state; then
  display_error "Appointment is currently in waiting state."
  echo >&2 "For more details, visit ${web_url}."
  exit
fi

# Show link to website
echo "Appointment website: ${web_url}"

# Check every x seconds for current customers count and/or technician's travel time
while true; do
  current_count="$(count_customers)"

  # If no customer count is provided, check if technician is already on its way
  if [ -z "$current_count" ]; then
    current_travel_time="$(get_travel_time)"
  fi

  # Show error if neither customer count nor travel time are accessible
  if [ -z "$current_count" ] && [ -z "$current_travel_time" ]; then
    display_error "Error while checking appointment details. Trying again in ${wait_interval} seconds..."
    sleep "$wait_interval"
    continue
  fi

  # Display notice if technician is on its way
  if [ "$current_travel_time" -ne "$travel_time" ]; then
    current_count=0
    customers_count=0
    travel_time="$current_travel_time"

    display_travel_time
  fi

  # Display notice about customers in queue
  if [ "${current_count:-0}" -ne "$customers_count" ]; then
    customers_count="$current_count"
    current_travel_time=0
    travel_time=0

    display_customer_count
  fi

  # Mark global state change
  state_changed=true

  # Exit if appointment is finished
  if [ "$customers_count" -le 0 ] && [ "$current_travel_time" -le 0 ]; then
    exit
  fi

  sleep "$wait_interval"
done