#!/bin/bash

# this is just a library
# you will need to provide the following in the implementation:
# 1. the api url with it's corresponding token as
#    api_url="api.telegram.org/bot[insert your api token]/"
#    pay attention to the trailing forward slash
# 2. the bot id as
#    bot_id="[insert your bot_id]"
# 3. the following files to read and write from
#    updates.txt
#    sentmessages.txt
#    callbacks.txt
#    pay attention to the trailing forward slash
# 4. (optional) a directory for the bot's files as
#    bot_tmpdir="/some/path/"
#    pay attention to the trailing forward slash
# IMPORTANT: this library is not asynchronous, only one message
#            is read at a time and is done so in order
# IMPORTANT: this library uses the getUpdates method with
#            tcp_keepalive,NOT webhooks

calc_offset() {
  local current="$(bc -l <<< "$(tail -n 1 "${bot_tmpdir}updates.txt" | \
                   grep -om1 "\"update_id\":[0-9]\+" | \
                   grep -om1 "[0-9]\+") + 1" 2>/dev/null)"
  [ ! -z "${current}" ] && printf "%d" "${current}"
}

getupd() {
  local offset="$(calc_offset)"
  local update="$(curl -sX GET --keepalive-time 300 "${api_url}getUpdates" -d "offset=${offset}" \
   -d "limit=1" -d "timeout=300"\
   | sed 's/{"ok":true,"result":\[\]}\|^{"ok":false.*\|^{"ok":true,"result":\[{\?//g;:a;N;$!ba;s/\n//g;s/}\]}$//g;')"
  printf "%s" ${update}
  [ ! -z "${update}" ] && printf "%s\n" "${update}" >> "${bot_tmpdir}updates.txt"
}

getmsg_id() {
  tail -n1 "${bot_tmpdir}${1}" | grep -om1\
  "\"message\":{\"message_id\":[0-9]\+" | grep -om1 "[0-9]\+"
}

getusr_id() {
  tail -n1 "${bot_tmpdir}${1}" | grep -om1\
   "\"from\":{\"id\":[0-9]\+" | grep -om1 "[0-9]\+"
}

getchat_id() {
  tail -n1 "${bot_tmpdir}${1}" | grep -om1\
   "\"chat\":{\"id\":-\?[0-9]\+" | grep -om1 "\-\?[0-9]\+"
}

utf-16-surrogate-pair-decode() {
  # shamelessly stolen from stackoverflow
  local out="$1"
  local remain=""
  local regexp='(.*)\\u[dD]([0-9a-fA-F]{3})\\u[dD]([0-9a-fA-F]{3})(.*)'
  while [[ "${out}" =~ $regexp ]] ; do
   # match 2 \udxxx hex values, calculate new U, then split and replace
   local W1="$(( ( 0xd${BASH_REMATCH[2]} & 0x3ff) <<10 ))"
   local W2="$(( 0xd${BASH_REMATCH[3]} & 0x3ff ))"
   U="$(( ( W1 | W2 ) + 0x10000 ))"
   remain="$(printf '\\U%8.8x' "${U}")${BASH_REMATCH[4]}${remain}"
   out="${BASH_REMATCH[1]}"
  done
  echo -e "${out}${remain}"
}

gettext() {
  local text="$(tail -n 1 "${bot_tmpdir}${1}" | grep -om1\
   '\("text"\|"caption"\):"\(\\"\|[^"]*\)*"\(,\|}\)' | tail -n1)"
  grep "^\"text\"" <<< "${text}" >/dev/null && utf-16-surrogate-pair-decode "${text:8:-2}"\
  || {
    grep "^\"caption\"" <<< "${text}" >/dev/null && utf-16-surrogate-pair-decode "${text:11:-2}"
  }
}

getusr_name(){
  local user_name="$(tail -n 1 "${bot_tmpdir}${1}" | grep -om1\
   '"first_name":"\(\\"\|[^"]*\)*",\("username"\|"language_code"\)' | head -n1)"
  grep "\"username\"$" <<< "${user_name}" >/dev/null && utf-16-surrogate-pair-decode "${user_name:14:-12}"\
  || {
    grep "\"language_code\"$" <<< "${user_name}" >/dev/null && utf-16-surrogate-pair-decode "${user_name:14:-17}"
  }
}

getusrname(){
  local username="$(tail -n 1 "${bot_tmpdir}${1}" | grep -om1\
   '"username":"\(\\"\|[^"]*\)*","language_code"' | head -n1)"
  utf-16-surrogate-pair-decode "${username:12:-17}"
}

getchat_title(){
  local chat_title="$(tail -n 1 "${bot_tmpdir}${1}" | grep -om1\
   '"title":"\(\\"\|[^"]*\)*","type":"group"' | head -n1)"
  [ ! -z "${chat_title}" ] && utf-16-surrogate-pair-decode "${chat_title:9:-16}"\
  || getusr_name
}

get_cbks() {
  local callbacks="$(tail -n 1 "${bot_tmpdir}${1}"\
   | grep "\"callback_query\"" | grep "\"callback_data\":\"recheck\"")"
   [ ! -z "${callbacks}" ] && is_callback=0 && printf "%s\n" "${callbacks}"\
   >> "${bot_tmpdir}callbacks.txt"
}

sendmsg() {
  sentmsg="$(curl -sX GET "${api_url}sendMessage" -d "chat_id=${1}" \
   -d "text=${2}" \
   -d 'reply_markup={"inline_keyboard":[[{"text":"check again","callback_data":"recheck"}]]}')" \
   && [ ! -z "${sentmsg}" ] && printf "%s\n" "${sentmsg}"\
   | sed 's/^{"ok":false.*\|^{"ok":true,"result":{\|}$//g'\
   >> "${bot_tmpdir}sentmsgs.txt"
}

replymsg() {
  sentmsg="$(curl -sX GET "${api_url}sendMessage" -d "chat_id=${curmsg[chat_id]}" -d "reply_to_message_id=${curmsg[message_id]}" \
   -d "text=${curmsg[text]}" \
   && [ ! -z "${sentmsg}" ] && printf "%s\n" "${sentmsg}"\
   | sed 's/^{"ok":false.*\|^{"ok":true,"result":{\|}$//g'\
   >> "${bot_tmpdir}sentmsgs.txt"
}

# TODO
#editmsg() {
#  curl -sX GET "${api_url}editMessageText" -d "chat_id=${1}" -d "message_id=${2}" \
#   -d "text=${3}"
#}
#
#delmsg() {
#  curl -sX GET "${api_url}deleteMessage" -d "chat_id=${1}"\
#  -d "message_id=${2}"
#}

getmsg_content(){
  local -n _REF="${1}"
  _REF[user_id]="$(getusr_id "${2}")"
  _REF[user_name]="$(getusr_name "${2}")"
  _REF[username]="$(getusrname "${2}")"
  _REF[chat_id]="$(getchat_id "${2}")"
  _REF[chat_title]="$(getchat_title "${2}")"
  _REF[msg_id]="$(getmsg_id "${2}")"
  _REF[text]="$(gettext "${2}")"
}