tsctl

#!/usr/bin/env bash
#  terminalsession
#  Copyright (C) 2022 Danilo Queiroz
#
#  This program is free software: you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation, either version 3 of the License, or
#  (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program.  If not, see <http://www.gnu.org/licenses/>.

###
# Global constants
###
readonly TS_ESCAPE_KEY="^A"
readonly TS_SOCK_DIR=${XDG_RUNTIME_DIR:-"/tmp"}/terminalsession
readonly txt_bold=$(tput bold)
readonly txt_normal=$(tput sgr0)
readonly VERSION=1.0

###
# Session management functions
###
function list_sessions() {
  find ${TS_SOCK_DIR} -type s -exec basename {} \; 2>/dev/null
}

function attach_session() {
  local session_name=${1:?"Error: missing session_name"}
  TERMINALSESSION=$session_name dtach -A ${TS_SOCK_DIR}/${session_name} -e ${TS_ESCAPE_KEY} -z ${SHELL}
}

function kill_session() {
  local session_name=${1:?"Error: missing session_name"}
  pkill -u $USER -f "dtach -A ${TS_SOCK_DIR}/${session_name}"
}

###
# UX functions
###
function show_menu() {
  list_sessions | fzf \
      --bind="enter:replace-query+execute($0 attach {q})+clear-query+clear-screen+reload($0 list)" \
      --bind="ctrl-k:execute($0 kill {})+clear-query+clear-screen+reload($0 list)" \
      --bind="ctrl-r:clear-query+clear-screen+reload($0 list)" \
      --bind="ctrl-h:preview($0 __help)" \
      --bind="esc:close" \
      --keep-right \
      --preview-window="down,99%" \
      --layout=reverse \
      --cycle \
      --no-multi \
      --info=hidden \
      --header-first \
      --header "Press ${txt_bold}C-h${txt_normal} for help, ${txt_bold}C-c${txt_normal} to quit." \
      --prompt "terminalsession> "
}

function show_interactive_help() {
  cat << EOF
${txt_bold}Interactive mode help:${txt_normal}

- Select an existing session and press ${txt_bold}enter${txt_normal} to attach to it.
- To create and attach to a new session, just type the name of the session and
  then press ${txt_bold}enter${txt_normal}.
- To kill an existing session, select the session and press ${txt_bold}C-k${txt_normal} to kill it -
  it will send a ${txt_bold}SIGTERM${txt_normal} to the dtach process.
- To reload the sessions list, press ${txt_bold}C-r${txt_normal}.
- To detach from a session and return to the interactive mode, press ${txt_bold}C-a${txt_normal}.
- Use ${txt_bold}ESC${txt_normal} to close this help.

EOF
}

function show_version() {
  printf "terminalsession version ${VERSION}.\n"
}

function show_help() {
  cat << EOF
terminalsession is a simple terminal session manager built on top of
detach and fzf. You can create new sessions, list existing sessions,
attach to a session or kill a session. And that's all!

A session is simply a detachable '\$SHELL'.
Once attached to a session you can use 'CTRL+A' to detach from the
session. In each session, a environment variable '\$TERMINALSESSION'
is set with the name of the current session.

Usage:
  tsctl <operation> <params>

Operations:
  list                    lists current sessions
  attach <session_name>   attaches to an existing session or
                          creates a new one
  kill <session_name>     kills an existing session
  version                 shows version info
  help                    shows help info

If no operation is given, it enters interactive mode.
EOF
}

###
# App entry point
###
function check_is_terminalsession() {
  if [ ! -z ${TERMINALSESSION} ]; then
    echo "Trying to launch tsclt from within a terminalsession isn't supported."
    exit 1
  fi
}

function main() {
  # ensure sock dir
  if [ ! -d ${TS_SOCK_DIR} ]; then
      mkdir -p ${TS_SOCK_DIR}
  fi

  local op=$1
  shift
  case $op in
    list)
      list_sessions
      ;;
    attach)
      check_is_terminalsession
      attach_session $*
      ;;
    kill)
      check_is_terminalsession
      kill_session $*
      ;;
    version | -v | --version)
      show_version
      ;;
    help | -h | --help)
      show_help
      ;;
    __help)
      show_interactive_help
      ;;
    *)
      check_is_terminalsession
      show_menu
      ;;
  esac
}

main $*