#!/bin/sh

## SPDX-FileCopyrightText: 2023 Benjamin Grande M. S. <ben.grande.b@gmail.com>
##
## SPDX-License-Identifier: AGPL-3.0-or-later

set -eu

command -v tmux >/dev/null || exit 1
: "${TMUX:=}"
session="${1:-}"

## Attach to session if it exists or not and from inside tmux or not.
## If name is supplied and doesn't exist, create session with given name.
## If no name is supplied and there is last session, switch client to it,
## else ask for the user to choose the wanted session.
## usage: ta SESSION ARGS
## example: ta dotfiles -d
new(){
  ## Session name was not specified.
  list="$(tmux list-sessions 2>/dev/null)"

  printf '%s\n' "Choose session or create one by providing a new name:"
  if test -n "${list}"; then
    printf '\n%s\n' "${list}"
  fi

  printf '\n%s' "Enter session name: "
  read -r name

  if test -z "${name}"; then
    printf '%s\n' "Name cannot be empty."
    return 1
  fi
}

main(){
  if test -n "${TMUX}"; then
    ## Inside tmux.
    if test "${session}" && tmux has-session -t "${session}" >/dev/null 2>&1
    then
      ## Session name was specified and it exists.
      tmux switch-client -t "${session}"
      tmux display-message "Switched to session ${session}"

    elif test -n "${session}"; then
      ## Session name was specified but it doesn't exist.
      tmux new-session -d -s "${session}"
      tmux switch-client -t "${session}"
      tmux display-message "Created and switched to session ${session}"

    else

      ## Session name was not specified.
      last="$(tmux display-message -p "#{client_last_session}")"
      if test -n "${last}" && tmux has-session -t "${last}"; then
        ## If tmux has a last session, use it.
        tmux switch-client -t "${last}"
        tmux display-message "Switched to session ${last}"

      else

        ## No last session, choose one or create one.
        printf '%s\n' "Last session not found."
        new

        if tmux has-session -t "${name}" 2>/dev/null; then
          ## Chosen session exists.
          tmux switch-client -t "${name}"
          tmux display-message "Switched to session ${name}"

        else
          ## Chosen session doesn't exist.
          tmux new-session -d -s "${name}"
          tmux switch-client -t "${name}"
          tmux display-message "Created and switched to session ${name}"
        fi
      fi
    fi
  else

    ## Outside of tmux.
    if test -n "${session}" && ! tmux list-sessions >/dev/null 2>&1; then
      ## Session name was specified but server is not running.
      tmux new-session -s "${session}"
      tmux display-message "Created session ${session}"
      return 0

    elif ! tmux list-sessions >/dev/null 2>&1; then
      ## Server is not running.
      new
      tmux new-session -s "${name}"
      tmux display-message "Created session ${name}"
      return 0
    fi

    if test "${session}" && tmux has-session -t "${session}" >/dev/null 2>&1
    then
      ## Session name was specified and it exists.
      tmux attach-session -t "${session}"
      tmux display-message "Attached to session ${session}"

    elif test -n "${session}"; then
      ## Session name was specified but it doesn't exist.
      tmux new-session -s "${session}"
      tmux display-message "Created new session ${session}"

    else
      ## Session name was not specified.
      last="$(tmux display-message -p "#{session_name}")"

      if test -n "${last}" && tmux has-session -t "${last}"; then
        ## If tmux has a session name, use it.
        tmux attach-session -t "${last}"
        tmux display-message "Attached to session ${last}"

      else
        new

        if tmux has-session -t "${name}" 2>/dev/null; then
          ## Chosen session exists.
          tmux attach-session -t "${name}"
          tmux display-message "Attached to session ${name}"

        else
          ## Chosen session doesn't exist.
          tmux new-session -s "${name}"
          tmux display-message "Created session ${name}"
        fi
      fi
    fi
  fi
}

main "${@}"