Extend tm script to allow session file loading

With the `tm script.conf session-name` format, or `tm script.conf`
format, it now allows setting up pre-defined session setups to be loaded
by tmux.

.local/bin/tm

@@ -2,42 +2,120 @@
 #
 # Attach to a tmux session, or create it if it doesnt exist
 
-if [ -e $XDG_CONFIG_HOME/tmux/tmux.conf ]; then
-	start="tmux -f $XDG_CONFIG_HOME/tmux/tmux.conf"
-else
-	start=tmux
+if [ "$1" = '-h' ] || [ "$1" = '--help' ]; then
+cat <<-EOF
+  Usage: $0 [FILE] [NAME]
+  Attach to an existing tmux session, or bootstrap a new session.
+
+  If no session exists which fits the criteria, this will create a new one and
+  load it up obeying the commands contained in the FILE argument passed in. It
+  must contain commands which are tmux-command compatible since they will be
+  passed to tmux unmodified.
+
+  It will load the default tmux.conf in the following order:
+    - XDG_CONFIG_HOME/tmux/tmux.conf (usually ~/.config/tmux/tmux.conf)
+    - ~/.tmux.conf
+    - /etc/tmux.conf
+  Afterwards, it will apply the contents of the FILE argument passed into the command.
+
+  If no FILE argument is passed it will create an empty session, or attach itself to
+  the session specified.
+
+  If no NAME argument is passed it will automatically create a session name from the
+  FILE argument passed.
+EOF
+  exit 0
 fi
 
-path_name="$(basename "$PWD" | tr . -)"
-curr_dir=${1-$path_name}
-session_name=${1:-$curr_dir}
+# Make tmux obey the XDG specification on startup
+if [ -e "$XDG_CONFIG_HOME/tmux/tmux.conf" ]; then
+  start="tmux -f $XDG_CONFIG_HOME/tmux/tmux.conf"
+else
+  start=tmux
+fi
+
+_file_exists() {
+  if [ -f "$1" ]; then
+    true
+  else
+    false
+  fi
+}
 
 _not_in_tmux() {
   [ -z "$TMUX" ]
 }
 
 _session_exists() {
-  $start has-session -t "$session_name"
-}
-
-_create_detached_session() {
-  (TMUX='' $start new-session -Ad -s "$session_name")
-}
-
-_get_session_name() {
-  #${1:-$session_name}
-  return "blubb"
-}
-
-_attach_or_create() {
-  if _not_in_tmux; then
-    $start new-session -As "$session_name"
+  if tmux has-session -t "$session_name" > /dev/null 2>&1; then
+    true
   else
-    if ! _session_exists; then
-      _create_detached_session
-    fi
-    $start switch-client -t "$session_name"
+    false
   fi
 }
 
+_create_detached_session() {
+  ($start new-session -d -s "$session_name")
+}
+
+_load_session_file() {
+  xargs -L1 tmux < "$session_file"
+}
+
+_set_session_vars() {
+  if [ "$#" -eq 2 ]; then
+    session_file=${1}
+    if ! _file_exists "$session_file"; then
+      echo "$0: can not source configuration file: '${session_file}' does not exist."
+      exit 1
+    fi
+    session_name=${2}
+  elif [ "$#" -eq 1 ]; then
+    if _file_exists "${1}"; then
+      session_file=${1}
+    else
+      session_name=${1}
+    fi
+  fi
+
+  # set default session name if none was passed
+  if [ -z "$session_name" ]; then
+      # only if we have a filename should we append it to the session name
+      if [ -n "$session_file" ]; then
+        fname=/$(basename "$session_file" .conf)
+      fi
+      # default to parent directory name / config file name for the session
+      session_name=$(basename "$PWD" | sed 's/[^a-zA-Z0-9\-]//g' | tr . -)"$fname"
+  fi
+}
+
+_attach_or_create() {
+  # first create a new session if one doesn't exist
+  if ! _session_exists; then
+    _create_detached_session
+    _load_session_file
+  fi
+
+  # then attach or switch to the session
+  if _not_in_tmux; then
+    $start attach -t "$session_name"
+  else
+    $start switch-client -t "$session_name"
+  fi
+
+  _unset_functions
+}
+
+_unset_functions() {
+  unset _set_session_vars
+  unset _attach_or_create
+  unset _load_session_file
+  unset _create_detached_session
+  unset _session_exists
+  unset _not_in_tmux
+  unset _file_exists
+}
+
+_set_session_vars "$@"
 _attach_or_create
+exit 0