# Separate Command Histories for Restored Terminal Sessions

# Terminal assigns each terminal session a unique identifier and
# communicates it via the TERM_SESSION_ID environment variable so that
# programs running in a terminal can save/restore application-specific
# state when quitting and restarting Terminal with Resume enabled.

# The following script saves and restores the bash command history
# independently for each restored terminal session. It also merges
# commands into the global history for new sessions. Because of this
# it is recommended that you set HISTSIZE and HISTFILESIZE to larger
# values (their default value is 500). Old sessions are periodically
# deleted.

if [ -z "$BASH_SESSION" ] && [ -n "$TERM_SESSION_ID" ]; then

    # Only perform this setup once per shell session (which shouldn't
    # happen unless the user's ~/.bash_profile executes /etc/profile,
    # which is normally redundant).
    BASH_SESSION=1

    # Set up the session directory/file.
    if [ -z "$BASH_SESSION_DIR" ]; then
	BASH_SESSION_DIR="$HOME/.bash_sessions"
	BASH_SESSION_FILE="$BASH_SESSION_DIR/$TERM_SESSION_ID.session"
    elif [ -z "$BASH_SESSION_FILE" ]; then
	BASH_SESSION_FILE="$BASH_SESSION_DIR/$TERM_SESSION_ID.session"
    fi
    mkdir -p "$BASH_SESSION_DIR"

    # Arrange for session-specific shell command history. Users can
    # disable this via the existence of the following file.
    [ -f ~/.bash_session_no_history ] && BASH_SESSION_HISTORY=0 || BASH_SESSION_HISTORY=1
    if [ $BASH_SESSION_HISTORY -eq 1 ]; then
	BASH_SHARED_HISTFILE="$HISTFILE"
	BASH_SESSION_HISTFILE="$BASH_SESSION_DIR/$TERM_SESSION_ID.history"
	BASH_SESSION_HISTFILE_NEW="$BASH_SESSION_DIR/$TERM_SESSION_ID.historynew"
	# If the session history doesn't exist, copy the shared history
	if [ -f "$BASH_SHARED_HISTFILE" ] && [ ! -f "$BASH_SESSION_HISTFILE" ]; then
	    cp "$BASH_SHARED_HISTFILE" "$BASH_SESSION_HISTFILE"
	else
	    # Ensure the file exists and doesn't get expired.
	    touch "$BASH_SESSION_HISTFILE"
	fi
	history -r "$BASH_SESSION_HISTFILE"
	: >| "$BASH_SESSION_HISTFILE_NEW"
	HISTFILE="$BASH_SESSION_HISTFILE_NEW"
    fi

    if [ "$SHLVL" -eq 1 ]; then
	# Restore previous session state.
	if [ -f "$BASH_SESSION_FILE" ]; then
	    . "$BASH_SESSION_FILE"
	    rm "$BASH_SESSION_FILE"
	fi

	# Save the current state.
	bash_save_session_state() {
	    if [ "$SHLVL" -eq 1 ] && [ -n "$BASH_SESSION_FILE" ]; then
		echo -n Saving session...
		echo echo Restored session: $(date) > "$BASH_SESSION_FILE"

		# Users can add custom state by defining the following
		# function. e.g., to save an environment variable:
		#   bash_session_save_state() { echo MY_VAR="'$MY_VAR'" >> "$BASH_SESSION_FILE"; }
		declare -F bash_session_save_state >/dev/null && bash_session_save_state

		# Save new history commands.
		if [ $BASH_SESSION_HISTORY -eq 1 ]; then
		    history -a
		    cat "$BASH_SESSION_HISTFILE_NEW" >> "$BASH_SHARED_HISTFILE"
		    cat "$BASH_SESSION_HISTFILE_NEW" >> "$BASH_SESSION_HISTFILE"
		    # Empty this session's history file to keep track of
		    # which commands have already been copied.
		    : >| "$BASH_SESSION_HISTFILE_NEW"
		    # Read/write the files via the history command so they
		    # are truncated as appropriate.
		    history -r "$BASH_SHARED_HISTFILE"
		    history -w "$BASH_SHARED_HISTFILE"
		    history -r "$BASH_SESSION_HISTFILE"
		    history -w "$BASH_SESSION_HISTFILE"
		fi

		echo completed.
	    fi
	}

	# Delete old session files. Do not do this more frequently
	# than once a day.
	BASH_SESSION_TIMESTAMP_FILE="$BASH_SESSION_DIR/_expiration_check_timestamp"
	bash_delete_expired_session_state() {
	    if ([ ! -f "$BASH_SESSION_TIMESTAMP_FILE" ] || [ -z $(find "$BASH_SESSION_TIMESTAMP_FILE" -mtime -1d) ]); then
		local bash_session_lock_file="$BASH_SESSION_DIR/_expiration_lockfile"
		if shlock -f "$bash_session_lock_file" -p $$; then
		    echo -n Deleting expired sessions...
		    local delete_count=$(find "$BASH_SESSION_DIR" -type f -mtime +2w -print -delete | wc -l)
		    [ "$delete_count" -gt 0 ] && echo $delete_count completed. || echo none found.
		    touch "$BASH_SESSION_TIMESTAMP_FILE"
		    rm "$bash_session_lock_file"
		fi
	    fi
	}

	# Update saved session state when exiting.
	bash_update_session_state() {
	    bash_save_session_state && bash_delete_expired_session_state
	}
	trap bash_update_session_state EXIT
    fi
fi