save_shell.erl

%% Copyright 2010 Erlang Solutions Ltd (ESL). All rights reserved.
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%% @doc
%% A collection of functions to manage saved shell histories
%% @end

-module(save_shell).


-export([shell/0,
         h/0,
         cmds/0,
         w/1,
         r/1]).

%% @spec () -> [Item]
%%    Item = {{result,N}, any()} | {{command,N}, [Expr]} | {evaluator,pid()}
%%
%% @doc 
%% Returns the shell history from the current shell process.
%% @end
%%
h() ->
    shell_req(shell(), get_cmd).

%% @spec () -> {Seq::integer(), Exprs::list()}
%% @doc
%% Returns the shell history as a list of {CmdNo, Command}, where 
%% Command is the pretty-printed command (sequence of expressions) entered
%% into the shell.
%% @end
%%
cmds() ->
    CmdEs = [{N,Es} || {{command,N},Es} <- h()],
    lists:keysort(1,[{N,lists:flatten(erl_pp:exprs(Es))} ||
                        {N,Es} <- CmdEs]).


%% @spec w(string()) -> ok | {error,Reason}
%% @doc 
%% Writes the shell history to the output file F in a form that can be 
%% processed by `file:script/1'.
%% @end
%%
w(F) ->
    case cmds() of
        [] ->
            {error, empty_history};
        [_|_] = Cmds ->
            case file:open(F, [write]) of
                {ok, Fd} ->
                    try [io:fwrite(Fd,"~s.~n", [C]) || {_,C} <- Cmds]
                        after
                            file:close(Fd)
                        end,
                    ok;
                {error,_} = E ->
                    E
            end
    end.

%% @spec r(string()) -> any()
%% @doc
%% Reads a saved shell history and returns the value of the last 
%% expression.
%% @end
r(F) ->
    file:script(F).


%% @spec () -> pid()
%% @doc Returns the Pid of the shell process.
%% @end
%%
%% Modified version of shell:whereis_evaluator()
%%
shell() ->
    %% locate top group leader, always registered as user
    %% can be implemented by group (normally) or user 
    %% (if oldshell or noshell)
    case whereis(user) of
        undefined ->
            undefined;
        User ->
            %% get user_drv pid from group, or shell pid from user
            case group:interfaces(User) of
                [] ->                           % old- or noshell
                    case user:interfaces(User) of
                        [] ->
                            undefined;
                        [{shell,Shell}] ->
                            Shell
                    end;
                [{user_drv,UserDrv}] ->
                    %% get current group pid from user_drv
                    case user_drv:interfaces(UserDrv) of
                        [] ->
                            undefined;
                        [{current_group,Group}] ->
                            %% get shell pid from group
                            GrIfs = group:interfaces(Group),
                            case lists:keyfind(shell, 1, GrIfs) of
                                {shell, Shell} ->
                                    Shell;
                                false ->
                                    undefined
                            end
                    end
            end
    end.


shell_req(Shell, Req) ->
    Shell ! {shell_req,self(),Req},
    receive
        {shell_rep,Shell,Rep} -> Rep
    end.