#!/usr/bin/env escript

%%% This script converts an arbitrary binary file to an Erlang module with a
%%% single exported 'bin/0' function that returns the original binary.
%%%
%%% See the end of the file for how I figured out the correct terms.

main(["+debug_info" | Files]) ->
    io:format("Embedding binaries with debug_info...\n"),
    lists:foreach(fun(X) -> embed_file_in_beam(X, [debug_info]) end, Files);
main(Files) ->
    io:format("Embedding binaries...\n"),
    lists:foreach(fun(X) -> embed_file_in_beam(X, []) end, Files).

embed_file_in_beam(InputPath, CompilerOptions) ->
    % Read the source file.
    {ok, Bytes} = file:read_file(InputPath),

    % Work out what we're going to call the output.
    ModuleName = get_module_name(filename:basename(InputPath)),
    file:make_dir("ebin"),
    OutputPath = filename:join("ebin", ModuleName ++ ".beam"),
    io:format("  ~s -> ~s (~s)\n", [InputPath, ModuleName, OutputPath]),

    % We'll export a function Mod:bin/0.
    Mod = list_to_atom(ModuleName),
    Fun = 'bin',

    % An Erlang module is a list of forms; we need three:
    Forms = [
             module_form(Mod),          % -module(foo).
             export_form(Fun),          % -export([bin/0]).
             function_form(Fun, Bytes)  % bin() -> <<...>>.
            ],

    % Compile the forms into a binary.
    {ok, Mod, Bin} = compile:forms(Forms, CompilerOptions),

    % The binary _is_ the beam file, so write it out.
    ok = file:write_file(OutputPath, Bin).

% Given, e.g., "foo_bar.baz", return "foo_bar_baz".
get_module_name(Filename) ->
    re:replace(Filename, "\\.", "_", [global, {return, list}]).

module_form(Mod) ->
    {attribute, 1, module, Mod}.

export_form(Fun) ->
    {attribute, 1, export, [{Fun, 0}]}.

function_form(Fun, Binary) ->
    % a function,
    {function, 1, Fun, 0,
     % with one clause,
     [{clause, 1, [], [],
       % which has one expression, a binary,
       [{bin, 1, [
                  % made up of the stuff we first thought of.
                  {bin_element, 1, {integer, 1, Byte}, default, default}
                  || <<Byte:8>> <= Binary
                 ]}]}]}.

%%% How it works:
%%%
%%% See http://stackoverflow.com/a/2160696/8446, but...
%%%
%%%     {ok, MTs, _} = erl_scan:string("-module(foo).").
%%%     {ok, ETs, _} = erl_scan:string("-export([bin/0]).").
%%%     % bin() -> <<"Hello">>.
%%%     {ok, FTs, _} = erl_scan:string("bin() -> <<72, 101, 108, 108, 111>>.").
%%%
%%%     {ok, MF} = erl_parse:parse_form(MTs).
%%%     {ok, EF} = erl_parse:parse_form(ETs).
%%%     {ok, FF} = erl_parse:parse_form(FTs).
%%%
%%%     Forms = [MF, EF, FF].
%%%
%%% The above returns a readable AST, suitable for compile:forms/2.
%%%
%%% Debug Information
%%%
%%% By passing +debug_info to embed_binaries, you can persuade it to generate
%%% debug information. This can be verified by:
%%%
%%%     beam_lib:chunks("foo.beam", [abstract_code]).
%%%     % Without +debug_info:
%%%     %   {ok, {foo, [{abstract_code, no_abstract_code}]}}
%%%     % With +debug_info:
%%%     %   {ok, {foo, [{abstract_code, {raw_abstract_v1, [{attribute, ....

%% vi: ft=erlang