#!/usr/bin/env escript
%% -*- erlang -*-
%% Decompile .beam files into .erl source files when debug_info is available.
%% Usage: escript decompile_beam.erl <beam file or directory> [more paths...]

-mode(compile).

main(Args) ->
    case Args of
        [] ->
            usage();
        Paths ->
            lists:foreach(fun decompile_path/1, Paths)
    end.

usage() ->
    io:format("Usage: escript decompile_beam.erl <beam file or directory> [more paths...]~n", []),
    io:format("Example: escript decompile_beam.erl module.beam~n", []),
    io:format("         escript decompile_beam.erl ./ebin~n", []),
    io:format("~nNote: readable source can only be generated when the .beam was compiled with debug_info.~n", []),
    io:format("      Example: compile:file(File, [debug_info])~n", []),
    halt(1).

decompile_path(Path) ->
    case filelib:is_dir(Path) of
        true ->
            decompile_dir(Path);
        false ->
            case filelib:is_file(Path) of
                true ->
                    case filename:extension(Path) of
                        ".beam" -> decompile_beam(Path);
                        _ -> io:format("Skip non-.beam file: ~s~n", [Path])
                    end;
                false ->
                    io:format("Path does not exist: ~s~n", [Path])
            end
    end.

decompile_dir(Dir) ->
    case file:list_dir(Dir) of
        {ok, Files} ->
            Beams = [filename:join(Dir, F) || F <- Files, filename:extension(F) =:= ".beam"],
            io:format("Found ~p .beam files in ~s~n", [length(Beams), Dir]),
            lists:foreach(fun decompile_beam/1, Beams);
        {error, Reason} ->
            io:format("Failed to read directory ~s: ~p~n", [Dir, Reason])
    end.

decompile_beam(BeamPath) ->
    case beam_lib:chunks(BeamPath, [abstract_code]) of
        {ok, {_Module, [{abstract_code, {raw_abstract_v1, Forms}}]}} ->
            ErlPath = to_erl_path(BeamPath),
            case format_and_write(Forms, ErlPath) of
                ok ->
                    io:format("Generated: ~s~n", [ErlPath]);
                {error, Reason} ->
                    io:format("Write failed ~s: ~p~n", [ErlPath, Reason])
            end;
        {ok, {_Module, _}} ->
            io:format("Skip ~s: no abstract_code chunk (likely built without debug_info)~n", [BeamPath]);
        {error, beam_lib, {missing_chunk, _, "Abst"}} ->
            io:format("Skip ~s: missing abstract code chunk, rebuild with debug_info~n", [BeamPath]);
        {error, beam_lib, Reason} ->
            io:format("Read failed ~s: ~p~n", [BeamPath, Reason])
    end.

to_erl_path(BeamPath) ->
    Dir = filename:dirname(BeamPath),
    Base = filename:basename(BeamPath, ".beam"),
    OutDir =
        case filename:basename(Dir) of
            "ebin" -> filename:join(filename:dirname(Dir), "src");
            _ -> Dir
        end,
    filename:join(OutDir, Base ++ ".erl").

format_and_write(Forms, ErlPath) ->
    try
        Strings = lists:map(fun(F) -> erl_pp:form(F) end, Forms),
        Content = lists:flatten([S ++ ".\n\n" || S <- Strings]),
        ok = filelib:ensure_dir(ErlPath),
        file:write_file(ErlPath, Content, [write, {encoding, utf8}])
    catch
        _:Reason -> {error, Reason}
    end.