#!/usr/bin/env escript
%% vim: ts=4 sw=4 et sts=4 ft=erlang

main([]) ->
    crypto:start(),
    code:ensure_loaded(rand),
    code:ensure_loaded(uri_string),

    Filename = "include/compat.hrl",
    io:format("Generating compatibility macros...\n"),
    Encrypt = encrypt(),
    Decrypt = decrypt(),
    Hash = hash(),
    Unique = unique(),
    RandUniform1 = rand_uniform_1(),
    RandUniform2 = rand_uniform_2(),
    ParseQS = parse_qs(),

    io:format("...?WF_ENCRYPT will use: ~p~n",[Encrypt]),
    io:format("...?WF_DECRYPT will use: ~p~n",[Decrypt]),
    io:format("...?WF_HASH will use:    ~p~n",[Hash]),
    io:format("...?WF_UNIQUE will use:  ~p~n",[Unique]),
    io:format("...?WF_RAND_UNIFORM/1 will use: ~p~n",[RandUniform1]),
    io:format("...?WF_RAND_UNIFORM/2 will use: ~p~n",[RandUniform2]),
    io:format("...?WF_PARSE_QS/1 will use: ~p~n", [ParseQS]),

    Contents = [
        "-define(WF_ENCRYPT(Key, IV, Data), ",Encrypt,").\n",
        "-define(WF_DECRYPT(Key, IV, Data), ",Decrypt,").\n",
        "-define(WF_HASH(Data), ",Hash,").\n",
        "-define(WF_UNIQUE, ",Unique,").\n",
        "-define(WF_RAND_UNIFORM(Max), ",RandUniform1,").\n",
        "-define(WF_RAND_UNIFORM(Min,Max), ",RandUniform2,").\n",
        "-define(WF_PARSE_QS(String), ",ParseQS,").\n"
    ],

    ContentsBin = iolist_to_binary(Contents),
    case file:read_file(Filename) of
        {ok, ContentsBin} -> 
            io:format("...no changes needed to ~p. Skipping writing new file\n",[Filename]);
        _ -> 
            io:format("...writing ~p\n",[Filename]),
            file:write_file(Filename, Contents)
    end.

rand_uniform_1() ->
    case erlang:function_exported(rand, uniform, 1) of
        true ->
            "rand:uniform(Max)";
        false ->
            "crypto:rand_uniform(1, Max)"
    end.

rand_uniform_2() ->
    case erlang:function_exported(rand, uniform, 1) of
        true ->
            "(rand:uniform(Max-Min)+Min-1)";
        false ->
            "crypto:rand_uniform(Min, Max)"
    end.

encrypt() ->
    case erlang:function_exported(crypto, crypto_one_time, 5) of
        true ->
            "crypto:crypto_one_time(aes_128_cbc, Key, IV, Data, true)";
        false ->
            case erlang:function_exported(crypto, block_encrypt, 4) of
                true ->
                    "crypto:block_encrypt(aes_cbc128, Key, IV, Data)";
                false ->
                    "crypto:aes_cbc_128_encrypt(Key, IV, Data)"
            end
    end.

decrypt() ->
    case erlang:function_exported(crypto, crypto_one_time, 5) of
        true ->
            "crypto:crypto_one_time(aes_128_cbc, Key, IV, Data, false)";
        false ->
            case erlang:function_exported(crypto, block_decrypt, 4) of
                true ->
                    "crypto:block_decrypt(aes_cbc128, Key, IV, Data)";
                false ->
                    "crypto:aes_cbc_128_decrypt(Key, IV, Data)"
            end
    end.

hash() ->
    case erlang:function_exported(crypto, hash, 2) of
        true ->
            "crypto:hash(sha, Data)";
        false ->
            "crypto:sha(Data)"
    end.

unique() ->
    case erlang:function_exported(erlang, unique_integer, 1) of
        true ->
            "erlang:unique_integer([positive])";
        false ->
            "begin {_,S,US}=erlang:now(), S*1000000+US end"
    end.

parse_qs() ->
    case erlang:function_exported(uri_string, dissect_query, 1) of
        true ->
            "uri_string:dissect_query(String)";
        false ->
            "httpd:parse_query(String)"
    end.