vw deompose ak function

utils/vw/src/vw.erl

@@ -17,23 +17,27 @@ start(ArgV) ->
 %%
 %% WHEN back: get decompose to work
 
-go(["help"])                -> help();
-go(["--help"])              -> help();
-go(["decompose", TxStr])    -> decompose(TxStr);
-go(["generate", "keypair"]) -> generate_keypair();
-go(X)                       -> error({invalid_subcommand, X}).
+go(["help"])                   -> help();
+go(["--help"])                 -> help();
+go(["decompose", "ak", TxStr]) -> decompose(ak, TxStr);
+go(["decompose", "tx", TxStr]) -> decompose(tx, TxStr);
+go(["generate", "keypair"])    -> generate_keypair();
+go(X)                          -> error({invalid_subcommand, X}).
 
 
 help() ->
     io:format("you can't help people who won't help themselves~n", []).
 
 
-decompose(TxStr) ->
+decompose(ak, AkStr) ->
+    case decompose_ak(AkStr) of
+        {ok, Pubkey} -> io:format("~tw~n", [Pubkey]);
+        {error, Err} -> io:format("ERROR: ~tp~n", [Err])
+    end;
+decompose(tx, TxStr) ->
     case vd:decompose(TxStr) of
-        {ok, X} ->
-            io:format("~tp~n", [X]);
-        {error, Error} ->
-            io:format("ERROR: ~tp~n", [Error])
+        {ok, X}        -> io:format("~tp~n", [X]);
+        {error, Error} -> io:format("ERROR: ~tp~n", [Error])
     end.
 
 
@@ -42,3 +46,21 @@ generate_keypair() ->
       secret := SecretKey} = ecu_eddsa:sign_keypair(),
     io:format("Public Key: ~w~n", [PublicKey]),
     io:format("Secret Key: ~w~n", [SecretKey]).
+
+decompose_ak("ak_" ++ AkB58) ->
+    maybe_b58_shasha_bytes(AkB58).
+
+maybe_b58_shasha_bytes(Base58_string) ->
+    With_shasha_bytes = vb58:dec(Base58_string),
+    Total_size_int = byte_size(With_shasha_bytes),
+    Actual_data_size_int = Total_size_int - 4,
+    <<Actual_data:Actual_data_size_int/binary,
+      ShaSha4:4/binary>> = With_shasha_bytes,
+    case shasha4(Actual_data) =:= ShaSha4 of
+        true  -> {ok, Actual_data};
+        false -> {error, checksum_mismatch}
+    end.
+
+shasha4(Bytes) ->
+    <<Check:4/binary, _/binary>> = crypto:hash(sha256, crypto:hash(sha256, Bytes)),
+    Check.