Add is_account/1 and account_pubkey/1 helpers

Extended-auth account ids use an {account, Subtype} tag. These helpers
let callers test account membership and extract the 32-byte pubkey
without pattern-matching on specialize/1 results.

src/gmser_id.erl

@@ -14,6 +14,8 @@
         , specialize/1
         , specialize/2
         , specialize_type/1
+        , is_account/1
+        , account_pubkey/1
         , to_map/1
         , is_id/1
         ]).
@@ -104,6 +106,20 @@ specialize_type(#id{tag = {Tag, _}}) when ?IS_TAG(Tag) ->
 specialize_type(#id{tag = Tag}) when ?IS_TAG(Tag) ->
     Tag.
 
+-spec is_account(id() | term()) -> boolean().
+is_account(#id{tag = account}) ->
+    true;
+is_account(#id{tag = {account, _}}) ->
+    true;
+is_account(_) ->
+    false.
+
+-spec account_pubkey(id()) -> val().
+account_pubkey(#id{tag = account, val = Val}) when ?IS_VAL(Val) ->
+    Val;
+account_pubkey(#id{tag = {account, _}, val = Val}) when ?IS_VAL(Val) ->
+    Val.
+
 -spec to_map(id()) -> id_map().
 to_map(#id{tag = {Tag, SubType}, val = Val}) when ?IS_TAG(Tag) ->
     #{ type => Tag

test/gmser_id_tests.erl

@@ -0,0 +1,44 @@
+-module(gmser_id_tests).
+
+-include_lib("eunit/include/eunit.hrl").
+
+-define(PUBKEY, <<12345:32/unit:8>>).
+
+is_account_test() ->
+    {"is_account recognizes standard and extended account ids",
+     fun() ->
+             ?assert(gmser_id:is_account(gmser_id:create(account, ?PUBKEY))),
+             ?assert(gmser_id:is_account(gmser_id:create({account, 0}, ?PUBKEY))),
+             ?assert(gmser_id:is_account(gmser_id:create({account, 5}, ?PUBKEY))),
+             ?assertNot(gmser_id:is_account(gmser_id:create(contract, ?PUBKEY))),
+             ?assertNot(gmser_id:is_account(not_an_id))
+     end}.
+
+account_pubkey_test() ->
+    {"account_pubkey returns the 32-byte account hash",
+     fun() ->
+             ?assertEqual(?PUBKEY,
+                          gmser_id:account_pubkey(gmser_id:create(account, ?PUBKEY))),
+             ?assertEqual(?PUBKEY,
+                          gmser_id:account_pubkey(gmser_id:create({account, 3}, ?PUBKEY))),
+             ?assertEqual(?PUBKEY,
+                          gmser_id:account_pubkey(gmser_id:create({account, 6}, ?PUBKEY)))
+     end}.
+
+account_pubkey_matches_specialize_test() ->
+    {"account_pubkey agrees with specialize/2 for account ids",
+     fun() ->
+             Id = gmser_id:create({account, 2}, ?PUBKEY),
+             ?assertEqual(gmser_id:specialize(Id, account),
+                          gmser_id:account_pubkey(Id))
+     end}.
+
+extended_account_roundtrip_test() ->
+    {"extended account ids round-trip through encode/decode",
+     fun() ->
+             Id = gmser_id:create({account, 4}, ?PUBKEY),
+             ?assert(gmser_id:is_account(Id)),
+             Id1 = gmser_id:decode(gmser_id:encode(Id)),
+             ?assertEqual(?PUBKEY, gmser_id:account_pubkey(Id1)),
+             ?assertEqual(account, gmser_id:specialize_type(Id1))
+     end}.