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First pass at implementing a wrapper library.

Manually stub out the term_to_natural and 
natural_to_term functions for the time being, 
because the actual implementation is most likely 
not going to scale.
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cmeiklejohn committed Dec 15, 2013
1 parent db71176 commit 1d2dd68077e977c463b2344c56ad724f73e6a222
Showing with 141 additions and 0 deletions.
  1. +141 −0 src/vclock.erl
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%% @doc Provide a wrapper library which provides the same interface
%% as riak_core's vclock library, but uses the vvclock library to
%% support use of the verified version.
%%
%% Manually stub out the natural/term conversion calls for the time
%% being to optimize for testing the library with the current test
%% suite.
%%

-module(vclock).

-export([fresh/0,
descends/2,
merge/1,
get_counter/2,
get_timestamp/2,
increment/2,
increment/3,
all_nodes/1,
equal/2,
prune/3,
timestamp/0]).

%% @doc Return natural timestamp.
timestamp() ->
calendar:datetime_to_gregorian_seconds(erlang:universaltime()).

%% @doc Generate a fresh vector clock.
fresh() ->
vvclock:fresh().

%% @doc Increment a vector clock for a particular actor.
increment(Actor, VClock) ->
vvclock:increment(term_to_peano(Actor), VClock).

%% @doc Increment a vector clock with a particular timestamp.
increment(_Actor, _Timestamp, _VClock) ->
%% Not implementing this one for now.
erlang:error(deprecated).

%% @doc Return counter for a particular actor.
get_counter(Actor, VClock) ->
Counter = vvclock:get_counter(term_to_peano(Actor), VClock),
peano_to_term(Counter).

%% @doc Return timestamp for a particular actor.
get_timestamp(Actor, VClock) ->
Timestamp = vvclock:get_timestamp(term_to_peano(Actor), VClock),
peano_to_term(Timestamp).

%% @doc Determine if one vector clock is an ancestor of another.
descends(VClock1, VClock2) ->
case vvclock:descends(VClock1, VClock2) of
'True' ->
true;
'False' ->
false
end.

%% @doc Return list of all actors that have ever touched the vclock.
all_nodes(VClock) ->
[peano_to_term(Node) || Node <- vvclock:all_nodes(VClock)].

%% @doc Prune vclocks.
prune(VClock, _Timestamp, BProps) ->
Old = get_property(old_vclock, BProps),
Young = get_property(young_vclock, BProps),
Large = get_property(large_vclock, BProps),
Small = get_property(small_vclock, BProps),
vvclock:prune(VClock, Small, Large, Young, Old).

%% @doc Merge function which operates on a list of vector clocks.
merge([VClock1,VClock2|VClocks]) ->
merge([vvclock:merge(VClock1, VClock2)|VClocks]);
merge([VClock]) ->
VClock;
merge([]) ->
[].

%% @doc Compare equality of two vclocks.
equal(VClock1, VClock2) ->
vvclock:equal(VClock1, VClock2).

%% @doc Convert a peano number back into an erlang term.
peano_to_term(Peano) ->
natural_to_term(peano_to_natural(Peano)).

%% @doc Convert an erlang term into a peano number.
term_to_peano(Term) ->
natural_to_peano(term_to_natural(Term)).

%% @doc Convert a natural number to an erlang term.
natural_to_term(Natural) ->
case Natural of
1 ->
a;
2 ->
b;
3 ->
c;
4 ->
d;
_ ->
erlang:error(not_supported)
end.

%% @doc Convert an erlang term to a natural number.
term_to_natural(Term) ->
case Term of
a ->
1;
b ->
2;
c ->
3;
d ->
4;
_ ->
erlang:error(not_supported)
end.

%% @doc Convert a natural number into a peano.
natural_to_peano(0) ->
'O';
natural_to_peano(Natural) ->
{'S', natural_to_peano(Natural - 1)}.

%% @doc Convert a peano number into a natural.
peano_to_natural('O') ->
0;
peano_to_natural({'S', Peano}) ->
1 + Peano.

%% @doc Extract property from bucket properties.
get_property(Key, PairList) ->
case lists:keyfind(Key, 1, PairList) of
{_Key, Value} ->
Value;
false ->
undefined
end.

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