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%% @doc Built in operators.
-module(glc_ops).
-export([
lt/2, lte/2,
eq/2,
gt/2, gte/2,
wc/1,
nf/1
]).
-export([
all/1,
any/1,
null/1,
with/2
]).
-export([
union/1
]).
-type op() ::
{atom(), '=<', term()} |
{atom(), '=', term()} |
{atom(), '>', term()} |
{atom(), '>=', term()} |
{atom(), '*'} |
{atom(), '!'} |
{any, [op(), ...]} |
{all, [op(), ...]} |
{null, true|false}.
-export_type([op/0]).
%% @doc Test that a field value is less than a term.
-spec lt(atom(), term()) -> op().
lt(Key, Term) when is_atom(Key) ->
{Key, '<', Term};
lt(Key, Term) ->
erlang:error(badarg, [Key, Term]).
%% @doc Test that a field value is less than or equal to a term.
-spec lte(atom(), term()) -> op().
lte(Key, Term) when is_atom(Key) ->
{Key, '=<', Term};
lte(Key, Term) ->
erlang:error(badarg, [Key, Term]).
%% @doc Test that a field value is equal to a term.
-spec eq(atom(), term()) -> op().
eq(Key, Term) when is_atom(Key) ->
{Key, '=', Term};
eq(Key, Term) ->
erlang:error(badarg, [Key, Term]).
%% @doc Test that a field value is greater than a term.
-spec gt(atom(), term()) -> op().
gt(Key, Term) when is_atom(Key) ->
{Key, '>', Term};
gt(Key, Term) ->
erlang:error(badarg, [Key, Term]).
%% @doc Test that a field value is greater than or equal to a term.
-spec gte(atom(), term()) -> op().
gte(Key, Term) when is_atom(Key) ->
{Key, '>=', Term};
gte(Key, Term) ->
erlang:error(badarg, [Key, Term]).
%% @doc Test that a field exists.
-spec wc(atom()) -> op().
wc(Key) when is_atom(Key) ->
{Key, '*'};
wc(Key) ->
erlang:error(badarg, [Key]).
%% @doc Test that a field is not found.
-spec nf(atom()) -> op().
nf(Key) when is_atom(Key) ->
{Key, '!'};
nf(Key) ->
erlang:error(badarg, [Key]).
%% @doc Filter the input using multiple filters.
%%
%% For an input to be considered valid output the all filters specified
%% in the list must hold for the input event. The list is expected to
%% be a non-empty list. If the list of filters is an empty list a `badarg'
%% error will be thrown.
-spec all([op()]) -> op().
all([_|_]=Conds) ->
{all, Conds};
all(Other) ->
erlang:error(badarg, [Other]).
%% @doc Filter the input using one of multiple filters.
%%
%% For an input to be considered valid output on of the filters specified
%% in the list must hold for the input event. The list is expected to be
%% a non-empty list. If the list of filters is an empty list a `badarg'
%% error will be thrown.
-spec any([op()]) -> op().
any([_|_]=Conds) ->
{any, Conds};
any(Other) ->
erlang:error(badarg, [Other]).
%% @doc Always return `true' or `false'.
-spec null(boolean()) -> op().
null(Result) when is_boolean(Result) ->
{null, Result};
null(Result) ->
erlang:error(badarg, [Result]).
%% @doc Apply a function to each output of a query.
%%
%% Updating the output action of a query finalizes it. Attempting
%% to use a finalized query to construct a new query will result
%% in a `badarg' error.
-spec with(op(), fun((gre:event()) -> term())) -> op().
with(Query, Fun) when is_function(Fun, 1);
is_function(Fun, 2) ->
{with, Query, Fun};
with(Query, Fun) ->
erlang:error(badarg, [Query, Fun]).
%% @doc Return a union of multiple queries.
%%
%% The union of multiple queries is the equivalent of executing multiple
%% queries separately on the same input event. The advantage is that filter
%% conditions that are common to all or some of the queries only need to
%% be tested once.
%%
%% All queries are expected to be valid and have an output action other
%% than the default which is `output'. If these expectations don't hold
%% a `badarg' error will be thrown.
-spec union([op()]) -> op().
union(Queries) ->
case [Query || Query <- Queries, glc_lib:onoutput(Query) =:= output] of
[] -> {union, Queries};
[_|_] -> erlang:error(badarg, [Queries])
end.
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