%%--------------------------------------------------------------------
%% Copyright (c) 2020-2021 EMQ Technologies Co., Ltd. All Rights Reserved.
%%
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%%
%%     http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
%%--------------------------------------------------------------------

-module(emqx_rule_sqlparser).

-include("rule_engine.hrl").

-export([parse/1]).

-export([ select_fields/1
        , select_is_foreach/1
        , select_doeach/1
        , select_incase/1
        , select_from/1
        , select_where/1
        ]).

-import(proplists, [ get_value/2
                   , get_value/3
                   ]).

-record(select, {fields, from, where, is_foreach, doeach, incase}).

-opaque(select() :: #select{}).

-type const() :: {const, number()|binary()}.

-type variable() :: binary() | list(binary()).

-type alias() :: binary() | list(binary()).

-type field() :: const() | variable()
               | {as, field(), alias()}
               | {'fun', atom(), list(field())}.

-export_type([select/0]).

%% Parse one select statement.
-spec(parse(string() | binary()) -> {ok, select()} | {error, term()}).
parse(Sql) ->
    try case rulesql:parsetree(Sql) of
            {ok, {select, Clauses}} ->
                {ok, #select{
                        is_foreach = false,
                        fields = get_value(fields, Clauses),
                        doeach = [],
                        incase = {},
                        from = get_value(from, Clauses),
                        where = get_value(where, Clauses)
                    }};
            {ok, {foreach, Clauses}} ->
                {ok, #select{
                        is_foreach = true,
                        fields = get_value(fields, Clauses),
                        doeach = get_value(do, Clauses, []),
                        incase = get_value(incase, Clauses, {}),
                        from = get_value(from, Clauses),
                        where = get_value(where, Clauses)
                    }};
            Error -> {error, Error}
        end
    catch
        _Error:Reason:StackTrace ->
            {error, {Reason, StackTrace}}
    end.

-spec(select_fields(select()) -> list(field())).
select_fields(#select{fields = Fields}) ->
    Fields.

-spec(select_is_foreach(select()) -> boolean()).
select_is_foreach(#select{is_foreach = IsForeach}) ->
    IsForeach.

-spec(select_doeach(select()) -> list(field())).
select_doeach(#select{doeach = DoEach}) ->
    DoEach.

-spec(select_incase(select()) -> list(field())).
select_incase(#select{incase = InCase}) ->
    InCase.

-spec(select_from(select()) -> list(binary())).
select_from(#select{from = From}) ->
    From.

-spec(select_where(select()) -> tuple()).
select_where(#select{where = Where}) ->
    Where.