%%%-------------------------------------------------------------------
%%% @doc Digilent Pmod_ALS module
%%% This component provides ambient light-to-digital
%%% sensing through the SPI2 interface on a 6-pin connector.
%%%
%%% For further information about the Digilent Pmod_ALS
%%% and its components :
%%% https://store.digilentinc.com/pmod-als-ambient-light-sensor/
%%%
%%% Texas Instrument's ADC081S021 analog-to-digital converter
%%% http://www.ti.com/lit/ds/symlink/adc081s021.pdf
%%%
%%% Vishay Semiconductor's TEMT6000X01.
%%% http://www.vishay.com/docs/81579/temt6000.pdf
%%%
%%% @end
%%% Created : 06. Nov 2018 21:47
%%%-------------------------------------------------------------------
-module(pmod_als).

-behaviour(gen_server).

-include("grisp.hrl").

%% API
-export([start_link/2]).
-export([read/0]).
-export([percentage/0]).

%% gen_server callbacks
-export([init/1]).
-export([handle_call/3]).
-export([handle_cast/2]).
-export([handle_info/2]).
-export([terminate/2]).
-export([code_change/3]).

 %%%===================================================================
 %%% Macros
 %%%===================================================================

-define(SPI_MODE, #{cpol => high, cpha => trailing}).

%%%===================================================================
%%% Records
%%%===================================================================

-record(state , {
    options = []
}).

%%%===================================================================
%%% API
%%%===================================================================

%% @private
start_link(Slot, Opts) ->
    gen_server:start_link(?MODULE, [Slot, Opts], []).

%% @doc Returns the ambient light value that is currently sensed
%% by the ALS module. On success, the return value is a number
%% in the 0..255 range that is proportional to the luminous
%% intensity.
%%
%% Technically, the values are representative of the
%% power perceived by the phototransistor from the light source
%% incoming at an angle of ±60°. It is a model of the response
%% of the human eye to the same light source that is obtained
%% by calculating the luminosity function.
%%
%% The peak wavelength sensitivity of the module is at 570nm
%% making it close to the human eye (555nm). This implies that
%% return values will be the highest when the ALS is exposed to
%% wavelengths of green light with a slight yellow tint.
-spec read() -> 0..255 | no_return().
read() ->
    Dev = grisp_devices:default(?MODULE),
    case gen_server:call(Dev#device.pid, {read, Dev#device.slot}) of
        {error, Reason} -> error(Reason);
        Result          -> Result
    end.

%% @doc Returns a the percentage of current ambient light
%% based on the {@link pmod_als:read} function. The value
%% is rounded to the closest integer.
-spec percentage() -> 0..100.
percentage() ->
    Raw = read(),
    round((Raw / 255) * 100).

%%%===================================================================
%%% gen_server callbacks
%%%===================================================================

%% @private
init([Slot = spi2, Opts]) ->
    ok = grisp_devices:register(Slot, ?MODULE),
    {ok, #state{options = Opts}};
init(Slot) ->
    error({incompatible_slot, Slot}).

%%--------------------------------------------------------------------
%% @private
handle_call({read, Slot} , _From , State) when Slot =:= spi2 ->
    Val = get_value(Slot),
    {reply, Val, State};

handle_call(Request , _From , _State) ->
    error({unknown_call, Request}).

%% @private
handle_cast(Request , _State) ->
    error({unknown_cast, Request}).

%% @private
handle_info(Info , _State) ->
    error({unknown_info, Info}).

%% @private
terminate(_Reason , _State) ->
    ok.

%% @private
code_change(_OldVsn , State , _Extra) ->
    {ok , State}.

%%%===================================================================
%%% Internal functions
%%%===================================================================

%% @private
get_value(Slot) ->
    <<_:3,Resp:8,_Pad:5>> = grisp_spi:send_recv(Slot, ?SPI_MODE, <<0:8>>, 0, 1),
    Resp.