sensor.erl

-module(sensor).
-include("light.hrl").

-export([start/0,stop/0]).

% web interface
-export([graph/3]).

start() ->
    dets:open_file(?TABLE, [{file, ?STORE}]),
    application:start(inets),
    inets:start(httpd, [
            {modules, [
                    mod_alias,
                    mod_auth,
                    mod_esi,
                    mod_actions,
                    mod_cgi,
                    mod_dir,
                    mod_get,
                    mod_head,
                    mod_log,
                    mod_disk_log
                ]},
            {port, 8889},
            {server_name, "foo"},
            {server_root, "log"},
            {document_root, "www"},
            {directory_index, ["index.html"]},
            {error_log, "error.log"},
            {security_log, "security.log"},
            {transfer_log, "transfer.log"},
            {erl_script_alias, {"/web", [sensor]}}
        ]).

stop() ->
    inets:stop().


%%%
%%% web services
%%%

graph(SessionID, _Env, _Input) ->
    mod_esi:deliver(SessionID, header(png)),
    B = generate_graph(),
    mod_esi:deliver(SessionID, binary_to_list(B)).


%%%
%%% helper functions
%%%

generate_graph() ->
    L = get_values(),
    egd_chart:graph([{"light",L}], [
            {bg_rgba, {255,255,255,255}},
            {width, 1024},
            {height, 800}
        ]).

header(png) ->
    "Content-Type: image/png\r\n\r\n".

get_values() ->
    L = lists:sort([
            {calendar:datetime_to_gregorian_seconds(calendar:now_to_universal_time(K)), V}
            || [{K, V}] <- dets:match(sensor, '$1') ]),
    [ {K - element(1,hd(L)), V} || {K,V} <- L ].