import matlab.net.*
import matlab.net.http.*
import matlab.net.http.field.*
import matlab.net.http.io.*

%% Obtain API Access Token
% Add your Client-ID and Client-secret from the API Client configuration GUI to
% your environment variable first
IPNT_CLIENT_ID = getenv('IPNT_CLIENT_ID');
IPNT_CLIENT_SECRET = getenv('IPNT_CLIENT_SECRET');

% URL to request token from
scope = URI('https://identity.netztransparenz.de/users/connect/token');
% 20 second timeout
opts = HTTPOptions('ConnectTimeout', 20);

% Send request (url encoded form data)
body = FormProvider('grant_type', 'client_credentials', ...
'client_id', IPNT_CLIENT_ID, ...
'client_secret', IPNT_CLIENT_SECRET);
request = RequestMessage('POST',[],body);
resp = request.send(scope, opts);

% Status code is OK if request was processed correctly
if resp.StatusCode ~= StatusCode.OK
error('Failed to obtain an access token for IPNT');
end

%% Download data as .csv
from = datetime('yesterday')-days(7);
to = datetime('yesterday');
data = 'hochrechnung';
product = 'solar';

% Read the access token from the response body
token = resp.Body.Data.access_token;

% This is the base URL for querying data
baseURL = 'https://ds.netztransparenz.de/api/v1/data';

% Create message header that include access token
header = [ContentTypeField('application/x-www-form-urlencoded'), ...
AcceptField('text/plain'), ...
HeaderField('Authorization', ['Bearer ', token])]; 

% TimeZone needs to be UTC for our requests
from.TimeZone = 'UTC';
to.TimeZone = 'UTC';

% Build URL to data
scope = strjoin({baseURL, data, product, ...
datestr(from, 'yyyy-mm-ddTHH:MM:SS'), ...
datestr(to, 'yyyy-mm-ddTHH:MM:SS')} , '/');

% We download to a .csv-File
from.TimeZone = 'Europe/Zurich';
to.TimeZone = 'Europe/Zurich';
filename = [strjoin({datestr(from, 'yyyymmdd'), ...
datestr(to, 'yyyymmdd'), ...
data, product } , '_') '.csv'];

% Do nothing if the file already exists (no overwriting)
if ~exist(filename, 'file')
% Open the file for writing
sinkFID = fopen(filename, 'w');

% Send download request
request = RequestMessage('GET', header);
% FileConsumer is used to write message payload directly to a file
resp = request.send(scope, opts, FileConsumer(sinkFID));

% Close the file again
fclose(sinkFID);
end