"""Access to CSA with the new TAP protocol

"""
from	 __future__ import print_function
import	requests
import	lxml.etree as ET
import	datetime
import	time
import	os
import	re

BASE_URL = "https://csa.esac.esa.int/csa-sl-tap"

__user = "abarthe"
__pswd = "pm2mdp2CSA!"

DELAY = 3

session = requests.Session()


def	isotime (d):
	"""
	datetime => yyyy-mm-ddThh:mm:ssZ
	"""
	return d.strftime ("%FT%TZ")


def	login ():
	"""
	Login to CSA and create a cookie, embedded in session
	"""
	login_url = "%s/login" % BASE_URL

	print ("Login on", login_url)

	auth = dict (username = __user, password = __pswd)

	r = session.post (login_url, data = auth)

	if r.status_code != 200:
		print ("Error: status code =", r.status_code)


def	download_file (url):
	"""
	Download the resulting file (add .zip extension)
	"""
	r = session.get (url)

	output_file = os.path.basename (url) + ".zip"

	print ("OUTPUT =", output_file)

	with open (output_file, "w") as output:

		output.write (r.content)

	print ("Done...")


def	parse_xml_response (content):
	"""
	Parse XML response to extract (url, phase, href)
	"""
	root = ET.XML (content)

	url = root.xpath ("//uws:parameter[@id='email_base_url']/text()", namespaces = root.nsmap)[0]

	phase = root.xpath ("//uws:phase/text()", namespaces = root.nsmap)[0]

	if phase == "ERROR":
		print (content)

	if phase == "COMPLETED":
		href = root.xpath ("//uws:result/@xlink:href", namespaces = root.nsmap)[0]
	else:
		href = None

	return url, phase, href


def	get_async_data (dataset, start, end):
	"""
	Asynchronous data request using TAP protocol
	"""
	print ("REQUEST =", dataset, ":", isotime (start), "/", isotime (end))

	async_url = "%s/data" % BASE_URL

	param = dict (
		RETRIEVAL_TYPE = "product",
		RETRIEVAL_ACCESS = "DEFERRED",
		DATASET_ID = dataset,
		START_DATE = isotime (start),
		END_DATE = isotime (end)
	)
	
	r = session.get (async_url, params = param)

	if not r.headers["Content-Type"].startswith ("text/xml"):

		print ("Unexpected content type :", r.headers["Content-Type"])
		return

	url, phase, href = parse_xml_response (r.content)

	print ("URL =", url)

	print ("PHASE =", phase)

	while	phase != "COMPLETED":

		time.sleep (DELAY)

		r = session.get (url)

		url, phase, href = parse_xml_response (r.content)

		print ("PHASE =", phase)

	print ("HREF =", href)

	download_file (href)


def	get_data (dataset, start, end):
	"""
	Synchronous data request using TAP protocol
	"""
	print ("REQUEST =", dataset, ":", isotime (start), "/", isotime (end))

	url = "%s/data" % BASE_URL

	param = dict (
		RETRIEVAL_TYPE = "product",
		DELIVERY_FORMAT = "CDF",
		DATASET_ID = dataset,
		START_DATE = isotime (start),
		END_DATE = isotime (end)
	)
	
	print (url, param)	
	r = session.get (url, params = param)

	expr = re.compile ("filename=\"([^\"]*)")

	s = expr.search (r.headers["Content-disposition"])

	if s:
		filename = s.group(1)

		print ("Extracting", filename)

		with open (filename, "w") as output:
			output.write (r.content)

		print ("Done.")


def	get_stream_data (dataset, start, end):
	"""
	Download CEF data using streaming mode
	"""
	url = "%s/data" % BASE_URL

	param = dict (
		RETRIEVAL_TYPE = "product",
		DATASET_ID = dataset,
		START_DATE = isotime (start),
		END_DATE = isotime (end),
		RETRIEVAL_ACCESS = "streamed"
	)

	print (url, param)

	r = session.get (url, params = param)

	return r.content

	
def	test():
	"""
	Example of use
	"""
	login()

	start = datetime.datetime (2020, 4, 14, 12, 0)
	stop  = start + datetime.timedelta (hours = 3)

	dataset = "C4_CP_FGM_SPIN"

	print (get_stream_data (dataset, start, stop))
	#	print (get_data (dataset, start, stop))


if	__name__ == "__main__":

	test()