Add utils file with helper methods to request data from linz + docs

backend/right_tree/api/utils.py

@@ -0,0 +1,87 @@
+import json
+import os
+import requests
+from urllib.parse import urlencode
+
+from django.contrib.gis.geos import Point, GEOSGeometry
+from django.conf import settings
+
+LINZ_API_KEY = os.getenv("LINZ_API_KEY")
+LINZ_WFS_ENDPOINT = f"https://data.linz.govt.nz/services;key={LINZ_API_KEY}/wfs"
+PROPERTY_TILE_LAYER = "layer-50804"
+PROPERTY_INFO_LAYER = "layer-53353"
+
+
+class WFSError(Exception):
+    pass
+
+
+def get_point_from_coordinates(coordinates):
+    """Given a coordinates json string, returns the coordinates as a Point object"""
+    coordinates_json = json.loads(coordinates)
+    pnt = Point(coordinates_json["lng"],
+                coordinates_json["lat"], srid=4326)
+    return pnt
+
+
+def wfs_getfeature(endpoint, **kwargs):
+    """Perform a WFS request with the with all keyword arguments as parameters
+    within the URL query, returning the JSON-formatted response"""
+    params = {
+        'service': "WFS",
+        'request': "GetFeature",
+        'outputFormat': "application/json",
+        **kwargs,
+    }
+
+    query = urlencode(params)
+    url = f"{endpoint}?{query}"
+    response = requests.get(url)
+
+    try:
+        return response.json()
+    except json.JSONDecodeError as e:
+        raise WFSError(
+            f"Failed to make WFS request to {url}: {response.content}")
+
+
+def linz_wfs_getfeature(**kwargs):
+    """Perform a WFS request via the LINZ endpoint"""
+    return wfs_getfeature(LINZ_WFS_ENDPOINT, version="2.0.0", **kwargs)
+
+
+def intersecting_property(coordinates):
+    """Finds the property that intersects with the coordinates and returns its definition as a dictionary"""
+    point = get_point_from_coordinates(coordinates)
+    cql_filter = f"Intersects(shape,{point})"
+    json = linz_wfs_getfeature(
+        typeNames=PROPERTY_TILE_LAYER, cql_filter=cql_filter, count=1)
+    features = json.get("features")
+
+    if len(features) > 0:
+        return features[0]
+
+
+def get_address(polygon):
+    """Fetch the address string that intersects with the specified polygon"""
+
+    # Don't perform request if the input polygon WKT is too long to fit into URL
+    # Limit is 2048 characters
+    if len(str(polygon)) > 1500:
+        return None
+
+    cql_filter = f"Within(shape,{polygon})"
+    json = linz_wfs_getfeature(
+        typeNames=PROPERTY_INFO_LAYER, cql_filter=cql_filter, count=1)
+    features = json.get("features")
+
+    if len(features) > 0:
+        feature = features[0]
+        return feature['properties']
+
+
+def get_address_from_coordinates(coordinates):
+    propertyPolygon = intersecting_property(coordinates)
+    if propertyPolygon is not None:
+        prop_geom = GEOSGeometry(json.dumps(propertyPolygon['geometry']))
+        return get_address(prop_geom)