From 2302ed6fc61e4b814cc9de6daf8e95b3fb4b2862 Mon Sep 17 00:00:00 2001
From: Dana Lambert <danalambert@catalyst.net.nz>
Date: Fri, 22 Oct 2021 16:01:31 +1300
Subject: [PATCH] Add utils file with helper methods to request data from linz
 + docs

---
 README.md                       |  6 +++
 backend/requirements.txt        |  3 +-
 backend/right_tree/api/utils.py | 87 +++++++++++++++++++++++++++++++++
 docker-compose.yaml             |  2 +
 4 files changed, 97 insertions(+), 1 deletion(-)
 create mode 100644 backend/right_tree/api/utils.py

diff --git a/README.md b/README.md
index a8d3ceb..f69e28f 100644
--- a/README.md
+++ b/README.md
@@ -13,6 +13,12 @@ $ sudo apt install git docker-compose
 
 To install `docker`, follow the [official installation documentation](https://docs.docker.com/get-docker/). [Instructions are also available for `docker-compose`](https://docs.docker.com/compose/install/).
 
+In order to recieve address data while running in development mode you will need to set an environment variable containing a valid linz data service api key. Such a key can be retrieved by signing up to https://data.linz.govt.nz/. One way of setting the variable is exporting it in the same terminal window that you will run the application. To do this please run the following command:
+
+```bash
+export LINZ_API_KEY=<YOUR_API_KEY>
+```
+
 You may also need to give the `dev` script executable permissions using the following command:
 
 ```
diff --git a/backend/requirements.txt b/backend/requirements.txt
index 35f9bd1..266dc2c 100644
--- a/backend/requirements.txt
+++ b/backend/requirements.txt
@@ -2,4 +2,5 @@ Django==3.2.8
 psycopg2-binary>=2.8
 djangorestframework==3.12.4
 django-cors-headers==3.10.0
-openpyxl==3.0.9
\ No newline at end of file
+openpyxl==3.0.9
+requests==2.26.0
\ No newline at end of file
diff --git a/backend/right_tree/api/utils.py b/backend/right_tree/api/utils.py
new file mode 100644
index 0000000..65d3eb4
--- /dev/null
+++ b/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)
diff --git a/docker-compose.yaml b/docker-compose.yaml
index aa48ae5..4333724 100644
--- a/docker-compose.yaml
+++ b/docker-compose.yaml
@@ -15,6 +15,8 @@ services:
       - postgres
     volumes:
       - ./backend:/app
+    environment:
+      - LINZ_API_KEY=${LINZ_API_KEY}
     ports:
       - "8000:8000"
     command: bash -c "./manage.py runserver 0.0.0.0:8000"