From 236cab7a4e197c99c9ffcdcdf881314cb5a6b797 Mon Sep 17 00:00:00 2001
From: Tom Brooks <tombrooks248@gmail.com>
Date: Fri, 26 Jun 2026 15:43:19 +0100
Subject: [PATCH] fix: handle edge case where two end points provide same
 resouce which refers two 2 datasets

---
 digital_land/collection.py    | 19 ++++---
 tests/unit/test_collection.py | 94 +++++++++++++++++++++++++++++++++++
 2 files changed, 107 insertions(+), 6 deletions(-)

diff --git a/digital_land/collection.py b/digital_land/collection.py
index 377ab0466..fed8b1520 100644
--- a/digital_land/collection.py
+++ b/digital_land/collection.py
@@ -187,9 +187,13 @@ def load(
 
                 for entry in source.records[endpoint]:
                     organisations.add(entry["organisation"])
-                    datasets = set(
-                        entry.get("datasets", entry.get("pipelines", "")).split(";")
-                    )
+                    datasets |= {
+                        dataset
+                        for dataset in entry.get(
+                            "datasets", entry.get("pipelines", "")
+                        ).split(";")
+                        if dataset
+                    }
 
             new_entries[key] = {
                 "bytes": resource["bytes"],
@@ -227,11 +231,14 @@ def load(
                 for endpoint in entry["endpoints"].split(";"):
                     for r_source in source.records[endpoint]:
                         organisations.add(r_source["organisation"])
-                        datasets = set(
-                            r_source.get(
+                        datasets |= {
+                            dataset
+                            for dataset in r_source.get(
                                 "datasets", r_source.get("pipelines", "")
                             ).split(";")
-                        )
+                            if dataset
+                        }
+
                 entry["organisations"] = ";".join(sorted(organisations))
                 entry["datasets"] = ";".join(sorted(datasets))
 
diff --git a/tests/unit/test_collection.py b/tests/unit/test_collection.py
index 7c9f7c5a2..b9d10e09a 100644
--- a/tests/unit/test_collection.py
+++ b/tests/unit/test_collection.py
@@ -118,3 +118,97 @@ def test_endpoint_source_mismatch():
     resource = ResourceLogStore(Schema("resource"))
     with pytest.raises(RuntimeError):
         resource.load(log, source)
+
+
+def test_resource_shared_by_two_endpoints_gets_both_datasets():
+    """A resource collected from two endpoints that feed DIFFERENT datasets
+    must be recorded against BOTH datasets (the Adur A4D/A4DA edge case).
+
+    Regression guard: `datasets` used to be overwritten per-endpoint instead
+    of accumulated, so only the last-visited endpoint's dataset survived.
+    """
+    # the same resource hash collected from two different endpoints
+    log = LogStore(Schema("log"))
+    for endpoint in ["endpoint-a4da", "endpoint-a4d"]:
+        log.add_entry(
+            {
+                "endpoint": endpoint,
+                "entry-date": "2025-01-06",
+                "resource": "shared-resource",
+                "bytes": "1024",
+            }
+        )
+
+    # each endpoint feeds a different dataset
+    source = CSVStore(Schema("source"))
+    source.add_entry(
+        {
+            "endpoint": "endpoint-a4da",
+            "organisation": "test-org",
+            "pipelines": "article-4-direction-area",
+        }
+    )
+    source.add_entry(
+        {
+            "endpoint": "endpoint-a4d",
+            "organisation": "test-org",
+            "pipelines": "article-4-direction",
+        }
+    )
+
+    resource = ResourceLogStore(Schema("resource"))
+    resource.load(log, source)
+
+    assert len(resource.entries) == 1
+    entry = resource.entries[0]
+    assert entry["resource"] == "shared-resource"
+    # both datasets present, not just the last endpoint visited
+    assert set(entry["datasets"].split(";")) == {
+        "article-4-direction",
+        "article-4-direction-area",
+    }
+    # endpoints were already accumulated correctly - guard against regression
+    assert set(entry["endpoints"].split(";")) == {"endpoint-a4da", "endpoint-a4d"}
+
+
+def test_existing_resource_datasets_recomputed_from_all_endpoints():
+    """The config-change branch (updating an existing resource entry) must also
+    accumulate datasets across all of a resource's endpoints, not overwrite."""
+    source = CSVStore(Schema("source"))
+    source.add_entry(
+        {
+            "endpoint": "endpoint-a4da",
+            "organisation": "test-org",
+            "pipelines": "article-4-direction-area",
+        }
+    )
+    source.add_entry(
+        {
+            "endpoint": "endpoint-a4d",
+            "organisation": "test-org",
+            "pipelines": "article-4-direction",
+        }
+    )
+
+    resource = ResourceLogStore(Schema("resource"))
+    # pre-existing entry from both endpoints but with a stale, single dataset
+    resource.add_entry(
+        {
+            "resource": "shared-resource",
+            "bytes": "1024",
+            "endpoints": "endpoint-a4da;endpoint-a4d",
+            "organisations": "test-org",
+            "datasets": "article-4-direction-area",
+            "start-date": "2025-01-06",
+            "end-date": "",
+        }
+    )
+
+    # empty log -> the existing entry takes the config-recompute (else) branch
+    resource.load(LogStore(Schema("log")), source)
+
+    entry = next(e for e in resource.entries if e["resource"] == "shared-resource")
+    assert set(entry["datasets"].split(";")) == {
+        "article-4-direction",
+        "article-4-direction-area",
+    }