[Feature] Minimal IUCLID export (#338)

This is an initial implementation that creates a working minimal .i6z document.
It passes schema validation and can be imported into IUCLID.

Caveat:
IUCLID files target individual compounds.
Pathway is not actually covered by the format.

It can be added in either soil or water and soil OECD endpoints.
**I currently only implemented the soil endpoint for all data.**

This sort of works, and I can report all degradation products in a pathway (not a nice view, but we can report many transformation products and add a diagram attachment in the future).

Adding additional information is an absolute pain, as we need to explicitly map each type of information to the relevant OECD field.
I use the XSD scheme for validation, but unfortunately the IUCLID parser is not fully compliant and requires a specific order, etc.

The workflow is: finding the AI structure from the XSD scheme -> make the scheme validation pass -> upload to IUCLID to get obscure error messages -> guess what could be wrong -> repeat 💣

New specifications get released once per year, so we will have to update accordingly.
I believe that this should be a more expensive feature, as it requires significant effort to uphold.

Currently implemented for root compound only in SOIL:

- Soil Texture 2
- Soil Texture 1
- pH value
- Half-life per soil sample / scenario (mapped to disappearance; not sure about that).
- CEC
- Organic Matter (only Carbon)
- Moisture content
- Humidity

<img width="2123" alt="image.png" src="attachments/d29830e1-65ef-4136-8939-1825e0959c62">
<img width="2124" alt="image.png" src="attachments/ac9de2ac-bf68-4ba4-b40b-82f810a9de93">
<img width="2139" alt="image.png" src="attachments/5674c7e6-865e-420e-974a-6b825b331e6c">

Reviewed-on: enviPath/enviPy#338
Co-authored-by: Tobias O <tobias.olenyi@envipath.com>
Co-committed-by: Tobias O <tobias.olenyi@envipath.com>

epiuclid/tests/test_api.py

@@ -0,0 +1,92 @@
+"""Integration tests for IUCLID export API endpoint."""
+
+import io
+import zipfile
+from uuid import uuid4
+
+from django.test import TestCase, tag
+
+from epdb.logic import PackageManager, UserManager
+from epdb.models import Node, Pathway
+
+
+@tag("iuclid")
+class IUCLIDExportAPITest(TestCase):
+    @classmethod
+    def setUpTestData(cls):
+        cls.user = UserManager.create_user(
+            "iuclid-api-user",
+            "iuclid-api@test.com",
+            "TestPass123",
+            set_setting=False,
+            add_to_group=False,
+            is_active=True,
+        )
+        default_pkg = cls.user.default_package
+        cls.user.default_package = None
+        cls.user.save()
+        default_pkg.delete()
+
+        cls.package = PackageManager.create_package(cls.user, "IUCLID API Test Package")
+
+        cls.pathway = Pathway.create(
+            cls.package,
+            "c1ccccc1",
+            name="Export Test Pathway",
+        )
+        Node.create(cls.pathway, "c1ccc(O)cc1", depth=1, name="Phenol")
+
+        # Unauthorized user
+        cls.other_user = UserManager.create_user(
+            "iuclid-other-user",
+            "other@test.com",
+            "TestPass123",
+            set_setting=False,
+            add_to_group=False,
+            is_active=True,
+        )
+        other_pkg = cls.other_user.default_package
+        cls.other_user.default_package = None
+        cls.other_user.save()
+        other_pkg.delete()
+
+    def test_export_returns_zip(self):
+        self.client.force_login(self.user)
+        url = f"/api/v1/pathway/{self.pathway.uuid}/export/iuclid"
+        response = self.client.get(url)
+
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response["Content-Type"], "application/zip")
+        self.assertIn(".i6z", response["Content-Disposition"])
+
+        self.assertTrue(zipfile.is_zipfile(io.BytesIO(response.content)))
+
+    def test_export_contains_expected_files(self):
+        self.client.force_login(self.user)
+        url = f"/api/v1/pathway/{self.pathway.uuid}/export/iuclid"
+        response = self.client.get(url)
+
+        with zipfile.ZipFile(io.BytesIO(response.content)) as zf:
+            names = zf.namelist()
+            self.assertIn("manifest.xml", names)
+            i6d_files = [n for n in names if n.endswith(".i6d")]
+            # 2 substances + 2 ref substances + 1 ESR = 5 i6d files
+            self.assertEqual(len(i6d_files), 5)
+
+    def test_anonymous_returns_401(self):
+        self.client.logout()
+        url = f"/api/v1/pathway/{self.pathway.uuid}/export/iuclid"
+        response = self.client.get(url)
+        self.assertEqual(response.status_code, 401)
+
+    def test_unauthorized_user_returns_403(self):
+        self.client.force_login(self.other_user)
+        url = f"/api/v1/pathway/{self.pathway.uuid}/export/iuclid"
+        response = self.client.get(url)
+        self.assertEqual(response.status_code, 403)
+
+    def test_nonexistent_pathway_returns_404(self):
+        self.client.force_login(self.user)
+        url = f"/api/v1/pathway/{uuid4()}/export/iuclid"
+        response = self.client.get(url)
+        self.assertEqual(response.status_code, 404)