feat: add Docling JSON ingestion (#783)

* feat: add Docling JSON ingestion

Signed-off-by: Panos Vagenas <35837085+vagenas@users.noreply.github.com>

* update conversion as per review comments, add tests, revert Docling JSON disambiguation, document intricacies

Signed-off-by: Panos Vagenas <35837085+vagenas@users.noreply.github.com>

* Update docling/backend/json/docling_json_backend.py

Co-authored-by: Cesar Berrospi Ramis <75900930+ceberam@users.noreply.github.com>
Signed-off-by: Panos Vagenas <35837085+vagenas@users.noreply.github.com>

---------

Signed-off-by: Panos Vagenas <35837085+vagenas@users.noreply.github.com>
Co-authored-by: Cesar Berrospi Ramis <75900930+ceberam@users.noreply.github.com>

tests/test_backend_docling_json.py

@@ -0,0 +1,58 @@
+"""Test methods in module docling.backend.json.docling_json_backend.py."""
+
+from io import BytesIO
+from pathlib import Path
+
+import pytest
+from pydantic import ValidationError
+
+from docling.backend.json.docling_json_backend import DoclingJSONBackend
+from docling.datamodel.base_models import InputFormat
+from docling.datamodel.document import DoclingDocument, InputDocument
+
+GT_PATH: Path = Path("./tests/data/groundtruth/docling_v2/2206.01062.json")
+
+
+def test_convert_valid_docling_json():
+    """Test ingestion of valid Docling JSON."""
+    cls = DoclingJSONBackend
+    path_or_stream = GT_PATH
+    in_doc = InputDocument(
+        path_or_stream=path_or_stream,
+        format=InputFormat.JSON_DOCLING,
+        backend=cls,
+    )
+    backend = cls(
+        in_doc=in_doc,
+        path_or_stream=path_or_stream,
+    )
+    assert backend.is_valid()
+
+    act_doc = backend.convert()
+    act_data = act_doc.export_to_dict()
+
+    exp_doc = DoclingDocument.load_from_json(GT_PATH)
+    exp_data = exp_doc.export_to_dict()
+
+    assert act_data == exp_data
+
+
+def test_invalid_docling_json():
+    """Test ingestion of invalid Docling JSON."""
+    cls = DoclingJSONBackend
+    path_or_stream = BytesIO(b"{}")
+    in_doc = InputDocument(
+        path_or_stream=path_or_stream,
+        format=InputFormat.JSON_DOCLING,
+        backend=cls,
+        filename="foo",
+    )
+    backend = cls(
+        in_doc=in_doc,
+        path_or_stream=path_or_stream,
+    )
+
+    assert not backend.is_valid()
+
+    with pytest.raises(ValidationError):
+        backend.convert()