feat(backend): endpoint to download files by id (#21)

* feat(backend): endpoint to download files by id

* test(backend) coverage for file downloads

backend/rotini/api/files.py

@@ -8,7 +8,7 @@ files that live in the system.
 import pathlib
 
 from fastapi import APIRouter, HTTPException, UploadFile
-
+from fastapi.responses import FileResponse
 import use_cases.files as files_use_cases
 from settings import settings
 
@@ -46,6 +46,35 @@ def get_file_details(file_id: str):
     return file
 
 
+@router.get("/{file_id}/content/")
+def get_file_content(file_id: str) -> FileResponse:
+    """
+    Retrieves the file data associated with a given File ID.
+
+    This returns the file for download as a streamed file.
+
+    GET /files/{file_id}/content/
+
+    200 { <File> }
+
+        The file data is returned as a stream if the file exists.
+
+    404 {}
+
+        The file ID did not map to anything.
+    """
+    file = files_use_cases.get_file_record_by_id(file_id)
+
+    if file is None:
+        raise HTTPException(status_code=404)
+
+    return FileResponse(
+        path=file["path"],
+        media_type="application/octet-stream",
+        filename=file["filename"],
+    )
+
+
 @router.delete("/{file_id}/")
 def delete_file(file_id: str) -> files_use_cases.FileRecord:
     """

backend/tests/test_api_files.py

@@ -92,3 +92,26 @@ def test_file_deletion_200_and_return_deleted_resource(client, tmp_path):
 
     assert response.status_code == 200
     assert response.json() == response_data
+
+
+def test_file_downloads_200_and_return_file(client, tmp_path):
+    mock_file = tmp_path / "test.txt"
+    mock_file.write_text("testtest")
+
+    with open(str(mock_file), "rb") as mock_file_stream:
+        response = client.post("/files/", files={"file": mock_file_stream})
+
+    response_data = response.json()
+    file_id = response_data["id"]
+
+    response = client.get(f"/files/{file_id}/content/")
+
+    assert response.status_code == 200
+    assert response.text == mock_file.read_text()
+
+
+def test_file_downloads_404_if_does_not_exist(client):
+    non_existent_id = "06f02980-864d-4832-a894-2e9d2543a79a"
+    response = client.get(f"/files/{non_existent_id}/content/")
+
+    assert response.status_code == 404