Extract grouping logic into shared function (#19)

Add group_rows_by_project_and_version() to report_builder.py and replace
the duplicated inline grouping in both html.py and odt.py with a single
call to the shared function. This ensures consistent grouping behavior
across formatters and removes a maintenance burden — any change to
grouping logic now happens in one place.

Closes #19

tests/test_report_builder.py

@@ -1,4 +1,8 @@
-from redmine_reporter.report_builder import STATUS_TRANSLATION, build_grouped_report
+from redmine_reporter.report_builder import (
+    STATUS_TRANSLATION,
+    build_grouped_report,
+    group_rows_by_project_and_version,
+)
 
 
 class MockIssue:
@@ -117,3 +121,104 @@ def test_build_grouped_report_deterministic_order_within_group():
     ]
     rows = build_grouped_report(issues)
     assert [r["issue_id"] for r in rows] == [101, 102, 103]
+
+
+# -- #19: Общая функция группировки --
+
+
+def test_group_rows_basic():
+    """Два проекта, в одном две версии — структура корректна."""
+    rows = [
+        {
+            "project": "A",
+            "version": "v1",
+            "issue_id": 1,
+            "subject": "T1",
+            "status_ru": "S",
+            "time_text": "1ч",
+        },
+        {
+            "project": "A",
+            "version": "v2",
+            "issue_id": 2,
+            "subject": "T2",
+            "status_ru": "S",
+            "time_text": "2ч",
+        },
+        {
+            "project": "B",
+            "version": "v1",
+            "issue_id": 3,
+            "subject": "T3",
+            "status_ru": "S",
+            "time_text": "3ч",
+        },
+    ]
+    grouped = group_rows_by_project_and_version(rows)
+
+    assert list(grouped.keys()) == ["A", "B"]
+    assert list(grouped["A"].keys()) == ["v1", "v2"]
+    assert list(grouped["B"].keys()) == ["v1"]
+    assert len(grouped["A"]["v1"]) == 1
+    assert len(grouped["A"]["v2"]) == 1
+    assert len(grouped["B"]["v1"]) == 1
+
+
+def test_group_rows_multiple_tasks_per_version():
+    """Несколько задач в одной версии — все попадают в список."""
+    rows = [
+        {
+            "project": "A",
+            "version": "v1",
+            "issue_id": 1,
+            "subject": "T1",
+            "status_ru": "S",
+            "time_text": "1ч",
+        },
+        {
+            "project": "A",
+            "version": "v1",
+            "issue_id": 2,
+            "subject": "T2",
+            "status_ru": "S",
+            "time_text": "2ч",
+        },
+        {
+            "project": "A",
+            "version": "v1",
+            "issue_id": 3,
+            "subject": "T3",
+            "status_ru": "S",
+            "time_text": "3ч",
+        },
+    ]
+    grouped = group_rows_by_project_and_version(rows)
+
+    assert len(grouped["A"]["v1"]) == 3
+    assert [r["issue_id"] for r in grouped["A"]["v1"]] == [1, 2, 3]
+
+
+def test_group_rows_preserves_row_data():
+    """Строки в группировке — те же объекты, без потери данных."""
+    rows = [
+        {
+            "project": "P",
+            "version": "v1",
+            "issue_id": 42,
+            "subject": "Task",
+            "status_ru": "Готово",
+            "time_text": "5ч",
+        },
+    ]
+    grouped = group_rows_by_project_and_version(rows)
+
+    row = grouped["P"]["v1"][0]
+    assert row["issue_id"] == 42
+    assert row["subject"] == "Task"
+    assert row["status_ru"] == "Готово"
+    assert row["time_text"] == "5ч"
+
+
+def test_group_rows_empty():
+    """Пустой список — пустой словарь."""
+    assert group_rows_by_project_and_version([]) == {}