Implement per-resource last_update timestamps

Closes #62

tests/test_incremental_per_repository.py

@@ -0,0 +1,189 @@
+"""Tests for per-resource incremental checkpoints."""
+
+import json
+import os
+
+from github_backup import github_backup
+
+
+def _repo(name, updated_at, pushed_at=None):
+    return {
+        "name": name,
+        "full_name": "owner/{0}".format(name),
+        "owner": {"login": "owner"},
+        "clone_url": "https://github.com/owner/{0}.git".format(name),
+        "private": False,
+        "fork": False,
+        "has_wiki": False,
+        "updated_at": updated_at,
+        "pushed_at": pushed_at,
+    }
+
+
+def test_incremental_uses_per_resource_last_update(
+    create_args, tmp_path, monkeypatch
+):
+    args = create_args(incremental=True, include_issues=True)
+    repositories = [
+        _repo("repo-one", "2026-02-01T00:00:00Z"),
+        _repo("repo-two", "2026-03-01T00:00:00Z"),
+    ]
+    repo_one_issues = tmp_path / "repositories" / "repo-one" / "issues"
+    repo_two_issues = tmp_path / "repositories" / "repo-two" / "issues"
+    repo_one_issues.mkdir(parents=True)
+    repo_two_issues.mkdir(parents=True)
+    (repo_one_issues / "last_update").write_text("2026-01-01T00:00:00Z")
+    (repo_two_issues / "last_update").write_text("2025-01-01T00:00:00Z")
+
+    seen_since = []
+
+    def fake_backup_issues(passed_args, repo_cwd, repository, repos_template):
+        seen_since.append((repository["name"], passed_args.since))
+
+    monkeypatch.setattr(github_backup, "backup_issues", fake_backup_issues)
+
+    github_backup.backup_repositories(args, tmp_path, repositories)
+
+    assert seen_since == [
+        ("repo-one", "2026-01-01T00:00:00Z"),
+        ("repo-two", "2025-01-01T00:00:00Z"),
+    ]
+    assert (repo_one_issues / "last_update").read_text() == "2026-02-01T00:00:00Z"
+    assert (repo_two_issues / "last_update").read_text() == "2026-03-01T00:00:00Z"
+    assert not os.path.exists(tmp_path / "last_update")
+
+
+def test_incremental_uses_independent_issue_and_pull_checkpoints(
+    create_args, tmp_path, monkeypatch
+):
+    args = create_args(incremental=True, include_issues=True, include_pulls=True)
+    repository = _repo("repo-one", "2026-02-01T00:00:00Z")
+    repo_dir = tmp_path / "repositories" / "repo-one"
+    issues_dir = repo_dir / "issues"
+    pulls_dir = repo_dir / "pulls"
+    issues_dir.mkdir(parents=True)
+    pulls_dir.mkdir(parents=True)
+    (issues_dir / "last_update").write_text("2026-01-01T00:00:00Z")
+    (pulls_dir / "last_update").write_text("2025-01-01T00:00:00Z")
+
+    seen_since = []
+
+    def fake_backup_issues(passed_args, repo_cwd, repository, repos_template):
+        seen_since.append(("issues", passed_args.since))
+
+    def fake_backup_pulls(passed_args, repo_cwd, repository, repos_template):
+        seen_since.append(("pulls", passed_args.since))
+
+    monkeypatch.setattr(github_backup, "backup_issues", fake_backup_issues)
+    monkeypatch.setattr(github_backup, "backup_pulls", fake_backup_pulls)
+
+    github_backup.backup_repositories(args, tmp_path, [repository])
+
+    assert seen_since == [
+        ("issues", "2026-01-01T00:00:00Z"),
+        ("pulls", "2025-01-01T00:00:00Z"),
+    ]
+    assert (issues_dir / "last_update").read_text() == "2026-02-01T00:00:00Z"
+    assert (pulls_dir / "last_update").read_text() == "2026-02-01T00:00:00Z"
+
+
+def test_incremental_uses_legacy_global_last_update_for_existing_resource_backup(
+    create_args, tmp_path, monkeypatch
+):
+    args = create_args(incremental=True, include_issues=True)
+    repository = _repo("repo-one", "2026-02-01T00:00:00Z")
+    (tmp_path / "last_update").write_text("2026-01-01T00:00:00Z")
+    issues_dir = tmp_path / "repositories" / "repo-one" / "issues"
+    issues_dir.mkdir(parents=True)
+    with open(issues_dir / "1.json", "w", encoding="utf-8") as f:
+        json.dump({"number": 1}, f)
+
+    seen_since = []
+
+    def fake_backup_issues(passed_args, repo_cwd, repository, repos_template):
+        seen_since.append(passed_args.since)
+
+    monkeypatch.setattr(github_backup, "backup_issues", fake_backup_issues)
+
+    github_backup.backup_repositories(args, tmp_path, [repository])
+
+    assert seen_since == ["2026-01-01T00:00:00Z"]
+    assert (issues_dir / "last_update").read_text() == "2026-02-01T00:00:00Z"
+    assert not os.path.exists(tmp_path / "last_update")
+
+
+def test_incremental_does_not_use_legacy_global_last_update_for_new_resource_backup(
+    create_args, tmp_path, monkeypatch
+):
+    args = create_args(incremental=True, include_issues=True)
+    repository = _repo("repo-one", "2026-02-01T00:00:00Z")
+    (tmp_path / "last_update").write_text("2099-01-01T00:00:00Z")
+
+    seen_since = []
+
+    def fake_backup_issues(passed_args, repo_cwd, repository, repos_template):
+        seen_since.append(passed_args.since)
+
+    monkeypatch.setattr(github_backup, "backup_issues", fake_backup_issues)
+
+    github_backup.backup_repositories(args, tmp_path, [repository])
+
+    assert seen_since == [None]
+    assert (
+        tmp_path / "repositories" / "repo-one" / "issues" / "last_update"
+    ).read_text() == "2026-02-01T00:00:00Z"
+    assert not os.path.exists(tmp_path / "last_update")
+
+
+def test_incremental_keeps_legacy_global_last_update_until_all_existing_resources_migrated(
+    create_args, tmp_path, monkeypatch
+):
+    args = create_args(incremental=True, include_issues=True)
+    repository = _repo("repo-one", "2026-02-01T00:00:00Z")
+    (tmp_path / "last_update").write_text("2026-01-01T00:00:00Z")
+    repo_one_issues = tmp_path / "repositories" / "repo-one" / "issues"
+    repo_two_issues = tmp_path / "repositories" / "repo-two" / "issues"
+    repo_one_issues.mkdir(parents=True)
+    repo_two_issues.mkdir(parents=True)
+    with open(repo_one_issues / "1.json", "w", encoding="utf-8") as f:
+        json.dump({"number": 1}, f)
+    with open(repo_two_issues / "2.json", "w", encoding="utf-8") as f:
+        json.dump({"number": 2}, f)
+
+    def fake_backup_issues(passed_args, repo_cwd, repository, repos_template):
+        pass
+
+    monkeypatch.setattr(github_backup, "backup_issues", fake_backup_issues)
+
+    github_backup.backup_repositories(args, tmp_path, [repository])
+
+    assert (repo_one_issues / "last_update").read_text() == "2026-02-01T00:00:00Z"
+    assert not os.path.exists(repo_two_issues / "last_update")
+    assert (tmp_path / "last_update").read_text() == "2026-01-01T00:00:00Z"
+
+
+def test_incremental_does_not_remove_legacy_checkpoint_without_resource_work(
+    create_args, tmp_path
+):
+    args = create_args(incremental=True, include_repository=True)
+    repository = _repo("repo-one", "2026-02-01T00:00:00Z")
+    (tmp_path / "last_update").write_text("2026-01-01T00:00:00Z")
+
+    github_backup.backup_repositories(args, tmp_path, [repository])
+
+    assert (tmp_path / "last_update").read_text() == "2026-01-01T00:00:00Z"
+    assert not os.path.exists(
+        tmp_path / "repositories" / "repo-one" / "issues" / "last_update"
+    )
+
+
+def test_repository_checkpoint_time_uses_newest_available_repo_timestamp():
+    repository = _repo(
+        "repo-one",
+        updated_at="2026-02-01T00:00:00Z",
+        pushed_at="2026-03-01T00:00:00Z",
+    )
+
+    assert github_backup.get_repository_checkpoint_time(repository) == (
+        "2026-03-01T00:00:00Z"
+    )