Name downloaded books with a template

The new "Book Downloads" group in Settings holds a Calibre template for the file name of a
direct download. Without a template, the name stays the title. The name is also the title if
the template fails or gives no name for a book.

tests/test_api_flows.py

@@ -147,6 +147,55 @@ def test_download_builds_from_stored_chapters_without_changing_them(client, stor
     response.close()
 
 
+def download_name(client, sid):
+    response = client.get(f"/api/stories/{sid}/epub")
+    response.close()
+    return response.headers["Content-Disposition"]
+
+
+def test_download_template_names_the_file(client, story):
+    sid, _ = story
+    site = {"title": "The Book", "authors": ["Ann Writer"], "series": "The Saga", "series_index": 2.0}
+    o.store.update_story(sid, metahtml=metahtml(), title="The Book", site_values=site)
+    assert client.get("/api/config").json["download_fields"]["id"].startswith("The CWA book ID")
+    saved = client.put("/api/settings", json={"download_template": " {series:|| - }{title} - {id} "}, headers=H)
+    assert saved.json["download_template"] == "{series:|| - }{title} - {id}"
+    assert f'filename="Saga, The - Book, The - {sid}.epub"' in download_name(client, sid)
+    # The ID is that of the CWA book, when the story has one.
+    o.store.update_story(sid, calibre_id=77, pinned={"title": "Caf\u00e9", "series": ["", None]})
+    name = download_name(client, sid)
+    assert 'filename="Cafe - 77.epub"' in name and "filename*=UTF-8''Caf%C3%A9%20-%2077.epub" in name
+    # A template with folders gives the name of the file alone.
+    client.put("/api/settings", json={"download_template": "{author_sort}/{title} - {authors}"}, headers=H)
+    assert "filename*=UTF-8''Caf%C3%A9%20-%20Ann%20Writer.epub" in download_name(client, sid)
+    # Without a template, the name is the title of the story, with its article in front.
+    assert client.put("/api/settings", json={"download_template": ""}, headers=H).json["download_template"] == ""
+    assert 'filename="The Book.epub"' in download_name(client, sid)
+
+
+def test_download_template_that_fails_gives_the_title(client, story, caplog):
+    sid, _ = story
+    o.store.update_story(sid, metahtml=metahtml())
+    for template in ("{title:d}", "{series}/{series_index}"):
+        client.put("/api/settings", json={"download_template": template}, headers=H)
+        assert "filename=Story.epub" in download_name(client, sid)
+    assert "The download template fails for https://www.royalroad.com/fiction/1234" in caplog.text
+    assert caplog.text.count("The download template fails") == 1
+
+
+def test_bad_download_template_is_not_saved(client):
+    client.put("/api/settings", json={"download_template": "{title}"}, headers=H)
+    for template, error in [
+        ("{title:uppercase()}", "Bindery does not support template functions, such as {title:uppercase()}"),
+        ("{title", "The braces of the template do not match: expected '}' before end of string"),
+        (7, "The download template must be text"),
+    ]:
+        response = client.put("/api/settings", json={"download_template": template, "recent_chapters": 9}, headers=H)
+        assert (response.status_code, response.json) == (400, {"error": error})
+    assert client.get("/api/settings").json["download_template"] == "{title}"
+    assert client.get("/api/settings").json["recent_chapters"] == 0
+
+
 def test_unexpected_backend_error_returns_json(client, monkeypatch, caplog):
     monkeypatch.setattr(o, "list_stories", Mock(side_effect=RuntimeError("broken")))
     response = client.get("/api/stories")