From 9c3806a17542ae6dc7ea4ece4ba87670172e556b Mon Sep 17 00:00:00 2001
From: Andrew Godwin <andrew@aeracode.org>
Date: Thu, 29 Dec 2022 11:46:25 -0700
Subject: [PATCH] Refactor link header and fix empty page case

---
 api/pagination.py          | 30 ++++++++++++++++++++++++------
 api/views/accounts.py      | 25 +++++++++++--------------
 api/views/notifications.py |  8 +-------
 api/views/timelines.py     | 25 +++++++------------------
 4 files changed, 43 insertions(+), 45 deletions(-)

diff --git a/api/pagination.py b/api/pagination.py
index 8ebbd92..7b12d87 100644
--- a/api/pagination.py
+++ b/api/pagination.py
@@ -7,11 +7,19 @@ from django.http import HttpRequest
 
 @dataclasses.dataclass
 class PaginationResult:
+    """
+    Represents a pagination result for Mastodon (it does Link header stuff)
+    """
+
     #: A list of objects that matched the pagination query.
     results: list[models.Model]
+
     #: The actual applied limit, which may be different from what was requested.
     limit: int
-    sort_attribute: str
+
+    @classmethod
+    def empty(cls):
+        return cls(results=[], limit=20)
 
     def next(self, request: HttpRequest, allowed_params: list[str]):
         """
@@ -37,6 +45,17 @@ class PaginationResult:
 
         return f"{request.build_absolute_uri(request.path)}?{urllib.parse.urlencode(params)}"
 
+    def link_header(self, request: HttpRequest, allowed_params: list[str]):
+        """
+        Creates a link header for the given request
+        """
+        return ", ".join(
+            (
+                f'<{self.next(request, allowed_params)}>; rel="next"',
+                f'<{self.prev(request, allowed_params)}>; rel="prev"',
+            )
+        )
+
     @staticmethod
     def filter_params(request: HttpRequest, allowed_params: list[str]):
         params = {}
@@ -71,12 +90,12 @@ class MastodonPaginator:
         max_id: str | None,
         since_id: str | None,
         limit: int | None,
-    ):
+    ) -> PaginationResult:
         if max_id:
             try:
                 anchor = self.anchor_model.objects.get(pk=max_id)
             except self.anchor_model.DoesNotExist:
-                return []
+                return PaginationResult.empty()
             queryset = queryset.filter(
                 **{self.sort_attribute + "__lt": getattr(anchor, self.sort_attribute)}
             )
@@ -85,7 +104,7 @@ class MastodonPaginator:
             try:
                 anchor = self.anchor_model.objects.get(pk=since_id)
             except self.anchor_model.DoesNotExist:
-                return []
+                return PaginationResult.empty()
             queryset = queryset.filter(
                 **{self.sort_attribute + "__gt": getattr(anchor, self.sort_attribute)}
             )
@@ -96,7 +115,7 @@ class MastodonPaginator:
             try:
                 anchor = self.anchor_model.objects.get(pk=min_id)
             except self.anchor_model.DoesNotExist:
-                return []
+                return PaginationResult.empty()
             queryset = queryset.filter(
                 **{self.sort_attribute + "__gt": getattr(anchor, self.sort_attribute)}
             ).order_by(self.sort_attribute)
@@ -107,5 +126,4 @@ class MastodonPaginator:
         return PaginationResult(
             results=list(queryset[:limit]),
             limit=limit,
-            sort_attribute=self.sort_attribute,
         )
diff --git a/api/views/accounts.py b/api/views/accounts.py
index 71a5c74..f3328b2 100644
--- a/api/views/accounts.py
+++ b/api/views/accounts.py
@@ -132,20 +132,17 @@ def account_statuses(
     )
 
     if pager.results:
-        params = [
-            "limit",
-            "id",
-            "exclude_reblogs",
-            "exclude_replies",
-            "only_media",
-            "pinned",
-            "tagged",
-        ]
-        response.headers["Link"] = ", ".join(
-            (
-                f'<{pager.next(request, params)}>; rel="next"',
-                f'<{pager.prev(request, params)}>; rel="prev"',
-            )
+        response.headers["Link"] = pager.link_header(
+            request,
+            [
+                "limit",
+                "id",
+                "exclude_reblogs",
+                "exclude_replies",
+                "only_media",
+                "pinned",
+                "tagged",
+            ],
         )
 
     interactions = PostInteraction.get_post_interactions(
diff --git a/api/views/notifications.py b/api/views/notifications.py
index 79a3a7d..1d31e40 100644
--- a/api/views/notifications.py
+++ b/api/views/notifications.py
@@ -45,13 +45,7 @@ def notifications(
     )
 
     if pager.results:
-        params = ["limit", "account_id"]
-        response.headers["Link"] = ", ".join(
-            (
-                f'<{pager.next(request, params)}>; rel="next"',
-                f'<{pager.prev(request, params)}>; rel="prev"',
-            )
-        )
+        response.headers["Link"] = pager.link_header(request, ["limit", "account_id"])
 
     interactions = PostInteraction.get_event_interactions(
         pager.results, request.identity
diff --git a/api/views/timelines.py b/api/views/timelines.py
index 1ac4964..e767fde 100644
--- a/api/views/timelines.py
+++ b/api/views/timelines.py
@@ -33,12 +33,7 @@ def home(
     )
 
     if pager.results:
-        response.headers["Link"] = ", ".join(
-            (
-                f"<{pager.next(request, ['limit'])}>; rel=\"next\"",
-                f"<{pager.prev(request, ['limit'])}>; rel=\"prev\"",
-            )
-        )
+        response.headers["Link"] = pager.link_header(request, ["limit"])
 
     return [
         event.to_mastodon_status_json(interactions=interactions)
@@ -79,12 +74,9 @@ def public(
     )
 
     if pager.results:
-        params = ["limit", "local", "remote", "only_media"]
-        response.headers["Link"] = ", ".join(
-            (
-                f'<{pager.next(request, params)}>; rel="next"',
-                f'<{pager.prev(request, params)}>; rel="prev"',
-            )
+        response.headers["Link"] = pager.link_header(
+            request,
+            ["limit", "local", "remote", "only_media"],
         )
 
     interactions = PostInteraction.get_post_interactions(
@@ -123,12 +115,9 @@ def hashtag(
     )
 
     if pager.results:
-        params = ["limit", "local", "hashtag", "only_media"]
-        response.headers["Link"] = ", ".join(
-            (
-                f'<{pager.next(request, params)}>; rel="next"',
-                f'<{pager.prev(request, params)}>; rel="prev"',
-            )
+        response.headers["Link"] = pager.link_header(
+            request,
+            ["limit", "local", "remote", "only_media"],
         )
 
     interactions = PostInteraction.get_post_interactions(