import dataclasses import urllib.parse from django.db import models from django.http import HttpRequest from activities.models import PostInteraction @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 @classmethod def empty(cls): return cls(results=[], limit=20) def next(self, request: HttpRequest, allowed_params: list[str]): """ Returns a URL to the next page of results. """ if not self.results: return None params = self.filter_params(request, allowed_params) params["max_id"] = self.results[-1].pk return f"{request.build_absolute_uri(request.path)}?{urllib.parse.urlencode(params)}" def prev(self, request: HttpRequest, allowed_params: list[str]): """ Returns a URL to the previous page of results. """ if not self.results: return None params = self.filter_params(request, allowed_params) params["min_id"] = self.results[0].pk 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 = {} for key in allowed_params: value = request.GET.get(key, None) if value: params[key] = value return params class MastodonPaginator: """ Paginates in the Mastodon style (max_id, min_id, etc). """ def __init__( self, anchor_model: type[models.Model], sort_attribute: str = "created", default_limit: int = 20, max_limit: int = 40, ): self.anchor_model = anchor_model self.sort_attribute = sort_attribute self.default_limit = default_limit self.max_limit = max_limit def get_anchor(self, anchor_id: str): """ Gets an anchor object by ID. It's possible that the anchor object might be an interaction, in which case we recurse down to its post. """ if anchor_id.startswith("interaction-"): try: return PostInteraction.objects.get(pk=anchor_id[12:]) except PostInteraction.DoesNotExist: return PaginationResult.empty() try: return self.anchor_model.objects.get(pk=anchor_id) except self.anchor_model.DoesNotExist: return PaginationResult.empty() def paginate( self, queryset, min_id: str | None, max_id: str | None, since_id: str | None, limit: int | None, ) -> PaginationResult: if max_id: anchor = self.get_anchor(max_id) queryset = queryset.filter( **{self.sort_attribute + "__lt": getattr(anchor, self.sort_attribute)} ) if since_id: anchor = self.get_anchor(since_id) queryset = queryset.filter( **{self.sort_attribute + "__gt": getattr(anchor, self.sort_attribute)} ) if min_id: # Min ID requires items _immediately_ newer than specified, so we # invert the ordering to accommodate anchor = self.get_anchor(min_id) queryset = queryset.filter( **{self.sort_attribute + "__gt": getattr(anchor, self.sort_attribute)} ).order_by(self.sort_attribute) else: queryset = queryset.order_by("-" + self.sort_attribute) limit = min(limit or self.default_limit, self.max_limit) return PaginationResult( results=list(queryset[:limit]), limit=limit, )