takahe/api/pagination.py

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import dataclasses
import urllib.parse
from collections.abc import Callable
from typing import Any
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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
#: A list of transformed JSON objects
json_results: list[dict] | None = None
@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
if self.json_results is None:
raise ValueError("You must JSONify the results first")
params = self.filter_params(request, allowed_params)
params["max_id"] = self.json_results[-1]["id"]
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
if self.json_results is None:
raise ValueError("You must JSONify the results first")
params = self.filter_params(request, allowed_params)
params["min_id"] = self.json_results[0]["id"]
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"',
)
)
def jsonify_results(self, map_function: Callable[[Any], Any]):
"""
Replaces our results with ones transformed via map_function
"""
self.json_results = [map_function(result) for result in self.results]
def jsonify_posts(self, identity):
"""
Predefined way of JSON-ifying Post objects
"""
interactions = PostInteraction.get_post_interactions(self.results, identity)
self.jsonify_results(
lambda post: post.to_mastodon_json(interactions=interactions)
)
def jsonify_status_events(self, identity):
"""
Predefined way of JSON-ifying TimelineEvent objects representing statuses
"""
interactions = PostInteraction.get_event_interactions(self.results, identity)
self.jsonify_results(
lambda event: event.to_mastodon_status_json(interactions=interactions)
)
def jsonify_notification_events(self, identity):
"""
Predefined way of JSON-ifying TimelineEvent objects representing notifications
"""
interactions = PostInteraction.get_event_interactions(self.results, identity)
self.jsonify_results(
lambda event: event.to_mastodon_notification_json(interactions=interactions)
)
def jsonify_identities(self):
"""
Predefined way of JSON-ifying Identity objects
"""
self.jsonify_results(lambda identity: identity.to_mastodon_json())
@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
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class MastodonPaginator:
"""
Paginates in the Mastodon style (max_id, min_id, etc).
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Note that this basically _requires_ us to always do it on IDs, so we do.
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"""
def __init__(
self,
default_limit: int = 20,
max_limit: int = 40,
):
self.default_limit = default_limit
self.max_limit = max_limit
def paginate(
self,
queryset,
min_id: str | None,
max_id: str | None,
since_id: str | None,
limit: int | None,
) -> PaginationResult:
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if max_id:
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queryset = queryset.filter(id__lt=max_id)
if since_id:
queryset = queryset.filter(id__gt=since_id)
if min_id:
# Min ID requires items _immediately_ newer than specified, so we
# invert the ordering to accommodate
queryset = queryset.filter(id__gt=min_id).order_by("id")
else:
queryset = queryset.order_by("-id")
limit = min(limit or self.default_limit, self.max_limit)
return PaginationResult(
results=list(queryset[:limit]),
limit=limit,
)
def paginate_home(
self,
queryset,
min_id: str | None,
max_id: str | None,
since_id: str | None,
limit: int | None,
) -> PaginationResult:
"""
The home timeline requires special handling where we mix Posts and
PostInteractions together.
"""
if max_id:
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queryset = queryset.filter(
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models.Q(subject_post_id__lt=max_id)
| models.Q(subject_post_interaction_id__lt=max_id)
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)
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if since_id:
queryset = queryset.filter(
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models.Q(subject_post_id__gt=max_id)
| models.Q(subject_post_interaction_id__gt=max_id)
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)
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if min_id:
# Min ID requires items _immediately_ newer than specified, so we
# invert the ordering to accommodate
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queryset = queryset.filter(
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models.Q(subject_post_id__gt=max_id)
| models.Q(subject_post_interaction_id__gt=max_id)
).order_by("id")
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else:
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queryset = queryset.order_by("-id")
limit = min(limit or self.default_limit, self.max_limit)
return PaginationResult(
results=list(queryset[:limit]),
limit=limit,
)