63 lines
2.0 KiB
TypeScript
63 lines
2.0 KiB
TypeScript
/*
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* Copyright (C) 2026 Fluxer Contributors
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*
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* This file is part of Fluxer.
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*
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* Fluxer is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Fluxer is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Affero General Public License for more details.
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*
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* You should have received a copy of the GNU Affero General Public License
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* along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
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*/
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export interface ScrollMetrics {
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scrollTop: number;
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scrollHeight: number;
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offsetHeight: number;
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}
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export interface ScrollPinOptions {
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tolerance?: number;
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stickyTolerance?: number;
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hasMoreAfter?: boolean;
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wasPinned?: boolean;
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allowPinWhenHasMoreAfter?: boolean;
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}
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export interface ScrollPinResult {
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distanceFromBottom: number;
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isAtBottom: boolean;
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isPinned: boolean;
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}
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const DEFAULT_TOLERANCE = 8;
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const DEFAULT_STICKY_TOLERANCE = 64;
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export function evaluateScrollPinning(metrics: ScrollMetrics, options: ScrollPinOptions = {}): ScrollPinResult {
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const tolerance = options.tolerance ?? DEFAULT_TOLERANCE;
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const stickyTolerance = options.stickyTolerance ?? DEFAULT_STICKY_TOLERANCE;
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const hasMoreAfter = options.hasMoreAfter ?? false;
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const allowPinWhenHasMoreAfter = options.allowPinWhenHasMoreAfter ?? true;
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const wasPinned = options.wasPinned ?? false;
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const distanceFromBottom = Math.max(metrics.scrollHeight - metrics.offsetHeight - metrics.scrollTop, 0);
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const isWithinTolerance = distanceFromBottom <= tolerance;
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const isWithinStickyRange = distanceFromBottom <= stickyTolerance;
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const shouldPin =
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(isWithinTolerance || (wasPinned && isWithinStickyRange)) && (allowPinWhenHasMoreAfter || !hasMoreAfter);
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return {
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distanceFromBottom,
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isAtBottom: isWithinTolerance,
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isPinned: shouldPin,
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};
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}
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