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fluxer_app/src/stores/DimensionStore.tsx

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+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import {action, makeObservable, observable} from 'mobx';
+
+const BOTTOM_TOLERANCE = 2;
+
+interface ChannelDimensions {
+	channelId: string;
+	scrollTop: number;
+	scrollHeight: number;
+	offsetHeight: number;
+}
+
+interface GuildDimensions {
+	guildId: string;
+	scrollTop: number | null;
+	scrollTo: number | null;
+}
+
+interface GuildListDimensions {
+	scrollTop: number;
+}
+
+function createDefaultGuildDimensions(guildId: string): GuildDimensions {
+	return {
+		guildId,
+		scrollTop: null,
+		scrollTo: null,
+	};
+}
+
+class DimensionStore {
+	channelDimensions = observable.map(new Map<string, ChannelDimensions>());
+
+	guildDimensions = observable.map(new Map<string, GuildDimensions>());
+
+	guildListDimensions = observable.box({
+		scrollTop: 0,
+	});
+
+	constructor() {
+		makeObservable(this, {
+			updateChannelDimensions: action,
+			updateGuildDimensions: action,
+			updateGuildListDimensions: action,
+			clearChannelDimensions: action,
+		});
+	}
+
+	percentageScrolled(channelId: string): number {
+		const dimensions = this.channelDimensions.get(channelId);
+		if (dimensions != null) {
+			const {scrollTop, scrollHeight} = dimensions;
+			return scrollTop / scrollHeight;
+		}
+		return 1;
+	}
+
+	getChannelDimensions(channelId: string): ChannelDimensions | undefined {
+		return this.channelDimensions.get(channelId);
+	}
+
+	getGuildDimensions(guildId: string): GuildDimensions {
+		const existing = this.guildDimensions.get(guildId);
+		if (existing != null) {
+			return existing;
+		}
+		return createDefaultGuildDimensions(guildId);
+	}
+
+	getGuildListDimensions(): GuildListDimensions {
+		return this.guildListDimensions.get();
+	}
+
+	isAtBottom(channelId: string): boolean {
+		const dimensions = this.channelDimensions.get(channelId);
+		if (dimensions == null) {
+			return true;
+		}
+		const {scrollTop, scrollHeight, offsetHeight} = dimensions;
+		return scrollTop >= scrollHeight - offsetHeight - BOTTOM_TOLERANCE;
+	}
+
+	updateChannelDimensions(
+		channelId: string,
+		scrollTop: number | null,
+		scrollHeight: number | null,
+		offsetHeight: number | null,
+		callback?: () => void,
+	): void {
+		const existing = this.channelDimensions.get(channelId);
+
+		if (scrollTop == null || scrollHeight == null || offsetHeight == null) {
+			if (existing != null) {
+				this.channelDimensions.delete(channelId);
+			}
+			callback?.();
+			return;
+		}
+
+		const newDimensions: ChannelDimensions = {
+			channelId,
+			scrollTop,
+			scrollHeight,
+			offsetHeight,
+		};
+
+		if (
+			existing == null ||
+			existing.scrollTop !== scrollTop ||
+			existing.scrollHeight !== scrollHeight ||
+			existing.offsetHeight !== offsetHeight
+		) {
+			this.channelDimensions.set(channelId, newDimensions);
+		}
+
+		callback?.();
+	}
+
+	updateGuildDimensions(guildId: string, scrollTop?: number | null, scrollTo?: number | null): void {
+		let dimensions = this.guildDimensions.get(guildId);
+
+		if (dimensions == null) {
+			dimensions = createDefaultGuildDimensions(guildId);
+		}
+
+		const updated: GuildDimensions = {
+			...dimensions,
+			scrollTop: scrollTop !== undefined ? scrollTop : dimensions.scrollTop,
+			scrollTo: scrollTo !== undefined ? scrollTo : dimensions.scrollTo,
+		};
+
+		this.guildDimensions.set(guildId, updated);
+	}
+
+	updateGuildListDimensions(scrollTop: number): void {
+		this.guildListDimensions.set({scrollTop});
+	}
+
+	clearChannelDimensions(channelId: string): void {
+		this.channelDimensions.delete(channelId);
+	}
+
+	scrollGuildListTo(guildId: string, scrollTo: number): void {
+		this.updateGuildDimensions(guildId, undefined, scrollTo);
+	}
+
+	clearGuildListScrollTo(guildId: string): void {
+		this.updateGuildDimensions(guildId, undefined, null);
+	}
+
+	handleCallCreate(channelId: string): void {
+		this.clearChannelDimensions(channelId);
+	}
+}
+
+export default new DimensionStore();