fluxer/fluxer_app/src/features/app/utils/PlaceholderSpecs.ts

// SPDX-License-Identifier: AGPL-3.0-or-later

import {useMemo} from 'react';

function hashSeed(input: string): number {
	let hash = 2166136261;
	for (let index = 0; index < input.length; index++) {
		hash ^= input.charCodeAt(index);
		hash = Math.imul(hash, 16777619);
	}
	return hash >>> 0;
}

function createSeededRandom(seed: number): () => number {
	let state = seed === 0 ? 0x9e3779b9 : seed >>> 0;
	return () => {
		state ^= state << 13;
		state ^= state >>> 17;
		state ^= state << 5;
		return (state >>> 0) / 4294967296;
	};
}

function generatePlaceholderSpecs(options: {
	compact: boolean;
	messageGroups: number;
	groupRange: number;
	attachments: number;
	fontSize: number;
	groupSpacing: number;
	random: () => number;
}): {
	messages: Array<number>;
	attachmentSpecs: Array<
		| [
				number,
				{
					width: number;
					height: number;
				},
		  ]
		| undefined
	>;
	totalHeight: number;
	groupSpacing: number;
} {
	const {compact, messageGroups, groupRange, attachments, fontSize, groupSpacing, random} = options;
	if (attachments > messageGroups) {
		throw new Error(
			`generatePlaceholderSpecs: too many attachments relative to messageGroups: ${messageGroups}, ${attachments}`,
		);
	}
	const DEFAULT_FONT_SIZE = 16;
	const scale = fontSize / DEFAULT_FONT_SIZE;
	const MESSAGE_HEIGHT_COZY = 22;
	const MESSAGE_HEIGHT_COMPACT = 16;
	const ATTACHMENT_MARGIN = 8;
	const messageHeight = compact ? MESSAGE_HEIGHT_COMPACT : MESSAGE_HEIGHT_COZY;
	let totalHeight = 0;
	const messageCounts: Array<number> = [];
	for (let i = 0; i < messageGroups; i++) {
		const count = Math.floor(random() * groupRange) + 1;
		messageCounts.push(count);
		totalHeight += groupSpacing * scale;
		totalHeight += messageHeight * scale;
		totalHeight += (count - 1) * messageHeight * scale;
	}
	const availableGroupIndices = messageCounts.map((_, i) => i);
	const attachmentSpecs: Array<
		| [
				number,
				{
					width: number;
					height: number;
				},
		  ]
		| undefined
	> = Array(messageGroups).fill(undefined);
	for (let i = 0; i < attachments; i++) {
		const randomIndex = Math.floor(random() * availableGroupIndices.length);
		const groupIndex = availableGroupIndices.splice(randomIndex, 1)[0];
		const width = Math.floor(random() * (400 - 140 + 1)) + 140;
		const height = Math.floor(random() * (320 - 100 + 1)) + 100;
		attachmentSpecs[groupIndex] = [groupIndex, {width, height}];
		totalHeight += height + ATTACHMENT_MARGIN * scale;
	}
	return {
		messages: messageCounts,
		attachmentSpecs,
		totalHeight,
		groupSpacing,
	};
}

export function usePlaceholderSpecs(compact: boolean, groupSpacing: number, fontSize: number, seedKey: string) {
	return useMemo(() => {
		const seed = hashSeed(`${seedKey}|${compact ? '1' : '0'}|${groupSpacing}|${fontSize}`);
		const random = createSeededRandom(seed);
		return compact
			? generatePlaceholderSpecs({
					compact: true,
					messageGroups: 30,
					groupRange: 4,
					attachments: 8,
					fontSize,
					groupSpacing,
					random,
				})
			: generatePlaceholderSpecs({
					compact: false,
					messageGroups: 26,
					groupRange: 4,
					attachments: 8,
					fontSize,
					groupSpacing,
					random,
				});
	}, [compact, fontSize, groupSpacing, seedKey]);
}