const seriesOf = (
	history: readonly HistoryPoint[],
	engines: readonly Engine[]
): Series[] => [
	{
		key: OVERALL,
		label: "All AIs",
		color: "var(--chart-1)",
		values: history.map((point) => point.score),
	},
	...engines.map((engine) => ({
		key: engine,
		label: engineName(engine),
		color: `var(${ENGINE_META[engine].token})`,
		values: history.map((point) => point.perEngine[engine] ?? null),
	})),
];

/** "ChatGPT rose from 31% to 47%." for the chart's text alternative. */
export const trendSentence = (series: Series): string | null => {
	const known = series.values.filter(
		(value): value is number => value !== null
	);
	const first = known[0];
	const last = known.at(-1);
	if (first === undefined || last === undefined) {
		return null;
	}
	if (Math.abs(last - first) < SAME_POINTS) {
		return `${series.label} stayed at ${percent(last)}.`;
	}
	const verb = last > first ? "rose" : "fell";
	return `${series.label} ${verb} from ${percent(first)} to ${percent(last)}.`;
};