export const ACTIVITY_METRICS = ["pulls", "commits", "repos", "issues"] as const;

export type ActivityMetric = (typeof ACTIVITY_METRICS)[number];

export interface ActivityChartColumn {
	left: number;
	width: number;
	divider: boolean;
}

export interface ActivityChartPoint {
	x: number;
	y: number;
	value: number;
}

export interface ActivityChartSegment {
	d: string;
	rising: boolean;
}

export interface ActivityChartLayout {
	width: number;
	height: number;
	columns: ActivityChartColumn[];
	points: Record<ActivityMetric, ActivityChartPoint[]>;
	segments: Record<ActivityMetric, ActivityChartSegment[]>;
}

const MIN_WIDTH = 988;
const HEIGHT = 256;
const PLOT_TOP = 20;
const PLOT_BOTTOM = 196;
const POINT_GAP = 30;
const POINT_INSET = 12;
const COLUMN_WEIGHTS = [146, 146, 146, 146, 146, 258];

const normalizedY = (values: number[]): number[] => {
	const min = Math.min(...values);
	const max = Math.max(...values);
	if (min === max) return values.map(() => (PLOT_TOP + PLOT_BOTTOM) / 2);
	return values.map(
		(value) => PLOT_BOTTOM - ((value - min) / (max - min)) * (PLOT_BOTTOM - PLOT_TOP)
	);
};

const resolvePointCollisions = (
	points: { metric: ActivityMetric; y: number }[]
): Map<ActivityMetric, number> => {
	const sorted = points.toSorted((a, b) => a.y - b.y);
	const clusters = sorted.map((point) => ({ metrics: [point.metric], sum: point.y }));
	const topOf = (cluster: { metrics: ActivityMetric[]; sum: number }) => {
		const span = (cluster.metrics.length - 1) * POINT_GAP;
		const centered = cluster.sum / cluster.metrics.length;
		return Math.min(Math.max(centered, PLOT_TOP), PLOT_BOTTOM - span);
	};

	let index = 1;
	while (index < clusters.length) {
		const previous = clusters[index - 1];
		const current = clusters[index];
		if (topOf(previous) + previous.metrics.length * POINT_GAP <= topOf(current)) {
			index += 1;
			continue;
		}
		clusters.splice(index - 1, 2, {
			metrics: [...previous.metrics, ...current.metrics],
			sum:
				previous.sum +
				current.sum -
				previous.metrics.length * current.metrics.length * POINT_GAP
		});
		index = Math.max(index - 1, 1);
	}

	const resolved = new Map<ActivityMetric, number>();
	for (const cluster of clusters) {
		const top = topOf(cluster);
		for (const [offset, metric] of cluster.metrics.entries()) {
			resolved.set(metric, top + offset * POINT_GAP);
		}
	}
	return resolved;
};

export const layoutActivityChart = (
	values: Record<ActivityMetric, number[]>,
	availableWidth: number
): ActivityChartLayout => {
	const width = Math.max(MIN_WIDTH, availableWidth);
	const scale = width / MIN_WIDTH;
	const columns: ActivityChartColumn[] = [];
	let left = 0;
	for (const [index, weight] of COLUMN_WEIGHTS.entries()) {
		const columnWidth = index === COLUMN_WEIGHTS.length - 1 ? width - left : weight * scale;
		columns.push({ left, width: columnWidth, divider: index > 0 });
		left += columnWidth;
	}

	const rawY = Object.fromEntries(
		ACTIVITY_METRICS.map((metric) => [metric, normalizedY(values[metric])])
	) as Record<ActivityMetric, number[]>;
	const points = Object.fromEntries(
		ACTIVITY_METRICS.map((metric) => [metric, [] as ActivityChartPoint[]])
	) as Record<ActivityMetric, ActivityChartPoint[]>;

	for (const [monthIndex, column] of columns.entries()) {
		const resolved = resolvePointCollisions(
			ACTIVITY_METRICS.map((metric) => ({ metric, y: rawY[metric][monthIndex] }))
		);
		for (const metric of ACTIVITY_METRICS) {
			points[metric].push({
				x: column.left + POINT_INSET,
				y: resolved.get(metric)!,
				value: values[metric][monthIndex]
			});
		}
	}

	const segments = Object.fromEntries(
		ACTIVITY_METRICS.map((metric) => {
			const metricPoints = points[metric];
			const connectors = metricPoints.slice(0, -1).map((point, index) => {
				const next = metricPoints[index + 1];
				const control = (next.x - point.x) / 2;
				return {
					d: `M ${point.x} ${point.y} C ${point.x + control} ${point.y}, ${next.x - control} ${next.y}, ${next.x} ${next.y}`,
					rising: next.value >= point.value
				};
			});
			const first = metricPoints[0];
			const last = metricPoints.at(-1)!;
			return [
				metric,
				[
					{
						d: `M 0 ${first.y} L ${first.x} ${first.y}`,
						rising: connectors[0]?.rising ?? true
					},
					...connectors,
					{
						d: `M ${last.x} ${last.y} L ${width} ${last.y}`,
						rising: connectors.at(-1)?.rising ?? true
					}
				]
			];
		})
	) as Record<ActivityMetric, ActivityChartSegment[]>;

	return { width, height: HEIGHT, columns, points, segments };
};