import type { Save } from "../mirror/queries.ts";
import { type Html, html } from "./html.ts";
import { formatDate } from "./layout.ts";

const TIP_CHARS = 120;

/** One dot of the drifting timeline, as kepr.js reads it from `/<repo>/timeline`. */
export type TimelineSave = { id: string; t: number; message: string; meta: string };

/**
 * §21.4's dotted timeline as SVG, so it draws without JavaScript: one dot per save on a dashed
 * line, x by time (as a percentage, so it scales without squashing dots), brighter and fuller where
 * neighbours crowd within a fortieth of the span. kepr.js swaps it for Kepr 2's drifting canvas,
 * fetching each save's words from `data-src` after the page has drawn: carried as tooltips in the
 * page, they were most of a big repo's page.
 */
export function timelineSvg(repo: string, saves: Save[]): Html {
	const times = saves.map((save) => save.created_at);
	// Replayed saves keep their own times, so the line is not in time order.
	const sorted = times.toSorted((a, b) => a - b);
	const first = sorted[0] ?? 0;
	const span = (sorted.at(-1) ?? first) - first;
	const reach = Math.max(span / 40, 3600);
	const dots = times.map((t) => {
		const x = span === 0 ? 50 : 1 + (98 * (t - first)) / span;
		const near = countBetween(sorted, t - reach, t + reach);
		const level = near >= 8 ? 3 : near >= 4 ? 2 : near >= 2 ? 1 : 0;
		return html`<circle class="dot d${level}" cx="${x.toFixed(3)}%" cy="32" r="${2.5 + level * 0.5}"/>`;
	});
	return html`<svg class="timeline" width="100%" height="64" role="img" aria-label="${
		saves.length
	} saves over time" data-src="/${repo}/timeline">
<line class="timeline-line" x1="0" x2="100%" y1="32" y2="32"/>
${dots}
</svg>`;
}

/** Each save's ID, time, first line (cut to fit the 340 px tip) and when, who and in what session. */
export function timelineSaves(saves: Save[]): TimelineSave[] {
	return saves.map((save) => {
		const line = save.message.split("\n")[0] as string;
		return {
			id: save.id,
			t: save.created_at,
			message: line.length > TIP_CHARS ? `${line.slice(0, TIP_CHARS - 1)}…` : line,
			meta: [formatDate(save.created_at), save.agent, save.session].filter(Boolean).join(" · "),
		};
	});
}

// How many of the sorted times fall within [low, high].
function countBetween(sorted: number[], low: number, high: number): number {
	// The index of the first time that `before` no longer holds for.
	const first = (before: (time: number) => boolean) => {
		let [lo, hi] = [0, sorted.length];
		while (lo < hi) {
			const mid = (lo + hi) >> 1;
			if (before(sorted[mid] as number)) lo = mid + 1;
			else hi = mid;
		}
		return lo;
	};
	return first((t) => t <= high) - first((t) => t < low);
}