/**
 * usage-status — footer block showing live token + $ usage for the session.
 *
 * Accumulates `usage` totals from every assistant `turn_end` event and
 * renders them into a `setStatus("usage", ...)` entry. Pairs with
 * `status-line.ts` (turn indicator) and `model-status.ts` (model badge) —
 * three independent footer slots, three independent extensions.
 *
 * Format:
 *   $0.043  12.3k tok  (1.1k in / 240 out)
 *
 * Counts session-cumulative cost; resets on every new session_start.
 */

import type { ExtensionAPI } from "@earendil-works/pi-coding-agent";

const KEY = "usage";

function fmtTokens(n: number): string {
	if (n < 1000) return String(n);
	if (n < 10_000) return `${(n / 1000).toFixed(1)}k`;
	return `${Math.round(n / 1000)}k`;
}

function fmtCost(c: number): string {
	if (c >= 1) return `$${c.toFixed(2)}`;
	return `$${c.toFixed(4)}`;
}

export default function usageStatusExtension(pi: ExtensionAPI) {
	let costTotal = 0;
	let inputTotal = 0;
	let outputTotal = 0;
	let cacheReadTotal = 0;
	let cacheWriteTotal = 0;

	const render = (ctx: any) => {
		const total = inputTotal + outputTotal + cacheReadTotal + cacheWriteTotal;
		if (total === 0 && costTotal === 0) {
			ctx.ui.setStatus(KEY, undefined);
			return;
		}
		const theme = ctx.ui.theme;
		const costStr = theme.fg("accent", fmtCost(costTotal));
		const tokStr = theme.fg("dim", `${fmtTokens(total)} tok`);
		const breakdown = theme.fg("dim", `(${fmtTokens(inputTotal)} in / ${fmtTokens(outputTotal)} out)`);
		ctx.ui.setStatus(KEY, `${costStr}  ${tokStr}  ${breakdown}`);
	};

	const reset = () => {
		costTotal = 0;
		inputTotal = 0;
		outputTotal = 0;
		cacheReadTotal = 0;
		cacheWriteTotal = 0;
	};

	pi.on("session_start", (_event, ctx) => {
		reset();
		render(ctx);
	});

	pi.on("turn_end", (event, ctx) => {
		const msg: any = (event as any).message;
		const usage: any = msg?.usage;
		if (!usage) return;
		const cost = usage.cost?.total ?? 0;
		costTotal += Number(cost) || 0;
		inputTotal += Number(usage.input) || 0;
		outputTotal += Number(usage.output) || 0;
		cacheReadTotal += Number(usage.cacheRead) || 0;
		cacheWriteTotal += Number(usage.cacheWrite) || 0;
		render(ctx);
	});
}