/**
 * @fileoverview Output truncation helper that stores the full payload and returns a trimmed inline preview.
 */
import { PI_TRUNCATION_LIMITS } from "../../defaults.ts";
import type { ResponseStorageMetadata } from "../../types.ts";
import { storeResponse } from "./store.ts";
import type { StoreResponseOptions } from "./store.ts";

export interface TruncatedOutput {
	text: string;
	truncated: boolean;
	metadata?: ResponseStorageMetadata;
}

export async function truncateAndStore(
	text: string,
	value: unknown,
	options: StoreResponseOptions = {},
): Promise<TruncatedOutput> {
	const limits = PI_TRUNCATION_LIMITS;
	const byteLength = Buffer.byteLength(text);
	const lineLimited = firstLines(text, limits.maxLines);
	const overBytes = byteLength > limits.maxBytes;
	const overLines = lineLimited.length < text.length;
	if (!overBytes && !overLines) return { text, truncated: false };

	const metadata = await storeResponse(value, options);
	return {
		text: trimToBytes(lineLimited, limits.maxBytes),
		truncated: true,
		metadata,
	};
}

function firstLines(text: string, maxLines: number): string {
	if (maxLines <= 0) return "";
	let lines = 1;
	for (const match of text.matchAll(/\r?\n/gu)) {
		if (lines >= maxLines) return text.slice(0, match.index);
		lines += 1;
	}
	return text;
}

function trimToBytes(text: string, maxBytes: number): string {
	if (Buffer.byteLength(text) <= maxBytes) return text;
	let low = 0;
	let high = text.length;
	while (low < high) {
		const mid = Math.ceil((low + high) / 2);
		if (Buffer.byteLength(text.slice(0, mid)) <= maxBytes) low = mid;
		else high = mid - 1;
	}
	return text.slice(0, low);
}