import type { CharlesBody, CharlesEntry, SimplifiedEntry } from "./types.js";

/** Shannon entropy in bits/char. */
export function calcEntropy(s: string): number {
	if (!s || s.length < 5) return 0;
	const n = s.length;
	const counts = new Map<string, number>();
	for (const ch of s) {
		counts.set(ch, (counts.get(ch) ?? 0) + 1);
	}
	let entropy = 0;
	for (const c of counts.values()) {
		const p = c / n;
		entropy -= p * Math.log2(p);
	}
	return entropy;
}

/** Where a keyword hits inside an entry. */
export function getHitLocations(
	entry: CharlesEntry,
	keyword: string,
): string[] {
	const k = keyword.toLowerCase();
	const req = entry.request ?? {};
	const res = entry.response ?? {};
	const hits: string[] = [];

	if ((entry.path ?? "").toLowerCase().includes(k)) hits.push("url_path");

	const reqHeaders = req.header?.headers ?? [];
	if (JSON.stringify(reqHeaders).toLowerCase().includes(k))
		hits.push("req_header");
	if ((req.body?.text ?? "").toLowerCase().includes(k)) hits.push("req_body");

	const resHeaders = res.header?.headers ?? [];
	if (JSON.stringify(resHeaders).toLowerCase().includes(k))
		hits.push("res_header");
	if ((res.body?.text ?? "").toLowerCase().includes(k)) hits.push("res_body");

	return hits;
}

const RESOURCE_MIME_PREFIXES = [
	"image/",
	"video/",
	"audio/",
	"font/",
	"application/javascript",
	"text/javascript",
	"text/css",
	"application/octet-stream",
	"application/wasm",
] as const;

function fmtSize(n: number): string {
	if (n >= 1024 * 1024) return `${(n / 1024 / 1024).toFixed(1)}MB`;
	if (n >= 1024) return `${(n / 1024).toFixed(1)}KB`;
	return `${n}B`;
}

function bodyPreview(
	body: CharlesBody | undefined,
	mimeType: string,
	bodySize: number,
	previewChars: number,
): string | null {
	if (!body) return null;

	const encoded = body.encoded ?? false;
	const text = body.text ?? "";
	const mime = (mimeType || "").toLowerCase().split(";")[0]?.trim() ?? "";
	const isResource =
		encoded || RESOURCE_MIME_PREFIXES.some((p) => mime.startsWith(p));

	if (isResource) {
		const size = bodySize || text.length;
		const label = mime || "binary";
		return `[${label} ${fmtSize(size)}]`;
	}

	return text.slice(0, previewChars) || null;
}

/** Compact view for agent decision-making. */
export function simplifyEntry(
	entry: CharlesEntry,
	previewChars = 300,
): SimplifiedEntry {
	const req = entry.request ?? {};
	const res = entry.response ?? {};
	const reqBody = req.body ?? {};
	const resBody = res.body ?? {};

	return {
		id: entry._mcp_id ?? entry.id,
		method: entry.method,
		host: entry.host,
		path: entry.path,
		status: res.status,
		req_preview: bodyPreview(
			reqBody,
			req.mimeType ?? "",
			req.sizes?.body ?? 0,
			previewChars,
		),
		res_preview: bodyPreview(
			resBody,
			res.mimeType ?? "",
			res.sizes?.body ?? 0,
			previewChars,
		),
	};
}

export function entryStartTime(entry: CharlesEntry): string {
	return entry.times?.start ?? "";
}

/** Parse Charles times.start (ISO 8601) to epoch millis. */
export function entryMillis(entry: CharlesEntry): number {
	const iso = entryStartTime(entry);
	if (!iso) return 0;
	const ms = Date.parse(iso);
	return Number.isFinite(ms) ? ms : 0;
}