import { mkdirSync, readFileSync, renameSync, writeFileSync } from "node:fs";
import { dirname, join } from "node:path";

export type CondenseDefaultResult = "updated" | "unchanged" | "skipped-invalid";

const CONDENSE_BUNDLE_DEFAULTS = {
	enabled: true,
	pruneOn: "agent-message",
	batchingMode: "turn",
	autoBudgetThreshold: 0.735,
	budgetTurnDelta: 0.04,
	summarizerModel: "default",
	summarizerThinking: "default",
	summarizerIdleTimeoutMs: 90_000,
	summarizerMaxTimeoutMs: 300_000,
	quietOversizedSkips: false,
} as const;

function isObject(value: unknown): value is Record<string, unknown> {
	return value !== null && typeof value === "object" && !Array.isArray(value);
}

/** Fill missing pi-condense settings with bundle defaults while preserving every explicit user choice. */
export function ensureCondenseDefaults(agentDir: string): CondenseDefaultResult {
	const targetPath = join(agentDir, "settings.json");
	let settings: Record<string, unknown> = {};

	try {
		const parsed: unknown = JSON.parse(readFileSync(targetPath, "utf8"));
		if (!isObject(parsed)) return "skipped-invalid";
		settings = parsed;
	} catch (error) {
		if ((error as NodeJS.ErrnoException).code !== "ENOENT") return "skipped-invalid";
	}

	const existing = settings.contextPrune;
	if (existing !== undefined && !isObject(existing)) return "skipped-invalid";

	const contextPrune = existing ?? {};
	const alreadyComplete = Object.keys(CONDENSE_BUNDLE_DEFAULTS).every((key) => Object.hasOwn(contextPrune, key));
	if (alreadyComplete) return "unchanged";

	settings.contextPrune = { ...CONDENSE_BUNDLE_DEFAULTS, ...contextPrune };
	mkdirSync(dirname(targetPath), { recursive: true });
	const temporaryPath = `${targetPath}.my-pi.tmp`;
	writeFileSync(temporaryPath, `${JSON.stringify(settings, null, 2)}\n`, "utf8");
	renameSync(temporaryPath, targetPath);
	return "updated";
}