#!/usr/bin/env node
// Node built-ins only. Pinned to docs/contract.md, "Proof and source session".
import { createPrivateKey, createPublicKey, sign } from "node:crypto"
import { readFileSync } from "node:fs"

const base64 = (value) => Buffer.from(value, "utf8").toString("base64")

try {
	const [requestFile, challengeFile, keyOption, keyName, ...extra] =
		process.argv.slice(2)
	if (
		!requestFile ||
		!challengeFile ||
		!keyName ||
		extra.length ||
		!["--key-file", "--key-env"].includes(keyOption)
	)
		throw new Error("usage")
	const request = JSON.parse(readFileSync(requestFile, "utf8"))
	const envelope = JSON.parse(readFileSync(challengeFile, "utf8"))
	const challenge = envelope.data
	const hex = /^[0-9a-f]{64}$/
	if (
		envelope.code !== null ||
		!challenge ||
		Object.keys(request).some(
			(key) =>
				!["public_key", "username", "legal_acceptance_version"].includes(key),
		) ||
		!hex.test(request.public_key) ||
		!hex.test(challenge.challenge) ||
		typeof request.legal_acceptance_version !== "string" ||
		!request.legal_acceptance_version ||
		(request.username !== undefined && typeof request.username !== "string") ||
		challenge.issuer !== "https://api.uno.fun" ||
		challenge.audience !== "https://mpp.uno.fun" ||
		challenge.kit_audience !== "https://kit.uno.fun" ||
		!(typeof challenge.expires_at === "string"
			? /^(0|[1-9][0-9]*)$/.test(challenge.expires_at)
			: Number.isSafeInteger(challenge.expires_at) &&
				challenge.expires_at >= 0) ||
		typeof challenge.signing_bytes !== "string"
	)
		throw new Error("inputs")
	const bytes = Buffer.from(challenge.signing_bytes, "base64")
	if (bytes.toString("base64") !== challenge.signing_bytes)
		throw new Error("encoding")
	const expected = [
		"uno-account-key-kit-session",
		"https://api.uno.fun",
		"https://mpp.uno.fun",
		"https://kit.uno.fun",
		challenge.challenge,
		request.public_key,
		base64(request.username ?? ""),
		base64(request.legal_acceptance_version),
		String(challenge.expires_at),
	]
	const lines = new TextDecoder("utf-8", { fatal: true })
		.decode(bytes)
		.split("\n")
	if (
		lines.length !== 9 ||
		lines.some((line, index) => line !== expected[index]) ||
		!bytes.equals(Buffer.from(expected.join("\n"), "utf8"))
	)
		throw new Error("statement")

	// Read the caller-named seed only after checking every statement line.
	const seed = (
		keyOption === "--key-file"
			? readFileSync(keyName, "utf8")
			: process.env[keyName]
	)?.trim()
	if (!seed || !hex.test(seed)) throw new Error("key")
	const key = createPrivateKey({
		key: Buffer.concat([
			Buffer.from("302e020100300506032b657004220420", "hex"),
			Buffer.from(seed, "hex"),
		]),
		format: "der",
		type: "pkcs8",
	})
	const publicKey = createPublicKey(key).export({ format: "der", type: "spki" })
	if (publicKey.subarray(-32).toString("hex") !== request.public_key)
		throw new Error("key mismatch")
	process.stdout.write(
		`${JSON.stringify({
			...request,
			challenge: challenge.challenge,
			expires_at: challenge.expires_at,
			signature: sign(null, bytes, key).toString("base64"),
		})}\n`,
	)
} catch {
	// Never echo input, paths, environment values, or key parsing errors.
	process.stderr.write(
		"Refused to sign. Check the request, challenge, pinned contract, and key source.\n" +
			"Usage: node sign-session.mjs request.json challenge.json --key-file PATH | --key-env NAME\n",
	)
	process.exitCode = 1
}