export type DeviceIdentity = {
  ed25519Public: string;
  x25519Public: string;
  fingerprint: string;
};

const PAIRING_ID = /^pair_[0-9a-f]{32}$/;
const PAIRING_CODE = /^[0-9A-F]{20}$/;
const PUBLIC_KEY = /^[A-Za-z0-9_-]{43}$/;
const ED25519_SIGNATURE = /^[A-Za-z0-9_-]{86}$/;
const HEX_64 = /^[0-9a-f]{64}$/;
const REGISTRATION_PROOF_DOMAIN = new TextEncoder().encode(
  "nekonest-cloud/device-registration-proof/v1",
);

function bytesToHex(bytes: Uint8Array): string {
  return Array.from(bytes, (byte) => byte.toString(16).padStart(2, "0")).join("");
}

function concatBytes(left: Uint8Array, right: Uint8Array): Uint8Array {
  const result = new Uint8Array(left.length + right.length);
  result.set(left);
  result.set(right, left.length);
  return result;
}

function decodeBase64Url(value: string): Uint8Array {
  if (!PUBLIC_KEY.test(value)) throw new Error("invalid_public_key");
  const base64 = `${value.replaceAll("-", "+").replaceAll("_", "/")}=`;
  let decoded: string;
  try {
    decoded = atob(base64);
  } catch {
    throw new Error("invalid_public_key");
  }
  const bytes = Uint8Array.from(decoded, (character) => character.charCodeAt(0));
  if (bytes.length !== 32) throw new Error("invalid_public_key");
  return bytes;
}

function decodeEd25519Signature(value: string): Uint8Array {
  if (!ED25519_SIGNATURE.test(value)) throw new Error("invalid_registration_proof");
  const base64 = `${value.replaceAll("-", "+").replaceAll("_", "/")}==`;
  let decoded: string;
  try {
    decoded = atob(base64);
  } catch {
    throw new Error("invalid_registration_proof");
  }
  const bytes = Uint8Array.from(decoded, (character) => character.charCodeAt(0));
  if (bytes.length !== 64) throw new Error("invalid_registration_proof");
  return bytes;
}

function lengthPrefixed(value: string): Uint8Array {
  const encoded = new TextEncoder().encode(value);
  const result = new Uint8Array(4 + encoded.length);
  new DataView(result.buffer).setUint32(0, encoded.length, false);
  result.set(encoded, 4);
  return result;
}

export function deviceRegistrationProofTranscript(input: {
  bootstrapToken: string;
  os: string;
  ed25519Public: string;
  x25519Public: string;
  identityFingerprint: string;
  transportMode: string;
}): Uint8Array {
  const fields = [
    input.bootstrapToken.trim(),
    input.os.trim().toLowerCase(),
    input.ed25519Public.trim(),
    input.x25519Public.trim(),
    input.identityFingerprint.trim().toLowerCase(),
    input.transportMode.trim(),
  ].map(lengthPrefixed);
  const totalLength = fields.reduce(
    (total, field) => total + field.length,
    REGISTRATION_PROOF_DOMAIN.length,
  );
  const transcript = new Uint8Array(totalLength);
  transcript.set(REGISTRATION_PROOF_DOMAIN);
  let offset = REGISTRATION_PROOF_DOMAIN.length;
  for (const field of fields) {
    transcript.set(field, offset);
    offset += field.length;
  }
  return transcript;
}

export async function verifyDeviceRegistrationProof(input: {
  bootstrapToken: string;
  os: string;
  ed25519Public: string;
  x25519Public: string;
  identityFingerprint: string;
  transportMode: string;
  registrationProof: string;
}): Promise<boolean> {
  try {
    const publicKey = decodeBase64Url(input.ed25519Public.trim());
    const signature = decodeEd25519Signature(input.registrationProof.trim());
    const key = await crypto.subtle.importKey(
      "raw",
      Uint8Array.from(publicKey).buffer,
      { name: "Ed25519" },
      false,
      ["verify"],
    );
    return crypto.subtle.verify(
      { name: "Ed25519" },
      key,
      Uint8Array.from(signature).buffer,
      Uint8Array.from(deviceRegistrationProofTranscript(input)).buffer,
    );
  } catch {
    return false;
  }
}

export function normalizePairingCode(value: string): string {
  const normalized = value.trim().toUpperCase();
  if (!PAIRING_CODE.test(normalized)) throw new Error("invalid_pairing_code");
  return normalized;
}

export function parseBootstrapToken(value: string): {
  pairingId: string;
  code: string;
} {
  const trimmed = value.trim();
  const separator = trimmed.indexOf(".");
  if (separator < 0 || separator !== trimmed.lastIndexOf(".")) {
    throw new Error("invalid_bootstrap_token");
  }
  const pairingId = trimmed.slice(0, separator);
  if (!PAIRING_ID.test(pairingId)) throw new Error("invalid_bootstrap_token");
  return {
    pairingId,
    code: normalizePairingCode(trimmed.slice(separator + 1)),
  };
}

export async function sha256Hex(value: string | Uint8Array): Promise<string> {
  const bytes = typeof value === "string" ? new TextEncoder().encode(value) : value;
  const input = Uint8Array.from(bytes).buffer;
  return bytesToHex(new Uint8Array(await crypto.subtle.digest("SHA-256", input)));
}

export function constantTimeEqualHex(left: string, right: string): boolean {
  const leftNormalized = left.toLowerCase();
  const rightNormalized = right.toLowerCase();
  let difference = leftNormalized.length ^ rightNormalized.length;
  const length = Math.max(leftNormalized.length, rightNormalized.length);
  for (let index = 0; index < length; index += 1) {
    difference |=
      (leftNormalized.charCodeAt(index) || 0) ^
      (rightNormalized.charCodeAt(index) || 0);
  }
  return difference === 0;
}

export async function validateDeviceIdentity(input: {
  ed25519Public: string;
  x25519Public: string;
  identityFingerprint: string;
}): Promise<DeviceIdentity> {
  const ed25519Public = input.ed25519Public.trim();
  const x25519Public = input.x25519Public.trim();
  const fingerprint = input.identityFingerprint.trim().toLowerCase();
  const ed25519Bytes = decodeBase64Url(ed25519Public);
  const x25519Bytes = decodeBase64Url(x25519Public);
  if (!HEX_64.test(fingerprint)) throw new Error("invalid_identity_fingerprint");
  const expected = await sha256Hex(concatBytes(ed25519Bytes, x25519Bytes));
  if (!constantTimeEqualHex(expected, fingerprint)) {
    throw new Error("invalid_identity_fingerprint");
  }
  return { ed25519Public, x25519Public, fingerprint };
}

export function randomDeviceToken(): string {
  return bytesToHex(crypto.getRandomValues(new Uint8Array(32)));
}

export function rateWindowStart(now: Date): string {
  const windowMilliseconds = 10 * 60_000;
  return new Date(
    Math.floor(now.getTime() / windowMilliseconds) * windowMilliseconds,
  ).toISOString();
}

export async function sourceFingerprint(
  rootSecret: string,
  source: string,
): Promise<string> {
  const key = await crypto.subtle.importKey(
    "raw",
    new TextEncoder().encode(rootSecret),
    { name: "HMAC", hash: "SHA-256" },
    false,
    ["sign"],
  );
  const signature = await crypto.subtle.sign(
    "HMAC",
    key,
    new TextEncoder().encode(`pairing-source-v1\0${source}`),
  );
  return bytesToHex(new Uint8Array(signature));
}

export function requestSource(request: Request, production: boolean): string {
  const edgeSource = request.headers.get("cf-connecting-ip")?.trim() ?? "";
  if (/^[0-9A-Fa-f:.]{3,64}$/.test(edgeSource)) return edgeSource.toLowerCase();
  if (production) throw new Error("trusted_source_unavailable");
  return "local-development";
}