import { chacha20poly1305 } from "@noble/ciphers/chacha";
import { x25519 } from "@noble/curves/ed25519";
import { hkdf } from "@noble/hashes/hkdf";
import { sha256 } from "@noble/hashes/sha256";
import { randomBytes } from "@noble/hashes/utils";

const HKDF_SALT = new TextEncoder().encode("backchannel-dm-salt-v1");
const HKDF_INFO = new TextEncoder().encode("backchannel-dm-key-v1");

const encoder = new TextEncoder();
const decoder = new TextDecoder();

export function bytesToBase64(input: Uint8Array): string {
  let bin = "";
  for (const b of input) {
    bin += String.fromCharCode(b);
  }
  return btoa(bin);
}

export function base64ToBytes(input: string): Uint8Array {
  const bin = atob(input);
  const bytes = new Uint8Array(bin.length);
  for (let i = 0; i < bin.length; i += 1) {
    bytes[i] = bin.charCodeAt(i);
  }
  return bytes;
}

export function getOrCreateIdentityKey(): string {
  const current = localStorage.getItem("bc.identity_key");
  if (current) {
    return current;
  }

  const key = bytesToBase64(randomBytes(32));
  localStorage.setItem("bc.identity_key", key);
  return key;
}

export function createEphemeralKeypair(): { privateKey: Uint8Array; publicKeyB64: string } {
  const privateKey = x25519.utils.randomPrivateKey();
  const publicKey = x25519.getPublicKey(privateKey);
  return { privateKey, publicKeyB64: bytesToBase64(publicKey) };
}

export function deriveDmKey(privateKey: Uint8Array, theirPublicKeyB64: string): Uint8Array {
  const theirPublicKey = base64ToBytes(theirPublicKeyB64);
  const sharedSecret = x25519.getSharedSecret(privateKey, theirPublicKey);
  return hkdf(sha256, sharedSecret, HKDF_SALT, HKDF_INFO, 32);
}

export function encryptDm(key: Uint8Array, plaintext: string): { nonce: string; ciphertext: string } {
  const nonceBytes = randomBytes(12);
  const cipher = chacha20poly1305(key, nonceBytes);
  const ciphertext = cipher.encrypt(encoder.encode(plaintext));
  return {
    nonce: bytesToBase64(nonceBytes),
    ciphertext: bytesToBase64(ciphertext),
  };
}

export function decryptDm(key: Uint8Array, nonceB64: string, ciphertextB64: string): string {
  const nonceBytes = base64ToBytes(nonceB64);
  const ciphertext = base64ToBytes(ciphertextB64);
  const cipher = chacha20poly1305(key, nonceBytes);
  const plaintext = cipher.decrypt(ciphertext);
  return decoder.decode(plaintext);
}