// Thin wrappers over @scure/bip39 (a small, audited BIP39 implementation that
// ships the English wordlist and the mnemonic<->entropy conversions). We do not
// roll our own checksum logic — getting the BIP39 checksum wrong silently is a
// classic footgun, so the conversion stays in the library.

import {
  generateMnemonic,
  validateMnemonic,
  mnemonicToEntropy,
} from "@scure/bip39";
import { wordlist } from "@scure/bip39/wordlists/english.js";

// MNEMONIC_STRENGTH_BITS = 128 bits of entropy => exactly 12 words.
export const MNEMONIC_STRENGTH_BITS = 128;
export const MNEMONIC_WORD_COUNT = 12;

// newMnemonic returns a fresh 12-word mnemonic from a CSPRNG (crypto.getRandomValues
// inside @scure). The caller must show it to the user once and never persist it.
export function newMnemonic(): string {
  return generateMnemonic(wordlist, MNEMONIC_STRENGTH_BITS);
}

// normalizeMnemonic lowercases, trims and collapses whitespace so a phrase the
// user typed (extra spaces, trailing newline, mixed case) validates the same way
// it would have been generated.
export function normalizeMnemonic(input: string): string {
  return input.trim().toLowerCase().split(/\s+/).filter(Boolean).join(" ");
}

// mnemonicWords splits a phrase into its individual words (normalized).
export function mnemonicWords(input: string): string[] {
  const n = normalizeMnemonic(input);
  return n ? n.split(" ") : [];
}

// isValidMnemonic checks word count, that every word is in the wordlist, and the
// BIP39 checksum. A phrase that fails this must not be used to derive an identity.
export function isValidMnemonic(input: string): boolean {
  const n = normalizeMnemonic(input);
  if (mnemonicWords(n).length !== MNEMONIC_WORD_COUNT) return false;
  try {
    return validateMnemonic(n, wordlist);
  } catch {
    return false;
  }
}

// entropyHex returns the underlying entropy (hex) of a valid mnemonic. Used only
// for diagnostics / tests, never sent anywhere.
export function entropyHex(input: string): string {
  const bytes = mnemonicToEntropy(normalizeMnemonic(input), wordlist);
  return Array.from(bytes)
    .map((b) => b.toString(16).padStart(2, "0"))
    .join("");
}