add monero seed support (#252)

* add monero seed support

* fix some of the pr comments

* remove languages module and unnecessary error returns

* Clean classic seed impl

Fixes a few issues regarding Zeroize usage/API safety. Mainly a cleanup.

---------

Co-authored-by: Luke Parker <lukeparker5132@gmail.com>

coins/monero/src/wallet/seed/mod.rs

@@ -0,0 +1,92 @@
+use core::fmt;
+
+use zeroize::{Zeroize, ZeroizeOnDrop, Zeroizing};
+use rand_core::{RngCore, CryptoRng};
+
+use thiserror::Error;
+
+pub(crate) mod classic;
+use classic::{CLASSIC_SEED_LENGTH, CLASSIC_SEED_LENGTH_WITH_CHECKSUM, ClassicSeed};
+
+/// Error when decoding a seed.
+#[derive(Clone, Copy, PartialEq, Eq, Debug, Error)]
+pub enum SeedError {
+  #[error("invalid number of words in seed")]
+  InvalidSeedLength,
+  #[error("unknown language")]
+  UnknownLanguage,
+  #[error("invalid checksum")]
+  InvalidChecksum,
+  #[error("english old seeds don't support checksums")]
+  EnglishOldWithChecksum,
+  #[error("invalid seed")]
+  InvalidSeed,
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, Debug, Hash)]
+pub enum Language {
+  Chinese,
+  English,
+  Dutch,
+  French,
+  Spanish,
+  German,
+  Italian,
+  Portuguese,
+  Japanese,
+  Russian,
+  Esperanto,
+  Lojban,
+  EnglishOld,
+}
+
+/// A Monero seed.
+// TODO: Add polyseed to enum
+#[derive(Clone, PartialEq, Eq, Zeroize, ZeroizeOnDrop)]
+pub enum Seed {
+  Classic(ClassicSeed),
+}
+
+impl fmt::Debug for Seed {
+  fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+    match self {
+      Seed::Classic(_) => f.debug_struct("Seed::Classic").finish_non_exhaustive(),
+    }
+  }
+}
+
+impl Seed {
+  /// Create a new seed.
+  pub fn new<R: RngCore + CryptoRng>(rng: &mut R, lang: Language) -> Seed {
+    Seed::Classic(ClassicSeed::new(rng, lang))
+  }
+
+  /// Parse a seed from a String.
+  pub fn from_string(words: Zeroizing<String>) -> Result<Seed, SeedError> {
+    match words.split_whitespace().count() {
+      CLASSIC_SEED_LENGTH | CLASSIC_SEED_LENGTH_WITH_CHECKSUM => {
+        ClassicSeed::from_string(words).map(Seed::Classic)
+      }
+      _ => Err(SeedError::InvalidSeedLength)?,
+    }
+  }
+
+  /// Create a Seed from entropy.
+  pub fn from_entropy(lang: Language, entropy: Zeroizing<[u8; 32]>) -> Option<Seed> {
+    ClassicSeed::from_entropy(lang, entropy).map(Seed::Classic)
+  }
+
+  /// Convert a seed to a String.
+  pub fn to_string(&self) -> Zeroizing<String> {
+    match self {
+      Seed::Classic(seed) => seed.to_string(),
+    }
+  }
+
+  /// Return the entropy for this seed.
+  pub fn entropy(&self) -> Zeroizing<[u8; 32]> {
+    match self {
+      Seed::Classic(seed) => seed.entropy(),
+    }
+  }
+}