keyfork/crates/derive/keyfork-derive-util/src/path.rs

use crate::index::DerivationIndex;
use serde::{Deserialize, Serialize};
use thiserror::Error;

/// Errors associated with creating a [`DerivationPath`].
#[derive(Error, Debug)]
pub enum Error {
    /// A [`DerivationIndex`] was not able to be created.
    #[error("Unable to create index: {0}")]
    UnableToCreateIndex(#[from] super::index::Error),

    /// The path could not be parsed due to a bad prefix. Paths must be in the format:
    ///
    /// m [/ index [']]+
    ///
    /// The prefix for the path must be `m`, and all indices must be integers between 0 and
    /// 2^31.
    #[error("Unable to parse path due to bad path prefix")]
    UnknownPathPrefix,
}

type Result<T, E = Error> = std::result::Result<T, E>;

const PREFIX: &str = "m";

/// A fully qualified path to derive a key.
#[derive(Serialize, Deserialize, Clone, Debug, Default, Eq, PartialEq, PartialOrd, Ord)]
pub struct DerivationPath {
    pub(crate) path: Vec<DerivationIndex>,
}

impl DerivationPath {
    /// Returns an iterator over the [`DerivationPath`].
    pub fn iter(&self) -> impl Iterator<Item = &DerivationIndex> {
        self.path.iter()
    }

    /// The amount of segments in the DerivationPath. For consistency, a [`usize`] is returned, but
    /// BIP-0032 dictates that the depth should be no larger than `255`, [`u8::MAX`].
    pub fn len(&self) -> usize {
        self.path.len()
    }

    /// Returns true if there are no path segments.
    pub fn is_empty(&self) -> bool {
        self.path.is_empty()
    }

    /// Append an index to the path.
    pub fn push(&mut self, index: DerivationIndex) {
        self.path.push(index);
    }

    /// Append an index to the path, returning self to allow chaining method calls.
    pub fn chain_push(mut self, index: DerivationIndex) -> Self {
        self.path.push(index);
        self
    }
}

impl std::str::FromStr for DerivationPath {
    type Err = Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let mut iter = s.split('/');
        if iter.next() != Some(PREFIX) {
            return Err(Error::UnknownPathPrefix);
        }
        Ok(Self {
            path: iter
                .map(DerivationIndex::from_str)
                .map(|maybe_err| maybe_err.map_err(From::from))
                .collect::<Result<_>>()?,
        })
    }
}

impl std::fmt::Display for DerivationPath {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{PREFIX}")?;
        for index in self.iter() {
            write!(f, "/{index}")?;
        }
        Ok(())
    }
}

impl std::ops::Add<DerivationIndex> for DerivationPath {
    type Output = DerivationPath;

    fn add(self, rhs: DerivationIndex) -> Self::Output {
        let mut output = self.clone();
        output.path.push(rhs);
        output
    }
}

impl std::ops::Add<&[DerivationIndex]> for DerivationPath {
    type Output = DerivationPath;

    fn add(self, rhs: &[DerivationIndex]) -> Self::Output {
        let mut output = self.clone();
        output.path.extend(rhs.iter().cloned());
        output
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::str::FromStr;

    #[test]
    #[should_panic]
    fn requires_master_path() {
        DerivationPath::from_str("1234/5678'").unwrap();
    }

    #[test]
    fn equivalency() -> Result<()> {
        let paths = ["m/1234'/5678", "m/44'/0'/0'", "m"];
        for path in paths {
            assert_eq!(&DerivationPath::from_str(path)?.to_string(), path);
        }
        Ok(())
    }

    #[test]
    fn add() -> Result<(), Box<dyn std::error::Error>> {
        let path = DerivationPath::from_str("m")?;
        let path = path + DerivationIndex::new(72, true)?;
        let path = path + DerivationIndex::new(47, false)?;
        let path = path + DerivationIndex::new((i32::MAX) as u32, false)?;
        assert_eq!(path, DerivationPath::from_str("m/72'/47/2147483647")?);

        Ok(())
    }

    #[test]
    fn add_vec() -> Result<(), Box<dyn std::error::Error>> {
        let path = DerivationPath::from_str("m")?;
        let other_path = [
            DerivationIndex::new(72, true)?,
            DerivationIndex::new(47, false)?,
            DerivationIndex::new((i32::MAX) as u32, false)?,
        ];
        let path = path + &other_path[..];
        assert_eq!(path, DerivationPath::from_str("m/72'/47/2147483647")?);

        Ok(())
    }
}