derivation_path.rs

use crate::no_std::*;
use core::{
    fmt,
    fmt::{Debug, Display},
    str::FromStr,
};

/// The interface for a generic derivation path.
pub trait DerivationPath: Clone + Debug + Display + FromStr + Send + Sync + 'static + Eq + Sized {
    /// Returns a child index vector given the derivation path.
    fn to_vec(&self) -> Result<Vec<ChildIndex>, DerivationPathError>;

    /// Returns a derivation path given the child index vector.
    fn from_vec(path: &Vec<ChildIndex>) -> Result<Self, DerivationPathError>;
}

#[derive(Debug, Fail, PartialEq, Eq)]
pub enum DerivationPathError {
    #[fail(display = "expected BIP32 path")]
    ExpectedBIP32Path,

    #[fail(display = "expected BIP44 path")]
    ExpectedBIP44Path,

    #[fail(display = "expected BIP49 path")]
    ExpectedBIP49Path,

    #[fail(display = "expected valid Ethereum derivation path")]
    ExpectedValidEthereumDerivationPath,

    #[fail(display = "expected ZIP32 path")]
    ExpectedZIP32Path,

    #[fail(display = "expected hardened path")]
    ExpectedHardenedPath,

    #[fail(display = "expected normal path")]
    ExpectedNormalPath,

    #[fail(display = "invalid child number: {}", _0)]
    InvalidChildNumber(u32),

    #[fail(display = "invalid child number format")]
    InvalidChildNumberFormat,

    #[fail(display = "invalid derivation path: {}", _0)]
    InvalidDerivationPath(String),
}

/// Represents a child index for a derivation path
#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
pub enum ChildIndex {
    // A non-hardened index: Normal(n) == n in path notation
    Normal(u32),
    // A hardened index: Hardened(n) == n + (1 << 31) == n' in path notation
    Hardened(u32),
}

impl ChildIndex {
    /// Returns [`Normal`] from an index, or errors if the index is not within [0, 2^31 - 1].
    pub fn normal(index: u32) -> Result<Self, DerivationPathError> {
        if index & (1 << 31) == 0 {
            Ok(ChildIndex::Normal(index))
        } else {
            Err(DerivationPathError::InvalidChildNumber(index))
        }
    }

    /// Returns [`Hardened`] from an index, or errors if the index is not within [0, 2^31 - 1].
    pub fn hardened(index: u32) -> Result<Self, DerivationPathError> {
        if index & (1 << 31) == 0 {
            Ok(ChildIndex::Hardened(index))
        } else {
            Err(DerivationPathError::InvalidChildNumber(index))
        }
    }

    /// Returns `true` if the child index is a [`Normal`] value.
    pub fn is_normal(&self) -> bool {
        !self.is_hardened()
    }

    /// Returns `true` if the child index is a [`Hardened`] value.
    pub fn is_hardened(&self) -> bool {
        match *self {
            ChildIndex::Hardened(_) => true,
            ChildIndex::Normal(_) => false,
        }
    }

    /// Returns the child index.
    pub fn to_index(&self) -> u32 {
        match self {
            &ChildIndex::Hardened(i) => i + (1 << 31),
            &ChildIndex::Normal(i) => i,
        }
    }
}

impl From<u32> for ChildIndex {
    fn from(number: u32) -> Self {
        if number & (1 << 31) != 0 {
            ChildIndex::Hardened(number ^ (1 << 31))
        } else {
            ChildIndex::Normal(number)
        }
    }
}

impl From<ChildIndex> for u32 {
    fn from(index: ChildIndex) -> Self {
        match index {
            ChildIndex::Normal(number) => number,
            ChildIndex::Hardened(number) => number | (1 << 31),
        }
    }
}

impl FromStr for ChildIndex {
    type Err = DerivationPathError;

    fn from_str(inp: &str) -> Result<Self, Self::Err> {
        Ok(match inp.chars().last().map_or(false, |l| l == '\'' || l == 'h') {
            true => Self::hardened(
                inp[0..inp.len() - 1]
                    .parse()
                    .map_err(|_| DerivationPathError::InvalidChildNumberFormat)?,
            )?,
            false => Self::normal(inp.parse().map_err(|_| DerivationPathError::InvalidChildNumberFormat)?)?,
        })
    }
}

impl fmt::Display for ChildIndex {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            ChildIndex::Hardened(number) => write!(f, "{}'", number),
            ChildIndex::Normal(number) => write!(f, "{}", number),
        }
    }
}

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

    mod child_index {
        use super::*;

        #[test]
        fn normal() {
            for i in 0..1 << 31 {
                assert_eq!(ChildIndex::Normal(i), ChildIndex::normal(i).unwrap());
            }
            for i in 1 << 31..core::u32::MAX {
                assert_eq!(Err(DerivationPathError::InvalidChildNumber(i)), ChildIndex::normal(i));
            }
        }

        #[test]
        fn hardened() {
            for i in 0..1 << 31 {
                assert_eq!(ChildIndex::Hardened(i), ChildIndex::hardened(i).unwrap());
            }
            for i in 1 << 31..core::u32::MAX {
                assert_eq!(Err(DerivationPathError::InvalidChildNumber(i)), ChildIndex::hardened(i));
            }
        }

        #[test]
        fn is_normal() {
            for i in 0..1 << 31 {
                assert!(ChildIndex::Normal(i).is_normal());
                assert!(!ChildIndex::Hardened(i).is_normal());
            }
        }

        #[test]
        fn is_hardened() {
            for i in 0..1 << 31 {
                assert!(!ChildIndex::Normal(i).is_hardened());
                assert!(ChildIndex::Hardened(i).is_hardened());
            }
        }

        #[test]
        fn to_index() {
            for i in 0..1 << 31 {
                assert_eq!(i, ChildIndex::Normal(i).to_index());
                assert_eq!(i | (1 << 31), ChildIndex::Hardened(i).to_index());
            }
        }

        #[test]
        fn from() {
            const THRESHOLD: u32 = 1 << 31;
            for i in 0..core::u32::MAX {
                match i < THRESHOLD {
                    true => assert_eq!(ChildIndex::Normal(i), ChildIndex::from(i)),
                    false => assert_eq!(ChildIndex::Hardened(i ^ 1 << 31), ChildIndex::from(i)),
                }
            }
        }

        #[test]
        fn from_str() {
            for i in (0..1 << 31).step_by(1 << 10) {
                assert_eq!(ChildIndex::Normal(i), ChildIndex::from_str(&format!("{}", i)).unwrap());
                assert_eq!(
                    ChildIndex::Hardened(i),
                    ChildIndex::from_str(&format!("{}\'", i)).unwrap()
                );
                assert_eq!(
                    ChildIndex::Hardened(i),
                    ChildIndex::from_str(&format!("{}h", i)).unwrap()
                );
            }
        }

        #[test]
        fn to_string() {
            for i in (0..1 << 31).step_by(1 << 10) {
                assert_eq!(format!("{}", i), ChildIndex::Normal(i).to_string());
                assert_eq!(format!("{}\'", i), ChildIndex::Hardened(i).to_string());
            }
        }
    }
}