tonality 0.1.1

Tonal pitch classes with enharmonic distinction
Documentation 
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//! A position on a music staff
use std::convert::TryFrom;
use std::ops::{Add, Sub};

use num_derive::FromPrimitive;

use crate::Accidental;
use crate::Key;
use crate::Tpc;

/// A `Step` corresponds to a position on a music staff, and relates to
/// a `Tpc` by stripping the latter of any alterations.
#[derive(Clone, Copy, Debug, PartialEq, PartialOrd, Eq, Ord, FromPrimitive)]
#[must_use]
#[allow(missing_docs)]
pub enum Step {
    C = 0,
    D,
    E,
    F,
    G,
    A,
    B,
}

impl From<Tpc> for Step {
    fn from(tpc: Tpc) -> Self {
        tpc.step()
    }
}

impl Step {
    /// C is the lowest step
    pub const MIN: Step = Step::C;
    /// B is the highest step
    pub const MAX: Step = Step::B;

    /// The tonal pitch class resulting from applying an accidental to the step
    /// ```
    /// # use tonality::{Accidental, Step, Tpc};
    /// assert_eq!(Tpc::Ab, Step::A.with_accidental(Accidental::Flat));
    /// ```
    pub fn with_accidental(self, alter: Accidental) -> Tpc {
        #[rustfmt::skip]
        const SPELLINGS: [Tpc; 35] = [
            Tpc::Cbb, Tpc::Cb, Tpc::C, Tpc::Cs, Tpc::Css,
            Tpc::Dbb, Tpc::Db, Tpc::D, Tpc::Ds, Tpc::Dss,
            Tpc::Ebb, Tpc::Eb, Tpc::E, Tpc::Es, Tpc::Ess,
            Tpc::Fbb, Tpc::Fb, Tpc::F, Tpc::Fs, Tpc::Fss,
            Tpc::Gbb, Tpc::Gb, Tpc::G, Tpc::Gs, Tpc::Gss,
            Tpc::Abb, Tpc::Ab, Tpc::A, Tpc::As, Tpc::Ass,
            Tpc::Bbb, Tpc::Bb, Tpc::B, Tpc::Bs, Tpc::Bss,
        ];
        let step = self as i8;
        let alter = alter as i8;
        let i = step * 5 + alter + 2;
        SPELLINGS[usize::try_from(i).unwrap()]
    }

    /// The tonal pitch class of the step in the given key
    /// ```
    /// # use tonality::{Key, Step, Tpc};
    /// assert_eq!(Tpc::Ab, Step::A.with_key(Key::Eb));
    /// ```
    pub fn with_key(self, key: Key) -> Tpc {
        #[rustfmt::skip]
        const BY_STEP_AND_KEY: [Tpc; 7 * Key::NUM_OF as usize] = [
            Tpc::Cb, Tpc::Db, Tpc::Eb, Tpc::Fb, Tpc::Gb, Tpc::Ab, Tpc::Bb, // Cb
            Tpc::Cb, Tpc::Db, Tpc::Eb, Tpc::F,  Tpc::Gb, Tpc::Ab, Tpc::Bb, // Gb
            Tpc::C,  Tpc::Db, Tpc::Eb, Tpc::F,  Tpc::Gb, Tpc::Ab, Tpc::Bb, // Db
            Tpc::C,  Tpc::Db, Tpc::Eb, Tpc::F,  Tpc::G,  Tpc::Ab, Tpc::Bb, // Ab
            Tpc::C,  Tpc::D,  Tpc::Eb, Tpc::F,  Tpc::G,  Tpc::Ab, Tpc::Bb, // Eb
            Tpc::C,  Tpc::D,  Tpc::Eb, Tpc::F,  Tpc::G,  Tpc::A,  Tpc::Bb, // B
            Tpc::C,  Tpc::D,  Tpc::E,  Tpc::F,  Tpc::G,  Tpc::A,  Tpc::Bb, // F
            Tpc::C,  Tpc::D,  Tpc::E,  Tpc::F,  Tpc::G,  Tpc::A,  Tpc::B,  // C
            Tpc::C,  Tpc::D,  Tpc::E,  Tpc::Fs, Tpc::G,  Tpc::A,  Tpc::B,  // G
            Tpc::Cs, Tpc::D,  Tpc::E,  Tpc::Fs, Tpc::G,  Tpc::A,  Tpc::B,  // D
            Tpc::Cs, Tpc::D,  Tpc::E,  Tpc::Fs, Tpc::Gs, Tpc::A,  Tpc::B,  // A
            Tpc::Cs, Tpc::Ds, Tpc::E,  Tpc::Fs, Tpc::Gs, Tpc::A,  Tpc::B,  // E
            Tpc::Cs, Tpc::Ds, Tpc::E,  Tpc::Fs, Tpc::Gs, Tpc::As, Tpc::B,  // H
            Tpc::Cs, Tpc::Ds, Tpc::Es, Tpc::Fs, Tpc::Gs, Tpc::As, Tpc::B,  // F#
            Tpc::Cs, Tpc::Ds, Tpc::Es, Tpc::Fs, Tpc::Gs, Tpc::As, Tpc::Bs, // C#
        ];
        let key = usize::try_from(key as i8 - Key::MIN as i8).unwrap();
        BY_STEP_AND_KEY[7 * key + self as usize]
    }
}

impl Add<isize> for Step {
    type Output = Step;

    fn add(self, rhs: isize) -> Self::Output {
        use num_traits::FromPrimitive;

        let new_step = (self as isize + rhs).rem_euclid(7);
        FromPrimitive::from_isize(new_step).unwrap()
    }
}

impl Sub<isize> for Step {
    type Output = Step;

    fn sub(self, rhs: isize) -> Self::Output {
        self.add(-rhs)
    }
}

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

    #[test]
    fn test_step_to_tpc() {
        assert_eq!(Step::C.with_accidental(Accidental::Natural), Tpc::C);
        assert_eq!(Step::F.with_accidental(Accidental::Sharp), Tpc::Fs);
        assert_eq!(Step::A.with_accidental(Accidental::Flat), Tpc::Ab);
        assert_eq!(Step::E.with_accidental(Accidental::DblFlat), Tpc::Ebb);
        assert_eq!(Step::B.with_accidental(Accidental::Sharp), Tpc::Bs);
    }

    #[test]
    fn test_with_key() {
        assert_eq!(Tpc::C, Step::C.with_key(Key::C));
        assert_eq!(Tpc::Cs, Step::C.with_key(Key::D));
        assert_eq!(Tpc::B, Step::B.with_key(Key::Fs));
        assert_eq!(Tpc::Bb, Step::B.with_key(Key::Ab));
        assert_eq!(Tpc::G, Step::G.with_key(Key::D));
        assert_eq!(Tpc::E, Step::E.with_key(Key::F));
    }
}