1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145

use crate::Handedness;

#[cfg(feature = "serde")]
use serde::{Deserialize, Serialize};

/// Whether to output a traditional `Monoscale` style neck with the same scale
/// across it's entire width, or a modern `Multiscale` neck, with a shorter scale
/// along the treble side, also known as *fan fret*.
#[derive(Clone, Copy, Debug, PartialEq)]
#[cfg_attr(feature = "serde", derive(Deserialize, Serialize))]
pub enum Variant {
    /// A traditional fretbaord where the same scale length is used all of the
    /// way across the fretboard.
    Monoscale,
    /// A modern style of neck where there is a longer scale length along the
    /// bass side of the neck and a shorter scale along the treble side of the
    /// neck, allowing for more natural string tension, greater flexibility in
    /// tuning, and better ergonomics.
    Multiscale {
        /// The scale length along the treble side of the neck
        scale: f64,
        /// Right or left handed output
        handedness: Handedness,
        /// Which fret is perpendicular to the centerline
        pfret: f64,
    },
}

impl Default for Variant {
    fn default() -> Self {
        Self::Monoscale
    }
}

impl Variant {
    pub fn multi() -> Self {
        Self::Multiscale {
            scale: 610.0,
            handedness: Handedness::default(),
            pfret: 8.0,
        }
    }

    /// Return the treble side scale length if the neck is `Multiscale`, or else
    /// `None`
    pub fn scale(&self) -> Option<f64> {
        match self {
            Self::Monoscale => None,
            Self::Multiscale { scale: x, .. } => Some(*x),
        }
    }

    /// Returns whether the resulting neck is right or left handed, or `None` if
    /// the neck is `Monoscale`
    pub fn handedness(&self) -> Option<Handedness> {
        match self {
            Self::Monoscale => None,
            Self::Multiscale { handedness: x, .. } => Some(*x),
        }
    }

    /// Returns which fret is perpendicular to the centerline, or `None` if the
    /// fretboard is Monoscale
    pub fn pfret(&self) -> Option<f64> {
        match self {
            Self::Monoscale => None,
            Self::Multiscale { pfret: x, .. } => Some(*x),
        }
    }
}

/// A builder pattern struct for building a `Variant::Multiscale` struct
pub struct MultiscaleBuilder {
    scale: f64,
    handedness: Handedness,
    pfret: f64,
}

impl Default for MultiscaleBuilder {
    fn default() -> Self {
        Self {
            scale: 610.0,
            handedness: Handedness::default(),
            pfret: 8.0,
        }
    }
}

impl MultiscaleBuilder {
    #[must_use]
    pub fn new() -> Self {
        Self::default()
    }

    #[must_use]
    pub fn scale(mut self, scale: f64) -> Self {
        self.scale = scale;
        self
    }

    #[must_use]
    pub fn handedness(mut self, handedness: Handedness) -> Self {
        self.handedness = handedness;
        self
    }

    #[must_use]
    pub fn pfret(mut self, pfret: f64) -> Self {
        self.pfret = pfret;
        self
    }

    #[must_use]
    pub fn build(self) -> Variant {
        Variant::Multiscale {
            scale: self.scale,
            handedness: self.handedness,
            pfret: self.pfret,
        }
    }
}

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

    #[test]
    fn variant_default() {
        let var = Variant::default();
        assert_eq!(Variant::Monoscale, var);
    }

    #[test]
    fn variant_value() {
        let var = Variant::Multiscale {
            scale: 23.5,
            handedness: Handedness::Right,
            pfret: 8.0,
        };
        let val = var.scale();
        assert_eq!(val.unwrap(), 23.5);
        let hand = var.handedness();
        assert_eq!(hand.unwrap(), Handedness::Right);
    }
}