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

//! Color module that helps generating and operating on rgb colors
use std::str::FromStr;
use std::u8;
use std::iter::FromIterator;
use image::Rgba;
use error::Error;

#[derive(Debug, PartialEq, Copy, Clone)]
pub struct RgbColor(u8, u8, u8);

impl RgbColor {
    pub fn new(red: u8, green: u8, blue: u8) -> RgbColor {
        RgbColor(red, green, blue)
    }

    /// Generate a random rgb color
    pub fn random() -> Self {
        use rand::prelude::*;

        let mut rng = thread_rng();

        RgbColor(rng.gen(), rng.gen(), rng.gen())
    }

    /// Calculate the contrast ratio between colors
    pub fn find_ratio(&self, other: &RgbColor) -> f32 {
        self.calculate_luminance() / other.calculate_luminance()
    }

    /// Convert to rgba (including transparency) for image creation
    pub fn to_rgba(self, alpha: u8) -> Rgba<u8> {
        Rgba {
            data: [self.0, self.1, self.2, alpha]
        }
    }

    fn calculate_luminance(&self) -> f32 {
        0.299 * f32::from(self.0) +
        0.587 * f32::from(self.1) +
        0.114 * f32::from(self.2) +
        0.05
    }
}

/// Parse hex code and generate RGB vector accordingly.
impl FromStr for RgbColor {
    type Err = Error;

    fn from_str(hex: &str) -> Result<RgbColor, Error> {
        if hex.is_empty() {
            return Err(Error::InvalidHexFormat {
                expected: String::from("Color hex code must not be empty"),
                actual: String::from("Color hex was empty"),
            });
        }

        if !hex.starts_with('#') {
            return Err(Error::InvalidHexFormat {
                expected: String::from("Color hex code must start with `#`"),
                actual: format!("Color hex starts with `{}`", hex.chars().nth(0).unwrap())
            });
        }

        if hex.len() != 7 {
            return Err(Error::InvalidHexFormat {
                expected: String::from("Hex code must be `7` characters long. Example: `#00FF00`"),
                actual: format!("Hex code is `{}` characters long!", hex.len())
            });
        }

        // collect characters from the String
        let raw: Vec<char> = hex.chars().collect();

        Ok(RgbColor(
            u8::from_str_radix(&String::from_iter(&raw[1 .. 3]), 16)?,
            u8::from_str_radix(&String::from_iter(&raw[3 .. 5]), 16)?,
            u8::from_str_radix(&String::from_iter(&raw[5 .. 7]), 16)?,
        ))
    }
}

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

    #[test]
    fn test_invalid_hex_empty_str() {
        let res: Result<RgbColor, Error> = "".parse();
        assert!(res.is_err());
        assert_eq!(
            format!("{}", res.unwrap_err()), 
            "unexpected hex color format: expected(Color hex code must not be empty), got(Color hex was empty)"
        );
    }

    #[test]
    fn test_invalid_hex_with_missing_prefix() {
        let res: Result<RgbColor, Error> = "00ff00".parse();
        assert!(res.is_err());
        assert_eq!(
            format!("{}", res.unwrap_err()), 
            "unexpected hex color format: expected(Color hex code must start with `#`), got(Color hex starts with `0`)"
        );
    }

    #[test]
    fn test_invalid_hex_with_wrong_size() {
        let res: Result<RgbColor, Error> = "#ff00".parse();
        assert!(res.is_err());
        assert_eq!(
            format!("{}", res.unwrap_err()), 
            "unexpected hex color format: expected(Hex code must be `7` characters long. Example: `#00FF00`), got(Hex code is `5` characters long!)"
        );
    }

    #[test]
    fn test_invalid_hex_with_parse_error() {
        let res: Result<RgbColor, Error> = "#0qfd00".parse();
        assert!(res.is_err());
        assert_eq!(format!("{}", res.unwrap_err()), "couldn't parse hex value: invalid digit found in string");
    }

    #[test]
    fn test_valid_hex() {
        let res: Result<RgbColor, Error> = "#00ff00".parse();
        assert!(res.is_ok());
        assert_eq!(res.unwrap(), RgbColor(0, 255, 0));
    }

    #[test]
    fn test_contrast_ratio() {
        let rgb_white = RgbColor(255, 255, 255);
        let rgb_yellow = RgbColor(255, 255, 0);
        assert_eq!(rgb_white.find_ratio(&rgb_yellow).floor(), 1.);
        let rgb_blue =  RgbColor(0, 0, 255);
        assert_eq!(rgb_white.find_ratio(&rgb_blue).floor(), 8.);
    }
}