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//! Hamming distance calculation

/// A trait for calculating hamming distance
pub trait HammingDistancable<RHS = Self> {
    /// The output type of the hamming distance
    type Output;
    fn hamming_distance(self, other: RHS) -> Self::Output;
}

impl<'a, 'b, T> HammingDistancable<&'b Vec<T>> for &'a Vec<T>
    where T : Eq {
    type Output = Result<u32, &'static str>;
    /// Calculate the hamming distance between vectors
    fn hamming_distance(self, other: &'b Vec<T>) -> Result<u32, &'static str> {
        if self.len() != other.len() {
            return Err("Vectors do not have equal length");
        }

        let mut distance = 0;
        for (a, b) in self.iter().zip(other.iter()) {
            if a != b {
                distance += 1;
            }
        }

        return Ok(distance);
    }
}

impl<'a, 'b, T> HammingDistancable<&'b [T]> for &'a [T]
    where T : Eq {
    type Output = Result<u32, &'static str>;
    /// Calculate the hamming distance between slices
    fn hamming_distance(self, other: &'b [T]) -> Result<u32, &'static str> {
        if self.len() != other.len() {
            return Err("Slices do not have equal length");
        }

        let mut distance = 0;
        for (a, b) in self.iter().zip(other.iter()) {
            if a != b {
                distance += 1;
            }
        }

        return Ok(distance);
    }
}

impl <'a, 'b> HammingDistancable<&'b String> for &'a String {
    type Output = Result<u32, &'static str>;
    /// Calculate the hamming distance between strings
     fn hamming_distance(self, other: &'b String) -> Result<u32, &'static str> {
        if self.len() != other.len() {
            return Err("Strings do not have equal length");
        }

        let mut distance = 0;
        for (a, b) in self.chars().zip(other.chars()) {
            if a != b {
                distance += 1;
            }
        }

        return Ok(distance);
    }
}

impl <'a, 'b> HammingDistancable<&'b str> for &'a str {
    type Output = Result<u32, &'static str>;
    /// Calculate the hamming distance between borrowed strings
     fn hamming_distance(self, other: &'b str) -> Result<u32, &'static str> {
        if self.len() != other.len() {
            return Err("Strings do not have equal length");
        }

        let mut distance = 0;
        for (a, b) in self.chars().zip(other.chars()) {
            if a != b {
                distance += 1;
            }
        }

        return Ok(distance);
    }
}

#[cfg(test)]
mod tests {
    use hamming_distance::HammingDistancable;
    
    #[test]
    fn vec_hamming_distance() {
        let mut vec1 : Vec<char> = Vec::new();
        let mut vec2 : Vec<char> = Vec::new();

        vec1.push('a');
        vec1.push('b');

        vec2.push('c');
        vec2.push('d');

        assert!(vec1.hamming_distance(&vec2).unwrap() == 2);
    }

    #[test]
    fn vec_hamming_distance_error() {
        let mut vec1 : Vec<char> = Vec::new();
        let mut vec2 : Vec<char> = Vec::new();

        vec1.push('a');
        vec1.push('b');

        vec2.push('c');

        assert!(vec1.hamming_distance(&vec2).unwrap_err() == 
            "Vectors do not have equal length");
    }

    #[test]
    fn slice_hamming_distance() {
        let byte_slice1 : &[u8] = &[0x01, 0x01];
        let byte_slice2 : &[u8] = &[0x01, 0xFF];

        assert!(byte_slice1.hamming_distance(byte_slice2).unwrap() == 1);
    }

    #[test]
    fn slice_hamming_distance_error() {
        let byte_slice1 : &[u8] = &[0x01];
        let byte_slice2 : &[u8] = &[0x01, 0xFF];

        assert!(byte_slice1.hamming_distance(byte_slice2).unwrap_err() == 
            "Slices do not have equal length");
    }

    #[test]
    fn string_hamming_distance() {
        let string1 : String = "Cat".to_owned();
        let string2 : String = "Hat".to_owned();

        assert!(string1.hamming_distance(&string2).unwrap() == 1);
    }

    #[test]
    fn string_hamming_distance_error() {
        let string1 : String = "Cats".to_owned();
        let string2 : String = "Hat".to_owned();

        assert!(string1.hamming_distance(&string2).unwrap_err() == 
            "Strings do not have equal length");
    }

    #[test]
    fn borrowed_string_hamming_distance() {
        let string1 : &str = "Cat";
        let string2 : &str = "Hat";

        assert!(string1.hamming_distance(string2).unwrap() == 1);
    }

    #[test]
    fn borrowed_string_hamming_distance_error() {
        let string1 : &str = "Cats";
        let string2 : &str = "Hat";

        assert!(string1.hamming_distance(string2).unwrap_err() == 
            "Strings do not have equal length");
    }
}