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#![warn(clippy::all, clippy::pedantic, clippy::nursery, clippy::perf)]

pub mod err;

type Result<T> = std::result::Result<T, err::ShortError>;

pub static DEFAULT_ALPHABET: &str = "mn6j2c4rv8bpygw95z7hsdaetxuk3fq";
pub static DEFAULT_BLOCK_SIZE: usize = 24;
pub static MIN_LENGTH: usize = 5;

pub struct UrlEncoder {
    alphabet: Vec<char>,
    mask: usize,
    mapping: Vec<usize>,
}

impl UrlEncoder {
    /// Creates a new `UrlEncoder` decoder/encoder.
    ///
    /// ```
    /// use short_url::UrlEncoder;
    ///
    /// let encoder = UrlEncoder::new("mn6j2c4rv8bpygw95z7hsdaetxuk3fq", 24);
    /// ```
    #[must_use]
    pub fn new(alp: &str, block: usize) -> Self {
        Self {
            alphabet: alp.chars().collect(),
            mask: (1 << block) - 1,
            mapping: (0..block).map(std::convert::From::from).collect(),
        }
    }
    /// Encodes a number into a string based on the `UrlEncoder`
    ///
    /// ```
    /// use short_url::UrlEncoder;
    /// let encoder = UrlEncoder::new("mn6j2c4rv8bpygw95z7hsdaetxuk3fq", 24);
    ///
    /// assert_eq!(String::from("867nv"), encoder.encode_url(1, 5));
    /// ```
    #[must_use]
    pub fn encode_url(&self, n: usize, min_length: usize) -> String { self.enbase(self.encode(n), min_length) }

    /// Decodes a string into a`usize`
    ///
    ///```
    /// use short_url::UrlEncoder;
    /// let e = UrlEncoder::new("mn6j2c4rv8bpygw95z7hsdaetxuk3fq", 24);
    ///
    /// assert_eq!(1, e.decode_url("867nv").unwrap());
    /// ```
    /// # Errors
    /// This method will error if the provided string is not valid with the
    /// alphabet used to construct the `UrlEncoder`
    pub fn decode_url(&self, x: &str) -> Result<usize> { Ok(self.decode(self.debase(x)?)) }

    fn encode(&self, n: usize) -> usize { n & !self.mask | self._encode(n & self.mask) }

    fn _encode(&self, n: usize) -> usize {
        let mut result = 0;

        self.mapping.iter().rev().enumerate().for_each(|(i, b)| {
            if n & (1 << i) != 0 {
                result |= 1 << b;
            }
        });

        result
    }

    fn decode(&self, n: usize) -> usize { (n & !self.mask) | self._decode(n & self.mask) }

    fn _decode(&self, n: usize) -> usize {
        let mut result = 0;

        self.mapping.iter().rev().enumerate().for_each(|(i, b)| {
            if n & (1 << b) != 0 {
                result |= 1 << i;
            }
        });

        result
    }

    fn enbase(&self, x: usize, min_length: usize) -> String {
        let result = self._enbase(x);

        let pad_num = if min_length < result.chars().count() {
            0
        } else {
            min_length - result.chars().count()
        };

        let padding = self.alphabet[0].to_string().repeat(pad_num);

        format!("{}{}", padding, result)
    }

    fn _enbase(&self, x: usize) -> String {
        let n = self.alphabet.len();
        if x < n {
            return self.alphabet[x].to_string();
        }

        let mut rt = Vec::new();
        let mut xx = x;

        while xx >= n {
            rt.insert(0, self.alphabet[xx % n]);
            xx /= n;
        }

        rt.insert(0, self.alphabet[xx]);

        rt.into_iter().collect()
    }

    #[allow(clippy::cast_possible_truncation)]
    fn debase(&self, x: &str) -> Result<usize> {
        let n = self.alphabet.len();
        let mut result = 0;

        for (i, c) in x.chars().into_iter().rev().enumerate() {
            result += self
                .alphabet
                .iter()
                .position(|&x| x == c)
                .ok_or(err::ShortError::InvalidString)?
                * (n.pow(i as u32));
        }

        Ok(result)
    }
}

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

    #[test]
    fn encode_url() {
        let e = UrlEncoder::new("mn6j2c4rv8bpygw95z7hsdaetxuk3fq", 24);

        assert_eq!(String::from("867nv"), e.encode_url(1, 5));
    }

    #[test]
    fn decode_url() {
        let e = UrlEncoder::new("mn6j2c4rv8bpygw95z7hsdaetxuk3fq", 24);

        assert_eq!(1, e.decode_url("867nv").unwrap());
    }
}