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//! FASTA record definition and components.

use std::{
    error, fmt,
    str::{self, FromStr},
};

const PREFIX: char = '>';

/// A FASTA record definition.
///
/// A definition represents a definition line, i.e, a reference sequence name and, optionally, a
/// description.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Definition {
    name: Vec<u8>,
    description: Option<Vec<u8>>,
}

impl Definition {
    /// Creates a FASTA record definition.
    ///
    /// # Examples
    ///
    /// ```
    /// use noodles_fasta::record::Definition;
    /// let definition = Definition::new("sq0", None);
    /// ```
    pub fn new<N>(name: N, description: Option<Vec<u8>>) -> Self
    where
        N: Into<Vec<u8>>,
    {
        Self {
            name: name.into(),
            description,
        }
    }

    /// Returns the record name.
    ///
    /// # Examples
    ///
    /// ```
    /// use noodles_fasta::record::Definition;
    /// let definition = Definition::new("sq0", None);
    /// assert_eq!(definition.name(), b"sq0");
    /// ```
    pub fn name(&self) -> &[u8] {
        &self.name
    }

    /// Returns the description if it is set.
    ///
    /// # Examples
    ///
    /// ```
    /// use noodles_fasta::record::Definition;
    ///
    /// let definition = Definition::new("sq0", None);
    /// assert_eq!(definition.description(), None);
    ///
    /// let definition = Definition::new("sq0", Some(Vec::from("LN:13")));
    /// assert_eq!(definition.description(), Some(&b"LN:13"[..]));
    /// ```
    pub fn description(&self) -> Option<&[u8]> {
        self.description.as_deref()
    }
}

impl fmt::Display for Definition {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let name = str::from_utf8(self.name()).map_err(|_| fmt::Error)?;
        write!(f, "{PREFIX}{name}")?;

        if let Some(buf) = self.description() {
            let description = str::from_utf8(buf).map_err(|_| fmt::Error)?;
            write!(f, " {description}")?;
        }

        Ok(())
    }
}

/// An error returned when a raw record definition fails to parse.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum ParseError {
    /// The input is empty.
    Empty,
    /// The prefix (`>`) is missing.
    MissingPrefix,
    /// The sequence name is missing.
    MissingName,
}

impl error::Error for ParseError {}

impl fmt::Display for ParseError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Empty => f.write_str("empty input"),
            Self::MissingPrefix => write!(f, "missing prefix ('{PREFIX}')"),
            Self::MissingName => f.write_str("missing name"),
        }
    }
}

impl FromStr for Definition {
    type Err = ParseError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        if s.is_empty() {
            return Err(ParseError::Empty);
        } else if !s.starts_with(PREFIX) {
            return Err(ParseError::MissingPrefix);
        }

        let line = &s[1..];
        let mut components = line.splitn(2, |c: char| c.is_ascii_whitespace());

        let name = components
            .next()
            .and_then(|s| if s.is_empty() { None } else { Some(s.into()) })
            .ok_or(ParseError::MissingName)?;

        let description = components.next().map(|s| s.trim().into());

        Ok(Self { name, description })
    }
}

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

    #[test]
    fn test_fmt() {
        let definition = Definition::new("sq0", None);
        assert_eq!(definition.to_string(), ">sq0");

        let definition = Definition::new("sq0", Some(Vec::from("LN:13")));
        assert_eq!(definition.to_string(), ">sq0 LN:13");
    }

    #[test]
    fn test_from_str() {
        assert_eq!(">sq0".parse(), Ok(Definition::new("sq0", None)));

        assert_eq!(
            ">sq0  LN:13".parse(),
            Ok(Definition::new("sq0", Some(Vec::from("LN:13"))))
        );

        assert_eq!("".parse::<Definition>(), Err(ParseError::Empty));
        assert_eq!("sq0".parse::<Definition>(), Err(ParseError::MissingPrefix));
        assert_eq!(">".parse::<Definition>(), Err(ParseError::MissingName));
    }
}