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//! GFF record attributes field.

pub mod tag;
pub mod value;

pub use self::{tag::Tag, value::Value};

use std::{
    borrow::Cow,
    error,
    fmt::{self, Display},
    str,
};

use percent_encoding::{percent_decode_str, utf8_percent_encode, AsciiSet, CONTROLS};

pub(super) const SEPARATOR: char = '=';

const PERCENT_ENCODE_SET: &AsciiSet = &CONTROLS
    .add(b'\t')
    .add(b'\n')
    .add(b'\r')
    .add(b'%')
    .add(b';')
    .add(b'=')
    .add(b'&')
    .add(b',');

pub(super) fn field_fmt((key, value): (&Tag, &Value), f: &mut fmt::Formatter<'_>) -> fmt::Result {
    percent_encode(key).fmt(f)?;
    SEPARATOR.fmt(f)?;
    value.fmt(f)?;
    Ok(())
}

/// An error returned when a raw attributes field fails to parse.
#[derive(Clone, Debug, Eq, PartialEq)]
pub enum ParseError {
    /// The input is invalid.
    Invalid,
    /// A key is invalid.
    InvalidKey(str::Utf8Error),
    /// A value is invalid.
    InvalidValue(Tag, value::ParseError),
}

impl ParseError {
    /// Returns the key of the field that caused the failure.
    pub fn key(&self) -> Option<&Tag> {
        match self {
            Self::InvalidValue(key, _) => Some(key),
            _ => None,
        }
    }
}

impl error::Error for ParseError {
    fn source(&self) -> Option<&(dyn error::Error + 'static)> {
        match self {
            Self::InvalidKey(e) => Some(e),
            Self::InvalidValue(_, e) => Some(e),
            _ => None,
        }
    }
}

impl fmt::Display for ParseError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Invalid => write!(f, "invalid input"),
            Self::InvalidKey(_) => write!(f, "invalid key"),
            Self::InvalidValue(..) => write!(f, "invalid value"),
        }
    }
}

pub(super) fn parse_field(s: &str) -> Result<(Tag, Value), ParseError> {
    let (raw_key, raw_value) = s.split_once(SEPARATOR).ok_or(ParseError::Invalid)?;

    let key: Tag = percent_decode(raw_key)
        .map(|k| k.into())
        .map_err(ParseError::InvalidKey)?;

    let value = raw_value
        .parse()
        .map_err(|e| ParseError::InvalidValue(key.clone(), e))?;

    Ok((key, value))
}

pub(super) fn percent_decode(s: &str) -> Result<Cow<'_, str>, str::Utf8Error> {
    percent_decode_str(s).decode_utf8()
}

pub(super) fn percent_encode(s: &str) -> Cow<'_, str> {
    utf8_percent_encode(s, PERCENT_ENCODE_SET).into()
}

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

    #[test]
    fn test_field_fmt() {
        struct F(Tag, Value);

        impl fmt::Display for F {
            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                field_fmt((&self.0, &self.1), f)
            }
        }

        let field = F(Tag::from("gene_id"), Value::from("gene0"));
        assert_eq!(field.to_string(), "gene_id=gene0");

        let field = F(Tag::from("%s"), Value::from("13,21"));
        assert_eq!(field.to_string(), "%25s=13%2C21");
    }

    #[test]
    fn test_parse_field() {
        assert_eq!(
            parse_field("gene_id=gene0"),
            Ok((String::from("gene_id"), Value::from("gene0")))
        );

        assert_eq!(
            parse_field("%25s=13%2C21"),
            Ok((String::from("%s"), Value::from("13,21")))
        );

        assert_eq!(parse_field(""), Err(ParseError::Invalid));
    }
}