use alloc::{str::FromStr, string::String};

/// Type of line endings in markdown.
///
/// Particularly when working with Windows, you might want to use
/// `LineEnding::CarriageReturnLineFeed`.
///
/// ## Examples
///
/// ```
/// use markdown::LineEnding;
/// # fn main() {
///
/// // Use a CR + LF combination:
/// let crlf = LineEnding::CarriageReturnLineFeed;
/// # }
/// ```
#[derive(Clone, Debug, Default, Eq, PartialEq)]
pub enum LineEnding {
    /// Both a carriage return (`\r`) and a line feed (`\n`).
    ///
    /// ## Example
    ///
    /// ```markdown
    /// a␍␊
    /// b
    /// ```
    CarriageReturnLineFeed,
    /// Sole carriage return (`\r`).
    ///
    /// ## Example
    ///
    /// ```markdown
    /// a␍
    /// b
    /// ```
    CarriageReturn,
    /// Sole line feed (`\n`).
    ///
    /// ## Example
    ///
    /// ```markdown
    /// a␊
    /// b
    /// ```
    #[default]
    LineFeed,
}

// xxxxxxxxxxxxxxx
impl LineEnding {
    /// Turn the line ending into a [str].
    #[must_use]
    pub fn as_str(&self) -> &str {
        match self {
            LineEnding::CarriageReturnLineFeed => "\r\n",
            LineEnding::CarriageReturn => "\r",
            LineEnding::LineFeed => "\n",
        }
    }
}

impl FromStr for LineEnding {
    type Err = String;

    /// Turn a string into a line ending.
    ///
    /// ## Panics
    ///
    /// Panics if `code` is not `\r\n`, `\r`, or `\n`.
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        match s {
            "\r\n" => Ok(LineEnding::CarriageReturnLineFeed),
            "\r" => Ok(LineEnding::CarriageReturn),
            "\n" => Ok(LineEnding::LineFeed),
            _ => Err("Expected CR, LF, or CRLF".into()),
        }
    }
}

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

    #[test]
    fn test_line_ending() {
        assert_eq!(
            "\r".parse(),
            Ok(LineEnding::CarriageReturn),
            "should support turning a string into a carriage return"
        );
        assert_eq!(
            LineEnding::CarriageReturn.as_str(),
            "\r",
            "should support turning a carriage return into a string"
        );

        assert_eq!(
            "\n".parse(),
            Ok(LineEnding::LineFeed),
            "should support turning a string into a line feed"
        );
        assert_eq!(
            LineEnding::LineFeed.as_str(),
            "\n",
            "should support turning a line feed into a string"
        );

        assert_eq!(
            "\r\n".parse(),
            Ok(LineEnding::CarriageReturnLineFeed),
            "should support turning a string into a carriage return + line feed"
        );
        assert_eq!(
            LineEnding::CarriageReturnLineFeed.as_str(),
            "\r\n",
            "should support turning a carriage return + line feed into a string"
        );

        assert_eq!(
            "aaa".parse::<LineEnding>(),
            Err("Expected CR, LF, or CRLF".into()),
            "should error when parsing a non-eol"
        );
    }
}