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use read_token::ReadToken;
use range::Range;

use {
    DebugId,
    ParseError,
};

/// Stores information about whitespace.
#[derive(Clone, Debug, PartialEq)]
pub struct Whitespace {
    /// Whether the whitespace is optional or required.
    pub optional: bool,
    /// A debug id to track down the rule generating an error.
    pub debug_id: DebugId,
}

impl Whitespace {
    /// Parse whitespace.
    /// If whitespace is required and no whitespace is found,
    /// an error will be reported.
    pub fn parse(&self, read_token: &ReadToken) ->
        Result<Range, Range<ParseError>>
    {
        let range = read_token.whitespace();
        if range.length == 0 && !self.optional {
            Err(range.wrap(ParseError::ExpectedWhitespace(self.debug_id)))
        } else {
            Ok(range)
        }
    }
}

#[cfg(test)]
mod tests {
    use all::*;
    use meta_rules::Whitespace;
    use range::Range;
    use read_token::ReadToken;

    #[test]
    fn optional() {
        let text = "a,b, c";
        let optional_whitespace = Whitespace { debug_id: 0, optional: true };
        assert_eq!(optional_whitespace.parse(&ReadToken::new(&text, 0)),
            Ok(Range::new(0, 0)));
        assert_eq!(optional_whitespace.parse(&ReadToken::new(&text[4..], 4)),
            Ok(Range::new(4, 1)));
    }

    #[test]
    fn required() {
        let text = "a,   b,c";
        let required_whitespace = Whitespace { debug_id: 0, optional: false };
        assert_eq!(required_whitespace.parse(&ReadToken::new(&text[2..], 2)),
            Ok(Range::new(2, 3)));
        // Prints an error message to standard error output.
        assert_eq!(required_whitespace.parse(&ReadToken::new(&text[7..], 7)),
            Err(Range::new(7, 0).wrap(ParseError::ExpectedWhitespace(0))));
    }
}