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use std::error::Error;
use std::fmt;
mod spdx;

use self::LicenseExpr::*;

#[derive(Debug, Clone, Copy)]
pub enum LicenseExpr<'a> {
    License(&'a str),
    Exception(&'a str),
    And, Or, With,
}

impl<'a> fmt::Display for LicenseExpr<'a> {
    fn fmt(&self, format: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        match *self {
            With => format.write_str("WITH"),
            And  => format.write_str("AND"),
            Or   => format.write_str("OR"),
            License(info) | Exception(info) => format.write_str(info),
        }
    }
}

#[derive(Debug, Clone, Copy)]
pub enum ParseError<'a> {
    UnknownLicenseId(&'a str),
    InvalidStructure(LicenseExpr<'a>)
}

impl<'a> fmt::Display for ParseError<'a> {
    fn fmt(&self, format: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        match *self {
            ParseError::UnknownLicenseId(info)
                => format.write_fmt(format_args!("{}: {}", self.description(), info)),
            ParseError::InvalidStructure(info)
                => format.write_fmt(format_args!("{}: {}", self.description(), info)),
        }
    }
}

impl<'a> Error for ParseError<'a> {
    fn description(&self) -> &str {
        match *self {
            ParseError::UnknownLicenseId(_) => "unknown license or other term",
            ParseError::InvalidStructure(_) => "invalid license expression",
        }
    }
}

pub fn validate_license_expr(license_expr: &str) -> Result<(), ParseError> {
    license_expr.split_whitespace().map(|word| match word {
        "AND"   => Ok(And),
        "OR"    => Ok(Or),
        "WITH"  => Ok(With),
        _ if spdx::LICENSES.binary_search(&word.trim_right_matches('+')).is_ok()
                => Ok(License(word)),
        _ if spdx::EXCEPTIONS.binary_search(&word).is_ok()
                => Ok(Exception(word)),
        _       => Err(ParseError::UnknownLicenseId(word))
    }).fold(Ok(Or), |prev, word| match (prev, word) {
        (err @ Err(_), _) | (_, err @ Err(_)) => err,
        (Ok(License(_)), Ok(With))
            | (Ok(License(_)), Ok(And))
            | (Ok(License(_)), Ok(Or))
            | (Ok(Exception(_)), Ok(And))
            | (Ok(Exception(_)), Ok(Or))
            | (Ok(And), Ok(License(_)))
            | (Ok(Or), Ok(License(_)))
            | (Ok(With), Ok(Exception(_)))
            => word,
        _ => Err(ParseError::InvalidStructure(word.unwrap()))
    }).and(Ok(()))
}

pub fn license_version() -> &'static str {
    spdx::VERSION
}