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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_end_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
}