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// Copyright 2018 Gerrit Viljoen

// This file is part of prange.
//
// prange is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// prange is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with prange.  If not, see <http://www.gnu.org/licenses/>.

//! Parse numeric ranges for indexing.
//!
//! Inclusive-inclusive 1-based integer ranges. Parsed from strings.
//!
//! # Examples
//!
//! ```ignore
//! "2"         => [2]
//! "1-5"       => [1, 2, 3, 4, 5]
//! "1-3,5-6"   => [1, 2, 3, 5, 6]
//! "-3"        => [1, 2, 3]
//! "1-"        => [1, 2, 3, ..]
//! "1-3,2-4,7" => [1, 2, 3, 2, 3, 4, 7]
//! ```

#[cfg(test)]
mod test;

use std::error::Error;
use std::fmt;
use std::num::ParseIntError;
use std::ops::Range;
use std::str::FromStr;

pub fn parse<T>(x: &T) -> Result<RangeIter, ParseError>
where T: AsRef<str> {
    if x.as_ref().is_empty() {
        return Ok(RangeIter{ranges: Vec::new()})
    }
    let x2 = x.as_ref().to_string() + ",";
    let mut res = Vec::new();
    let mut tok1 = String::new();
    let mut tok2 = String::new();
    let mut first = true;
    for (i, x) in x2.chars().enumerate() {
        match x {
            ',' => {
                if tok1.is_empty() && tok2.is_empty() {
                    if first {
                        return Err(ParseError::EmptyRange(i))
                    } else {
                        return Err(ParseError::InvalidRange(i))
                    }
                }
                let num1 = if tok1.is_empty() {
                    1
                } else {
                    match u64::from_str(&tok1) {
                        Ok(x) => x,
                        Err(x) => return Err(ParseError::Integer(i, x))
                    }
                };
                let num2 = if first {
                    num1 + 1
                } else if tok2.is_empty() {
                    u64::max_value()
                } else {
                    match u64::from_str(&tok2) {
                        Ok(x) => x + 1,
                        Err(x) => return Err(ParseError::Integer(i, x))
                    }
                };
                res.push(Range{start: num1, end: num2});
                tok1.clear();
                tok2.clear();
                first = true;
            },
            '-' => {
                if first {
                    first = false
                } else {
                    return Err(ParseError::InvalidRange(i))
                }
            },
            '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' => {
                if first {
                    tok1.push(x)
                } else {
                    tok2.push(x)
                }
            },
            x => return Err(ParseError::IllegalChar(i, x))
        }
    }
    res.reverse();
    Ok(RangeIter{ranges: res})
}

#[derive(Debug)]
pub struct RangeIter {
    ranges: Vec<Range<u64>>
}

impl Iterator for RangeIter {
    type Item = u64;

    fn next(&mut self) -> Option<u64> {
        if self.ranges.is_empty() {
            None
        } else {
            let x = self.ranges.last_mut().unwrap().next();
            if x.is_none() {
                self.ranges.pop();
                self.next()
            } else {
                x
            }
        }
    }
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub enum ParseError {
    IllegalChar(usize, char),
    EmptyRange(usize),
    InvalidRange(usize),
    Integer(usize, ParseIntError)
}

impl fmt::Display for ParseError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self.description().fmt(f)
    }
}

impl Error for ParseError {
    fn description(&self) -> &str {
        use self::ParseError::*;
        match *self {
            IllegalChar(..) => "input contains invalid characters",
            EmptyRange(..) => "input contains an empty range",
            InvalidRange(..) => "input contains an invalid range",
            Integer(_, ref x) => x.description(),
        }
    }

    fn cause(&self) -> Option<&Error> {
        use self::ParseError::*;
        match *self {
            IllegalChar(..) => None,
            EmptyRange(..) => None,
            InvalidRange(..) => None,
            Integer(_, ref x) => Some(x),
        }
    }
}