// Copyright 2022 Christian Ulrich
//
// This program 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.
//
// This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.

use std::cmp::{Ordering, PartialOrd};
use std::io;

#[derive(Debug, PartialEq, Clone, Eq, Ord)]
pub enum Token {
    Integer(u64),
    List(Vec<Token>),
}

pub struct PacketPairs {}

impl Token {
    fn parse_integer(input: &str) -> Result<Token, &'static str> {
        Ok(Self::Integer(
            input.parse().map_err(|_| "cannot parse integer")?,
        ))
    }

    fn parse_list(input: &str) -> Result<Token, &'static str> {
        let mut elements = Vec::new();
        let mut element = String::new();
        let mut bracket_counter = 0;
        for c in input.chars() {
            match c {
                ']' if { bracket_counter > 0 } => {
                    element.push(c);
                    bracket_counter -= 1;
                }
                '[' => {
                    element.push(c);
                    bracket_counter += 1;
                }
                ',' if { bracket_counter == 0 } => {
                    elements.push(Self::from_str(&element)?);
                    element.clear();
                }
                _ => element.push(c),
            }
        }
        if element.len() > 0 {
            elements.push(Self::from_str(&element)?);
        }
        Ok(Self::List(elements))
    }

    pub fn from_str(input: &str) -> Result<Token, &'static str> {
        let input = input.trim();
        if input.starts_with('[') && input.ends_with(']') {
            Self::parse_list(&input[1..input.len() - 1])
        } else {
            Self::parse_integer(input)
        }
    }
}

impl PartialOrd for Token {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        type T = Token;

        match (self, other) {
            (T::Integer(a), T::Integer(b)) => a.partial_cmp(b),
            (T::List(a), T::List(b)) => {
                let common_len = usize::min(a.len(), b.len());
                for (left, right) in Iterator::zip(a[..common_len].iter(), b[..common_len].iter()) {
                    if left > right {
                        return Some(Ordering::Greater);
                    }
                    if left < right {
                        return Some(Ordering::Less);
                    }
                }
                if a.len() > common_len {
                    return Some(Ordering::Greater);
                }
                if b.len() > common_len {
                    return Some(Ordering::Less);
                }
                Some(Ordering::Equal)
            }
            (T::List(_), T::Integer(_)) => self.partial_cmp(&T::List(vec![other.clone()])),
            (T::Integer(_), T::List(_)) => T::List(vec![self.clone()]).partial_cmp(other),
        }
    }
}

pub fn packet_pairs() -> PacketPairs {
    PacketPairs {}
}

impl Iterator for PacketPairs {
    type Item = Result<(Token, Token), &'static str>;

    fn next(&mut self) -> Option<Self::Item> {
        const ERROR: &str = "cannot parse packet pair";

        let left = match io::stdin().lines().next()?.unwrap().as_str() {
            "" => return None,
            line => Token::from_str(&line),
        };
        let right = match io::stdin().lines().next()?.unwrap().as_str() {
            "" => return None,
            line => Token::from_str(&line),
        };
        match io::stdin().lines().next()?.unwrap().as_str() {
            "" => match (left, right) {
                (Ok(left), Ok(right)) => Some(Ok((left, right))),
                e => {
                    println!("{:?}", e);
                    Some(Err(ERROR))
                }
            },
            _ => Some(Err(ERROR)),
        }
    }
}