use std::cmp::Ordering;

use super::template::{DayTrait, ResultType};
use itertools::Itertools;
use thiserror::Error;

const DAY_NUMBER: usize = 13;

pub struct Day;

impl DayTrait for Day {
    fn get_day_number(&self) -> usize {
        DAY_NUMBER
    }

    fn part1(&self, lines: &[String]) -> anyhow::Result<ResultType> {
        let packets = Packets::parse_all(lines)?;
        let result: i64 = packets
            .iter()
            .tuples()
            .enumerate()
            .filter_map(|(pos, (first, second))| {
                if first < second {
                    Some(pos as i64 + 1)
                } else {
                    None
                }
            })
            .sum();
        Ok(ResultType::Integer(result))
    }

    fn part2(&self, lines: &[String]) -> anyhow::Result<ResultType> {
        let small = Packets::parse("[[2]]")?;
        let large = Packets::parse("[[6]]")?;
        let mut pos_small = 1;
        let mut pos_large = 2;
        let packets = Packets::parse_all(lines)?;
        for packet in packets {
            if packet < small {
                pos_small += 1;
                pos_large += 1;
            } else if packet < large {
                pos_large += 1;
            }
        }
        Ok(ResultType::Integer(pos_small * pos_large))
    }
}

#[derive(Debug, Error)]
enum PacketError {
    #[error("Empty Packet not allowed")]
    EmptyPacketNotAllowed,
    #[error("Packtet must start with a [ was: {0}")]
    ExpectedSquare(char),
    #[error("Unknown char: {0}")]
    UnknownChar(char),
    #[error("End of input reached to early")]
    PrematureEndOfInput,
    #[error("Number was not terminated correctly")]
    UnfinishedNumber,
}

#[derive(Debug, PartialEq, Eq, Clone)]
enum Packets {
    Number(u32),
    List(Vec<Packets>),
}

impl PartialOrd for Packets {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        match (self, other) {
            (Packets::Number(first), Packets::Number(second)) => first.partial_cmp(second),
            (Packets::List(first), Packets::List(second)) => {
                for pair in first.iter().zip_longest(second.iter()) {
                    let result = match pair {
                        itertools::EitherOrBoth::Left(_) => Some(Ordering::Greater),
                        itertools::EitherOrBoth::Right(_) => Some(Ordering::Less),
                        itertools::EitherOrBoth::Both(first, second) => first.partial_cmp(second),
                    };
                    if !matches!(result, Some(Ordering::Equal)) {
                        return result;
                    }
                }
                Some(Ordering::Equal)
            }
            (Packets::Number(_), Packets::List(_)) => self.as_list().partial_cmp(other),
            (Packets::List(_), Packets::Number(_)) => self.partial_cmp(&other.as_list()),
        }
    }
}

impl Packets {
    pub fn as_list(&self) -> Packets {
        match self {
            Packets::Number(_) => Packets::List(vec![self.clone()]),
            Packets::List(_) => self.clone(),
        }
    }

    pub fn parse(line: &str) -> Result<Packets, PacketError> {
        let mut chars = line.chars();
        let Some(start) = chars.next() else {
            return Err(PacketError::EmptyPacketNotAllowed);
        };
        if start != '[' {
            return Err(PacketError::ExpectedSquare(start));
        }
        let packet = Packets::parse_one(&mut chars)?;
        Ok(packet)
    }

    fn parse_one(chars: &mut dyn Iterator<Item = char>) -> Result<Packets, PacketError> {
        let mut list = Vec::new();
        let mut number = None;
        while let Some(next) = chars.next() {
            match next {
                '[' => {
                    if number.is_some() {
                        return Err(PacketError::UnfinishedNumber);
                    }
                    list.push(Packets::parse_one(chars)?);
                }
                ']' => {
                    if let Some(number) = number {
                        list.push(Packets::Number(number));
                    }
                    return Ok(Packets::List(list));
                }
                ',' => {
                    if let Some(number) = number {
                        list.push(Packets::Number(number));
                    }
                    number = None;
                }
                '0'..='9' => match number {
                    None => number = Some(next.to_digit(10).unwrap()),
                    Some(prev) => number = Some(prev * 10 + next.to_digit(10).unwrap()),
                },
                _ => return Err(PacketError::UnknownChar(next)),
            }
        }
        Err(PacketError::PrematureEndOfInput)
    }

    pub fn parse_all(lines: &[String]) -> Result<Vec<Packets>, PacketError> {
        lines
            .iter()
            .filter(|line| !line.is_empty())
            .map(|line| Packets::parse(line))
            .collect::<Result<Vec<_>, _>>()
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use crate::common::file::read_lines;
    use anyhow::Result;

    #[test]
    fn test_parse() -> Result<()> {
        let input = "[[1],[2,3]]";
        let expected = Packets::List(vec![
            Packets::List(vec![Packets::Number(1)]),
            Packets::List(vec![Packets::Number(2), Packets::Number(3)]),
        ]);
        let result = Packets::parse(input)?;
        assert_eq!(result, expected);
        Ok(())
    }

    #[test]
    fn test_parse_all() -> Result<()> {
        let day = Day {};
        let lines = read_lines(day.get_day_number(), "example01.txt")?;
        let result = Packets::parse_all(&lines)?;
        assert_eq!(result.len(), 16);
        Ok(())
    }

    #[test]
    fn test_compare_all() -> Result<()> {
        let day = Day {};
        let lines = read_lines(day.get_day_number(), "example01.txt")?;
        let expected = vec![true, true, false, true, false, true, false, false];
        let result = Packets::parse_all(&lines)?;
        let compare = result
            .iter()
            .tuples()
            .map(|(first, second)| first < second)
            .collect::<Vec<_>>();
        assert_eq!(compare, expected);

        Ok(())
    }

    #[test]
    fn test_part1() -> Result<()> {
        let day = Day {};
        let lines = read_lines(day.get_day_number(), "example01.txt")?;
        let expected = ResultType::Integer(13);
        let result = day.part1(&lines)?;
        assert_eq!(result, expected);

        Ok(())
    }

    #[test]
    fn test_part2() -> Result<()> {
        let day = Day {};
        let lines = read_lines(day.get_day_number(), "example01.txt")?;
        let expected = ResultType::Integer(140);
        let result = day.part2(&lines)?;
        assert_eq!(result, expected);

        Ok(())
    }
}