enum PairsState<N> {
    Fresh,
    Running(N),
    Finished,
}
struct Pairs<I, N> {
    inner: I,
    state: PairsState<N>,
}
impl<I: Iterator<Item = N>, N> Pairs<I, N> {
    fn new(inner: I) -> Self {
        Self {
            inner: inner,
            state: PairsState::Fresh,
        }
    }
}
impl<I: Iterator<Item = N>, N: Copy> Iterator for Pairs<I, N> {
    type Item = (N, N);
    fn next(&mut self) -> Option<Self::Item> {
        match self.state {
            PairsState::Fresh => match self.inner.next() {
                None => {
                    self.state = PairsState::Finished;
                    None
                }
                Some(x) => {
                    self.state = PairsState::Running(x);
                    self.next()
                }
            },
            PairsState::Running(last) => match self.inner.next() {
                None => {
                    self.state = PairsState::Finished;
                    None
                }
                Some(x) => {
                    self.state = PairsState::Running(x);
                    Some((last, x))
                }
            },
            PairsState::Finished => None,
        }
    }
}
struct SlidingWindow<I, N> {
    inner: I,
    size: usize,
    window: std::collections::VecDeque<N>,
}
impl<I, N> SlidingWindow<I, N> {
    fn new(inner: I, size: usize) -> Self {
        Self {
            inner: inner,
            size: size,
            window: std::collections::VecDeque::new(),
        }
    }
}
impl<I: Iterator<Item = N>, N: Copy> Iterator for SlidingWindow<I, N> {
    type Item = Vec<N>;
    fn next(&mut self) -> Option<Self::Item> {
        match self.inner.next() {
            None => None,
            Some(x) => {
                self.window.push_back(x);
                if self.window.len() < self.size {
                    self.next()
                } else {
                    let result = self.window.iter().map(|x| *x).collect();
                    self.window.pop_front();
                    Some(result)
                }
            }
        }
    }
}
fn count_increments<I: Iterator<Item = N>, N: Copy + std::cmp::PartialOrd>(source: I) -> usize {
    Pairs::new(source)
        .map(|(last, current)| if current > last { 1 } else { 0 })
        .sum()
}
fn main() {
    use std::fs::File;
    use std::io::BufRead;
    use std::io::BufReader;
    use std::path::Path;
    let args: Vec<_> = std::env::args().collect();
    let file = BufReader::new(File::open(<String as AsRef<Path>>::as_ref(&args[1])).unwrap());
    let measurements: Vec<u64> = file
        .lines()
        .flat_map(|line| line.ok().and_then(|line| str::parse(line.as_ref()).ok()))
        .collect();
    println!(
        "Depth measurement increases {} times (measurements); {} times (moving window)",
        count_increments(measurements.iter()),
        count_increments(
            SlidingWindow::new(measurements.iter(), 3).map(|w| w.into_iter().sum::<u64>())
        )
    );
}

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version = "0.1.0"
edition = "2018"
# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
[dependencies]
[[bin]]
name = "day1"
path = "day1.rs"

# This file is automatically @generated by Cargo.
# It is not intended for manual editing.
version = 3
[[package]]
name = "aoc-2020"
version = "0.1.0"

#![feature(async_stream)]
use bytes::Bytes;
use std::collections::HashSet;
use std::future::Future;
use std::marker::Unpin;
use std::stream::Stream;
use tokio::io::{self, AsyncBufRead, AsyncBufReadExt, BufReader};
enum Rule {
    Match(String),
    Branch(Vec<Vec<usize>>),
}
fn parse_rule(s: String) -> Option<Rule> {
    let s = s.trim();
    s.split_once(':').and_then(|(_ix, body)| {
        let body = body.trim();
        parse_match_rule(body).or_else(|| parse_branch_rule(body))
    })
}
fn parse_match_rule(body: &str) -> Option<Rule> {
    let oqi = body.find('\"')?;
    let cqi = body.rfind('\"')?;
    Some(Rule::Match(String::from(&body[oqi + 1 .. cqi])))
}
fn parse_branch_rule(body: &str) -> Option<Rule> {
    use std::str::FromStr;
    let mut result = Vec::new();
    for a in body.split('|') {
        let mut branch = Vec::new();
        for b in a.split_whitespace() {
            branch.push(usize::from_str(b).ok()?);
        }
        result.push(branch);
    }
    Some(Rule::Branch(result))
}
async fn read_rules<I: Unpin + AsyncBufRead>(source: &mut I) -> Vec<Rule> {
    let mut result = Vec::new();
    loop {
        let mut buf = String::new();
        match source.read_line(&mut buf).await {
            Ok(0) => break,
            Ok(_) => match parse_rule(buf) {
                None => break,
                Some(rule) => {
                    result.push(rule);
                }
            },
            _ => break,
        }
    }
    result
}
async fn check_match(rules: Vec<Rule>, rule_index: usize, text: String) -> Option<HashSet<String>> {
    tokio::task::yield_now().await;
    match &rules[rule_index] {
        Rule::Match(lit) => text.strip_prefix(<String as AsRef<str>>::as_ref(lit)).map(|s| {
            let mut r = HashSet::with_capacity(1);
            r.insert(String::from(s));
            r
        }),
        Rule::Branch(branches) => {
            let jhs: Vec<_> = branches.iter().map(|branch| {
                let branch = branch.clone();
                let text = text.clone();
                tokio::spawn(async {
                    tokio::task::yield_now().await;
                    let mut remainders = HashSet::with_capacity(1);
                    remainders.insert(text);
                    for child in branch {
                        let mut nr: HashSet<String> = HashSet::new();
                        for r in remainders {
                            let recursive = Box::new(check_match(rules, child, r)) as Box<dyn Future<Output=Option<HashSet<String>>> + Unpin + Send>;
                            for r2 in recursive.await.unwrap_or_else(|| HashSet::new()) {
                            }
                        }
                    }
                    Some(remainders)
                })
            }).collect();
            todo!()
        }
    }
}
async fn write_str<S: io::AsyncWriteExt + Unpin>(sink: &mut S, text: String) -> io::Result<usize> {
    sink.write_buf(&mut Bytes::from(text)).await
}
#[tokio::main(flavor = "multi_thread")]
async fn main() -> io::Result<()> {
    let stdout = &mut io::stdout();
    let args: Vec<_> = std::env::args().collect();
    let mut input = BufReader::new(tokio::fs::File::open(args[1].clone()).await?);
    let rules = read_rules(&mut input).await;
    write_str(stdout, format!("rules.len() = {}\n", rules.len())).await?;
    Ok(())
}

[package]
name = "aoc-2020"
version = "0.1.0"
edition = "2018"
# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
[dependencies]
tokio = { version = "1", features = ["full"] }
bytes = "1"
[[bin]]
name = "day1"
path = "day1.rs"
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name = "day3"
path = "day3.rs"
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name = "day5"
path = "day5.rs"
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path = "day6.rs"
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path = "day7.rs"
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[[bin]]
name = "day12"
path = "day12.rs"
[[bin]]
name = "day14"
path = "day14.rs"
[[bin]]
name = "day15"
path = "day15.rs"
[[bin]]
name = "day19"
path = "day19.rs"

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