use std::cmp;
use std::collections::HashMap;
use std::convert::TryFrom;
use std::fs;
use std::ops::Deref;
use std::ops::RangeInclusive;
use std::ops::Sub;
use std::panic;
use std::process;
use std::str;
use std::sync::Arc;
use std::thread;

#[derive(Default, Debug, PartialEq)]
struct Location {
    x: isize,
    y: isize,
}
impl<'a> Sub for &'a Location {
    type Output = isize;

    fn sub(self, other: &'a Location) -> isize {
        (self.x - other.x).abs() + (self.y - other.y).abs()
    }
}
#[derive(Default, PartialEq)]
struct Sensor {
    loc: Location,
    visibility: usize,
}
#[derive(Default, Debug, PartialEq)]
struct Beacon {
    loc: Location,
}

struct ComparableRange(RangeInclusive<isize>);

impl ComparableRange {
    pub fn intersects(&self, other: &ComparableRange) -> bool {
        self.contains(other.start()) || other.contains(self.start())
    }

    pub fn intersection(&self, other: &ComparableRange) -> ComparableRange {
        match self.intersects(other) {
            false => panic!("Ranges do not intersect"),
            true => ComparableRange(
                cmp::min(*self.start(), *other.start())..=cmp::max(*self.end(), *other.end()),
            ),
        }
    }
}

impl Deref for ComparableRange {
    type Target = RangeInclusive<isize>;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

const PART_1_CONST: isize = 2000000;
const PART_2_CONST: isize = 4000000;

fn main() {
    run();
}

fn run() {
    let contents = fs::read_to_string("15").unwrap();
    process_part_1(contents.lines());
    process_part_2(contents.lines());
}

fn process_part_2<'a, T>(lines: T)
where
    T: IntoIterator<Item = &'a str>,
{
    let (sensors, worker_bundles) = prep_work(lines);

    let mut handles = Vec::new();
    let bundle_storage = Arc::new(worker_bundles);
    let sensor_storage = Arc::new(sensors);
    for worker in 0..=99 {
        let worker_bundles = Arc::clone(&bundle_storage);
        let sensors = Arc::clone(&sensor_storage);
        let bounds = 0..=PART_2_CONST;
        let handle = thread::spawn(move || do_part2_work(worker_bundles, worker, &bounds, sensors));
        handles.push(handle);
    }
    handles.into_iter().for_each(|handle| {
        handle.join();
    });
}

fn prep_work<'a, T>(lines: T) -> (Vec<Sensor>, HashMap<isize, Vec<usize>>)
where
    T: IntoIterator<Item = &'a str>,
{
    let (sensors, _) = parse(lines);
    let mut worker_bundles = HashMap::new();
    for worker in 0..99 {
        let mut work_item = Vec::new();
        for sensor in &sensors {
            let chunk_s = sensor.visibility / 100;
            work_item.push(chunk_s);
        }
        worker_bundles.insert(worker, work_item);
    }
    // remainder worker
    let worker = 99;
    let mut work_item = Vec::new();
    for sensor in &sensors {
        let chunk_s = sensor.visibility / 100;
        let remainder = sensor.visibility - (99 * chunk_s);
        work_item.push(remainder);
    }
    worker_bundles.insert(worker, work_item);
    (sensors, worker_bundles)
}

fn do_part2_work(
    worker_bundles: Arc<HashMap<isize, Vec<usize>>>,
    worker: isize,
    bounds: &RangeInclusive<isize>,
    sensors: Arc<Vec<Sensor>>,
) {
    worker_bundles.get(&worker).and_then(|x| {
        for (work_idx, work_item) in x.into_iter().enumerate() {
            for idx in 0..*work_item {
                let dist =
                    isize::try_from(idx).unwrap() + worker * isize::try_from(*work_item).unwrap();
                let sensor = &sensors[work_idx];
                let visibility = isize::try_from(sensor.visibility).unwrap();
                let x_left = sensor.loc.x - dist;
                let x_right = sensor.loc.x + dist;
                let y_lower = sensor.loc.y + (visibility - dist) + 1;
                let y_upper = sensor.loc.y - (visibility - dist) - 1;
                [
                    (x_left, y_upper),
                    (x_right, y_upper),
                    (x_left, y_lower),
                    (x_right, y_lower),
                ]
                .into_iter()
                .for_each(|coord| {
                    if !(bounds).contains(&coord.0) || !(bounds).contains(&coord.1) {
                        return;
                    }
                    if sensors.iter().all(|tgt_sensor| {
                        &tgt_sensor.loc
                            - &Location {
                                x: coord.0,
                                y: coord.1,
                            }
                            > isize::try_from(tgt_sensor.visibility).unwrap()
                    }) {
                        println!("{:?}", coord.0 * 4000000 + coord.1);
                        process::exit(0);
                    }
                })
            }
        }
        Some(())
    });
}

fn process_part_1<'a, T>(lines: T)
where
    T: IntoIterator<Item = &'a str>,
{
    let (sensors, beacons) = parse(lines);
    let target_row = PART_1_CONST;
    let mut impossible_ranges: Vec<ComparableRange> = Vec::new();
    for sensor in (&sensors).into_iter() {
        let visibility = isize::try_from(sensor.visibility).unwrap();
        let dist_to_target = &sensor.loc
            - &(Location {
                x: sensor.loc.x,
                y: target_row,
            });
        if dist_to_target > visibility {
            continue;
        }

        let impossible_width = visibility - dist_to_target;
        let impossible_range = sensor.loc.x - impossible_width..=sensor.loc.x + impossible_width;
        impossible_ranges.push(ComparableRange(impossible_range));
    }
    impossible_ranges.sort_by(|a, b| a.start().cmp(b.start()));

    merge(&mut impossible_ranges);

    let beacons_in_row = beacons
        .into_iter()
        .filter(|b| {
            if b.loc.y != target_row {
                return false;
            }
            (&impossible_ranges)
                .into_iter()
                .any(|r| r.contains(&b.loc.x))
        })
        .count();
    println!(
        "{}",
        impossible_ranges
            .into_iter()
            .map(|r| r.end() - r.start() + 1)
            .sum::<isize>()
            - isize::try_from(beacons_in_row).unwrap()
    );
}

fn merge(impossible_ranges: &mut Vec<ComparableRange>) {
    let mut merge_idx = 0;
    while merge_idx < impossible_ranges.len() - 1 {
        if (*impossible_ranges)[merge_idx].intersects(&impossible_ranges[merge_idx + 1]) {
            let r1 = &impossible_ranges[merge_idx];
            let r2 = &impossible_ranges[merge_idx + 1];
            impossible_ranges.insert(merge_idx + 2, r1.intersection(&r2));
            impossible_ranges.remove(merge_idx + 1);
            impossible_ranges.remove(merge_idx);
        } else {
            merge_idx += 1;
        }
    }
}

fn parse<'a, T>(lines: T) -> (Vec<Sensor>, Vec<Beacon>)
where
    T: IntoIterator<Item = &'a str>,
{
    let mut sensors = Vec::new();
    let mut beacons = Vec::new();
    let extract_ints = |s: &str| {
        s.split(&['=', ',', ':'][..])
            .filter_map(|s| s.parse::<isize>().ok())
            .collect::<Vec<isize>>()
    };
    let loc_sets = lines.into_iter().map(extract_ints);
    loc_sets.for_each(|loc_set| {
        let sensor_loc = Location {
            x: loc_set[0],
            y: loc_set[1],
        };
        let beacon_loc = Location {
            x: loc_set[2],
            y: loc_set[3],
        };
        let visibility = usize::try_from(&sensor_loc - &beacon_loc).unwrap();
        sensors.push(Sensor {
            loc: sensor_loc,
            visibility: visibility,
        });
        let beacon = Beacon { loc: beacon_loc };
        if !beacons.contains(&beacon) {
            beacons.push(beacon);
        }
    });
    (sensors, beacons)
}