use rand::prelude::{StdRng, SliceRandom};
use rand::{SeedableRng, Rng, thread_rng};

pub const SIZE: usize = 16384;

pub struct City {
    prices: Vec<u16>,
    buyable_house_count: usize
}

impl City {
    pub fn read_from_file(filename: &str) -> Self {
        let values = std::fs::read(filename).unwrap();
        let mut prices: Vec<u16> = Vec::new();

        for y in 0..SIZE {
            for x in 0..SIZE {
                let price = (values[(y * SIZE + x) * 2] as u16) | ((values[(y * SIZE + x) * 2 + 1] as u16) << 8);
                prices.push(price);
            }
        }

        City::new(prices)
    }

    pub fn new(prices: Vec<u16>) -> Self {
        let mut buyable_house_count = 0;
        for &price in &prices {
            if price > 0 {
                buyable_house_count += 1;
            }
        }
        City { prices, buyable_house_count }
    }

    pub fn get_price(&self, house: &House) -> u16 {
        self.prices[house.y * SIZE + house.x]
    }

    pub fn get_price_xy(&self, x: usize, y: usize) -> u16 {
        self.prices[y * SIZE + x]
    }

    pub fn is_house(&self, house: &House) -> bool {
        self.get_price(&house) > 0
    }

    pub fn is_house_xy(&self, x: usize, y: usize) -> bool {
        self.get_price_xy(x, y) > 0
    }

    pub fn get_house_count(&self) -> usize {
        self.buyable_house_count
    }
}

#[derive(Eq, PartialEq, Hash, Copy, Clone)]
pub struct House {
    x: usize,
    y: usize,
}

impl House {
    pub fn new(x: usize, y: usize) -> Self {
        House { x, y }
    }
}

fn main() {
    let city = City::read_from_file("01.in");

    let mut best_price: Option<u32> = None;
    loop {
        let seed: u64 = thread_rng().gen();
        eprintln!("Starting seed {}", seed);

        let mut rng = StdRng::seed_from_u64(seed);
        let mut reachable = vec![false; SIZE * SIZE];
        let mut houses: Vec<House> = Vec::new();
        let mut claimed_houses = 0;
        loop {
            loop {
                let x = rng.gen_range(0..SIZE);
                let y = rng.gen_range(0..SIZE);
                let house = House::new(x, y);
                if city.is_house_xy(x, y) && !reachable[y * SIZE + x] {
                    for y in (house.y as i32 - 500).max(0)..=(house.y as i32 + 500).min((SIZE - 1) as i32) {
                        for x in (house.x as i32 - 500).max(0)..=(house.x as i32 + 500).min((SIZE - 1) as i32) {
                            let index = y as usize * SIZE + x as usize;
                            if !reachable[index] {
                                reachable[index] = true;
                                if city.is_house_xy(x as usize, y as usize) {
                                    claimed_houses += 1;
                                }
                            }
                        }
                    }
                    houses.push(house);
                    //eprintln!("{} houses", houses.len());
                    break;
                }
            }

            let finished = claimed_houses == city.get_house_count();

            if finished {
                break;
            }
        }

        let mut price = get_price(&city, &houses);
        eprintln!("Finished random init, price: {}", price);

        const AROUND_RANGE: i32 = 50;
        const MAX_CANDIDATES: usize = 20;
        const MAX_FAILED_ITERATIONS: usize = 50;

        let mut failed_iterations = 0;
        while failed_iterations < MAX_FAILED_ITERATIONS {
            let house = &houses.choose(&mut rng).unwrap();
            let mut new_candidates = Vec::new();
            for delta_y in -AROUND_RANGE..=AROUND_RANGE {
                for delta_x in -AROUND_RANGE..=AROUND_RANGE {
                    let new_x = (house.x as i32 + delta_x).max(0).min(SIZE as i32 - 1) as usize;
                    let new_y = (house.y as i32 + delta_y).max(0).min(SIZE as i32 - 1) as usize;
                    if city.is_house_xy(new_x, new_y) && city.get_price_xy(new_x, new_y) < city.get_price(&house) {
                        new_candidates.push(House::new(new_x, new_y));
                    }
                }
            }

            new_candidates.sort_by(|a, b| city.get_price(&a).cmp(&city.get_price(&b)));
            if new_candidates.len() == 0 {
                eprintln!("Did not find candidate");
            } else {
                for (i, &candidate) in new_candidates.iter().enumerate() {
                    if i > MAX_CANDIDATES {
                        break;
                    }

                    eprint!("Found candidate {}...", i);
                    let mut new_houses: Vec<_> = houses.to_vec().into_iter().filter(|h| &h != house).collect();
                    new_houses.push(candidate);
                    // TODO: This is_valid check could be way more efficient
                    if let Some(new_price) = is_valid(&city, &new_houses) {
                        let price_diff = new_price as i64 - price as i64;
                        eprintln!(" candidate is valid, price diff: {}.", price_diff);
                        eprintln!("Improved price: {}", new_price);
                        price = new_price;
                        houses = new_houses;
                        failed_iterations = 0;
                        break;
                    } else {
                        eprintln!(" candidate is invalid.");
                    }
                }
            }

            // Successful iterations always break
            failed_iterations += 1;
        }

        if best_price.is_none() || price < best_price.unwrap() {
            best_price = Some(price);
            eprintln!("Finished randomization, price: {}, new best, printing", price);
            println!("Price {}, seed {}", price, seed);
            print_houses(&houses);
            println!();
        } else {
            eprintln!("Finished randomization, price: {}, printing", price);
            println!("Price {}, seed {}", price, seed);
            print_houses(&houses);
            println!();
        }
    }
}

pub fn get_neighbors(city: &City, house: &House) -> Vec<House> {
    let mut neighbors = Vec::new();
    for y in (house.y as i32 - 500).max(0)..=(house.y as i32 + 500).min((SIZE - 1) as i32) {
        for x in (house.x as i32 - 500).max(0)..=(house.x as i32 + 500).min((SIZE - 1) as i32) {
            let house = House::new(x as usize, y as usize);
            if city.get_price(&house) > 0 {
                neighbors.push(house);
            }
        }
    }

    neighbors
}

fn print_houses(houses: &Vec<House>) {
    println!("{}", houses.len());
    for house in houses {
        println!("{} {}", house.y, house.x);
    }
}

fn get_price(city: &City, houses: &Vec<House>) -> u32 {
    let mut price = 0u32;
    for house in houses {
        price += city.get_price(&house) as u32;
    }

    price
}

fn is_valid(city: &City, houses: &Vec<House>) -> Option<u32> {
    let mut reachable = vec![false; SIZE * SIZE];
    let mut price = 0u32;

    for house in houses {
        assert!(city.prices[house.y * SIZE + house.x] > 0);

        for y in (house.y as i32 - 500).max(0)..=(house.y as i32 + 500).min((SIZE - 1) as i32) {
            for x in (house.x as i32 - 500).max(0)..=(house.x as i32 + 500).min((SIZE - 1) as i32) {
                reachable[y as usize * SIZE + x as usize] = true;
            }
        }
        price += city.get_price(&house) as u32;
    }

    for y in 0..SIZE {
        for x in 0..SIZE {
            if !reachable[y * SIZE + x] && city.prices[y * SIZE + x] > 0 {
                return None;
            }
        }
    }

    Some(price)
}