You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: solver.rs
    path of file: ./repos/rustrogueliketutorial/chapter-35-vaults2/src/map_builders/waveform_collapse
    
    the code of the file until where you have to start completion: use super::{MapChunk, Map};
use std::collections::HashSet;

pub struct Solver {
    constraints: Vec<MapChunk>,
    chunk_size : i32,
    chunks : Vec<Option<usize>>,
    chunks_x : usize,
    chunks_y : usize,
    remaining : Vec<(usize, i32)>, // (index, # neighbors)
    pub possible: bool
}

impl Solver {
    pub fn new(constraints: Vec<MapChunk>, chunk_size: i32, map : &Map) -> Solver {
        let chunks_x = (map.width / chunk_size) as usize;
        let chunks_y = (map.height / chunk_size) as usize;
        let mut remaining : Vec<(usize, i32)> = Vec::new();
        for i in 0..(chunks_x*chunks_y) {
            remaining.push((i, 0));
        }

        Solver {
            constraints,
            chunk_size,
            chunks: vec![None; chunks_x * chunks_y],
            chunks_x,
            chunks_y,
            remaining,
            possible: true
        }
    }

    fn chunk_idx(&self, x:usize, y:usize) -> usize {
        ((y * self.chunks_x) + x) as usize
    }

    fn count_neighbors(&self, chunk_x:usize, chunk_y:usize) -> i32 {
        let mut neighbors = 0;

        if chunk_x > 0 {
            let left_idx = self.chunk_idx(chunk_x-1, chunk_y);
            match self.chunks[left_idx] {
                None => {}
                Some(_) => {
                    neighbors += 1;
                }
            }
        }

        if chunk_x < self.chunks_x-1 {
            let right_idx = self.chunk_idx(chunk_x+1, chunk_y);
            match self.chunks[right_idx] {
                None => {}
                Some(_) => {
                    neighbors += 1;
                }
            }
        }

        if chunk_y > 0 {
            let up_idx = self.chunk_idx(chunk_x, chunk_y-1);
            match self.chunks[up_idx] {
                None => {}
                Some(_) => {
                    neighbors += 1;
                }
            }
        }

        if chunk_y < self.chunks_y-1 {
            let down_idx = self.chunk_idx(chunk_x, chunk_y+1);
            match self.chunks[down_idx] {
                None => {}
                Some(_) => {
                    neighbors += 1;
                }
            }
        }
        neighbors
    }

    pub fn iteration(&mut self, map: &mut Map, rng : &mut super::RandomNumberGenerator) -> bool {
        if self.remaining.is_empty() { return true; }

        // Populate the neighbor count of the remaining list
        let mut remain_copy = self.remaining.clone();
        let mut neighbors_exist = false;
        for r in remain_copy.iter_mut() {
            let idx = r.0;
            let chunk_x = idx % self.chunks_x;
            let chunk_y = idx / self.chunks_x;
            let neighbor_count = self.count_neighbors(chunk_x, chunk_y);
            if neighbor_count > 0 { neighbors_exist = true; }
            *r = (r.0, neighbor_count);
        }
        remain_copy.sort_by(|a,b| b.1.cmp(&a.1));
        self.remaining = remain_copy;

        // Pick a random chunk we haven't dealt with yet and get its index, remove from remaining list
        let remaining_index = if !neighbors_exist {
            (rng.roll_dice(1, self.remaining.len() as i32)-1) as usize
        } else {
            0usize
        };
        let chunk_index = self.remaining[remaining_index].0;
        self.remaining.remove(remaining_index);

        let chunk_x = chunk_index % self.chunks_x;
  
    
    pub fn iteration(&mut self, map: &mut Map, rng : &mut super::RandomNumberGenerator) -> bool {
        if self.remaining.is_empty() { return true; }

        // Populate the neighbor count of the remaining list
        let mut remain_copy = self.remaining.clone();
        let mut neighbors_exist = false;
        for r in remain_copy.iter_mut() {
            let idx = r.0;
            let chunk_x = idx % self.chunks_x;
            let chunk_y = idx / self.chunks_x;
            let neighbor_count = self.count_neighbors(chunk_x, chunk_y);
            if neighbor_count > 0 { neighbors_exist = true; }
            *r = (r.0, neighbor_count);
        }
        remain_copy.sort_by(|a,b| b.1.cmp(&a.1));
        self.remaining = remain_copy;

        // Pick a random chunk we haven't dealt with yet and get its index, remove from remaining list
        let remaining_index = if !neighbors_exist {
            (rng.roll_dice(1, self.remaining.len() as i32)-1) as usize
        } else {
            0usize
        };
        let chunk_index = self.remaining[remaining_index].0;
        self.remaining.remove(remaining_index);

        let chunk_x = chunk_index % self.chunks_x;
        let chunk_y = chunk_index / self.chunks_x;

        let mut neighbors = 0;
        let mut options : Vec<Vec<usize>> = Vec::new();

        if chunk_x > 0 {
            let left_idx = self.chunk_idx(chunk_x-1, chunk_y);
            match self.chunks[left_idx] {
                None => {}
                Some(nt) => {
                    neighbors += 1;
                    options.push(self.constraints[nt].compatible_with[3].clone());
                }
            }
        }

        if chunk_x < self.chunks_x-1 {
            let right_idx = self.chunk_idx(chunk_x+1, chunk_y);
            match self.chunks[right_idx] {
                None => {}
                Some(nt) => {
                    neighbors += 1;
                    options.push(self.constraints[nt].compatible_with[2].clone());
                }
            }
        }

        if chunk_y > 0 {
            let up_idx = self.chunk_idx(chunk_x, chunk_y-1);
            match self.chunks[up_idx] {
                None => {}
                Some(nt) => {
                    neighbors += 1;
                    options.push(self.constraints[nt].compatible_with[1].clone());
                }
            }
        }

        if chunk_y < self.chunks_y-1 {
            let down_idx = self.chunk_idx(chunk_x, chunk_y+1);
            match self.chunks[down_idx] {
                None => {}
                Some(nt) => {
                    neighbors += 1;
                    options.push(self.constraints[nt].compatible_with[0].clone());
                }
            }
        }

        if neighbors == 0 {
            // There is nothing nearby, so we can have anything!
            let new_chunk_idx = (rng.roll_dice(1, self.constraints.len() as i32)-1) as usize;
            self.chunks[chunk_index] = Some(new_chunk_idx);
            let left_x = chunk_x as i32 * self.chunk_size as i32;
            let right_x = (chunk_x as i32+1) * self.chunk_size as i32;
            let top_y = chunk_y as i32 * self.chunk_size as i32;
            let bottom_y = (chunk_y as i32+1) * self.chunk_size as i32;


            let mut i : usize = 0;
            for y in top_y .. bottom_y {
                for x in left_x .. right_x {
                    let mapidx = map.xy_idx(x, y);
                    let tile = self.constraints[new_chunk_idx].pattern[i];
                    map.tiles[mapidx] = tile;
                    i += 1;
                }
            }
        }
        else {
            // There are neighbors, so we try to be compatible with them
            let mut options_to_check : HashSet<usize> = HashSet::new();
            for o in options.iter() {
                for i in o.iter() {
                    options_to_check.insert(*i);
                }
            }

            let mut possible_options : Vec<usize> = Vec::new();
            for new_chunk_idx in options_to_check.iter() {
                let mut possible = true;
                for o in options.iter() {
                    if !o.contains(new_chunk_idx) { possible = false; }
                }
                if possible {
                    possible_options.push(*new_chunk_idx);
                }
            }

            if possible_options.is_empty() {
                rltk::console::log("Oh no! It's not possible!");
                self.possible = false;
                return true;
            } else {
                let new_chunk_idx = if possible_options.len() == 1 { 0 }
                    else { rng.roll_dice(1, possible_options.len() as i32)-1 };

                self.chunks[chunk_index] = Some(possible_options[new_chunk_idx as usize]);
                let left_x = chunk_x as i32 * self.chunk_size as i32;
                let right_x = (chunk_x as i32+1) * self.chunk_size as i32;
                let top_y = chunk_y as i32 * self.chunk_size as i32;
                let bottom_y = (chunk_y as i32+1) * self.chunk_size as i32;


                let mut i : usize = 0;
                for y in top_y .. bottom_y {
                    for x in left_x .. right_x {
                        let mapidx = map.xy_idx(x, y);
                        let tile = self.constraints[possible_options[new_chunk_idx as usize]].pattern[i];
                        map.tiles[mapidx] = tile;
                        i += 1;
                    }
                }
            }
        }

        false
    }