use integral_geometry::Size;

use std::collections::HashSet;

use vec2d::Vec2D;

#[derive(PartialEq, Eq, Hash, Clone, Copy, Debug)]

pub enum Tile {

    Empty,

    Outside,

    Numbered(usize),

}

impl Default for Tile {

    fn default() -> Self {

        Tile::Outside

    }

}

#[derive(Debug)]

pub struct CollapseRule {

    pub tile: Tile,

    pub right: HashSet<Tile>,

    pub bottom: HashSet<Tile>,

    pub left: HashSet<Tile>,

    pub top: HashSet<Tile>,

}

pub struct WavefrontCollapse {

    rules: Vec<CollapseRule>,

    grid: Vec2D<Tile>,

}

impl Default for WavefrontCollapse {

    fn default() -> Self {

        Self {

            rules: Vec::new(),

            grid: Vec2D::new(&Size::new(1, 1), Tile::Empty),

        }

    }

}

impl WavefrontCollapse {

    pub fn generate_map<I: Iterator<Item = u32>, F: FnOnce(&mut Vec2D<Tile>)>(

        &mut self,

        map_size: &Size,

        seed_fn: F,

        random_numbers: &mut I,

    ) {

        self.grid = Vec2D::new(map_size, Tile::Empty);

        seed_fn(&mut self.grid);

        while self.collapse_step(random_numbers) {}

    }

    pub fn set_rules(&mut self, rules: Vec<CollapseRule>) {

        self.rules = rules;

    }

    fn get_tile(&self, y: usize, x: usize) -> Tile {

        self.grid.get(y, x).copied().unwrap_or_default()

    }

    fn collapse_step<I: Iterator<Item = u32>>(&mut self, random_numbers: &mut I) -> bool {

        let mut tiles_to_collapse = (usize::max_value(), Vec::new());

        // Iterate through the tiles in the land

        for x in 0..self.grid.width() {

            for y in 0..self.grid.height() {

                let current_tile = self.get_tile(y, x);

                if let Tile::Empty = current_tile {

                    // calc entropy

                    let right_tile = self.get_tile(y, x + 1);

                    let bottom_tile = self.get_tile(y + 1, x);

                    let left_tile = self.get_tile(y, x.wrapping_sub(1));

                    let top_tile = self.get_tile(y.wrapping_sub(1), x);

                    let possibilities: Vec<Tile> = self

                        .rules

                        .iter()

                        .filter_map(|rule| {

                            if rule.right.contains(&right_tile)

                                && rule.bottom.contains(&bottom_tile)

                                && rule.left.contains(&left_tile)

                                && rule.top.contains(&top_tile)

                            {

                                Some(rule.tile)

                            } else {

                                None

                            }

                        })

                        .collect();

                    let entropy = possibilities.len();

                    if entropy > 0 {

                        if entropy <= tiles_to_collapse.0 {

                            let entry = (

                                y,

                                x,

                                possibilities

                                    [random_numbers.next().unwrap_or_default() as usize % entropy],

                            );

                            if entropy < tiles_to_collapse.0 {

                                tiles_to_collapse = (entropy, vec![entry])

                            } else {

                                tiles_to_collapse.1.push(entry)

                            }

                        }

                    } else {

                        /*println!("We're here: {}, {}", x, y);

                        println!(

                            "Neighbour tiles are: {:?} {:?} {:?} {:?}",

                            right_tile, bottom_tile, left_tile, top_tile

                        );

                        println!("Rules are: {:?}", self.rules);*/

                        //todo!("no collapse possible - what to do?")

                    }

                }

            }

        }

        let tiles_to_collapse = tiles_to_collapse.1;

        let possibilities_number = tiles_to_collapse.len();

        if possibilities_number > 0 {

            let (y, x, tile) = tiles_to_collapse

                [random_numbers.next().unwrap_or_default() as usize % possibilities_number];

            *self

                .grid

                .get_mut(y, x)

                .expect("correct iteration over grid") = tile;

            true

        } else {

            false

        }

    }

    pub fn grid(&self) -> &Vec2D<Tile> {

        &self.grid

    }

}

#[cfg(test)]

mod tests {

    use super::{Tile, WavefrontCollapse};

    use integral_geometry::Size;

    use vec2d::Vec2D;

    #[test]

    fn test_wavefront_collapse() {

        let size = Size::new(4, 4);

        let mut rnd = [0u32; 64].into_iter().cycle();

        let mut wfc = WavefrontCollapse::default();

        wfc.generate_map(&size, |_| {}, &mut rnd);

        let empty_land = Vec2D::new(&size, Tile::Empty);

        assert_eq!(empty_land.as_slice(), wfc.grid().as_slice());

    }

}