mod utils;

use std::fmt::{Display, Formatter, Result};
use wasm_bindgen::prelude::*;

// When the `wee_alloc` feature is enabled, use `wee_alloc` as the global
// allocator.
#[cfg(feature = "wee_alloc")]
#[global_allocator]
static ALLOC: wee_alloc::WeeAlloc = wee_alloc::WeeAlloc::INIT;

#[wasm_bindgen]
#[repr(u8)]
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Cell {
    Dead  = 0,
    Alive = 1,
}

#[wasm_bindgen]
pub struct Universe {
    width  :u32,
    height :u32,
    cells  :Vec<Cell>,
}

#[wasm_bindgen]
impl Universe {
    pub fn new() -> Universe {
        let width  = 64;
        let height = 64;

        let init_cells = |i :u32| {
            if i % 2 == 0 || i % 7 == 0 { Cell::Alive } else { Cell::Dead }
        };

        let cells = (0..width * height).map(init_cells).collect();

        Universe {
            width:  width,
            height: height,
            cells:  cells,
        }
    }

    pub fn render(&self) -> String {
        self.to_string()
    }

    pub fn tick(&mut self) {
        let mut next = self.cells.clone();

        for row in 0..self.height {
            for col in 0..self.width {
                let idx            = self.get_index(row, col);
                let cell           = self.cells[idx];
                let live_neighbors = self.live_neighbor_count(row, col);

                // Game of life rules....
                let next_cell = match (cell, live_neighbors) {
                    (Cell::Alive, 2) |
                    (Cell::Alive, 3) => Cell::Alive,
                    (Cell::Alive, _) => Cell::Dead,
                    ( Cell::Dead, 3) => Cell::Alive,
                    (  otherwise, _) => otherwise,
                };

                next[idx] = next_cell;
            }
        }

        self.cells = next;
    }

    fn get_index(&self, row :u32, col :u32) -> usize {
        (row * self.width + col) as usize
    }

    fn live_neighbor_count(&self, row :u32, col :u32) -> u8 {
        let mut count = 0;

        for delta_row in [self.height - 1, 0, 1].iter().cloned() {
            for delta_col in [self.width - 1, 0, 1].iter().cloned() {
                if delta_row == 0 && delta_col == 0 {
                    continue;
                }

                let neighbor_row = (row + delta_row) % self.height;
                let neighbor_col = (col + delta_col) % self.width;
                let idx = self.get_index(neighbor_row, neighbor_col);
                count += self.cells[idx] as u8;
            }
        }

        count
    }
}

impl Display for Universe {
    fn fmt(&self, f :&mut Formatter) -> Result {
        for line in self.cells.as_slice().chunks(self.width as usize) {
            for &cell in line {
                let symbol = match cell {
                    Cell::Dead  => ' ',
                    Cell::Alive => '*',
                };
                write!(f, "{}", symbol)?;
            }
            write!(f, "\n")?;
        }

        Ok(())
    }
}