use std::rc::Rc;

use pixels::wgpu::Color;
use pixels::PixelsBuilder;
use pixels::SurfaceTexture;
use rand::distributions::Distribution;
use rand::distributions::Standard;
use wasm_bindgen::prelude::*;
use winit::dpi::LogicalSize;
use winit::event::Event;
use winit::event_loop::EventLoop;
use winit::window::Window;
use winit_input_helper::WinitInputHelper;

#[wasm_bindgen(start)]
async fn start() -> Result<(), JsValue> {
    return run().await.map_err(|err| JsValue::from(err.to_string()));
}

async fn run() -> anyhow::Result<()> {
    let event_loop = EventLoop::new();

    let window = Rc::new(Window::new(&event_loop)?);

    #[cfg(target_arch = "wasm32")]
    {
        use winit::platform::web::WindowExtWebSys;

        // Retrieve current width and height dimensions of browser client window
        let get_window_size = || {
            let client_window = web_sys::window().unwrap();
            LogicalSize::new(
                client_window.inner_width().unwrap().as_f64().unwrap(),
                client_window.inner_height().unwrap().as_f64().unwrap(),
            )
        };

        let window = Rc::clone(&window);

        // Initialize winit window with current dimensions of browser client
        window.set_inner_size(get_window_size());

        let client_window = web_sys::window().unwrap();

        // Attach winit canvas to body element
        web_sys::window()
            .and_then(|win| win.document())
            .and_then(|doc| doc.body())
            .and_then(|body| {
                body.append_child(&web_sys::Element::from(window.canvas()))
                    .ok()
            })
            .expect("couldn't append canvas to document body");

        // Listen for resize event on browser client. Adjust winit window dimensions
        // on event trigger
        let closure = wasm_bindgen::closure::Closure::wrap(Box::new(move |_e: web_sys::Event| {
            let size = get_window_size();
            window.set_inner_size(size)
        }) as Box<dyn FnMut(_)>);
        client_window
            .add_event_listener_with_callback("resize", closure.as_ref().unchecked_ref())
            .unwrap();
        closure.forget();
    }

    let mut input = WinitInputHelper::new();

    let window_size = window.inner_size();
    let surface_texture =
        SurfaceTexture::new(window_size.width, window_size.height, window.as_ref());

    let width = window_size.width / 8;
    let height = window_size.height / 8;

    web_sys::console::log_1(&format!("{} x {}", width, height).into());

    let mut pixels = PixelsBuilder::new(width, height, surface_texture)
        .clear_color(Color {
            r: 0.0,
            g: 0.0,
            b: 0.0,
            a: 1.0,
        })
        .build_async()
        .await?;
    let mut life = Life::new(width as usize, height as usize);

    event_loop.run(move |event, _, control_flow| {
        control_flow.set_poll();

        if let Event::RedrawRequested(_) = event {
            life.draw(pixels.frame_mut());
            pixels.render().expect("failed to render");
        }

        if input.update(&event) {
            if input.close_requested() || input.destroyed() {
                control_flow.set_exit();
                return;
            };

            life.update();
            window.request_redraw();
        };
    });
}

#[derive(Clone, Copy, Debug)]
enum Cell {
    Alive,
    Dead { since: u8 },
}

#[derive(Debug)]
struct Grid {
    pub width: usize,
    pub height: usize,
    pub cells: Vec<Vec<Cell>>,
}

enum FrontGrid {
    A,
    B,
}

struct Life {
    pub width: usize,
    pub height: usize,
    grid_a: Grid,
    grid_b: Grid,
    front_grid: FrontGrid,
}

impl Cell {
    pub fn is_alive(&self) -> bool {
        match self {
            Cell::Alive => true,
            Cell::Dead { .. } => false,
        }
    }
}

impl Grid {
    pub fn blank(width: usize, height: usize) -> Self {
        Self {
            width,
            height,
            cells: vec![vec![Cell::Dead { since: 0xff }; width]; height],
        }
    }

    pub fn with_random_borders(width: usize, height: usize) -> Self {
        let mut ret = Self::blank(width, height);
        ret.randomize_border();
        ret
    }

    pub fn randomize_border(&mut self) {
        for col in 0..self.width {
            self.cells[self.height - 1][col] = rand::random();
        }
    }

    pub fn draw(&self, frame: &mut [u8]) {
        for row in 0..self.height {
            for col in 0..self.width {
                let pixel_idx = 4 * (self.width * row + col);

                match self.cells[row][col] {
                    Cell::Alive => {
                        frame[pixel_idx + 0] = 0xff; // R
                        frame[pixel_idx + 1] = 0xff; // G
                        frame[pixel_idx + 2] = 0xff; // B
                        frame[pixel_idx + 3] = 0xff; // A
                    }
                    Cell::Dead { since } => {
                        frame[pixel_idx + 0] = 0xff - since.saturating_mul(16); // R
                        frame[pixel_idx + 1] = if since < 0x8 {
                            0
                        } else {
                            (since - 0x8).saturating_mul(0x8) / 2
                        };
                        // G
                        frame[pixel_idx + 2] = 0xff; // B
                        frame[pixel_idx + 3] = 0xff - since; // A
                    }
                };
            }
        }
    }

    pub fn num_alive_neighbors(&self, row: usize, col: usize) -> u8 {
        let mut ret = 0;

        for i in row.saturating_sub(1)..=(row + 1).min(self.height - 1) {
            for j in col.saturating_sub(1)..=(col + 1).min(self.width - 1) {
                if self.cells[i][j].is_alive() {
                    ret += 1;
                }
            }
        }
        if self.cells[row][col].is_alive() {
            ret -= 1;
        }

        ret
    }

    pub fn new_state(&self, row: usize, col: usize) -> Cell {
        match self.cells[row][col] {
            Cell::Alive => {
                if (2..=3).contains(&self.num_alive_neighbors(row, col)) {
                    Cell::Alive
                } else {
                    Cell::Dead { since: 0 }
                }
            }
            Cell::Dead { since } => {
                if self.num_alive_neighbors(row, col) == 3 {
                    Cell::Alive
                } else {
                    Cell::Dead {
                        since: since.saturating_add(1),
                    }
                }
            }
        }
    }
}

impl Life {
    pub fn new(width: usize, height: usize) -> Self {
        Life {
            width,
            height,
            grid_a: Grid::with_random_borders(width, height),
            grid_b: Grid::blank(width, height),
            front_grid: FrontGrid::A,
        }
    }

    pub fn draw(&self, frame: &mut [u8]) {
        self.front_grid().draw(frame);
    }

    pub fn update(&mut self) {
        let (width, height) = self.dimensions();
        let (front, back) = self.grids();

        for row in 0..height {
            for col in 0..width {
                back.cells[row][col] = front.new_state(row, col);
            }
        }
        back.randomize_border();

        self.swap_grids();
    }

    fn dimensions(&self) -> (usize, usize) {
        (self.width, self.height)
    }

    fn grids(&mut self) -> (&Grid, &mut Grid) {
        match self.front_grid {
            FrontGrid::A => (&self.grid_a, &mut self.grid_b),
            FrontGrid::B => (&self.grid_b, &mut self.grid_a),
        }
    }

    fn front_grid(&self) -> &Grid {
        match self.front_grid {
            FrontGrid::A => &self.grid_a,
            FrontGrid::B => &self.grid_b,
        }
    }

    fn swap_grids(&mut self) {
        self.front_grid = match self.front_grid {
            FrontGrid::A => FrontGrid::B,
            FrontGrid::B => FrontGrid::A,
        }
    }
}

impl Distribution<Cell> for Standard {
    fn sample<R: rand::Rng + ?Sized>(&self, rng: &mut R) -> Cell {
        if rng.gen() {
            Cell::Alive
        } else {
            Cell::Dead { since: 0xff }
        }
    }
}