// https://www.scratchapixel.com/lessons/procedural-generation-virtual-worlds/procedural-patterns-noise-part-1/creating-simple-2D-noise.html

use std::mem::{self};

use rand::{Rng, RngCore};

use crate::ppm::{Pixel, Ppm};
use crate::vec2::Vec2;

const MAX_TABLE_SIZE: usize = 256;
const MAX_TABLE_SIZE_MASK: usize = MAX_TABLE_SIZE - 1;

pub fn generate_noise(width: usize, height: usize, rng: impl RngCore) -> Ppm {
    let mut noise_map = vec![0.0; width * height];
    let noise = ValueNoise::new(rng);
    let frequency = 0.05;

    for j in 0..height {
        for i in 0..width {
            let vec = Vec2::new(i as f64, j as f64);
            noise_map[j * width + i] = noise.eval(vec * frequency);
        }
    }

    let data = noise_map
        .into_iter()
        .map(|f| {
            let v = (f * 256.0).floor() as u8;
            Pixel(v, v, v)
        })
        .collect();
    Ppm {
        width,
        height,
        data,
    }
}

pub struct ValueNoise {
    r: [f64; MAX_TABLE_SIZE * MAX_TABLE_SIZE],
}

impl ValueNoise {
    pub fn new(mut rng: impl RngCore) -> Self {
        let mut r: [f64; MAX_TABLE_SIZE * MAX_TABLE_SIZE] = unsafe { mem::zeroed() };
        for k in 0..MAX_TABLE_SIZE * MAX_TABLE_SIZE {
            r[k] = rng.gen_range(0.0..1.0);
        }
        ValueNoise { r }
    }

    pub fn eval(&self, point: Vec2) -> f64 {
        let xi = point.x.floor();
        let yi = point.y.floor();

        let tx = point.x - xi;
        let ty = point.y - yi;

        let xi = xi as usize;
        let yi = yi as usize;

        let rx0 = xi & MAX_TABLE_SIZE_MASK;
        let rx1 = (rx0 + 1) & MAX_TABLE_SIZE_MASK;
        let ry0 = yi & MAX_TABLE_SIZE_MASK;
        let ry1 = (ry0 + 1) & MAX_TABLE_SIZE_MASK;

        let c00 = self.r[ry0 * MAX_TABLE_SIZE_MASK + rx0];
        let c10 = self.r[ry0 * MAX_TABLE_SIZE_MASK + rx1];
        let c01 = self.r[ry1 * MAX_TABLE_SIZE_MASK + rx0];
        let c11 = self.r[ry1 * MAX_TABLE_SIZE_MASK + rx1];

        let sx = smooth_step(tx);
        let sy = smooth_step(ty);

        let nx0 = lerp(c00, c10, sx);
        let nx1 = lerp(c01, c11, sx);

        lerp(nx0, nx1, sy)
    }
}

fn smooth_step(t: f64) -> f64 {
    t * t * (3.0 - 2.0 * t)
}

fn lerp(lo: f64, hi: f64, t: f64) -> f64 {
    lo * (1.0 - t) + hi * t
}