import ImageRegion from './ImageRegion.mjs';

export function makeGaussianKernel(size) {
	const sz = Math.ceil(size * 3);
	const kernel = new Float32Array(sz * 2 + 1);
	const norm = 1 / (size * Math.sqrt(Math.PI * 2));
	const expNorm = -0.5 / (size * size);
	for(let i = -sz; i <= sz; ++ i) {
		kernel[i + sz] = Math.exp(i * i * expNorm) * norm;
	}
	return {kernel, sz};
}

export function blur1D(region, size, {target = null} = {}) {
	const tgt = region.checkOrMakeTarget(target);

	const {width, height, stepX, stepY, dim} = region;
	const {kernel, sz} = makeGaussianKernel(size);

	for(let x = 0; x < width; ++ x) {
		const i0 = -Math.min(sz, x);
		const i1 = Math.min(sz, width - x);
		for(let d = 0; d < dim; ++ d) {
			const psx = region.indexOf(x, 0, d);
			const ptx = tgt.indexOf(x, 0, d);
			for(let y = 0; y < height; ++ y) {
				const ps = psx + y * stepY;
				let accum = 0;
				for(let i = i0; i < i1; ++ i) {
					accum += region.values[ps + i * stepX] * kernel[i + sz];
				}
				tgt.values[ptx + y * tgt.stepY] = accum;
			}
		}
	}

	return tgt;
}

export function blur2D(region, size, {target = null, temp = null} = {}) {
	const tgt = region.checkOrMakeTarget(target);

	const tmp = blur1D(region, size, {target: temp});
	blur1D(tmp.transposed(), size, {target: tgt.transposed()});
	return tgt;
}

ImageRegion.prototype.blur = function(size, options) {
	return blur2D(this, size, options);
};