fn merge_layers(layers: &[&[u8]]) -> Vec<u8> {
	let mut image = Vec::new();
	image.resize(layers[0].len(), 2);
	for layer in layers {
		for (ndx, b) in layer.into_iter().enumerate() {
			let digit = *b - b'0';
			if image[ndx] != 2 { continue; }
			image[ndx] = digit;
		}
	}
	image
}

fn split_layers(input: &[u8], image_size: usize) -> Vec<&[u8]> {
	assert_eq!(input.len() % image_size, 0);
	input.chunks(image_size).collect::<Vec<_>>()
}

fn main() {
	let input = include_bytes!("input.txt");
	let layers = split_layers(input, 6*25);

	let min0_product12 = layers.iter().map(|layer| {
		let mut count = [0, 0, 0];
		for b in *layer {
			let digit = *b - b'0';
			if digit < 3 {
				count[digit as usize] += 1;
			}
		}
		(count[0], count[1]*count[2])
	}).min_by_key(|(zeroes, _product12)| *zeroes).unwrap().1;
	println!("Product of counts of 1 and 2 for the layer with min 0s: {}", min0_product12);

	let image = merge_layers(&layers);

	for row in image.chunks(25) {
		for cell in row {
			match cell {
				1 => print!("#"),
				_ => print!(" "),
			}
		}
		println!("");
	}
}

#[cfg(test)]
mod day8test {
	use super::*;

	#[test]
	fn examples1() {
		// no runnable examples
	}
	
	#[test]
	fn examples2() {
		let layers = split_layers(b"0222112222120000", 4);
		assert_eq!(merge_layers(&layers), [0, 1, 1, 0]);
	}
}