world: implement top_layer function

Implement one of the core functions of MinedMap: finding the topmost
visible block at each coordinate.

src/main.rs

@@ -3,6 +3,8 @@ use std::path::PathBuf;
 use anyhow::Result;
 use clap::Parser;
 
+use minedmap::{resource, world};
+
 #[derive(Debug, Parser)]
 struct Args {
 	/// Filename to dump
@@ -12,9 +14,22 @@ struct Args {
 fn main() -> Result<()> {
 	let args = Args::parse();
 
+	let block_types = resource::block_types();
+
 	minedmap::io::region::from_file(args.file.as_path())?.foreach_chunk(
-		|coords, value: minedmap::world::de::Chunk| {
-			println!("Chunk {:?}: {:#?}", coords, value);
+		|coords, data: world::de::Chunk| {
+			let chunk = match world::chunk::Chunk::new(&data) {
+				Ok(chunk) => chunk,
+				Err(err) => {
+					eprintln!("Chunk {:?}: {}", coords, err);
+					return;
+				}
+			};
+
+			match world::layer::top_layer(&chunk, &block_types) {
+				Ok(_) => {}
+				Err(err) => println!("{:?}", err),
+			}
 		},
 	)
 }