beautiful proc macro

gendays/lib.rs

@@ -0,0 +1,46 @@
+use std::fs;
+
+use proc_macro::TokenStream;
+
+#[proc_macro]
+pub fn gen_days(item: TokenStream) -> TokenStream {
+    let path = format!("{item}");
+    let mut days_in_dir: Vec<String> = Vec::new();
+    for entry in fs::read_dir(&path).unwrap() {
+        let entry = entry.unwrap();
+        let path = entry.path();
+        if let Some(file_stem) = path.file_stem() {
+            let (day_prefix, day_number) = file_stem.to_str().unwrap().split_at(3);
+            if day_prefix == "day" {
+                // do template stuff for this day
+                days_in_dir.push(day_number.to_string());
+            }
+        }
+    }
+    let mut module_imports = String::new();
+    let mut day_checks = String::new();
+    for day in days_in_dir {
+        module_imports += &format!("mod day{day};\n");
+        day_checks += &format!("
+            if day == \"day{day}\" {{
+                if part == \"1\" {{
+                    println!(\"{{}}\", day{day}::part1());
+                }} else if part == \"2\" {{
+                    println!(\"{{}}\", day{day}::part2());
+                }} else {{
+                    panic!(\"expecting 1 or 2 for argument 2\")
+                }}
+            }}
+        ");
+    }
+    format!("
+        {module_imports} 
+
+        fn main() {{
+            let day = std::env::args().nth(1).expect(\"needs to specify day for first argument\");
+            let part = std::env::args().nth(2).expect(\"needs to specify 1 or 2 for second argument\");
+
+            {day_checks}
+        }}
+        ").parse().unwrap()
+}