Implement garbage collect on the server

server/texture-sync-server/src/persistency/mod.rs

@@ -182,11 +182,47 @@ impl DataStore {
         self.textures.iter()
     }
 
-    pub fn garbage_collect(&mut self) -> io::Result<()> {
-        //unimplemented!()
+    pub fn extract_hash(filename: &std::ffi::OsStr) -> Option<Sha256> {
+        // directly return None for invalidly encoded file names
+        let str_name = filename.to_str()?;
+        let hash = Sha256::from_hex(str_name)?;
 
-        /// VERY TODO:
-        eprintln!("WARNING: We are sorry the GC isn't implemented yet :'( ");
+        // check back to ignore names with lowercase letters
+        if hash.as_hex_string() == str_name {
+            Some(hash)
+        } else {
+            None
+        }
+    }
+
+    pub fn garbage_collect(&mut self) -> io::Result<()> {
+        let texture_dir = std::fs::read_dir(self.texture_base_path())?;
+
+        let mut hashs_on_disk = HashSet::new();
+        for result_direntry in texture_dir {
+            let texture_path = result_direntry?.path();
+            let filename = match texture_path.file_name() {
+                Some(name) => name,
+                None => continue,
+            };
+            match Self::extract_hash(filename) {
+                Some(hash) => {
+                    hashs_on_disk.insert(hash);
+                }
+                None => (), // ignore other files
+            };
+        }
+
+        let mut unused_files = hashs_on_disk;
+        for texture in &self.textures {
+            unused_files.remove(&texture.texture_hash);
+        }
+
+        // remove what is still contained in the HashSet
+        for entry in unused_files {
+            let path = self.texture_file_path(&entry);
+            std::fs::remove_file(path)?;
+        }
         Ok(())
     }
 }