Add validator for file types + datapacks (#507)

* Add validator for file types + datapacks

* Make it compile

src/validate/datapack.rs

@@ -0,0 +1,38 @@
+use crate::validate::{
+    SupportedGameVersions, ValidationError, ValidationResult,
+};
+use std::io::Cursor;
+use zip::ZipArchive;
+
+pub struct DataPackValidator;
+
+impl super::Validator for DataPackValidator {
+    fn get_file_extensions(&self) -> &[&str] {
+        &["zip"]
+    }
+
+    fn get_project_types(&self) -> &[&str] {
+        &["mod"]
+    }
+
+    fn get_supported_loaders(&self) -> &[&str] {
+        &["datapack"]
+    }
+
+    fn get_supported_game_versions(&self) -> SupportedGameVersions {
+        SupportedGameVersions::All
+    }
+
+    fn validate(
+        &self,
+        archive: &mut ZipArchive<Cursor<bytes::Bytes>>,
+    ) -> Result<ValidationResult, ValidationError> {
+        archive.by_name("pack.mcmeta").map_err(|_| {
+            ValidationError::InvalidInput(
+                "No pack.mcmeta present for datapack file. Tip: Make sure pack.mcmeta is in the root directory of your datapack!".into(),
+            )
+        })?;
+
+        Ok(ValidationResult::Pass)
+    }
+}