refactor: unify function registry (Part 1) (#6262)

* refactor: unify function registry (Part 1)

Signed-off-by: Zhenchi <zhongzc_arch@outlook.com>

* refactor: simplify via register_scalar

Signed-off-by: Zhenchi <zhongzc_arch@outlook.com>

---------

Signed-off-by: Zhenchi <zhongzc_arch@outlook.com>

src/common/function/src/function_factory.rs

@@ -0,0 +1,63 @@
+// Copyright 2023 Greptime Team
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use std::sync::Arc;
+
+use datafusion_expr::ScalarUDF;
+
+use crate::function::{FunctionContext, FunctionRef};
+use crate::scalars::udf::create_udf;
+
+/// A factory for creating `ScalarUDF` that require a function context.
+#[derive(Clone)]
+pub struct ScalarFunctionFactory {
+    name: String,
+    factory: Arc<dyn Fn(FunctionContext) -> ScalarUDF + Send + Sync>,
+}
+
+impl ScalarFunctionFactory {
+    /// Returns the name of the function.
+    pub fn name(&self) -> &str {
+        &self.name
+    }
+
+    /// Returns a `ScalarUDF` when given a function context.
+    pub fn provide(&self, ctx: FunctionContext) -> ScalarUDF {
+        (self.factory)(ctx)
+    }
+}
+
+impl From<ScalarUDF> for ScalarFunctionFactory {
+    fn from(df_udf: ScalarUDF) -> Self {
+        let name = df_udf.name().to_string();
+        let func = Arc::new(move |_ctx| df_udf.clone());
+        Self {
+            name,
+            factory: func,
+        }
+    }
+}
+
+impl From<FunctionRef> for ScalarFunctionFactory {
+    fn from(func: FunctionRef) -> Self {
+        let name = func.name().to_string();
+        let func = Arc::new(move |ctx: FunctionContext| {
+            create_udf(func.clone(), ctx.query_ctx, ctx.state)
+        });
+        Self {
+            name,
+            factory: func,
+        }
+    }
+}