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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you 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.

//! Defines physical expressions that can evaluated at runtime during query execution

use std::any::Any;
use std::sync::Arc;

use crate::{AggregateExpr, PhysicalExpr};
use arrow::datatypes::DataType;
use arrow::datatypes::Field;
use datafusion_common::{DataFusionError, Result};
use datafusion_expr::Accumulator;

use crate::expressions::format_state_name;

/// GROUPING aggregate expression
/// Returns the amount of non-null values of the given expression.
#[derive(Debug)]
pub struct Grouping {
    name: String,
    data_type: DataType,
    nullable: bool,
    expr: Arc<dyn PhysicalExpr>,
}

impl Grouping {
    /// Create a new GROUPING aggregate function.
    pub fn new(
        expr: Arc<dyn PhysicalExpr>,
        name: impl Into<String>,
        data_type: DataType,
    ) -> Self {
        Self {
            name: name.into(),
            expr,
            data_type,
            nullable: true,
        }
    }
}

impl AggregateExpr for Grouping {
    /// Return a reference to Any that can be used for downcasting
    fn as_any(&self) -> &dyn Any {
        self
    }

    fn field(&self) -> Result<Field> {
        Ok(Field::new(
            &self.name,
            self.data_type.clone(),
            self.nullable,
        ))
    }

    fn state_fields(&self) -> Result<Vec<Field>> {
        Ok(vec![Field::new(
            format_state_name(&self.name, "grouping"),
            self.data_type.clone(),
            true,
        )])
    }

    fn expressions(&self) -> Vec<Arc<dyn PhysicalExpr>> {
        vec![self.expr.clone()]
    }

    fn create_accumulator(&self) -> Result<Box<dyn Accumulator>> {
        Err(DataFusionError::NotImplemented(
            "physical plan is not yet implemented for GROUPING aggregate function"
                .to_owned(),
        ))
    }

    fn name(&self) -> &str {
        &self.name
    }
}