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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.

use crate::optimizer::ApplyOrder;
use crate::{OptimizerConfig, OptimizerRule};
use datafusion_common::{DFSchemaRef, Result};
use datafusion_expr::logical_plan::LogicalPlan;
use datafusion_expr::{Expr, Projection};

/// Optimization rule that eliminate unnecessary [LogicalPlan::Projection].
#[derive(Default)]
pub struct EliminateProjection;

impl EliminateProjection {
    #[allow(missing_docs)]
    pub fn new() -> Self {
        Self {}
    }
}

impl OptimizerRule for EliminateProjection {
    fn try_optimize(
        &self,
        plan: &LogicalPlan,
        _config: &dyn OptimizerConfig,
    ) -> Result<Option<LogicalPlan>> {
        match plan {
            LogicalPlan::Projection(projection) => {
                let child_plan = projection.input.as_ref();
                match child_plan {
                    LogicalPlan::Union(_)
                    | LogicalPlan::Filter(_)
                    | LogicalPlan::TableScan(_)
                    | LogicalPlan::SubqueryAlias(_)
                    | LogicalPlan::Sort(_) => {
                        if can_eliminate(projection, child_plan.schema()) {
                            Ok(Some(child_plan.clone()))
                        } else {
                            Ok(None)
                        }
                    }
                    _ => {
                        if plan.schema() == child_plan.schema() {
                            Ok(Some(child_plan.clone()))
                        } else {
                            Ok(None)
                        }
                    }
                }
            }
            _ => Ok(None),
        }
    }

    fn name(&self) -> &str {
        "eliminate_projection"
    }

    fn apply_order(&self) -> Option<ApplyOrder> {
        Some(ApplyOrder::TopDown)
    }
}

pub(crate) fn can_eliminate(projection: &Projection, schema: &DFSchemaRef) -> bool {
    if projection.expr.len() != schema.fields().len() {
        return false;
    }
    for (i, e) in projection.expr.iter().enumerate() {
        match e {
            Expr::Column(c) => {
                let d = schema.fields().get(i).unwrap();
                if c != &d.qualified_column() && c != &d.unqualified_column() {
                    return false;
                }
            }
            _ => return false,
        }
    }
    true
}