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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::{PhysicalExpr, PhysicalSortExpr};
use arrow::compute::kernels::partition::lexicographical_partition_ranges;
use arrow::compute::kernels::sort::{SortColumn, SortOptions};
use arrow::record_batch::RecordBatch;
use arrow::{array::ArrayRef, datatypes::Field};
use datafusion_common::{DataFusionError, Result};
use std::any::Any;
use std::fmt::Debug;
use std::ops::Range;
use std::sync::Arc;

/// A window expression that:
/// * knows its resulting field
pub trait WindowExpr: Send + Sync + Debug {
    /// Returns the window expression as [`Any`](std::any::Any) so that it can be
    /// downcast to a specific implementation.
    fn as_any(&self) -> &dyn Any;

    /// the field of the final result of this window function.
    fn field(&self) -> Result<Field>;

    /// Human readable name such as `"MIN(c2)"` or `"RANK()"`. The default
    /// implementation returns placeholder text.
    fn name(&self) -> &str {
        "WindowExpr: default name"
    }

    /// expressions that are passed to the WindowAccumulator.
    /// Functions which take a single input argument, such as `sum`, return a single [`datafusion_expr::expr::Expr`],
    /// others (e.g. `cov`) return many.
    fn expressions(&self) -> Vec<Arc<dyn PhysicalExpr>>;

    /// evaluate the window function arguments against the batch and return
    /// array ref, normally the resulting vec is a single element one.
    fn evaluate_args(&self, batch: &RecordBatch) -> Result<Vec<ArrayRef>> {
        self.expressions()
            .iter()
            .map(|e| e.evaluate(batch))
            .map(|r| r.map(|v| v.into_array(batch.num_rows())))
            .collect()
    }

    /// evaluate the window function values against the batch
    fn evaluate(&self, batch: &RecordBatch) -> Result<ArrayRef>;

    /// evaluate the partition points given the sort columns; if the sort columns are
    /// empty then the result will be a single element vec of the whole column rows.
    fn evaluate_partition_points(
        &self,
        num_rows: usize,
        partition_columns: &[SortColumn],
    ) -> Result<Vec<Range<usize>>> {
        if partition_columns.is_empty() {
            Ok(vec![Range {
                start: 0,
                end: num_rows,
            }])
        } else {
            Ok(lexicographical_partition_ranges(partition_columns)
                .map_err(DataFusionError::ArrowError)?
                .collect::<Vec<_>>())
        }
    }

    /// expressions that's from the window function's partition by clause, empty if absent
    fn partition_by(&self) -> &[Arc<dyn PhysicalExpr>];

    /// expressions that's from the window function's order by clause, empty if absent
    fn order_by(&self) -> &[PhysicalSortExpr];

    /// get partition columns that can be used for partitioning, empty if absent
    fn partition_columns(&self, batch: &RecordBatch) -> Result<Vec<SortColumn>> {
        self.partition_by()
            .iter()
            .map(|expr| {
                PhysicalSortExpr {
                    expr: expr.clone(),
                    options: SortOptions::default(),
                }
                .evaluate_to_sort_column(batch)
            })
            .collect()
    }

    /// get sort columns that can be used for peer evaluation, empty if absent
    fn sort_columns(&self, batch: &RecordBatch) -> Result<Vec<SortColumn>> {
        let mut sort_columns = self.partition_columns(batch)?;
        let order_by_columns = self
            .order_by()
            .iter()
            .map(|e| e.evaluate_to_sort_column(batch))
            .collect::<Result<Vec<SortColumn>>>()?;
        sort_columns.extend(order_by_columns);
        Ok(sort_columns)
    }
}