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// 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,
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//! Utility functions for complex field access

use arrow::datatypes::{DataType, Field};
use datafusion_common::{DataFusionError, Result, ScalarValue};

/// Returns the field access indexed by `key` from a [`DataType::List`] or [`DataType::Struct`]
/// # Error
/// Errors if
/// * the `data_type` is not a Struct or,
/// * there is no field key is not of the required index type
pub fn get_indexed_field(data_type: &DataType, key: &ScalarValue) -> Result<Field> {
    match (data_type, key) {
        (DataType::List(lt), ScalarValue::Int64(Some(i))) => {
            Ok(Field::new(&i.to_string(), lt.data_type().clone(), true))
        }
        (DataType::Struct(fields), ScalarValue::Utf8(Some(s))) => {
            if s.is_empty() {
                Err(DataFusionError::Plan(
                    "Struct based indexed access requires a non empty string".to_string(),
                ))
            } else {
                let field = fields.iter().find(|f| f.name() == s);
                match field {
                    None => Err(DataFusionError::Plan(format!(
                        "Field {} not found in struct",
                        s
                    ))),
                    Some(f) => Ok(f.clone()),
                }
            }
        }
        (DataType::Struct(_), _) => Err(DataFusionError::Plan(
            "Only utf8 strings are valid as an indexed field in a struct".to_string(),
        )),
        (DataType::List(_), _) => Err(DataFusionError::Plan(
            "Only ints are valid as an indexed field in a list".to_string(),
        )),
        _ => Err(DataFusionError::Plan(
            "The expression to get an indexed field is only valid for `List` types"
                .to_string(),
        )),
    }
}
