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// 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 std::sync::Arc;

use crate::function::map::utils::{
    get_list_offsets, get_list_values, map_from_keys_values_offsets_nulls,
    map_type_from_key_value_types,
};
use arrow::array::{Array, ArrayRef, NullBufferBuilder, StructArray};
use arrow::buffer::NullBuffer;
use arrow::datatypes::{DataType, Field, FieldRef};
use datafusion_common::utils::take_function_args;
use datafusion_common::{Result, exec_err, internal_err};
use datafusion_expr::{
    ColumnarValue, ReturnFieldArgs, ScalarFunctionArgs, ScalarUDFImpl, Signature,
    Volatility,
};
use datafusion_functions::utils::make_scalar_function;

/// Spark-compatible `map_from_entries` expression
/// <https://spark.apache.org/docs/latest/api/sql/index.html#map_from_entries>
#[derive(Debug, PartialEq, Eq, Hash)]
pub struct MapFromEntries {
    signature: Signature,
}

impl Default for MapFromEntries {
    fn default() -> Self {
        Self::new()
    }
}

impl MapFromEntries {
    pub fn new() -> Self {
        Self {
            signature: Signature::array(Volatility::Immutable),
        }
    }
}

impl ScalarUDFImpl for MapFromEntries {
    fn name(&self) -> &str {
        "map_from_entries"
    }

    fn signature(&self) -> &Signature {
        &self.signature
    }

    fn return_type(&self, _arg_types: &[DataType]) -> Result<DataType> {
        internal_err!("return_field_from_args should be used instead")
    }

    fn return_field_from_args(&self, args: ReturnFieldArgs) -> Result<FieldRef> {
        let [entries_field] = args.arg_fields else {
            return exec_err!("map_from_entries: expected one argument");
        };

        let (entries_element_field, entries_element_type) =
            match entries_field.data_type() {
                DataType::List(field)
                | DataType::LargeList(field)
                | DataType::FixedSizeList(field, _) => {
                    Ok((field.as_ref(), field.data_type()))
                }
                wrong_type => exec_err!(
                    "map_from_entries: expected array<struct<key, value>>, got {:?}",
                    wrong_type
                ),
            }?;

        let (keys_type, values_type) = match entries_element_type {
            DataType::Struct(fields) if fields.len() == 2 => {
                Ok((fields[0].data_type(), fields[1].data_type()))
            }
            wrong_type => exec_err!(
                "map_from_entries: expected array<struct<key, value>>, got {:?}",
                wrong_type
            ),
        }?;

        let map_type = map_type_from_key_value_types(keys_type, values_type);
        let nullable = entries_field.is_nullable() || entries_element_field.is_nullable();

        Ok(Arc::new(Field::new(self.name(), map_type, nullable)))
    }

    fn invoke_with_args(&self, args: ScalarFunctionArgs) -> Result<ColumnarValue> {
        make_scalar_function(map_from_entries_inner, vec![])(&args.args)
    }
}

fn map_from_entries_inner(args: &[ArrayRef]) -> Result<ArrayRef> {
    let [entries] = take_function_args("map_from_entries", args)?;
    let entries_offsets = get_list_offsets(entries)?;
    let entries_values = get_list_values(entries)?;

    let (flat_keys, flat_values) =
        match entries_values.as_any().downcast_ref::<StructArray>() {
            Some(a) => Ok((a.column(0), a.column(1))),
            None => exec_err!(
                "map_from_entries: expected array<struct<key, value>>, got {:?}",
                entries_values.data_type()
            ),
        }?;

    let entries_with_nulls = entries_values.nulls().and_then(|entries_inner_nulls| {
        let mut builder = NullBufferBuilder::new_with_len(0);
        let mut cur_offset = entries_offsets
            .first()
            .map(|offset| *offset as usize)
            .unwrap_or(0);

        for next_offset in entries_offsets.iter().skip(1) {
            let num_entries = *next_offset as usize - cur_offset;
            builder.append(
                entries_inner_nulls
                    .slice(cur_offset, num_entries)
                    .null_count()
                    == 0,
            );
            cur_offset = *next_offset as usize;
        }
        builder.finish()
    });

    let res_nulls = NullBuffer::union(entries.nulls(), entries_with_nulls.as_ref());

    map_from_keys_values_offsets_nulls(
        flat_keys,
        flat_values,
        &entries_offsets,
        &entries_offsets,
        None,
        res_nulls.as_ref(),
    )
}

#[cfg(test)]
mod tests {
    use super::*;
    use arrow::datatypes::Fields;

    fn make_entries_field(array_nullable: bool, element_nullable: bool) -> FieldRef {
        let struct_type = DataType::Struct(Fields::from(vec![
            Field::new("key", DataType::Int32, false),
            Field::new("value", DataType::Utf8, true),
        ]));
        Arc::new(Field::new(
            "entries",
            DataType::List(Arc::new(Field::new("item", struct_type, element_nullable))),
            array_nullable,
        ))
    }

    #[test]
    fn test_map_from_entries_nullability_matches_input() {
        let func = MapFromEntries::new();
        let expected_type =
            map_type_from_key_value_types(&DataType::Int32, &DataType::Utf8);

        // Non-nullable array and elements => non-nullable result
        let non_nullable_field = make_entries_field(false, false);
        let result = func
            .return_field_from_args(ReturnFieldArgs {
                arg_fields: &[Arc::clone(&non_nullable_field)],
                scalar_arguments: &[None],
            })
            .expect("should infer field");
        assert!(!result.is_nullable());
        assert_eq!(result.data_type(), &expected_type);

        // Nullable elements should make result nullable even if array is non-nullable
        let element_nullable_field = make_entries_field(false, true);
        let result = func
            .return_field_from_args(ReturnFieldArgs {
                arg_fields: &[Arc::clone(&element_nullable_field)],
                scalar_arguments: &[None],
            })
            .expect("should infer field");
        assert!(result.is_nullable());
        assert_eq!(result.data_type(), &expected_type);

        // Nullable array should also yield nullable result
        let array_nullable_field = make_entries_field(true, false);
        let result = func
            .return_field_from_args(ReturnFieldArgs {
                arg_fields: &[Arc::clone(&array_nullable_field)],
                scalar_arguments: &[None],
            })
            .expect("should infer field");
        assert!(result.is_nullable());
        assert_eq!(result.data_type(), &expected_type);
    }
}
