/*
 * # Licensed to the LF AI & Data foundation 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.
 */

package chain

import (
	"fmt"

	"github.com/milvus-io/milvus/internal/util/function/chain/types"
	"github.com/milvus-io/milvus/pkg/v3/util/merr"
)

func init() {
	MustRegisterOperator(types.OpTypeSelect, NewSelectOpFromRepr)
}

// SelectOp selects specific columns from the DataFrame.
// Note: Uses BaseOp.inputs as the column names to select.
// BaseOp.outputs is set to the same as inputs since selected columns are output.
type SelectOp struct {
	BaseOp
}

// NewSelectOp creates a new SelectOp with the given columns.
func NewSelectOp(columns []string) *SelectOp {
	return &SelectOp{
		BaseOp: BaseOp{
			inputs:  columns,
			outputs: columns, // Selected columns are the outputs
		},
	}
}

func (o *SelectOp) Name() string { return "Select" }

// Inputs and Outputs are inherited from BaseOp

func (o *SelectOp) Execute(ctx *types.FuncContext, input *DataFrame) (*DataFrame, error) {
	builder := NewDataFrameBuilder()
	defer builder.Release()

	builder.SetChunkSizes(input.chunkSizes)

	columns := append([]string(nil), o.inputs...)
	selected := NewColumnSet(columns...)
	for _, colName := range input.ColumnNames() {
		if IsFunctionChainSystemName(colName) && !selected.Contains(colName) {
			columns = append(columns, colName)
		}
	}

	// Use ChunkCollector for selected chunks
	collector := NewChunkCollector(columns, input.NumChunks())
	defer collector.Release()

	for _, colName := range columns {
		col := input.Column(colName)
		if col == nil {
			return nil, merr.WrapErrServiceInternalMsg("select_op: column %q not found", colName)
		}

		// Copy chunks with retain
		for i, chunk := range col.Chunks() {
			chunk.Retain()
			collector.Set(colName, i, chunk)
		}

		if err := builder.AddColumnFromChunks(colName, collector.Consume(colName)); err != nil {
			return nil, err
		}
		builder.CopyFieldMetadata(input, colName)
	}

	return builder.Build(), nil
}

func (o *SelectOp) String() string {
	return fmt.Sprintf("Select(%v)", o.inputs)
}

// NewSelectOpFromRepr creates a SelectOp from an OperatorRepr.
func NewSelectOpFromRepr(repr *OperatorRepr) (Operator, error) {
	reader := types.NewParamReader("select_op", repr.Params)
	columns, err := reader.StringSlice("columns", false)
	if err != nil {
		return nil, err
	}
	if len(columns) == 0 {
		return nil, merr.WrapErrParameterMissingMsg("select_op: columns is required")
	}
	return NewSelectOp(columns), nil
}