You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: hint_utils.go
    path of file: ./repos/tidb/pkg/planner/core
    
    the code of the file until where you have to start completion: // Copyright 2023 PingCAP, Inc.
//
// Licensed 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 core

import (
	"github.com/pingcap/tidb/pkg/kv"
	"github.com/pingcap/tidb/pkg/parser/ast"
	"github.com/pingcap/tidb/pkg/parser/model"
	h "github.com/pingcap/tidb/pkg/util/hint"
)

// GenHintsFromFlatPlan generates hints from a FlatPhysicalPlan.
func GenHintsFromFlatPlan(flat *FlatPhysicalPlan) []*ast.TableOptimizerHint {
	if len(flat.Main) == 0 {
		return nil
	}
	nodeTp := h.TypeSelect
	switch flat.Main[0].Origin.(type) {
	case *Update:
		nodeTp = h.TypeUpdate
	case *Delete:
		nodeTp = h.TypeDelete
	}
	var hints []*ast
    
func genHintsFromSingle(p PhysicalPlan, nodeType h.NodeType, storeType kv.StoreType, res []*ast.TableOptimizerHint) []*ast.TableOptimizerHint {
	qbName, err := h.GenerateQBName(nodeType, p.QueryBlockOffset())
	if err != nil {
		return res
	}
	switch pp := p.(type) {
	case *PhysicalLimit, *PhysicalTopN:
		if storeType == kv.TiKV {
			res = append(res, &ast.TableOptimizerHint{
				QBName:   qbName,
				HintName: model.NewCIStr(h.HintLimitToCop),
			})
		}
	case *PhysicalTableReader:
		tbl, ok := pp.TablePlans[0].(*PhysicalTableScan)
		if !ok {
			return res
		}
		if tbl.StoreType == kv.TiFlash {
			res = append(res, &ast.TableOptimizerHint{
				QBName:   qbName,
				HintName: model.NewCIStr(h.HintReadFromStorage),
				HintData: model.NewCIStr(kv.TiFlash.Name()),
				Tables:   []ast.HintTable{{DBName: tbl.DBName, TableName: getTableName(tbl.Table.Name, tbl.TableAsName)}},
			})
		} else {
			res = append(res, &ast.TableOptimizerHint{
				QBName:   qbName,
				HintName: model.NewCIStr(h.HintUseIndex),
				Tables:   []ast.HintTable{{DBName: tbl.DBName, TableName: getTableName(tbl.Table.Name, tbl.TableAsName)}},
			})
			if tbl.Table.PKIsHandle || tbl.Table.IsCommonHandle { // it's a primary key
				orderHint := h.HintOrderIndex
				if !tbl.KeepOrder {
					orderHint = h.HintNoOrderIndex
				}
				res = append(res, &ast.TableOptimizerHint{
					QBName:   qbName,
					HintName: model.NewCIStr(orderHint),
					Tables:   []ast.HintTable{{DBName: tbl.DBName, TableName: getTableName(tbl.Table.Name, tbl.TableAsName)}},
					Indexes:  []model.CIStr{model.NewCIStr("primary")},
				})
			}
		}
	case *PhysicalIndexLookUpReader:
		index := pp.IndexPlans[0].(*PhysicalIndexScan)
		res = append(res, &ast.TableOptimizerHint{
			QBName:   qbName,
			HintName: model.NewCIStr(h.HintUseIndex),
			Tables:   []ast.HintTable{{DBName: index.DBName, TableName: getTableName(index.Table.Name, index.TableAsName)}},
			Indexes:  []model.CIStr{index.Index.Name},
		})
		orderHint := h.HintOrderIndex
		if !index.KeepOrder {
			orderHint = h.HintNoOrderIndex
		}
		res = append(res, &ast.TableOptimizerHint{
			QBName:   qbName,
			HintName: model.NewCIStr(orderHint),
			Tables:   []ast.HintTable{{DBName: index.DBName, TableName: getTableName(index.Table.Name, index.TableAsName)}},
			Indexes:  []model.CIStr{index.Index.Name},
		})
	case *PhysicalIndexReader:
		index := pp.IndexPlans[0].(*PhysicalIndexScan)
		res = append(res, &ast.TableOptimizerHint{
			QBName:   qbName,
			HintName: model.NewCIStr(h.HintUseIndex),
			Tables:   []ast.HintTable{{DBName: index.DBName, TableName: getTableName(index.Table.Name, index.TableAsName)}},
			Indexes:  []model.CIStr{index.Index.Name},
		})
		orderHint := h.HintOrderIndex
		if !index.KeepOrder {
			orderHint = h.HintNoOrderIndex
		}
		res = append(res, &ast.TableOptimizerHint{
			QBName:   qbName,
			HintName: model.NewCIStr(orderHint),
			Tables:   []ast.HintTable{{DBName: index.DBName, TableName: getTableName(index.Table.Name, index.TableAsName)}},
			Indexes:  []model.CIStr{index.Index.Name},
		})
	case *PhysicalIndexMergeReader:
		indexs := make([]model.CIStr, 0, 2)
		var tableName model.CIStr
		var tableAsName *model.CIStr
		for _, partialPlan := range pp.PartialPlans {
			if index, ok := partialPlan[0].(*PhysicalIndexScan); ok {
				indexs = append(indexs, index.Index.Name)
				tableName = index.Table.Name
				tableAsName = index.TableAsName
			} else {
				indexName := model.NewCIStr("PRIMARY")
				indexs = append(indexs, indexName)
			}
		}
		res = append(res, &ast.TableOptimizerHint{
			QBName:   qbName,
			HintName: model.NewCIStr(h.HintIndexMerge),
			Tables:   []ast.HintTable{{TableName: getTableName(tableName, tableAsName)}},
			Indexes:  indexs,
		})
	case *PhysicalHashAgg:
		res = append(res, &ast.TableOptimizerHint{
			QBName:   qbName,
			HintName: model.NewCIStr(h.HintHashAgg),
		})
		if storeType == kv.TiKV {
			res = append(res, &ast.TableOptimizerHint{
				QBName:   qbName,
				HintName: model.NewCIStr(h.HintAggToCop),
			})
		}
	case *PhysicalStreamAgg:
		res = append(res, &ast.TableOptimizerHint{
			QBName:   qbName,
			HintName: model.NewCIStr(h.HintStreamAgg),
		})
		if storeType == kv.TiKV {
			res = append(res, &ast.TableOptimizerHint{
				QBName:   qbName,
				HintName: model.NewCIStr(h.HintAggToCop),
			})
		}
	case *PhysicalMergeJoin:
		res = append(res, getJoinHints(p.SCtx(), h.HintSMJ, p.QueryBlockOffset(), nodeType, pp.children...)...)
	case *PhysicalHashJoin:
		// TODO: support the hash_join_build and hash_join_probe hint for auto capture
		res = append(res, getJoinHints(p.SCtx(), h.HintHJ, p.QueryBlockOffset(), nodeType, pp.children...)...)
	case *PhysicalIndexJoin:
		res = append(res, getJoinHints(p.SCtx(), h.HintINLJ, p.QueryBlockOffset(), nodeType, pp.children[pp.InnerChildIdx])...)
	case *PhysicalIndexMergeJoin:
		res = append(res, getJoinHints(p.SCtx(), h.HintINLMJ, p.QueryBlockOffset(), nodeType, pp.children[pp.InnerChildIdx])...)
	case *PhysicalIndexHashJoin:
		res = append(res, getJoinHints(p.SCtx(), h.HintINLHJ, p.QueryBlockOffset(), nodeType, pp.children[pp.InnerChildIdx])...)
	}
	return res
}