// Copyright 2021-2023 EMQ Technologies Co., Ltd.
//
// 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 planner

import (
	"github.com/lf-edge/ekuiper/internal/xsql"
	"github.com/lf-edge/ekuiper/pkg/ast"
)

type FilterPlan struct {
	baseLogicalPlan
	condition  ast.Expr
	stateFuncs []*ast.Call
}

func (p FilterPlan) Init() *FilterPlan {
	p.baseLogicalPlan.self = &p
	return &p
}

func (p *FilterPlan) PushDownPredicate(condition ast.Expr) (ast.Expr, LogicalPlan) {
	// if no child, swallow all conditions
	a := combine(condition, p.condition)
	if len(p.children) == 0 {
		p.condition = a
		return nil, p
	}

	rest, _ := p.baseLogicalPlan.PushDownPredicate(a)

	if rest != nil {
		p.condition = rest
		return nil, p
	} else if len(p.children) == 1 {
		// eliminate this filter
		return nil, p.children[0]
	} else {
		return nil, p
	}
}

func (p *FilterPlan) PruneColumns(fields []ast.Expr) error {
	f := getFields(p.condition)
	return p.baseLogicalPlan.PruneColumns(append(fields, f...))
}

func (p *FilterPlan) ExtractStateFunc() {
	aliases := make(map[string]ast.Expr)
	ast.WalkFunc(p.condition, func(n ast.Node) bool {
		switch f := n.(type) {
		case *ast.Call:
			p.transform(f)
		case *ast.FieldRef:
			if f.AliasRef != nil {
				aliases[f.Name] = f.AliasRef.Expression
			}
		}
		return true
	})
	for _, ex := range aliases {
		ast.WalkFunc(ex, func(n ast.Node) bool {
			switch f := n.(type) {
			case *ast.Call:
				p.transform(f)
			}
			return true
		})
	}
}

func (p *FilterPlan) transform(f *ast.Call) {
	if _, ok := xsql.ImplicitStateFuncs[f.Name]; ok {
		f.Cached = true
		p.stateFuncs = append(p.stateFuncs, &ast.Call{
			Name:     f.Name,
			FuncId:   f.FuncId,
			FuncType: f.FuncType,
		})
	}
}