github.com/vescale/zgraph@v0.0.0-20230410094002-959c02d50f95/planner/expr_rewriter.go (about)

     1  // Copyright 2022 zGraph Authors. All rights reserved.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package planner
    16  
    17  import (
    18  	"fmt"
    19  
    20  	"github.com/vescale/zgraph/expression"
    21  	"github.com/vescale/zgraph/parser/ast"
    22  )
    23  
    24  type exprRewriter struct {
    25  	p        LogicalPlan
    26  	ctxStack []expression.Expression
    27  	err      error
    28  }
    29  
    30  func RewriteExpr(expr ast.ExprNode, p LogicalPlan) (expression.Expression, error) {
    31  	rewriter := &exprRewriter{
    32  		p: p,
    33  	}
    34  	expr.Accept(rewriter)
    35  	if rewriter.err != nil {
    36  		return nil, rewriter.err
    37  	}
    38  	return rewriter.ctxStack[0], nil
    39  }
    40  
    41  // Enter implements the ast.Visitor interface.
    42  func (er *exprRewriter) Enter(n ast.Node) (node ast.Node, skipChildren bool) {
    43  	switch expr := n.(type) {
    44  	case *ast.ValueExpr:
    45  		_ = expr
    46  	}
    47  	return n, false
    48  }
    49  
    50  // Leave implements the ast.Visitor interface.
    51  func (er *exprRewriter) Leave(n ast.Node) (node ast.Node, ok bool) {
    52  	if er.err != nil {
    53  		return node, false
    54  	}
    55  
    56  	switch expr := n.(type) {
    57  	case *ast.ValueExpr:
    58  		er.ctxStackAppend(&expression.Constant{Value: expr.Datum})
    59  	case *ast.BinaryExpr:
    60  		lExpr := er.ctxStack[er.ctxStackLen()-2]
    61  		rExpr := er.ctxStack[er.ctxStackLen()-1]
    62  		er.ctxStackPop(2)
    63  		binExpr, err := expression.NewBinaryExpr(expr.Op, lExpr, rExpr)
    64  		if err != nil {
    65  			er.err = err
    66  			return n, true
    67  		}
    68  		er.ctxStackAppend(binExpr)
    69  	case *ast.UnaryExpr:
    70  		input := er.ctxStack[er.ctxStackLen()-1]
    71  		er.ctxStackPop(1)
    72  		unaryExpr, err := expression.NewUnaryExpr(expr.Op, input)
    73  		if err != nil {
    74  			er.err = err
    75  			return n, true
    76  		}
    77  		er.ctxStackAppend(unaryExpr)
    78  	case *ast.VariableReference:
    79  		idx := er.p.Columns().FindColumnIndex(expr.VariableName)
    80  		if idx == -1 {
    81  			er.err = fmt.Errorf("unresolved variable %s", expr.VariableName)
    82  			return n, true
    83  		}
    84  		er.ctxStackAppend(&expression.Column{
    85  			Index: idx,
    86  			Name:  expr.VariableName,
    87  			Type:  er.p.Columns()[idx].Type,
    88  		})
    89  	case *ast.PropertyAccess:
    90  		idx := er.p.Columns().FindColumnIndex(expr.VariableName)
    91  		if idx == -1 {
    92  			er.err = fmt.Errorf("unresolved variable %s", expr.VariableName)
    93  			return n, true
    94  		}
    95  		col := &expression.Column{
    96  			Index: idx,
    97  			Name:  expr.VariableName,
    98  			Type:  er.p.Columns()[idx].Type,
    99  		}
   100  		er.ctxStackAppend(&expression.PropertyAccess{
   101  			Expr:         col,
   102  			VariableName: expr.VariableName,
   103  			PropertyName: expr.PropertyName,
   104  		})
   105  	}
   106  
   107  	return n, true
   108  }
   109  
   110  func (er *exprRewriter) ctxStackLen() int {
   111  	return len(er.ctxStack)
   112  }
   113  
   114  func (er *exprRewriter) ctxStackPop(num int) {
   115  	l := er.ctxStackLen()
   116  	er.ctxStack = er.ctxStack[:l-num]
   117  }
   118  
   119  func (er *exprRewriter) ctxStackAppend(col expression.Expression) {
   120  	er.ctxStack = append(er.ctxStack, col)
   121  }