seata-go/pkg/saga/statemachine/engine/expr/cel_expression.go

/*
 * Licensed to the Apache Software Foundation (ASF) 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 expr

import (
	"github.com/google/cel-go/cel"
)

type CELExpression struct {
	env        *cel.Env
	program    cel.Program
	expression string
}

// This is used to make sure that the CELExpression implements the Expression interface.
var _ Expression = (*CELExpression)(nil)

// NewCELExpression creates a new CELExpression instance
// by compiling the provided expression.
// how to use cel: https://codelabs.developers.google.com/codelabs/cel-go
func NewCELExpression(expression string) (*CELExpression, error) {
	// Create the standard environment.
	env, err := cel.NewEnv(
		cel.Variable(
			"elContext", cel.DynType,
		),
	)

	if err != nil {
		return nil, err
	}

	// Check that the expression compiles and returns a String.
	ast, issues := env.Compile(expression)
	// Report syntax errors, if present.
	if issues != nil && issues.Err() != nil {
		return nil, issues.Err()
	}

	// Type-check the expression ofr correctness.
	checkedAst, issues := env.Check(ast)
	if issues.Err() != nil {
		return nil, issues.Err()
	}

	program, err := env.Program(checkedAst)
	if err != nil {
		return nil, err
	}

	CELExpression := &CELExpression{
		env:        env,
		program:    program,
		expression: expression,
	}

	return CELExpression, nil
}

// Value evaluates the expression with the provided context and returns the result.
func (c *CELExpression) Value(elContext any) any {
	result, _, err := c.program.Eval(map[string]any{
		"elContext": elContext,
	})
	if err != nil {
		return err
	}
	return result.Value()
}

// TODO: I think this is not needed.
// I see seata-java doesn't use this method.
// Do we need to implement this?
func (c *CELExpression) SetValue(val any, elContext any) {
	panic("implement me")
}

// ExpressionString returns the expression string.
func (c *CELExpression) ExpressionString() string {
	return c.expression
}