// Copyright 2022 Google LLC

//

// 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

//

// https://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 codelab.solutions;

import com.google.rpc.context.AttributeContext;

import dev.cel.common.CelAbstractSyntaxTree;

import dev.cel.common.CelValidationException;

import dev.cel.common.types.CelType;

import dev.cel.common.types.SimpleType;

import dev.cel.compiler.CelCompiler;

import dev.cel.compiler.CelCompilerFactory;

import dev.cel.runtime.CelEvaluationException;

import dev.cel.runtime.CelRuntime;

import dev.cel.runtime.CelRuntimeFactory;

import java.util.Map;

/**

* Exercise2 shows how to declare and use variables in expressions through two examples:

*

* <ul>

* <li>Given a user supplied integer value, test whether the value is negative

* <li>Given a request of type {@link com.google.rpc.context.AttributeContext.Request} determine

* whether a specific auth claim is set.

* </ul>

*/

final class Exercise2 {

/**

* Compiles the input expression with provided variable information.

*

* @throws IllegalArgumentException If the expression is malformed due to syntactic or semantic

* errors.

*/

CelAbstractSyntaxTree compile(String expression, String variableName, CelType variableType) {

// Compile (parse + type-check) the expression

// CelCompiler is immutable and when statically configured can be moved to a static final

CelCompiler celCompiler =

CelCompilerFactory.standardCelCompilerBuilder()

.addVar(variableName, variableType)

.addMessageTypes(AttributeContext.Request.getDescriptor())

.setResultType(SimpleType.BOOL)

.build();

try {

return celCompiler.compile(expression).getAst();

} catch (CelValidationException e) {

throw new IllegalArgumentException(

"Failed to compile expression. Reason: " + e.getMessage(), e);

}

}

/**

* Evaluates the compiled AST with the user provided parameter values.

*

* @throws IllegalArgumentException If the compiled expression in AST fails to evaluate.

*/

Object eval(CelAbstractSyntaxTree ast, Map<String, ?> parameterValues) {

CelRuntime celRuntime = CelRuntimeFactory.standardCelRuntimeBuilder().build();

try {

CelRuntime.Program program = celRuntime.createProgram(ast);

// Evaluate using the provided map as input variables (key: variableName, value:

// variableValue)

return program.eval(parameterValues);

} catch (CelEvaluationException e) {

// Report any evaluation errors, if present

throw new IllegalArgumentException(

"Evaluation error has occurred. Reason: " + e.getMessage(), e);

}

}

}