// Copyright 2024 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.CelValidationResult;

import dev.cel.common.types.SimpleType;

import dev.cel.common.types.StructTypeReference;

import dev.cel.compiler.CelCompiler;

import dev.cel.compiler.CelCompilerFactory;

import dev.cel.optimizer.CelOptimizationException;

import dev.cel.optimizer.CelOptimizer;

import dev.cel.optimizer.CelOptimizerFactory;

import dev.cel.optimizer.optimizers.ConstantFoldingOptimizer;

import dev.cel.optimizer.optimizers.SubexpressionOptimizer;

import dev.cel.optimizer.optimizers.SubexpressionOptimizer.SubexpressionOptimizerOptions;

import dev.cel.runtime.CelEvaluationException;

import dev.cel.runtime.CelRuntime;

import dev.cel.runtime.CelRuntimeFactory;

import dev.cel.validator.CelValidator;

import dev.cel.validator.CelValidatorFactory;

import dev.cel.validator.validators.DurationLiteralValidator;

import dev.cel.validator.validators.HomogeneousLiteralValidator;

import dev.cel.validator.validators.RegexLiteralValidator;

import dev.cel.validator.validators.TimestampLiteralValidator;

import java.util.Map;

/**

* Exercise8 demonstrates how to leverage canonical CEL validators to perform advanced validations

* on an AST and CEL optimizers to improve evaluation efficiency.

*/

final class Exercise8 {

private static final CelCompiler CEL_COMPILER =

CelCompilerFactory.standardCelCompilerBuilder()

.addVar("x", SimpleType.INT)

.addVar(

"request", StructTypeReference.create("google.rpc.context.AttributeContext.Request"))

.addMessageTypes(AttributeContext.Request.getDescriptor())

.build();

private static final CelRuntime CEL_RUNTIME =

CelRuntimeFactory.standardCelRuntimeBuilder()

.addMessageTypes(AttributeContext.Request.getDescriptor())

.build();

// Just like the compiler and runtime, the validator and optimizer can be statically

// initialized as their instances are immutable.

private static final CelValidator CEL_VALIDATOR =

CelValidatorFactory.standardCelValidatorBuilder(CEL_COMPILER, CEL_RUNTIME)

.addAstValidators(

TimestampLiteralValidator.INSTANCE,

DurationLiteralValidator.INSTANCE,

RegexLiteralValidator.INSTANCE,

HomogeneousLiteralValidator.newInstance())

.build();

private static final CelOptimizer CEL_OPTIMIZER =

CelOptimizerFactory.standardCelOptimizerBuilder(CEL_COMPILER, CEL_RUNTIME)

.addAstOptimizers(

ConstantFoldingOptimizer.getInstance(),

SubexpressionOptimizer.newInstance(

SubexpressionOptimizerOptions.newBuilder().enableCelBlock(true).build()))

.build();

/**

* Compiles the input expression.

*

* @throws CelValidationException If the expression contains parsing or type-checking errors.

*/

CelAbstractSyntaxTree compile(String expression) throws CelValidationException {

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

}

/** Validates a type-checked AST. */

CelValidationResult validate(CelAbstractSyntaxTree checkedAst) {

return CEL_VALIDATOR.validate(checkedAst);

}

/**

* Optimizes a type-checked AST.

*

* @throws CelOptimizationException If the optimization fails.

*/

CelAbstractSyntaxTree optimize(CelAbstractSyntaxTree checkedAst) throws CelOptimizationException {

return CEL_OPTIMIZER.optimize(checkedAst);

}

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

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

throws CelEvaluationException {

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

return program.eval(parameterValues);

}

}