// 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 dev.cel.common.CelAbstractSyntaxTree;

import dev.cel.common.CelValidationException;

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;

/**

* Exercise1 evaluates a simple literal expression: "Hello, World!"

*

* <p>Compile, eval, profit!

*/

final class Exercise1 {

/**

* Compile the input {@code expression} and produce an AST. This method parses and type-checks the

* given expression to validate the syntax and type-agreement of the expression.

*

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

* errors.

*/

CelAbstractSyntaxTree compile(String expression) {

// Construct a CelCompiler instance.

// "String" is the expected output type for the type-checked expression

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

// member.

CelCompiler celCompiler =

CelCompilerFactory.standardCelCompilerBuilder().setResultType(SimpleType.STRING).build();

CelAbstractSyntaxTree ast;

try {

// Parse the expression

ast = celCompiler.parse(expression).getAst();

} catch (CelValidationException e) {

// Report syntactic errors, if present

throw new IllegalArgumentException(

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

}

try {

// Type-check the expression for correctness

ast = celCompiler.check(ast).getAst();

} catch (CelValidationException e) {

// Report semantic errors, if present.

throw new IllegalArgumentException(

"Failed to type-check expression. Reason: " + e.getMessage(), e);

}

return ast;

}

/**

* Evaluates the compiled AST.

*

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

*/

Object eval(CelAbstractSyntaxTree ast) {

// Construct a CelRuntime instance

// CelRuntime is immutable just like the compiler and can be moved to a static final member.

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

try {

// Plan the program

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

// Evaluate the program without any additional arguments.

return program.eval();

} catch (CelEvaluationException e) {

// Report any evaluation errors, if present

throw new IllegalArgumentException(

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

}

}

}