// Copyright 2023 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.

#ifndef THIRD_PARTY_CEL_CPP_BASE_FUNCTION_H_

#define THIRD_PARTY_CEL_CPP_BASE_FUNCTION_H_

#include "absl/status/statusor.h"

#include "absl/types/span.h"

#include "base/handle.h"

#include "base/value.h"

#include "base/value_factory.h"

namespace cel {

// Interface for extension functions.

//

// The host for the CEL environment may provide implementations to define custom

// extensions functions.

//

// The interpreter expects functions to be deterministic and side-effect free.

class Function {

public:

virtual ~Function() = default;

// InvokeContext provides access to current evaluator state.

class InvokeContext final {

public:

explicit InvokeContext(ValueFactory& value_factory)

: value_factory_(value_factory) {}

// Return the value_factory defined for the evaluation invoking the

// extension function.

cel::ValueFactory& value_factory() const { return value_factory_; }

// TODO(issues/5): Add accessors for getting attribute stack and mutable

// value stack.

private:

cel::ValueFactory& value_factory_;

};

// Attempt to evaluate an extension function based on the runtime arguments

// during the evaluation of a CEL expression.

//

// A non-ok status is interpreted as an unrecoverable error in evaluation (

// e.g. data corruption). This stops evaluation and is propagated immediately.

//

// A cel::ErrorValue typed result is considered a recoverable error and

// follows CEL's logical short-circuiting behavior.

virtual absl::StatusOr<Handle<Value>> Invoke(

const InvokeContext& context,

absl::Span<const Handle<Value>> args) const = 0;

};

// Legacy type, aliased to the actual type.

using FunctionEvaluationContext = Function::InvokeContext;

} // namespace cel

#endif // THIRD_PARTY_CEL_CPP_BASE_FUNCTION_H_