#ifndef THIRD_PARTY_CEL_CPP_EVAL_PUBLIC_CEL_EXPRESSION_H_

#define THIRD_PARTY_CEL_CPP_EVAL_PUBLIC_CEL_EXPRESSION_H_

#include <cstdint>

#include <functional>

#include <memory>

#include <string>

#include "cel/expr/checked.pb.h"

#include "cel/expr/syntax.pb.h"

#include "absl/status/statusor.h"

#include "absl/strings/string_view.h"

#include "eval/public/base_activation.h"

#include "eval/public/cel_function_registry.h"

#include "eval/public/cel_type_registry.h"

#include "eval/public/cel_value.h"

namespace google::api::expr::runtime {

// CelEvaluationListener is the callback that is passed to (and called by)

// CelExpression::Trace. It gets an expression node ID from the original

// expression, its value and the arena object. If an expression node

// is evaluated multiple times (e.g. as a part of Comprehension.loop_step)

// then the order of the callback invocations is guaranteed to correspond

// the order of variable sub-elements (e.g. the order of elements returned

// by Comprehension.iter_range).

using CelEvaluationListener = std::function<absl::Status(

    int64_t expr_id, const CelValue&, google::protobuf::Arena*)>;

// An opaque state used for evaluation of a CEL expression.

class CelEvaluationState {

 public:

  virtual ~CelEvaluationState() = default;

};

// Base interface for expression evaluating objects.

class CelExpression {

 public:

  virtual ~CelExpression() = default;

  // Initializes the state

  virtual std::unique_ptr<CelEvaluationState> InitializeState(

      google::protobuf::Arena* arena) const = 0;

  // Evaluates expression and returns value.

  // activation contains bindings from parameter names to values

  // arena parameter specifies Arena object where output result and

  // internal data will be allocated.

  virtual absl::StatusOr<CelValue> Evaluate(const BaseActivation& activation,

                                            google::protobuf::Arena* arena) const = 0;

  // Evaluates expression and returns value.

  // activation contains bindings from parameter names to values

  // state must be non-null and created prior to calling Evaluate by

  // InitializeState.

  virtual absl::StatusOr<CelValue> Evaluate(

      const BaseActivation& activation, CelEvaluationState* state) const = 0;

  // Trace evaluates expression calling the callback on each sub-tree.

  virtual absl::StatusOr<CelValue> Trace(

      const BaseActivation& activation, google::protobuf::Arena* arena,

      CelEvaluationListener callback) const = 0;

  // Trace evaluates expression calling the callback on each sub-tree.

  // state must be non-null and created prior to calling Evaluate by

  // InitializeState.

  virtual absl::StatusOr<CelValue> Trace(

      const BaseActivation& activation, CelEvaluationState* state,

      CelEvaluationListener callback) const = 0;

};

// Base class for Expression Builder implementations

// Provides user with factory to register extension functions.

// ExpressionBuilder MUST NOT be destroyed before CelExpression objects

// it built.

class CelExpressionBuilder {

 public:

  CelExpressionBuilder() = default;

  virtual ~CelExpressionBuilder() = default;

  // Creates CelExpression object from AST tree.

  // expr specifies root of AST tree.

  // Method implementation is expected to create copies of expr and source_info,

  // so that the returned CelExpression is not dependent on the lifetime of

  // the input arguments.

  virtual absl::StatusOr<std::unique_ptr<CelExpression>> CreateExpression(

      const cel::expr::Expr* expr,

      const cel::expr::SourceInfo* source_info) const = 0;

  // Creates CelExpression object from AST tree.

  // expr specifies root of AST tree.

  // non-fatal build warnings are written to warnings if encountered.

  // Method implementation is expected to create copies of expr and source_info,

  // so that the returned CelExpression is not dependent on the lifetime of

  // the input arguments.

  virtual absl::StatusOr<std::unique_ptr<CelExpression>> CreateExpression(

      const cel::expr::Expr* expr,

      const cel::expr::SourceInfo* source_info,

      std::vector<absl::Status>* warnings) const = 0;

  // Creates CelExpression object from a checked expression.

  // This includes an AST, source info, type hints and ident hints.

  // Method implementation is expected to create copy of checked_expr,

  // so that the returned CelExpression is not dependent on the lifetime of

  // the input arguments.

  virtual absl::StatusOr<std::unique_ptr<CelExpression>> CreateExpression(

      const cel::expr::CheckedExpr* checked_expr) const {

    // Default implementation just passes through the expr and source info.

    return CreateExpression(&checked_expr->expr(),

                            &checked_expr->source_info());

  }

  // Creates CelExpression object from a checked expression.

  // This includes an AST, source info, type hints and ident hints.

  // non-fatal build warnings are written to warnings if encountered.

  // Method implementation is expected to create copy of checked_expr,

  // so that the returned CelExpression is not dependent on the lifetime of

  // the input arguments.

  virtual absl::StatusOr<std::unique_ptr<CelExpression>> CreateExpression(

      const cel::expr::CheckedExpr* checked_expr,

      std::vector<absl::Status>* warnings) const {

    // Default implementation just passes through the expr and source_info.

    return CreateExpression(&checked_expr->expr(), &checked_expr->source_info(),

                            warnings);

  }

  // CelFunction registry. Extension function should be registered with it

  // prior to expression creation.

  virtual CelFunctionRegistry* GetRegistry() const = 0;

  // CEL Type registry. Provides a means to resolve the CEL built-in types to

  // CelValue instances, and to extend the set of types and enums known to

  // expressions by registering them ahead of time.

  virtual CelTypeRegistry* GetTypeRegistry() const = 0;

  virtual void set_container(std::string container) = 0;

  virtual absl::string_view container() const = 0;

};

}  // namespace google::api::expr::runtime

#endif  // THIRD_PARTY_CEL_CPP_EVAL_PUBLIC_CEL_EXPRESSION_H_