// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

#ifndef EXECUTABLE_SEMANTICS_AST_STATIC_SCOPE_H_
#define EXECUTABLE_SEMANTICS_AST_STATIC_SCOPE_H_

#include <string>
#include <unordered_map>
#include <variant>
#include <vector>

#include "executable_semantics/ast/ast_node.h"
#include "executable_semantics/ast/source_location.h"
#include "executable_semantics/common/nonnull.h"

namespace Carbon {

class NamedEntity : public virtual AstNode {
 public:
  virtual ~NamedEntity() = 0;

  NamedEntity() = default;

  // TODO: This is unused, but is intended for casts after lookup.
  auto kind() const -> NamedEntityKind {
    return static_cast<NamedEntityKind>(root_kind());
  }
};

// Maps the names visible in a given scope to the entities they name.
// A scope may have parent scopes, whose names will also be visible in the
// child scope.
class StaticScope {
 public:
  // Defines `name` to be `entity` in this scope, or reports a compilation error
  // if `name` is already defined in this scope.
  void Add(std::string name, Nonnull<const NamedEntity*> entity);

  // Make `parent` a parent of this scope.
  // REQUIRES: `parent` is not already a parent of this scope.
  void AddParent(Nonnull<StaticScope*> parent) {
    parent_scopes_.push_back(parent);
  }

  // Returns the nearest definition of `name` in the ancestor graph of this
  // scope, or reports a compilation error at `source_loc` there isn't exactly
  // one such definition.
  auto Resolve(const std::string& name, SourceLocation source_loc) const
      -> Nonnull<const NamedEntity*>;

 private:
  // Equivalent to Resolve, but returns `nullopt` instead of raising an error
  // if no definition can be found. Still raises a compilation error if more
  // than one definition is found.
  auto TryResolve(const std::string& name, SourceLocation source_loc) const
      -> std::optional<Nonnull<const NamedEntity*>>;

  // Maps locally declared names to their entities.
  std::unordered_map<std::string, Nonnull<const NamedEntity*>> declared_names_;

  // A list of scopes used for name lookup within this scope.
  std::vector<Nonnull<StaticScope*>> parent_scopes_;
};

}  // namespace Carbon

#endif  // EXECUTABLE_SEMANTICS_AST_STATIC_SCOPE_H_