// 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 CARBON_TOOLCHAIN_SEM_IR_FUNCTION_H_
#define CARBON_TOOLCHAIN_SEM_IR_FUNCTION_H_

#include "toolchain/sem_ir/builtin_function_kind.h"
#include "toolchain/sem_ir/ids.h"
#include "toolchain/sem_ir/typed_insts.h"

namespace Carbon::SemIR {

// A function.
struct Function : public Printable<Function> {
  // A value that describes whether the function uses a return slot.
  enum class ReturnSlot : int8_t {
    // Not yet known: the function has not been called or defined.
    NotComputed,
    // The function is known to not use a return slot.
    Absent,
    // The function has a return slot, and a call to the function is expected to
    // have an additional final argument corresponding to the return slot.
    Present,
    // Computing whether the function should have a return slot failed, for
    // example because the return type was incomplete.
    Error
  };

  auto Print(llvm::raw_ostream& out) const -> void {
    out << "{name: " << name_id << ", parent_scope: " << parent_scope_id
        << ", param_refs: " << param_refs_id;
    if (return_storage_id.is_valid()) {
      out << ", return_storage: " << return_storage_id;
      out << ", return_slot: ";
      switch (return_slot) {
        case ReturnSlot::NotComputed:
          out << "unknown";
          break;
        case ReturnSlot::Absent:
          out << "absent";
          break;
        case ReturnSlot::Present:
          out << "present";
          break;
        case ReturnSlot::Error:
          out << "error";
          break;
      }
    }
    if (!body_block_ids.empty()) {
      out << llvm::formatv(
          ", body: [{0}]",
          llvm::make_range(body_block_ids.begin(), body_block_ids.end()));
    }
    out << "}";
  }

  // Given a parameter reference instruction from `param_refs_id` or
  // `implicit_param_refs_id`, returns the corresponding `Param` instruction
  // and its ID.
  static auto GetParamFromParamRefId(const File& sem_ir, InstId param_ref_id)
      -> std::pair<InstId, Param>;

  // Gets the declared return type of the function. Returns `Invalid` if no
  // return type was specified,
  auto declared_return_type(const File& file) const -> TypeId;

  // Returns whether the function has a return slot. Can only be called for a
  // function that has either been called or defined, otherwise this is not
  // known.
  auto has_return_slot() const -> bool {
    CARBON_CHECK(return_slot != ReturnSlot::NotComputed);
    // On error, we assume no return slot is used.
    return return_slot == ReturnSlot::Present;
  }

  // The following members always have values, and do not change throughout the
  // lifetime of the function.

  // The function name.
  NameId name_id;
  // The parent scope.
  NameScopeId parent_scope_id;
  // The first declaration of the function. This is a FunctionDecl.
  InstId decl_id;
  // If this is a generic function, information about the generic.
  GenericId generic_id;
  // A block containing a single reference instruction per implicit parameter.
  InstBlockId implicit_param_refs_id;
  // A block containing a single reference instruction per parameter.
  InstBlockId param_refs_id;
  // The storage for the return value, which is a reference expression whose
  // type is the return type of the function. This may or may not be used by the
  // function, depending on whether the return type needs a return slot, but is
  // always present if the function has a declared return type.
  InstId return_storage_id;
  // Whether the declaration is extern.
  bool is_extern;

  // The following member is set on the first call to the function, or at the
  // point where the function is defined.

  // Whether the function uses a return slot.
  ReturnSlot return_slot;

  // The following members are set at the end of a builtin function definition.

  // If this is a builtin function, the corresponding builtin kind.
  BuiltinFunctionKind builtin_kind = BuiltinFunctionKind::None;

  // The following members are set at the `{` of the function definition.

  // The definition, if the function has been defined or is currently being
  // defined. This is a FunctionDecl.
  InstId definition_id = InstId::Invalid;

  // The following members are accumulated throughout the function definition.

  // A list of the statically reachable code blocks in the body of the
  // function, in lexical order. The first block is the entry block. This will
  // be empty for declarations that don't have a visible definition.
  llvm::SmallVector<InstBlockId> body_block_ids = {};
};

class File;

struct CalleeFunction {
  // The function. Invalid if not a function.
  SemIR::FunctionId function_id;
  // The bound `self` parameter. Invalid if not a method.
  SemIR::InstId self_id;
  // True if an error instruction was found.
  bool is_error;
};

// Returns information for the function corresponding to callee_id.
auto GetCalleeFunction(const File& sem_ir, InstId callee_id) -> CalleeFunction;

}  // namespace Carbon::SemIR

#endif  // CARBON_TOOLCHAIN_SEM_IR_FUNCTION_H_