// 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

#include "toolchain/check/interface.h"

#include <algorithm>
#include <cstddef>
#include <optional>
#include <type_traits>

#include "common/concepts.h"
#include "toolchain/base/kind_switch.h"
#include "toolchain/check/context.h"
#include "toolchain/check/core_identifier.h"
#include "toolchain/check/eval.h"
#include "toolchain/check/generic.h"
#include "toolchain/check/inst.h"
#include "toolchain/check/merge.h"
#include "toolchain/check/name_lookup.h"
#include "toolchain/check/type.h"
#include "toolchain/sem_ir/entity_with_params_base.h"
#include "toolchain/sem_ir/ids.h"
#include "toolchain/sem_ir/inst.h"
#include "toolchain/sem_ir/typed_insts.h"

namespace Carbon::Check {

auto BuildAssociatedEntity(Context& context, SemIR::InterfaceId interface_id,
                           SemIR::InstId decl_id) -> SemIR::InstId {
  auto& interface_info = context.interfaces().Get(interface_id);
  if (!interface_info.is_being_defined()) {
    // This should only happen if the interface is erroneously defined more than
    // once.
    // TODO: Find a way to CHECK this.
    return SemIR::ErrorInst::InstId;
  }

  // This associated entity is being declared as a member of an interface. We
  // use the self-specific of the interface-without-self as the AssociatedEntity
  // names the externally facing SpecificInterface (without self).
  auto interface_without_self_specific_id =
      context.generics().GetSelfSpecific(interface_info.generic_id);

  // Register this declaration as declaring an associated entity.
  auto index = SemIR::ElementIndex(
      context.args_type_info_stack().PeekCurrentBlockContents().size());
  context.args_type_info_stack().AddInstId(decl_id);

  // Name lookup for the declaration's name should name the associated entity,
  // not the declaration itself.
  auto type_id = GetAssociatedEntityType(context, interface_id,
                                         interface_without_self_specific_id);
  return AddInst<SemIR::AssociatedEntity>(
      context, SemIR::LocId(decl_id),
      {.type_id = type_id, .index = index, .decl_id = decl_id});
}

auto GetSelfSpecificForInterfaceMemberWithSelfType(
    Context& context, SemIR::LocId loc_id,
    SemIR::SpecificId interface_with_self_specific_id,
    SemIR::GenericId generic_id, SemIR::SpecificId enclosing_specific_id)
    -> SemIR::SpecificId {
  const auto& generic = context.generics().Get(generic_id);
  auto self_specific_args = context.inst_blocks().Get(
      context.specifics().Get(generic.self_specific_id).args_id);

  auto arg_ids = llvm::SmallVector<SemIR::InstId>(context.inst_blocks().Get(
      context.specifics().GetArgsOrEmpty(interface_with_self_specific_id)));

  // Determine the number of specific arguments that enclose the point where
  // this self specific will be used from. In an impl, this will be the number
  // of parameters that the impl has.
  int num_enclosing_specific_args =
      context.inst_blocks()
          .Get(context.specifics().GetArgsOrEmpty(enclosing_specific_id))
          .size();
  // The index of each remaining generic parameter is adjusted to match the
  // numbering at the point where the self specific is used.
  int index_delta = num_enclosing_specific_args - arg_ids.size();

  // Take any trailing argument values from the self specific.
  // TODO: If these refer to outer arguments, for example in their types, we may
  // need to perform extra substitutions here.
  for (auto arg_id : self_specific_args.drop_front(arg_ids.size())) {
    auto new_arg_id = context.constant_values().GetConstantInstId(arg_id);
    if (index_delta) {
      // If this parameter would have a new index in the context described by
      // `enclosing_specific_id`, form a new binding with an adjusted index.
      auto bind_name = context.insts().GetAs<SemIR::SymbolicBinding>(
          context.constant_values().GetConstantInstId(arg_id));
      auto entity_name = context.entity_names().Get(bind_name.entity_name_id);
      entity_name.bind_index_value += index_delta;
      CARBON_CHECK(entity_name.bind_index_value >= 0);
      bind_name.entity_name_id =
          context.entity_names().AddCanonical(entity_name);
      new_arg_id =
          context.constant_values().GetInstId(TryEvalInst(context, bind_name));
    }
    arg_ids.push_back(new_arg_id);
  }

  return MakeSpecific(context, loc_id, generic_id, arg_ids);
}

auto GetTypeForSpecificAssociatedEntity(
    Context& context, SemIR::SpecificId interface_with_self_specific_id,
    SemIR::InstId decl_id) -> SemIR::TypeId {
  auto decl_constant_inst_id =
      context.constant_values().GetConstantInstId(decl_id);
  if (decl_constant_inst_id == SemIR::ErrorInst::InstId) {
    return SemIR::ErrorInst::TypeId;
  }

  auto decl = context.insts().Get(decl_constant_inst_id);
  if (auto assoc_const = decl.TryAs<SemIR::AssociatedConstantDecl>()) {
    return SemIR::GetTypeOfInstInSpecific(
        context.sem_ir(), interface_with_self_specific_id, decl_id);
  }

  if (auto fn = context.types().TryGetAs<SemIR::FunctionType>(decl.type_id())) {
    // Form the type of the function within the interface, and attach the `Self`
    // type.
    auto interface_fn_type_id = SemIR::GetTypeOfInstInSpecific(
        context.sem_ir(), interface_with_self_specific_id, decl_id);
    auto self_facet_id = context.inst_blocks()
                             .Get(context.specifics().GetArgsOrEmpty(
                                 interface_with_self_specific_id))
                             .back();
    return GetFunctionTypeWithSelfType(
        context, context.types().GetTypeInstId(interface_fn_type_id),
        self_facet_id);
  }

  CARBON_FATAL("Unexpected kind for associated constant {0}", decl);
}

auto AddSelfSymbolicBindingToScope(Context& context,
                                   SemIR::LocId definition_loc_id,
                                   SemIR::TypeId type_id,
                                   SemIR::NameScopeId scope_id,
                                   bool is_template) -> SemIR::InstId {
  auto entity_name_id = context.entity_names().AddSymbolicBindingName(
      SemIR::NameId::SelfType, scope_id,
      context.scope_stack().AddCompileTimeBinding(), is_template,
      /*is_unused=*/false, /*is_frozen_period_self=*/false);
  // Because there is no equivalent non-symbolic value, we use `None` as
  // the `value_id` on the `SymbolicBinding`.
  auto self_param_inst_id =
      AddInst<SemIR::SymbolicBinding>(context, definition_loc_id,
                                      {.type_id = type_id,
                                       .entity_name_id = entity_name_id,
                                       .value_id = SemIR::InstId::None});
  context.name_scopes().AddRequiredName(scope_id, SemIR::NameId::SelfType,
                                        self_param_inst_id);
  return self_param_inst_id;
}

}  // namespace Carbon::Check