// 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/context.h"
#include "toolchain/check/eval.h"
#include "toolchain/check/generic.h"
#include "toolchain/check/handle.h"
#include "toolchain/check/merge.h"
#include "toolchain/check/modifiers.h"
#include "toolchain/check/name_component.h"
#include "toolchain/sem_ir/typed_insts.h"

namespace Carbon::Check {

auto HandleInterfaceIntroducer(Context& context,
                               Parse::InterfaceIntroducerId node_id) -> bool {
  // Create an instruction block to hold the instructions created as part of the
  // interface signature, such as generic parameters.
  context.inst_block_stack().Push();
  // Push the bracketing node.
  context.node_stack().Push(node_id);
  // Optional modifiers and the name follow.
  context.decl_introducer_state_stack().Push<Lex::TokenKind::Interface>();
  context.decl_name_stack().PushScopeAndStartName();
  // This interface is potentially generic.
  StartGenericDecl(context);
  return true;
}

static auto BuildInterfaceDecl(Context& context,
                               Parse::AnyInterfaceDeclId node_id)
    -> std::tuple<SemIR::InterfaceId, SemIR::InstId> {
  auto name = PopNameComponent(context);
  auto name_context = context.decl_name_stack().FinishName(name);
  context.node_stack()
      .PopAndDiscardSoloNodeId<Parse::NodeKind::InterfaceIntroducer>();

  // Process modifiers.
  auto [_, parent_scope_inst] =
      context.name_scopes().GetInstIfValid(name_context.parent_scope_id);
  auto introducer =
      context.decl_introducer_state_stack().Pop<Lex::TokenKind::Interface>();
  CheckAccessModifiersOnDecl(context, introducer, parent_scope_inst);
  LimitModifiersOnDecl(context, introducer, KeywordModifierSet::Access);

  auto decl_block_id = context.inst_block_stack().Pop();

  // Add the interface declaration.
  auto interface_decl = SemIR::InterfaceDecl{
      SemIR::TypeId::TypeType, SemIR::InterfaceId::Invalid, decl_block_id};
  auto interface_decl_id =
      context.AddPlaceholderInst(SemIR::LocIdAndInst(node_id, interface_decl));

  // Check whether this is a redeclaration.
  auto existing_id = context.decl_name_stack().LookupOrAddName(
      name_context, interface_decl_id, introducer.modifier_set.GetAccessKind());
  if (existing_id.is_valid()) {
    if (auto existing_interface_decl =
            context.insts().Get(existing_id).TryAs<SemIR::InterfaceDecl>()) {
      // TODO: Implement full redeclaration checking. See `MergeClassDecl`. For
      // now we just check the generic parameters match.
      if (CheckRedeclParamsMatch(
              context,
              DeclParams(interface_decl_id, name.implicit_params_id,
                         name.params_id),
              DeclParams(context.interfaces().Get(
                  existing_interface_decl->interface_id)))) {
        // This is a redeclaration of an existing interface.
        interface_decl.interface_id = existing_interface_decl->interface_id;
        interface_decl.type_id = existing_interface_decl->type_id;
        // TODO: If the new declaration is a definition, keep its parameter
        // and implicit parameter lists rather than the ones from the
        // previous declaration.
      }
    } else {
      // This is a redeclaration of something other than a interface.
      context.DiagnoseDuplicateName(interface_decl_id, existing_id);
    }
  }

  // Create a new interface if this isn't a valid redeclaration.
  if (!interface_decl.interface_id.is_valid()) {
    auto generic_id = FinishGenericDecl(context, interface_decl_id);
    // TODO: If this is an invalid redeclaration of a non-interface entity or
    // there was an error in the qualifier, we will have lost track of the
    // interface name here. We should keep track of it even if the name is
    // invalid.
    SemIR::Interface interface_info = {
        .name_id = name_context.name_id_for_new_inst(),
        .parent_scope_id = name_context.parent_scope_id_for_new_inst(),
        .generic_id = generic_id,
        .implicit_param_refs_id = name.implicit_params_id,
        .param_refs_id = name.params_id,
        .decl_id = interface_decl_id};
    interface_decl.interface_id = context.interfaces().Add(interface_info);
    if (interface_info.is_generic()) {
      interface_decl.type_id =
          context.GetGenericInterfaceType(interface_decl.interface_id);
    }
  } else {
    FinishGenericRedecl(
        context, interface_decl_id,
        context.interfaces().Get(interface_decl.interface_id).generic_id);
  }

  // Write the interface ID into the InterfaceDecl.
  context.ReplaceInstBeforeConstantUse(interface_decl_id, interface_decl);

  return {interface_decl.interface_id, interface_decl_id};
}

auto HandleInterfaceDecl(Context& context, Parse::InterfaceDeclId node_id)
    -> bool {
  BuildInterfaceDecl(context, node_id);
  context.decl_name_stack().PopScope();
  return true;
}

auto HandleInterfaceDefinitionStart(Context& context,
                                    Parse::InterfaceDefinitionStartId node_id)
    -> bool {
  auto [interface_id, interface_decl_id] = BuildInterfaceDecl(context, node_id);
  auto& interface_info = context.interfaces().Get(interface_id);

  // Track that this declaration is the definition.
  if (interface_info.is_defined()) {
    CARBON_DIAGNOSTIC(InterfaceRedefinition, Error,
                      "Redefinition of interface {0}.", SemIR::NameId);
    CARBON_DIAGNOSTIC(InterfacePreviousDefinition, Note,
                      "Previous definition was here.");
    context.emitter()
        .Build(node_id, InterfaceRedefinition, interface_info.name_id)
        .Note(interface_info.definition_id, InterfacePreviousDefinition)
        .Emit();
  } else {
    interface_info.definition_id = interface_decl_id;
    interface_info.scope_id =
        context.name_scopes().Add(interface_decl_id, SemIR::NameId::Invalid,
                                  interface_info.parent_scope_id);
  }

  // Enter the interface scope.
  context.scope_stack().Push(interface_decl_id, interface_info.scope_id);
  StartGenericDefinition(context, interface_info.generic_id);

  context.inst_block_stack().Push();
  context.node_stack().Push(node_id, interface_id);

  // We use the arg stack to build the witness table type.
  context.args_type_info_stack().Push();

  // Declare and introduce `Self`.
  if (!interface_info.is_defined()) {
    SemIR::TypeId self_type_id = SemIR::TypeId::Invalid;
    if (interface_info.is_generic()) {
      auto instance_id =
          MakeGenericSelfInstance(context, interface_info.generic_id);
      self_type_id = context.GetTypeIdForTypeConstant(
          TryEvalInst(context, SemIR::InstId::Invalid,
                      SemIR::InterfaceType{.type_id = SemIR::TypeId::TypeType,
                                           .interface_id = interface_id,
                                           .instance_id = instance_id}));
    } else {
      self_type_id = context.GetTypeIdForTypeInst(interface_decl_id);
    }

    // We model `Self` as a symbolic binding whose type is the interface.
    // Because there is no equivalent non-symbolic value, we use `Invalid` as
    // the `value_id` on the `BindSymbolicName`.
    auto bind_name_id = context.bind_names().Add(
        {.name_id = SemIR::NameId::SelfType,
         .parent_scope_id = interface_info.scope_id,
         .bind_index = context.scope_stack().AddCompileTimeBinding()});
    interface_info.self_param_id = context.AddInst<SemIR::BindSymbolicName>(
        SemIR::LocId::Invalid, {.type_id = self_type_id,
                                .bind_name_id = bind_name_id,
                                .value_id = SemIR::InstId::Invalid});
    context.scope_stack().PushCompileTimeBinding(interface_info.self_param_id);
    context.name_scopes().AddRequiredName(interface_info.scope_id,
                                          SemIR::NameId::SelfType,
                                          interface_info.self_param_id);
  }

  // TODO: Handle the case where there's control flow in the interface body. For
  // example:
  //
  //   interface C {
  //     let v: if true then i32 else f64;
  //   }
  //
  // We may need to track a list of instruction blocks here, as we do for a
  // function.
  interface_info.body_block_id = context.inst_block_stack().PeekOrAdd();
  return true;
}

auto HandleInterfaceDefinition(Context& context,
                               Parse::InterfaceDefinitionId /*node_id*/)
    -> bool {
  auto interface_id =
      context.node_stack().Pop<Parse::NodeKind::InterfaceDefinitionStart>();
  context.inst_block_stack().Pop();
  auto associated_entities_id = context.args_type_info_stack().Pop();

  // The interface type is now fully defined.
  auto& interface_info = context.interfaces().Get(interface_id);
  if (!interface_info.associated_entities_id.is_valid()) {
    interface_info.associated_entities_id = associated_entities_id;
  }

  FinishGenericDefinition(context, interface_info.generic_id);

  // The decl_name_stack and scopes are popped by `ProcessNodeIds`.
  return true;
}

}  // namespace Carbon::Check