// 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/facet_type.h"

#include "toolchain/check/convert.h"
#include "toolchain/check/import_ref.h"
#include "toolchain/check/inst.h"
#include "toolchain/check/interface.h"
#include "toolchain/check/type.h"

namespace Carbon::Check {

auto FacetTypeFromInterface(Context& context, SemIR::InterfaceId interface_id,
                            SemIR::SpecificId specific_id) -> SemIR::FacetType {
  SemIR::FacetTypeId facet_type_id = context.facet_types().Add(
      SemIR::FacetTypeInfo{.impls_constraints = {{interface_id, specific_id}},
                           .other_requirements = false});
  return {.type_id = SemIR::TypeType::SingletonTypeId,
          .facet_type_id = facet_type_id};
}

// Returns `true` if the `FacetAccessWitness` of `witness_id` matches
// `interface`.
static auto WitnessAccessMatchesInterface(
    Context& context, SemIR::InstId witness_id,
    const SemIR::SpecificInterface& interface) -> bool {
  auto access = context.insts().GetAs<SemIR::FacetAccessWitness>(witness_id);
  auto type_id = context.insts().Get(access.facet_value_inst_id).type_id();
  auto facet_type = context.types().GetAs<SemIR::FacetType>(type_id);
  const auto& facet_info = context.facet_types().Get(facet_type.facet_type_id);
  if (auto impls = facet_info.TryAsSingleInterface()) {
    return impls->interface_id == interface.interface_id &&
           impls->specific_id == interface.specific_id;
  }
  return false;
}

auto ResolveFacetTypeImplWitness(
    Context& context, SemIR::LocId witness_loc_id,
    SemIR::InstId facet_type_inst_id, SemIR::InstId self_type_inst_id,
    const SemIR::SpecificInterface& interface_to_witness,
    SemIR::SpecificId self_specific_id) -> SemIR::InstId {
  // TODO: Finish facet type resolution. This code currently only handles
  // rewrite constraints that set associated constants to a concrete value.
  // Need logic to topologically sort rewrites to respect dependencies, and
  // afterwards reject duplicates that are not identical.

  const auto& interface =
      context.interfaces().Get(interface_to_witness.interface_id);
  auto assoc_entities =
      context.inst_blocks().Get(interface.associated_entities_id);
  // TODO: When this function is used for things other than just impls, may want
  // to only load the specific associated entities that are mentioned in rewrite
  // rules.
  for (auto decl_id : assoc_entities) {
    LoadImportRef(context, decl_id);
  }

  SemIR::InstId witness_inst_id = SemIR::InstId::None;
  llvm::MutableArrayRef<SemIR::InstId> table;
  {
    llvm::SmallVector<SemIR::InstId> empty_table(assoc_entities.size(),
                                                 SemIR::InstId::None);
    auto table_id = context.inst_blocks().Add(empty_table);
    table = context.inst_blocks().GetMutable(table_id);
    witness_inst_id = AddInst<SemIR::ImplWitness>(
        context, witness_loc_id,
        {.type_id =
             GetSingletonType(context, SemIR::WitnessType::SingletonInstId),
         .elements_id = table_id,
         .specific_id = self_specific_id});
  }

  auto facet_type_id =
      context.types().GetTypeIdForTypeInstId(facet_type_inst_id);
  CARBON_CHECK(facet_type_id != SemIR::ErrorInst::SingletonTypeId);
  auto facet_type = context.types().GetAs<SemIR::FacetType>(facet_type_id);
  // TODO: This is currently a copy because I'm not sure whether anything could
  // cause the facet type store to resize before we are done with it.
  auto facet_type_info = context.facet_types().Get(facet_type.facet_type_id);

  for (auto rewrite : facet_type_info.rewrite_constraints) {
    auto inst_id = context.constant_values().GetInstId(rewrite.lhs_const_id);
    auto access = context.insts().GetAs<SemIR::ImplWitnessAccess>(inst_id);
    if (!WitnessAccessMatchesInterface(context, access.witness_id,
                                       interface_to_witness)) {
      continue;
    }
    auto& table_entry = table[access.index.index];
    if (table_entry == SemIR::ErrorInst::SingletonInstId) {
      // Don't overwrite an error value. This prioritizes not generating
      // multiple errors for one associated constant over picking a value
      // for it to use to attempt recovery.
      continue;
    }
    auto rewrite_value = rewrite.rhs_const_id;

    if (table_entry.has_value()) {
      auto const_id = context.constant_values().Get(table_entry);
      if (const_id != rewrite_value &&
          rewrite_value != SemIR::ErrorInst::SingletonConstantId) {
        table_entry = SemIR::ErrorInst::SingletonInstId;
        // TODO: Figure out how to print the two different values
        // `const_id` & `rewrite_value` in the diagnostic
        // message.
        CARBON_DIAGNOSTIC(AssociatedConstantWithDifferentValues, Error,
                          "associated constant {0} given two different values",
                          SemIR::NameId);
        auto decl_id = assoc_entities[access.index.index];
        SemIR::NameId name_id = SemIR::NameId::None;
        if (auto decl = context.insts().TryGetAs<SemIR::AssociatedConstantDecl>(
                decl_id)) {
          auto& assoc_const =
              context.associated_constants().Get(decl->assoc_const_id);
          name_id = assoc_const.name_id;
        } else {
          auto import_ref = context.insts().GetAs<SemIR::AnyImportRef>(decl_id);
          const auto& entity_name =
              context.entity_names().Get(import_ref.entity_name_id);
          name_id = entity_name.name_id;
        }
        context.emitter().Emit(facet_type_inst_id,
                               AssociatedConstantWithDifferentValues, name_id);
      }
      continue;
    }
    auto decl_id = context.constant_values().GetConstantInstId(
        assoc_entities[access.index.index]);
    CARBON_CHECK(decl_id.has_value(), "Non-constant associated entity");
    if (auto decl =
            context.insts().TryGetAs<SemIR::AssociatedConstantDecl>(decl_id)) {
      // If the associated constant has a symbolic type, convert the rewrite
      // value to that type now we know the value of `Self`.
      SemIR::TypeId assoc_const_type_id = decl->type_id;
      if (assoc_const_type_id.is_symbolic()) {
        // Get the type of the associated constant in this interface with this
        // value for `Self`.
        assoc_const_type_id = GetTypeForSpecificAssociatedEntity(
            context, facet_type_inst_id, interface_to_witness.specific_id,
            decl_id, context.types().GetTypeIdForTypeInstId(self_type_inst_id),
            witness_inst_id);
        // Perform the conversion of the value to the type. We skipped this when
        // forming the facet type because the type of the associated constant
        // was symbolic.
        auto converted_inst_id = ConvertToValueOfType(
            context, context.insts().GetLocId(facet_type_inst_id),
            context.constant_values().GetInstId(rewrite_value),
            assoc_const_type_id);
        rewrite_value = context.constant_values().Get(converted_inst_id);
        // The result of conversion can be non-constant even if the original
        // value was constant.
        if (!rewrite_value.is_constant() &&
            rewrite_value != SemIR::ErrorInst::SingletonConstantId) {
          const auto& assoc_const =
              context.associated_constants().Get(decl->assoc_const_id);
          CARBON_DIAGNOSTIC(
              AssociatedConstantNotConstantAfterConversion, Error,
              "associated constant {0} given value that is not constant "
              "after conversion to {1}",
              SemIR::NameId, SemIR::TypeId);
          context.emitter().Emit(facet_type_inst_id,
                                 AssociatedConstantNotConstantAfterConversion,
                                 assoc_const.name_id, assoc_const_type_id);
          rewrite_value = SemIR::ErrorInst::SingletonConstantId;
        }
      }
    } else {
      if (decl_id != SemIR::ErrorInst::SingletonInstId) {
        auto type_id = context.insts().Get(decl_id).type_id();
        auto type_inst = context.types().GetAsInst(type_id);
        auto fn_type = type_inst.As<SemIR::FunctionType>();
        const auto& fn = context.functions().Get(fn_type.function_id);
        CARBON_DIAGNOSTIC(RewriteForAssociatedFunction, Error,
                          "rewrite specified for associated function {0}",
                          SemIR::NameId);
        context.emitter().Emit(facet_type_inst_id, RewriteForAssociatedFunction,
                               fn.name_id);
      }
      continue;
    }
    table_entry = context.constant_values().GetInstId(rewrite_value);
  }
  return witness_inst_id;
}

}  // namespace Carbon::Check