#include "query.h"

#include "indexer.h"
#include "serializers/json.h"

#include <doctest/doctest.h>
#include <optional.h>
#include <loguru.hpp>

#include <cassert>
#include <cstdint>
#include <functional>
#include <iostream>
#include <string>
#include <unordered_map>
#include <unordered_set>

// TODO: Make all copy constructors explicit.

namespace {

template <typename T>
void VerifyUnique(const std::vector<T>& values0) {
// FIXME: Run on a big code-base for a while and verify no assertions are
// triggered.
#if false
  auto values = values0;
  std::sort(values.begin(), values.end());
  assert(std::unique(values.begin(), values.end()) == values.end());
#endif
}

optional<QueryType::Def> ToQuery(const IdMap& id_map,
                                 const IndexType::Def& type) {
  if (type.detailed_name.empty())
    return nullopt;

  QueryType::Def result;
  result.short_name = type.short_name;
  result.detailed_name = type.detailed_name;
  result.kind = type.kind;
  result.hover = type.hover;
  result.comments = type.comments;
  result.definition_spelling = id_map.ToQuery(type.definition_spelling);
  result.definition_extent = id_map.ToQuery(type.definition_extent);
  result.alias_of = id_map.ToQuery(type.alias_of);
  result.parents = id_map.ToQuery(type.parents);
  result.types = id_map.ToQuery(type.types);
  result.funcs = id_map.ToQuery(type.funcs);
  result.vars = id_map.ToQuery(type.vars);
  return result;
}

optional<QueryFunc::Def> ToQuery(const IdMap& id_map,
                                 const IndexFunc::Def& func) {
  if (func.detailed_name.empty())
    return nullopt;

  QueryFunc::Def result;
  result.short_name = func.short_name;
  result.detailed_name = func.detailed_name;
  result.kind = func.kind;
  result.storage = func.storage;
  result.hover = func.hover;
  result.comments = func.comments;
  result.definition_spelling = id_map.ToQuery(func.definition_spelling);
  result.definition_extent = id_map.ToQuery(func.definition_extent);
  result.declaring_type = id_map.ToQuery(func.declaring_type);
  result.base = id_map.ToQuery(func.base);
  result.locals = id_map.ToQuery(func.locals);
  result.callees = id_map.ToQuery(func.callees);
  return result;
}

optional<QueryVar::Def> ToQuery(const IdMap& id_map, const IndexVar::Def& var) {
  if (var.detailed_name.empty())
    return nullopt;

  QueryVar::Def result;
  result.short_name = var.short_name;
  result.detailed_name = var.detailed_name;
  result.kind = var.kind;
  result.storage = var.storage;
  result.hover = var.hover;
  result.comments = var.comments;
  result.declarations = id_map.ToQuery(var.declarations);
  result.definition_spelling = id_map.ToQuery(var.definition_spelling);
  result.definition_extent = id_map.ToQuery(var.definition_extent);
  result.variable_type = id_map.ToQuery(var.variable_type);
  result.declaring_type = id_map.ToQuery(var.declaring_type);
  return result;
}

// Adds the mergeable updates in |source| to |dest|. If a mergeable update for
// the destination type already exists, it will be combined. This makes merging
// updates take longer but reduces import time on the querydb thread.
template <typename TId, typename TValue>
void AddMergeableRange(
    std::vector<MergeableUpdate<TId, TValue>>* dest,
    const std::vector<MergeableUpdate<TId, TValue>>& source) {
  // TODO: Consider caching the lookup table. It can probably save even more
  // time at the cost of some additional memory.

  // Build lookup table.
  spp::sparse_hash_map<TId, size_t> id_to_index;
  id_to_index.resize(dest->size());
  for (size_t i = 0; i < dest->size(); ++i)
    id_to_index[(*dest)[i].id] = i;

  // Add entries. Try to add them to an existing entry.
  for (const auto& entry : source) {
    auto it = id_to_index.find(entry.id);
    if (it != id_to_index.end()) {
      AddRange(&(*dest)[it->second].to_add, entry.to_add);
      AddRange(&(*dest)[it->second].to_remove, entry.to_remove);
    } else {
      dest->push_back(entry);
    }
  }
}

// Compares |previous| and |current|, adding all elements that are
// in |previous| but not |current| to |removed|, and all elements
// that are in |current| but not |previous| to |added|.
//
// Returns true iff |removed| or |added| are non-empty.
template <typename T>
bool ComputeDifferenceForUpdate(std::vector<T>& previous,
                                std::vector<T>& current,
                                std::vector<T>* removed,
                                std::vector<T>* added) {
  // We need to sort to use std::set_difference.
  std::sort(previous.begin(), previous.end());
  std::sort(current.begin(), current.end());

  auto it0 = previous.begin(), it1 = current.begin();
  while (it0 != previous.end() && it1 != current.end()) {
    // Elements in |previous| that are not in |current|.
    if (*it0 < *it1)
      removed->push_back(*it0++);
    // Elements in |current| that are not in |previous|.
    else if (*it1 < *it0)
      added->push_back(*it1++);
    else
      ++it0, ++it1;
  }
  while (it0 != previous.end())
    removed->push_back(*it0++);
  while (it1 != current.end())
    added->push_back(*it1++);

  return !removed->empty() || !added->empty();
}

template <typename T>
void CompareGroups(std::vector<T>& previous_data,
                   std::vector<T>& current_data,
                   std::function<void(T*)> on_removed,
                   std::function<void(T*)> on_added,
                   std::function<void(T*, T*)> on_found) {
  std::sort(previous_data.begin(), previous_data.end());
  std::sort(current_data.begin(), current_data.end());

  auto prev_it = previous_data.begin();
  auto curr_it = current_data.begin();
  while (prev_it != previous_data.end() && curr_it != current_data.end()) {
    // same id
    if (prev_it->usr == curr_it->usr) {
      on_found(&*prev_it, &*curr_it);
      ++prev_it;
      ++curr_it;
    }

    // prev_id is smaller - prev_it has data curr_it does not have.
    else if (prev_it->usr < curr_it->usr) {
      on_removed(&*prev_it);
      ++prev_it;
    }

    // prev_id is bigger - curr_it has data prev_it does not have.
    else {
      on_added(&*curr_it);
      ++curr_it;
    }
  }

  // if prev_it still has data, that means it is not in curr_it and was removed.
  while (prev_it != previous_data.end()) {
    on_removed(&*prev_it);
    ++prev_it;
  }

  // if curr_it still has data, that means it is not in prev_it and was added.
  while (curr_it != current_data.end()) {
    on_added(&*curr_it);
    ++curr_it;
  }
}

QueryFile::Def BuildFileDef(const IdMap& id_map, const IndexFile& indexed) {
  QueryFile::Def def;
  def.path = indexed.path;
  def.includes = indexed.includes;
  def.inactive_regions = indexed.skipped_by_preprocessor;

  // Convert enum to markdown compatible strings
  def.language = [indexed]() {
    switch (indexed.language) {
      case LanguageId::C:
        return "c";
      case LanguageId::Cpp:
        return "cpp";
      case LanguageId::ObjC:
        return "objectivec";
      default:
        return "";
    }
  }();

  auto add_outline = [&def, &id_map](SymbolIdx idx, Range range) {
    def.outline.push_back(SymbolRef(idx, id_map.ToQuery(range)));
  };
  auto add_all_symbols = [&def, &id_map](SymbolIdx idx, Range range) {
    def.all_symbols.push_back(SymbolRef(idx, id_map.ToQuery(range)));
  };

  for (const IndexType& type : indexed.types) {
    if (type.def.definition_spelling.has_value())
      add_all_symbols(id_map.ToSymbol(type.id),
                      type.def.definition_spelling.value());
    if (type.def.definition_extent.has_value())
      add_outline(id_map.ToSymbol(type.id), type.def.definition_extent.value());
    for (const Range& use : type.uses)
      add_all_symbols(id_map.ToSymbol(type.id), use);
  }
  for (const IndexFunc& func : indexed.funcs) {
    if (func.def.definition_spelling.has_value())
      add_all_symbols(id_map.ToSymbol(func.id),
                      func.def.definition_spelling.value());
    if (func.def.definition_extent.has_value())
      add_outline(id_map.ToSymbol(func.id), func.def.definition_extent.value());
    for (const IndexFunc::Declaration& decl : func.declarations) {
      // TODO: add more outline info?
      add_all_symbols(id_map.ToSymbol(func.id), decl.spelling);
      add_outline(id_map.ToSymbol(func.id), decl.spelling);
    }
    for (const IndexFuncRef& caller : func.callers) {
      // Make ranges of implicit function calls larger (spanning one more column
      // to the left/right). This is hacky but useful. e.g.
      // textDocument/definition on the space/semicolon in `A a;` or `return
      // 42;` will take you to the constructor.
      Range range = caller.loc;
      if (caller.is_implicit) {
        if (range.start.column > 0)
          range.start.column--;
        range.end.column++;
      }
      add_all_symbols(id_map.ToSymbol(func.id), range);
    }
  }
  for (const IndexVar& var : indexed.vars) {
    if (var.def.definition_spelling.has_value())
      add_all_symbols(id_map.ToSymbol(var.id),
                      var.def.definition_spelling.value());
    if (var.def.definition_extent.has_value())
      add_outline(id_map.ToSymbol(var.id), var.def.definition_extent.value());
    for (const Range& use : var.uses)
      add_all_symbols(id_map.ToSymbol(var.id), use);
  }

  std::sort(def.outline.begin(), def.outline.end(),
            [](const SymbolRef& a, const SymbolRef& b) {
              return a.loc.range.start < b.loc.range.start;
            });
  std::sort(def.all_symbols.begin(), def.all_symbols.end(),
            [](const SymbolRef& a, const SymbolRef& b) {
              return a.loc.range.start < b.loc.range.start;
            });

  return def;
}

inline optional<QueryFileId> GetQueryFileIdFromPath(QueryDatabase* query_db,
                                                    const std::string& path,
                                                    bool create_if_missing) {
  auto it = query_db->usr_to_file.find(LowerPathIfCaseInsensitive(path));
  if (it != query_db->usr_to_file.end())
    return QueryFileId(it->second.id);
  if (!create_if_missing)
    return {};

  size_t idx = query_db->files.size();
  query_db->usr_to_file[LowerPathIfCaseInsensitive(path)] = QueryFileId(idx);
  query_db->files.push_back(QueryFile(path));
  return QueryFileId(idx);
}

inline optional<QueryTypeId> GetQueryTypeIdFromUsr(QueryDatabase* query_db,
                                                   Usr usr,
                                                   bool create_if_missing) {
  auto it = query_db->usr_to_type.find(usr);
  if (it != query_db->usr_to_type.end())
    return QueryTypeId(it->second.id);
  if (!create_if_missing)
    return {};

  size_t idx = query_db->types.size();
  query_db->usr_to_type[usr] = QueryTypeId(idx);
  query_db->types.push_back(QueryType(usr));
  return QueryTypeId(idx);
}

inline optional<QueryFuncId> GetQueryFuncIdFromUsr(QueryDatabase* query_db,
                                            Usr usr,
                                            bool create_if_missing) {
  auto it = query_db->usr_to_func.find(usr);
  if (it != query_db->usr_to_func.end())
    return QueryFuncId(it->second.id);
  if (!create_if_missing)
    return {};

  size_t idx = query_db->funcs.size();
  query_db->usr_to_func[usr] = QueryFuncId(idx);
  query_db->funcs.push_back(QueryFunc(usr));
  return QueryFuncId(idx);
}

inline optional<QueryVarId> GetQueryVarIdFromUsr(QueryDatabase* query_db,
                                          Usr usr,
                                          bool create_if_missing) {
  auto it = query_db->usr_to_var.find(usr);
  if (it != query_db->usr_to_var.end())
    return QueryVarId(it->second.id);
  if (!create_if_missing)
    return {};

  size_t idx = query_db->vars.size();
  query_db->usr_to_var[usr] = QueryVarId(idx);
  query_db->vars.push_back(QueryVar(usr));
  return QueryVarId(idx);
}

}  // namespace

optional<QueryFileId> QueryDatabase::GetQueryFileIdFromPath(
    const std::string& path) {
  return ::GetQueryFileIdFromPath(this, path, false);
}

optional<QueryTypeId> QueryDatabase::GetQueryTypeIdFromUsr(Usr usr) {
  return ::GetQueryTypeIdFromUsr(this, usr, false);
}

optional<QueryFuncId> QueryDatabase::GetQueryFuncIdFromUsr(Usr usr) {
  return ::GetQueryFuncIdFromUsr(this, usr, false);
}

optional<QueryVarId> QueryDatabase::GetQueryVarIdFromUsr(Usr usr) {
  return ::GetQueryVarIdFromUsr(this, usr, false);
}

IdMap::IdMap(QueryDatabase* query_db, const IdCache& local_ids)
    : local_ids(local_ids) {
  // LOG_S(INFO) << "Creating IdMap for " << local_ids.primary_file;
  primary_file =
      GetQueryFileIdFromPath(query_db, local_ids.primary_file, true).value();

  cached_type_ids_.resize(local_ids.type_id_to_usr.size());
  for (const auto& entry : local_ids.type_id_to_usr)
    cached_type_ids_[entry.first] =
        GetQueryTypeIdFromUsr(query_db, entry.second, true).value();

  cached_func_ids_.resize(local_ids.func_id_to_usr.size());
  for (const auto& entry : local_ids.func_id_to_usr)
    cached_func_ids_[entry.first] =
        GetQueryFuncIdFromUsr(query_db, entry.second, true).value();

  cached_var_ids_.resize(local_ids.var_id_to_usr.size());
  for (const auto& entry : local_ids.var_id_to_usr)
    cached_var_ids_[entry.first] =
        GetQueryVarIdFromUsr(query_db, entry.second, true).value();
}

QueryLocation IdMap::ToQuery(Range range) const {
  return QueryLocation(primary_file, range);
}
QueryTypeId IdMap::ToQuery(IndexTypeId id) const {
  assert(cached_type_ids_.find(id) != cached_type_ids_.end());
  return QueryTypeId(cached_type_ids_.find(id)->second);
}
QueryFuncId IdMap::ToQuery(IndexFuncId id) const {
  if (id.id == -1)
    return QueryFuncId((size_t)-1);
  assert(cached_func_ids_.find(id) != cached_func_ids_.end());
  return QueryFuncId(cached_func_ids_.find(id)->second);
}
QueryVarId IdMap::ToQuery(IndexVarId id) const {
  assert(cached_var_ids_.find(id) != cached_var_ids_.end());
  return QueryVarId(cached_var_ids_.find(id)->second);
}
QueryFuncRef IdMap::ToQuery(IndexFuncRef ref) const {
  return QueryFuncRef(ToQuery(ref.id), ToQuery(ref.loc), ref.is_implicit);
}
QueryLocation IdMap::ToQuery(IndexFunc::Declaration decl) const {
  // TODO: expose more than just QueryLocation.
  return QueryLocation(primary_file, decl.spelling);
}

optional<QueryLocation> IdMap::ToQuery(optional<Range> range) const {
  if (!range)
    return nullopt;
  return ToQuery(range.value());
}
optional<QueryTypeId> IdMap::ToQuery(optional<IndexTypeId> id) const {
  if (!id)
    return nullopt;
  return ToQuery(id.value());
}
optional<QueryFuncId> IdMap::ToQuery(optional<IndexFuncId> id) const {
  if (!id)
    return nullopt;
  return ToQuery(id.value());
}
optional<QueryVarId> IdMap::ToQuery(optional<IndexVarId> id) const {
  if (!id)
    return nullopt;
  return ToQuery(id.value());
}
optional<QueryFuncRef> IdMap::ToQuery(optional<IndexFuncRef> ref) const {
  if (!ref)
    return nullopt;
  return ToQuery(ref.value());
}
optional<QueryLocation> IdMap::ToQuery(
    optional<IndexFunc::Declaration> decl) const {
  if (!decl)
    return nullopt;
  return ToQuery(decl.value());
}

template <typename In, typename Out>
std::vector<Out> ToQueryTransform(const IdMap& id_map,
                                  const std::vector<In>& input) {
  std::vector<Out> result;
  result.reserve(input.size());
  for (const In& in : input)
    result.push_back(id_map.ToQuery(in));
  return result;
}
std::vector<QueryLocation> IdMap::ToQuery(std::vector<Range> ranges) const {
  return ToQueryTransform<Range, QueryLocation>(*this, ranges);
}
std::vector<QueryTypeId> IdMap::ToQuery(std::vector<IndexTypeId> ids) const {
  return ToQueryTransform<IndexTypeId, QueryTypeId>(*this, ids);
}
std::vector<QueryFuncId> IdMap::ToQuery(std::vector<IndexFuncId> ids) const {
  return ToQueryTransform<IndexFuncId, QueryFuncId>(*this, ids);
}
std::vector<QueryVarId> IdMap::ToQuery(std::vector<IndexVarId> ids) const {
  return ToQueryTransform<IndexVarId, QueryVarId>(*this, ids);
}
std::vector<QueryFuncRef> IdMap::ToQuery(std::vector<IndexFuncRef> refs) const {
  return ToQueryTransform<IndexFuncRef, QueryFuncRef>(*this, refs);
}
std::vector<QueryLocation> IdMap::ToQuery(
    std::vector<IndexFunc::Declaration> decls) const {
  return ToQueryTransform<IndexFunc::Declaration, QueryLocation>(*this, decls);
}

SymbolIdx IdMap::ToSymbol(IndexTypeId id) const {
  return SymbolIdx(SymbolKind::Type, ToQuery(id).id);
}
SymbolIdx IdMap::ToSymbol(IndexFuncId id) const {
  return SymbolIdx(SymbolKind::Func, ToQuery(id).id);
}
SymbolIdx IdMap::ToSymbol(IndexVarId id) const {
  return SymbolIdx(SymbolKind::Var, ToQuery(id).id);
}

// ----------------------
// INDEX THREAD FUNCTIONS
// ----------------------

// static
IndexUpdate IndexUpdate::CreateDelta(const IdMap* previous_id_map,
                                     const IdMap* current_id_map,
                                     IndexFile* previous,
                                     IndexFile* current) {
  // This function runs on an indexer thread.

  if (!previous_id_map) {
    assert(!previous);
    IndexFile empty(current->path, nullopt);
    return IndexUpdate(*current_id_map, *current_id_map, empty, *current);
  }
  return IndexUpdate(*previous_id_map, *current_id_map, *previous, *current);
}

IndexUpdate::IndexUpdate(const IdMap& previous_id_map,
                         const IdMap& current_id_map,
                         IndexFile& previous_file,
                         IndexFile& current_file) {
// This function runs on an indexer thread.

// |query_name| is the name of the variable on the query type.
// |index_name| is the name of the variable on the index type.
// |type| is the type of the variable.
#define PROCESS_UPDATE_DIFF(type_id, query_name, index_name, type)           \
  {                                                                          \
    /* Check for changes. */                                                 \
    std::vector<type> removed, added;                                        \
    auto query_previous = previous_id_map.ToQuery(previous->index_name);     \
    auto query_current = current_id_map.ToQuery(current->index_name);        \
    bool did_add = ComputeDifferenceForUpdate(query_previous, query_current, \
                                              &removed, &added);             \
    if (did_add) {                                                           \
      query_name.push_back(MergeableUpdate<type_id, type>(                   \
          current_id_map.ToQuery(current->id), added, removed));             \
    }                                                                        \
  }
  // File
  files_def_update.push_back(BuildFileDef(current_id_map, current_file));

  // **NOTE** We only remove entries if they were defined in the previous index.
  // For example, if a type is included from another file it will be defined
  // simply so we can attribute the usage/reference to it. If the reference goes
  // away we don't want to remove the type/func/var usage.

  // Types
  CompareGroups<IndexType>(
      previous_file.types, current_file.types,
      /*onRemoved:*/
      [this, &previous_id_map](IndexType* type) {
        if (type->def.definition_spelling)
          types_removed.push_back(type->usr);
        else {
          if (!type->derived.empty())
            types_derived.push_back(QueryType::DerivedUpdate(
                previous_id_map.ToQuery(type->id), {},
                previous_id_map.ToQuery(type->derived)));
          if (!type->instances.empty())
            types_instances.push_back(QueryType::InstancesUpdate(
                previous_id_map.ToQuery(type->id), {},
                previous_id_map.ToQuery(type->instances)));
          if (!type->uses.empty())
            types_uses.push_back(
                QueryType::UsesUpdate(previous_id_map.ToQuery(type->id), {},
                                      previous_id_map.ToQuery(type->uses)));
        }
      },
      /*onAdded:*/
      [this, &current_id_map](IndexType* type) {
        optional<QueryType::Def> def_update =
            ToQuery(current_id_map, type->def);
        if (def_update)
          types_def_update.push_back(
              QueryType::DefUpdate(type->usr, *def_update));
        if (!type->derived.empty())
          types_derived.push_back(
              QueryType::DerivedUpdate(current_id_map.ToQuery(type->id),
                                       current_id_map.ToQuery(type->derived)));
        if (!type->instances.empty())
          types_instances.push_back(QueryType::InstancesUpdate(
              current_id_map.ToQuery(type->id),
              current_id_map.ToQuery(type->instances)));
        if (!type->uses.empty())
          types_uses.push_back(
              QueryType::UsesUpdate(current_id_map.ToQuery(type->id),
                                    current_id_map.ToQuery(type->uses)));
      },
      /*onFound:*/
      [this, &previous_id_map, &current_id_map](IndexType* previous,
                                                IndexType* current) {
        optional<QueryType::Def> previous_remapped_def =
            ToQuery(previous_id_map, previous->def);
        optional<QueryType::Def> current_remapped_def =
            ToQuery(current_id_map, current->def);
        if (current_remapped_def &&
            previous_remapped_def != current_remapped_def &&
            !current_remapped_def->detailed_name.empty()) {
          types_def_update.push_back(
              QueryType::DefUpdate(current->usr, *current_remapped_def));
        }

        PROCESS_UPDATE_DIFF(QueryTypeId, types_derived, derived, QueryTypeId);
        PROCESS_UPDATE_DIFF(QueryTypeId, types_instances, instances,
                            QueryVarId);
        PROCESS_UPDATE_DIFF(QueryTypeId, types_uses, uses, QueryLocation);
      });

  // Functions
  CompareGroups<IndexFunc>(
      previous_file.funcs, current_file.funcs,
      /*onRemoved:*/
      [this, &previous_id_map](IndexFunc* func) {
        if (func->def.definition_spelling) {
          funcs_removed.push_back(func->usr);
        } else {
          if (!func->declarations.empty())
            funcs_declarations.push_back(QueryFunc::DeclarationsUpdate(
                previous_id_map.ToQuery(func->id), {},
                previous_id_map.ToQuery(func->declarations)));
          if (!func->derived.empty())
            funcs_derived.push_back(QueryFunc::DerivedUpdate(
                previous_id_map.ToQuery(func->id), {},
                previous_id_map.ToQuery(func->derived)));
          if (!func->callers.empty())
            funcs_callers.push_back(QueryFunc::CallersUpdate(
                previous_id_map.ToQuery(func->id), {},
                previous_id_map.ToQuery(func->callers)));
        }
      },
      /*onAdded:*/
      [this, &current_id_map](IndexFunc* func) {
        optional<QueryFunc::Def> def_update =
            ToQuery(current_id_map, func->def);
        if (def_update)
          funcs_def_update.push_back(
              QueryFunc::DefUpdate(func->usr, *def_update));
        if (!func->declarations.empty())
          funcs_declarations.push_back(QueryFunc::DeclarationsUpdate(
              current_id_map.ToQuery(func->id),
              current_id_map.ToQuery(func->declarations)));
        if (!func->derived.empty())
          funcs_derived.push_back(
              QueryFunc::DerivedUpdate(current_id_map.ToQuery(func->id),
                                       current_id_map.ToQuery(func->derived)));
        if (!func->callers.empty())
          funcs_callers.push_back(
              QueryFunc::CallersUpdate(current_id_map.ToQuery(func->id),
                                       current_id_map.ToQuery(func->callers)));
      },
      /*onFound:*/
      [this, &previous_id_map, &current_id_map](IndexFunc* previous,
                                                IndexFunc* current) {
        optional<QueryFunc::Def> previous_remapped_def =
            ToQuery(previous_id_map, previous->def);
        optional<QueryFunc::Def> current_remapped_def =
            ToQuery(current_id_map, current->def);
        if (current_remapped_def &&
            previous_remapped_def != current_remapped_def &&
            !current_remapped_def->detailed_name.empty()) {
          funcs_def_update.push_back(
              QueryFunc::DefUpdate(current->usr, *current_remapped_def));
        }

        PROCESS_UPDATE_DIFF(QueryFuncId, funcs_declarations, declarations,
                            QueryLocation);
        PROCESS_UPDATE_DIFF(QueryFuncId, funcs_derived, derived, QueryFuncId);
        PROCESS_UPDATE_DIFF(QueryFuncId, funcs_callers, callers, QueryFuncRef);
      });

  // Variables
  CompareGroups<IndexVar>(
      previous_file.vars, current_file.vars,
      /*onRemoved:*/
      [this, &previous_id_map](IndexVar* var) {
        if (var->def.definition_spelling) {
          vars_removed.push_back(var->usr);
        } else {
          if (!var->uses.empty())
            vars_uses.push_back(
                QueryVar::UsesUpdate(previous_id_map.ToQuery(var->id), {},
                                     previous_id_map.ToQuery(var->uses)));
        }
      },
      /*onAdded:*/
      [this, &current_id_map](IndexVar* var) {
        optional<QueryVar::Def> def_update = ToQuery(current_id_map, var->def);
        if (def_update)
          vars_def_update.push_back(QueryVar::DefUpdate(var->usr, *def_update));
        if (!var->uses.empty())
          vars_uses.push_back(
              QueryVar::UsesUpdate(current_id_map.ToQuery(var->id),
                                   current_id_map.ToQuery(var->uses)));
      },
      /*onFound:*/
      [this, &previous_id_map, &current_id_map](IndexVar* previous,
                                                IndexVar* current) {
        optional<QueryVar::Def> previous_remapped_def =
            ToQuery(previous_id_map, previous->def);
        optional<QueryVar::Def> current_remapped_def =
            ToQuery(current_id_map, current->def);
        if (current_remapped_def &&
            previous_remapped_def != current_remapped_def &&
            !current_remapped_def->detailed_name.empty())
          vars_def_update.push_back(
              QueryVar::DefUpdate(current->usr, *current_remapped_def));

        PROCESS_UPDATE_DIFF(QueryVarId, vars_uses, uses, QueryLocation);
      });

#undef PROCESS_UPDATE_DIFF
}

// This function runs on an indexer thread.
void IndexUpdate::Merge(const IndexUpdate& update) {
#define INDEX_UPDATE_APPEND(name) AddRange(&name, update.name);
#define INDEX_UPDATE_MERGE(name) AddMergeableRange(&name, update.name);

  INDEX_UPDATE_APPEND(files_removed);
  INDEX_UPDATE_APPEND(files_def_update);

  INDEX_UPDATE_APPEND(types_removed);
  INDEX_UPDATE_APPEND(types_def_update);
  INDEX_UPDATE_MERGE(types_derived);
  INDEX_UPDATE_MERGE(types_instances);
  INDEX_UPDATE_MERGE(types_uses);

  INDEX_UPDATE_APPEND(funcs_removed);
  INDEX_UPDATE_APPEND(funcs_def_update);
  INDEX_UPDATE_MERGE(funcs_declarations);
  INDEX_UPDATE_MERGE(funcs_derived);
  INDEX_UPDATE_MERGE(funcs_callers);

  INDEX_UPDATE_APPEND(vars_removed);
  INDEX_UPDATE_APPEND(vars_def_update);
  INDEX_UPDATE_MERGE(vars_uses);

#undef INDEX_UPDATE_APPEND
#undef INDEX_UPDATE_MERGE
}

std::string IndexUpdate::ToString() {
  rapidjson::StringBuffer output;
  rapidjson::Writer<rapidjson::StringBuffer> writer;
  JsonWriter json_writer(&writer);
  IndexUpdate& update = *this;
  Reflect(json_writer, update);
  return output.GetString();
}

// ------------------------
// QUERYDB THREAD FUNCTIONS
// ------------------------

void QueryDatabase::RemoveUsrs(SymbolKind usr_kind,
                               const std::vector<Usr>& to_remove) {
  // This function runs on the querydb thread.

  // When we remove an element, we just erase the state from the storage. We do
  // not update array indices because that would take a huge amount of time for
  // a very large index.
  //
  // There means that there is some memory growth that will never be reclaimed,
  // but it should be pretty minimal and is solved by simply restarting the
  // indexer and loading from cache, which is a fast operation.
  //
  // TODO: Add "cquery: Reload Index" command which unloads all querydb state
  // and fully reloads from cache. This will address the memory leak above.

  switch (usr_kind) {
    case SymbolKind::Type: {
      for (const Usr& usr : to_remove)
        types[usr_to_type[usr].id].def = nullopt;
      break;
    }
    case SymbolKind::Func: {
      for (const Usr& usr : to_remove)
        funcs[usr_to_func[usr].id].def = nullopt;
      break;
    }
    case SymbolKind::Var: {
      for (const Usr& usr : to_remove)
        vars[usr_to_var[usr].id].def = nullopt;
      break;
    }
    case SymbolKind::File:
    case SymbolKind::Invalid:
      break;
  }
}

void QueryDatabase::ApplyIndexUpdate(IndexUpdate* update) {
// This function runs on the querydb thread.

// Example types:
//  storage_name       =>  std::vector<optional<QueryType>>
//  merge_update       =>  QueryType::DerivedUpdate =>
//  MergeableUpdate<QueryTypeId, QueryTypeId> def                =>  QueryType
//  def->def_var_name  =>  std::vector<QueryTypeId>
#define HANDLE_MERGEABLE(update_var_name, def_var_name, storage_name) \
  for (auto merge_update : update->update_var_name) {                 \
    auto& def = storage_name[merge_update.id.id];                     \
    AddRange(&def.def_var_name, merge_update.to_add);                 \
    RemoveRange(&def.def_var_name, merge_update.to_remove);           \
    VerifyUnique(def.def_var_name);                                   \
  }

  for (const std::string& filename : update->files_removed)
   files[usr_to_file[filename].id].def = nullopt;
  ImportOrUpdate(update->files_def_update);

  RemoveUsrs(SymbolKind::Type, update->types_removed);
  ImportOrUpdate(update->types_def_update);
  HANDLE_MERGEABLE(types_derived, derived, types);
  HANDLE_MERGEABLE(types_instances, instances, types);
  HANDLE_MERGEABLE(types_uses, uses, types);

  RemoveUsrs(SymbolKind::Func, update->funcs_removed);
  ImportOrUpdate(update->funcs_def_update);
  HANDLE_MERGEABLE(funcs_declarations, declarations, funcs);
  HANDLE_MERGEABLE(funcs_derived, derived, funcs);
  HANDLE_MERGEABLE(funcs_callers, callers, funcs);

  RemoveUsrs(SymbolKind::Var, update->vars_removed);
  ImportOrUpdate(update->vars_def_update);
  HANDLE_MERGEABLE(vars_uses, uses, vars);

#undef HANDLE_MERGEABLE
}

void QueryDatabase::ImportOrUpdate(
    const std::vector<QueryFile::DefUpdate>& updates) {
  // This function runs on the querydb thread.

  for (auto& def : updates) {
    auto it = usr_to_file.find(LowerPathIfCaseInsensitive(def.path));
    assert(it != usr_to_file.end());

    QueryFile& existing = files[it->second.id];

    existing.def = def;
    UpdateDetailedNames(&existing.detailed_name_idx, SymbolKind::File,
                        it->second.id, def.path, def.path);
  }
}

void QueryDatabase::ImportOrUpdate(
    const std::vector<QueryType::DefUpdate>& updates) {
  // This function runs on the querydb thread.

  for (auto& def : updates) {
    assert(!def.value.detailed_name.empty());

    auto it = usr_to_type.find(def.usr);
    assert(it != usr_to_type.end());

    assert(it->second.id >= 0 && it->second.id < types.size());
    QueryType& existing = types[it->second.id];

    // Keep the existing definition if it is higher quality.
    if (existing.def && existing.def->definition_spelling &&
        !def.value.definition_spelling)
      continue;

    existing.def = def.value;
    UpdateDetailedNames(&existing.detailed_name_idx, SymbolKind::Type,
                        it->second.id, def.value.short_name,
                        def.value.detailed_name);
  }
}

void QueryDatabase::ImportOrUpdate(
    const std::vector<QueryFunc::DefUpdate>& updates) {
  // This function runs on the querydb thread.

  for (auto& def : updates) {
    assert(!def.value.detailed_name.empty());

    auto it = usr_to_func.find(def.usr);
    assert(it != usr_to_func.end());

    assert(it->second.id >= 0 && it->second.id < funcs.size());
    QueryFunc& existing = funcs[it->second.id];

    // Keep the existing definition if it is higher quality.
    if (existing.def && existing.def->definition_spelling &&
        !def.value.definition_spelling)
      continue;

    existing.def = def.value;
    UpdateDetailedNames(&existing.detailed_name_idx, SymbolKind::Func,
                        it->second.id, def.value.short_name,
                        def.value.detailed_name);
  }
}

void QueryDatabase::ImportOrUpdate(
    const std::vector<QueryVar::DefUpdate>& updates) {
  // This function runs on the querydb thread.

  for (auto& def : updates) {
    assert(!def.value.detailed_name.empty());

    auto it = usr_to_var.find(def.usr);
    assert(it != usr_to_var.end());

    assert(it->second.id >= 0 && it->second.id < vars.size());
    QueryVar& existing = vars[it->second.id];

    // Keep the existing definition if it is higher quality.
    if (existing.def && existing.def->definition_spelling &&
        !def.value.definition_spelling)
      continue;

    existing.def = def.value;
    if (!def.value.is_local())
      UpdateDetailedNames(&existing.detailed_name_idx, SymbolKind::Var,
                          it->second.id, def.value.short_name,
                          def.value.detailed_name);
  }
}

void QueryDatabase::UpdateDetailedNames(size_t* qualified_name_index,
                                        SymbolKind kind,
                                        size_t symbol_index,
                                        const std::string& short_name,
                                        const std::string& detailed_name) {
  if (*qualified_name_index == -1) {
    short_names.push_back(short_name);
    detailed_names.push_back(detailed_name);
    symbols.push_back(SymbolIdx(kind, symbol_index));
    *qualified_name_index = detailed_names.size() - 1;
  } else {
    short_names[*qualified_name_index] = short_name;
    detailed_names[*qualified_name_index] = detailed_name;
  }
}

TEST_SUITE("query") {
  IndexUpdate GetDelta(IndexFile previous, IndexFile current) {
    QueryDatabase db;
    IdMap previous_map(&db, previous.id_cache);
    IdMap current_map(&db, current.id_cache);
    return IndexUpdate::CreateDelta(&previous_map, &current_map, &previous,
                                    &current);
  }

  TEST_CASE("remove defs") {
    IndexFile previous("foo.cc", nullopt);
    IndexFile current("foo.cc", nullopt);

    previous.Resolve(previous.ToTypeId(HashUsr("usr1")))
        ->def.definition_spelling = Range(Position(1, 0));
    previous.Resolve(previous.ToFuncId(HashUsr("usr2")))
        ->def.definition_spelling = Range(Position(2, 0));
    previous.Resolve(previous.ToVarId(HashUsr("usr3")))
        ->def.definition_spelling = Range(Position(3, 0));

    IndexUpdate update = GetDelta(previous, current);

    REQUIRE(update.types_removed == std::vector<Usr>{HashUsr("usr1")});
    REQUIRE(update.funcs_removed == std::vector<Usr>{HashUsr("usr2")});
    REQUIRE(update.vars_removed == std::vector<Usr>{HashUsr("usr3")});
  }

  TEST_CASE("do not remove ref-only defs") {
    IndexFile previous("foo.cc", nullopt);
    IndexFile current("foo.cc", nullopt);

    previous.Resolve(previous.ToTypeId(HashUsr("usr1")))
        ->uses.push_back(Range(Position(1, 0)));
    previous.Resolve(previous.ToFuncId(HashUsr("usr2")))
        ->callers.push_back(IndexFuncRef(IndexFuncId(0), Range(Position(2, 0)),
                                         false /*is_implicit*/));
    previous.Resolve(previous.ToVarId(HashUsr("usr3")))
        ->uses.push_back(Range(Position(3, 0)));

    IndexUpdate update = GetDelta(previous, current);

    REQUIRE(update.types_removed == std::vector<Usr>{});
    REQUIRE(update.funcs_removed == std::vector<Usr>{});
    REQUIRE(update.vars_removed == std::vector<Usr>{});
  }

  TEST_CASE("func callers") {
    IndexFile previous("foo.cc", nullopt);
    IndexFile current("foo.cc", nullopt);

    IndexFunc* pf = previous.Resolve(previous.ToFuncId(HashUsr("usr")));
    IndexFunc* cf = current.Resolve(current.ToFuncId(HashUsr("usr")));

    pf->callers.push_back(IndexFuncRef(IndexFuncId(0), Range(Position(1, 0)),
                                       false /*is_implicit*/));
    cf->callers.push_back(IndexFuncRef(IndexFuncId(0), Range(Position(2, 0)),
                                       false /*is_implicit*/));

    IndexUpdate update = GetDelta(previous, current);

    REQUIRE(update.funcs_removed == std::vector<Usr>{});
    REQUIRE(update.funcs_callers.size() == 1);
    REQUIRE(update.funcs_callers[0].id == QueryFuncId(0));
    REQUIRE(update.funcs_callers[0].to_remove.size() == 1);
    REQUIRE(update.funcs_callers[0].to_remove[0].loc.range ==
            Range(Position(1, 0)));
    REQUIRE(update.funcs_callers[0].to_add.size() == 1);
    REQUIRE(update.funcs_callers[0].to_add[0].loc.range ==
            Range(Position(2, 0)));
  }

  TEST_CASE("type usages") {
    IndexFile previous("foo.cc", nullopt);
    IndexFile current("foo.cc", nullopt);

    IndexType* pt = previous.Resolve(previous.ToTypeId(HashUsr("usr")));
    IndexType* ct = current.Resolve(current.ToTypeId(HashUsr("usr")));

    pt->uses.push_back(Range(Position(1, 0)));
    ct->uses.push_back(Range(Position(2, 0)));

    IndexUpdate update = GetDelta(previous, current);

    REQUIRE(update.types_removed == std::vector<Usr>{});
    REQUIRE(update.types_def_update.empty());
    REQUIRE(update.types_uses.size() == 1);
    REQUIRE(update.types_uses[0].to_remove.size() == 1);
    REQUIRE(update.types_uses[0].to_remove[0].range == Range(Position(1, 0)));
    REQUIRE(update.types_uses[0].to_add.size() == 1);
    REQUIRE(update.types_uses[0].to_add[0].range == Range(Position(2, 0)));
  }

  TEST_CASE("apply delta") {
    IndexFile previous("foo.cc", nullopt);
    IndexFile current("foo.cc", nullopt);

    IndexFunc* pf = previous.Resolve(previous.ToFuncId(HashUsr("usr")));
    IndexFunc* cf = current.Resolve(current.ToFuncId(HashUsr("usr")));
    pf->callers.push_back(IndexFuncRef(IndexFuncId(0), Range(Position(1, 0)),
                                       false /*is_implicit*/));
    pf->callers.push_back(IndexFuncRef(IndexFuncId(0), Range(Position(2, 0)),
                                       false /*is_implicit*/));
    cf->callers.push_back(IndexFuncRef(IndexFuncId(0), Range(Position(4, 0)),
                                       false /*is_implicit*/));
    cf->callers.push_back(IndexFuncRef(IndexFuncId(0), Range(Position(5, 0)),
                                       false /*is_implicit*/));

    QueryDatabase db;
    IdMap previous_map(&db, previous.id_cache);
    IdMap current_map(&db, current.id_cache);
    REQUIRE(db.funcs.size() == 1);

    IndexUpdate import_update =
        IndexUpdate::CreateDelta(nullptr, &previous_map, nullptr, &previous);
    IndexUpdate delta_update = IndexUpdate::CreateDelta(
        &previous_map, &current_map, &previous, &current);

    db.ApplyIndexUpdate(&import_update);
    REQUIRE(db.funcs[0].callers.size() == 2);
    REQUIRE(db.funcs[0].callers[0].loc.range == Range(Position(1, 0)));
    REQUIRE(db.funcs[0].callers[1].loc.range == Range(Position(2, 0)));

    db.ApplyIndexUpdate(&delta_update);
    REQUIRE(db.funcs[0].callers.size() == 2);
    REQUIRE(db.funcs[0].callers[0].loc.range == Range(Position(4, 0)));
    REQUIRE(db.funcs[0].callers[1].loc.range == Range(Position(5, 0)));
  }
}