ClickHouse/dbms/src/Common/IFactoryWithAliases.h

#pragma once

#include <Common/Exception.h>
#include <Common/NamePrompter.h>
#include <Core/Types.h>
#include <Poco/String.h>

#include <unordered_map>

namespace DB
{

namespace ErrorCodes
{
    extern const int LOGICAL_ERROR;
}

/** If stored objects may have several names (aliases)
 * this interface may be helpful
 * template parameter is available as Creator
 */
template <typename CreatorFunc>
class IFactoryWithAliases
{
protected:
    using Creator = CreatorFunc;

    String getAliasToOrName(const String & name) const
    {
        if (aliases.count(name))
            return aliases.at(name);
        else if (String name_lowercase = Poco::toLower(name); case_insensitive_aliases.count(name_lowercase))
            return case_insensitive_aliases.at(name_lowercase);
        else
            return name;
    }

public:
    /// For compatibility with SQL, it's possible to specify that certain function name is case insensitive.
    enum CaseSensitiveness
    {
        CaseSensitive,
        CaseInsensitive
    };

    /** Register additional name for creator
     * real_name have to be already registered.
     */
    void registerAlias(const String & alias_name, const String & real_name, CaseSensitiveness case_sensitiveness = CaseSensitive)
    {
        const auto & creator_map = getCreatorMap();
        const auto & case_insensitive_creator_map = getCaseInsensitiveCreatorMap();
        const String factory_name = getFactoryName();

        String real_dict_name;
        if (creator_map.count(real_name))
            real_dict_name = real_name;
        else if (auto real_name_lowercase = Poco::toLower(real_name); case_insensitive_creator_map.count(real_name_lowercase))
            real_dict_name = real_name_lowercase;
        else
            throw Exception(factory_name + ": can't create alias '" + alias_name + "', the real name '" + real_name + "' is not registered",
                ErrorCodes::LOGICAL_ERROR);

        String alias_name_lowercase = Poco::toLower(alias_name);

        if (creator_map.count(alias_name) || case_insensitive_creator_map.count(alias_name_lowercase))
            throw Exception(
                factory_name + ": the alias name '" + alias_name + "' is already registered as real name", ErrorCodes::LOGICAL_ERROR);

        if (case_sensitiveness == CaseInsensitive)
            if (!case_insensitive_aliases.emplace(alias_name_lowercase, real_dict_name).second)
                throw Exception(
                    factory_name + ": case insensitive alias name '" + alias_name + "' is not unique", ErrorCodes::LOGICAL_ERROR);

        if (!aliases.emplace(alias_name, real_dict_name).second)
            throw Exception(factory_name + ": alias name '" + alias_name + "' is not unique", ErrorCodes::LOGICAL_ERROR);
    }

    std::vector<String> getAllRegisteredNames() const
    {
        std::vector<String> result;
        auto getter = [](const auto & pair) { return pair.first; };
        std::transform(getCreatorMap().begin(), getCreatorMap().end(), std::back_inserter(result), getter);
        std::transform(aliases.begin(), aliases.end(), std::back_inserter(result), getter);
        return result;
    }

    bool isCaseInsensitive(const String & name) const
    {
        String name_lowercase = Poco::toLower(name);
        return getCaseInsensitiveCreatorMap().count(name_lowercase) || case_insensitive_aliases.count(name_lowercase);
    }

    const String & aliasTo(const String & name) const
    {
        if (auto it = aliases.find(name); it != aliases.end())
            return it->second;
        else if (auto jt = case_insensitive_aliases.find(Poco::toLower(name)); jt != case_insensitive_aliases.end())
            return jt->second;

        throw Exception(getFactoryName() + ": name '" + name + "' is not alias", ErrorCodes::LOGICAL_ERROR);
    }

    bool isAlias(const String & name) const
    {
        return aliases.count(name) || case_insensitive_aliases.count(name);
    }

    std::vector<String> getHints(const String & name) const
    {
        static const auto registered_names = getAllRegisteredNames();
        return prompter.getHints(name, registered_names);
    }

    virtual ~IFactoryWithAliases() {}

private:
    using InnerMap = std::unordered_map<String, Creator>; // name -> creator
    using AliasMap = std::unordered_map<String, String>; // alias -> original type

    virtual const InnerMap & getCreatorMap() const = 0;
    virtual const InnerMap & getCaseInsensitiveCreatorMap() const = 0;
    virtual String getFactoryName() const = 0;

    /// Alias map to data_types from previous two maps
    AliasMap aliases;

    /// Case insensitive aliases
    AliasMap case_insensitive_aliases;

    /**
      * prompter for names, if a person makes a typo for some function or type, it
      * helps to find best possible match (in particular, edit distance is one or two symbols)
      */
    NamePrompter</*MistakeFactor=*/2, /*MaxNumHints=*/2> prompter;
};

}