/*
 * Copyright (C) 2017-present ScyllaDB
 *
 */

/*
 * SPDX-License-Identifier: AGPL-3.0-or-later
 */

#pragma once

#include <fmt/format.h>
#include <fmt/ostream.h>
#include <unordered_map>
#include <iosfwd>
#include <string_view>

#include <boost/program_options.hpp>

#include <seastar/core/sstring.hh>
#include <seastar/core/future.hh>
#include <seastar/util/log.hh>

#include "utils/updateable_value.hh"

#include "seastarx.hh"

namespace seastar { class file; }
namespace seastar::json { class json_return_type; }
namespace YAML { class Node; }

namespace utils {

namespace bpo = boost::program_options;

class config_type {
    std::string_view _name;
    std::function<json::json_return_type (const void*)> _to_json;
private:
    template <typename NativeType>
    std::function<json::json_return_type (const void*)> make_to_json(json::json_return_type (*func)(const NativeType&)) {
        return [func] (const void* value) {
            return func(*static_cast<const NativeType*>(value));
        };
    }
public:
    template <typename NativeType>
    config_type(std::string_view name, json::json_return_type (*to_json)(const NativeType&)) : _name(name), _to_json(make_to_json(to_json)) {}
    std::string_view name() const { return _name; }
    json::json_return_type to_json(const void* value) const;
};

template <typename T>
extern const config_type config_type_for;

class config_file {
    static thread_local unsigned s_shard_id;
    struct any_value {
        virtual ~any_value() = default;
        virtual std::unique_ptr<any_value> clone() const = 0;
        virtual void update_from(const any_value* source) = 0;
    };
    std::vector<std::vector<std::unique_ptr<any_value>>> _per_shard_values { 1 };
public:
    typedef std::unordered_map<sstring, sstring> string_map;
    typedef std::vector<sstring> string_list;

    enum class value_status {
        Used,
        Unused,
        Invalid,
    };

    enum class liveness {
        LiveUpdate,
        MustRestart,
    };

    enum class config_source : uint8_t {
        None,
        SettingsFile,
        CommandLine,
        CQL,
        Internal
    };

    struct config_src {
        config_file* _cf;
        std::string_view _name, _alias, _desc;
        const config_type* _type;
        size_t _per_shard_values_offset;
    protected:
        virtual const void* current_value() const = 0;
    public:
        config_src(config_file* cf, std::string_view name, const config_type* type, std::string_view desc)
            : _cf(cf)
            , _name(name)
            , _desc(desc)
            , _type(type)
        {}
        config_src(config_file* cf, std::string_view name, std::string_view alias, const config_type* type, std::string_view desc)
            : _cf(cf)
            , _name(name)
            , _alias(alias)
            , _desc(desc)
            , _type(type)
        {}
        virtual ~config_src() {}

        const std::string_view & name() const {
            return _name;
        }
        std::string_view alias() const {
            return _alias;
        }
        const std::string_view & desc() const {
            return _desc;
        }
        std::string_view type_name() const {
            return _type->name();
        }
        config_file * get_config_file() const {
            return _cf;
        }
        bool matches(std::string_view name) const;
        virtual void add_command_line_option(bpo::options_description_easy_init&) = 0;
        virtual void set_value(const YAML::Node&) = 0;
        virtual bool set_value(sstring, config_source = config_source::Internal) = 0;
        virtual value_status status() const noexcept = 0;
        virtual config_source source() const noexcept = 0;
        sstring source_name() const noexcept;
        json::json_return_type value_as_json() const;
    };

    template<typename T>
    struct named_value : public config_src {
    private:
        friend class config;
        config_source _source = config_source::None;
        value_status _value_status;
        struct the_value_type final : any_value {
            the_value_type(T value) : value(std::move(value)) {}
            utils::updateable_value_source<T> value;
            virtual std::unique_ptr<any_value> clone() const override {
                return std::make_unique<the_value_type>(value());
            }
            virtual void update_from(const any_value* source) override {
                auto typed_source = static_cast<const the_value_type*>(source);
                value.set(typed_source->value());
            }
        };
        liveness _liveness;
        std::vector<T> _allowed_values;
    protected:
        updateable_value_source<T>& the_value() {
            any_value* av =_cf->_per_shard_values[_cf->s_shard_id][_per_shard_values_offset].get();
            return static_cast<the_value_type*>(av)->value;
        }
        const updateable_value_source<T>& the_value() const {
            return const_cast<named_value*>(this)->the_value();
        }
        virtual const void* current_value() const override {
            return &the_value().get();
        }
    public:
        typedef T type;
        typedef named_value<T> MyType;

        named_value(config_file* file, std::string_view name, std::string_view alias, liveness liveness_, value_status vs, const T& t = T(), std::string_view desc = {},
                std::initializer_list<T> allowed_values = {})
            : config_src(file, name, alias, &config_type_for<T>, desc)
            , _value_status(vs)
            , _liveness(liveness_)
            , _allowed_values(std::move(allowed_values)) {
            file->add(*this, std::make_unique<the_value_type>(std::move(t)));
        }
        named_value(config_file* file, std::string_view name, liveness liveness_, value_status vs, const T& t = T(), std::string_view desc = {},
                std::initializer_list<T> allowed_values = {})
            : named_value(file, name, {}, liveness_, vs, t, desc) {
        }
        named_value(config_file* file, std::string_view name, std::string_view alias, value_status vs, const T& t = T(), std::string_view desc = {},
                std::initializer_list<T> allowed_values = {})
                : named_value(file, name, alias, liveness::MustRestart, vs, t, desc, allowed_values) {
        }
        named_value(config_file* file, std::string_view name, value_status vs, const T& t = T(), std::string_view desc = {},
                std::initializer_list<T> allowed_values = {})
                : named_value(file, name, {}, liveness::MustRestart, vs, t, desc, allowed_values) {
        }
        value_status status() const noexcept override {
            return _value_status;
        }
        config_source source() const noexcept override {
            return _source;
        }
        bool is_set() const {
            return _source > config_source::None;
        }
        MyType & operator()(const T& t, config_source src = config_source::Internal) {
            if (!_allowed_values.empty() && std::find(_allowed_values.begin(), _allowed_values.end(), t) == _allowed_values.end()) {
                throw std::invalid_argument(format("Invalid value for {}: got {} which is not inside the set of allowed values {}", name(), t, _allowed_values));
            }
            the_value().set(t);
            if (src > config_source::None) {
                _source = src;
            }
            return *this;
        }
        MyType & operator()(T&& t, config_source src = config_source::Internal) {
            if (!_allowed_values.empty() && std::find(_allowed_values.begin(), _allowed_values.end(), t) == _allowed_values.end()) {
                throw std::invalid_argument(format("Invalid value for {}: got {} which is not inside the set of allowed values {}", name(), t, _allowed_values));
            }
            the_value().set(std::move(t));
            if (src > config_source::None) {
                _source = src;
            }
            return *this;
        }
        void set(T&& t, config_source src = config_source::None) {
            operator()(std::move(t), src);
        }
        const T& operator()() const {
            return the_value().get();
        }

        operator updateable_value<T>() const & {
            return updateable_value<T>(the_value());
        }

        observer<T> observe(std::function<void (const T&)> callback) const {
            return the_value().observe(std::move(callback));
        }

        void add_command_line_option(bpo::options_description_easy_init&) override;
        void set_value(const YAML::Node&) override;
        bool set_value(sstring, config_source = config_source::Internal) override;
    };

    typedef std::reference_wrapper<config_src> cfg_ref;

    config_file(std::initializer_list<cfg_ref> = {});
    config_file(const config_file&) = delete;

    void add(cfg_ref, std::unique_ptr<any_value> value);
    void add(std::initializer_list<cfg_ref>);
    void add(const std::vector<cfg_ref> &);

    boost::program_options::options_description get_options_description();
    boost::program_options::options_description get_options_description(boost::program_options::options_description);

    boost::program_options::options_description_easy_init&
    add_options(boost::program_options::options_description_easy_init&);

    /**
     * Default behaviour for yaml parser is to throw on
     * unknown stuff, invalid opts or conversion errors.
     *
     * Error handling function allows overriding this.
     *
     * error: <option name>, <message>, <optional value_status>
     *
     * The last arg, opt value_status will tell you the type of
     * error occurred. If not set, the option found does not exist.
     * If invalid, it is invalid. Otherwise, a parse error.
     *
     */
    using error_handler = std::function<void(const sstring&, const sstring&, std::optional<value_status>)>;

    void read_from_yaml(const sstring&, error_handler = {});
    void read_from_yaml(const char *, error_handler = {});
    future<> read_from_file(const sstring&, error_handler = {});
    future<> read_from_file(file, error_handler = {});

    using configs = std::vector<cfg_ref>;

    configs set_values() const;
    configs unset_values() const;
    const configs& values() const {
        return _cfgs;
    }
    future<> broadcast_to_all_shards();
private:
    configs
        _cfgs;
};

template <typename T>
requires requires (const config_file::named_value<T>& nv) {
    { nv().empty() } -> std::same_as<bool>;
}
const config_file::named_value<T>& operator||(const config_file::named_value<T>& a, const config_file::named_value<T>& b) {
    return !a().empty() ? a : b;
}

extern template struct config_file::named_value<seastar::log_level>;

}