/*
 * This source code is released into the public domain.
 */

module;

#include <cassert>
#include <cstdint>
#include <cstdlib>
#include <format>
#include <memory>
#include <optional>
#include <string>
#include <system_error>

#include <ucl.h>

export module nihil.ucl:map;

import :object;

namespace nihil::ucl {

// Exception thrown when map::operator[] does not find the key.
export struct key_not_found : error {
	key_not_found(std::string_view key)
		: error(std::format("key '{}' not found in map", key))
		, m_key(key)
	{}

	auto key(this key_not_found const &self) -> std::string_view
	{
		return self.m_key;
	}
	
private:
	std::string m_key;
};

export template<datatype T>
struct map;

template<datatype T>
struct map_iterator {
	using difference_type = std::ptrdiff_t;
	using value_type = std::pair<std::string_view, T>;
	using reference = value_type &;
	using const_reference = value_type const &;
	using pointer = value_type *;
	using const_pointer = value_type const *;

	struct sentinel{};

	[[nodiscard]] auto operator==(this map_iterator const &self, sentinel)
		-> bool
	{
		return (self.m_state->cur == nullptr);
	}

	auto operator++(this map_iterator &self) -> map_iterator &
	{
		self.m_state->next();
		return self;
	}

	auto operator++(this map_iterator &self, int) -> map_iterator &
	{
		self.m_state->next();
		return self;
	}

	[[nodiscard]] auto operator*(this map_iterator const &self)
		-> value_type
	{
		auto obj = T(ref, self.m_state->cur);
		return {obj.key(), std::move(obj)};
	}

private:
	friend struct map<T>;

	map_iterator(::ucl_object_t const *obj)
		: m_state(std::make_shared<state>(obj))
	{
		++(*this);
	}

	struct state {
		state(::ucl_object_t const *obj)
		{
			iter = ::ucl_object_iterate_new(obj);
			if (iter == nullptr)
				throw std::system_error(make_error_code(
					std::errc(errno)));
		}

		state(state const &) = delete;
		auto operator=(this state &, state const &) -> state& = delete;

		~state()
		{
			if (iter != nullptr)
				::ucl_object_iterate_free(iter);
		}

		auto next() -> void
		{
			cur = ::ucl_object_iterate_safe(iter, true);
		}

		ucl_object_iter_t iter = nullptr;
		ucl_object_t const *cur = nullptr;
	};

	std::shared_ptr<state> m_state;
};

export template<datatype T = object>
struct map final : object {
	inline static constexpr object_type ucl_type = object_type::object;

	using value_type = std::pair<std::string_view, T>;
	using size_type = std::size_t;
	using difference_type = std::ptrdiff_t;
	using iterator = map_iterator<T>;

	/*
	 * Create an empty map.  Throws std::system_error on failure.
	 */
	map()	: object(noref, [] {
			auto *uobj = ::ucl_object_typed_new(UCL_OBJECT);
			if (uobj == nullptr)
				throw std::system_error(
					std::make_error_code(std::errc(errno)));
			return uobj;
		}())
	{
	}

	/*
	 * Create a map from a UCL object.  Throws type_mismatch on failure.
	 *
	 * Unlike object_cast<>, this does not check the type of the contained
	 * elements, which means object access can throw type_mismatch.
	 */
	map(ref_t, ::ucl_object_t const *uobj)
		: object(nihil::ucl::ref, [&] {
			auto actual_type = static_cast<object_type>(
						::ucl_object_type(uobj));
			if (actual_type != map::ucl_type)
				throw type_mismatch(map::ucl_type,
						    actual_type);
			return uobj;
		}())
	{
		if (type() != ucl_type)
			throw type_mismatch(ucl_type, type());
	}

	map(noref_t, ::ucl_object_t *uobj)
		: object(nihil::ucl::noref, [&] {
			auto actual_type = static_cast<object_type>(
						::ucl_object_type(uobj));
			if (actual_type != map::ucl_type)
				throw type_mismatch(map::ucl_type,
						    actual_type);
			return uobj;
		}())
	{
	}

	/*
	 * Create a map from an iterator pair.
	 */
	template<std::input_iterator Iterator>
	requires(std::convertible_to<std::iter_value_t<Iterator>, value_type>)
	map(Iterator first, Iterator last)
		 : map()
	{
		// This is exception safe, because if we throw here the
		// base class destructor will free the map.
		while (first != last) {
			insert(*first);
			++first;
		}
	}

	/*
	 * Create a map from a range.
	 */
	template<std::ranges::range Range>
	requires(std::convertible_to<std::ranges::range_value_t<Range>,
		 		     value_type>)
	map(std::from_range_t, Range &&range)
		 : map(std::ranges::begin(range),
		       std::ranges::end(range))
	{
	}

	/*
	 * Create a map from an initializer_list.
	 */
	map(std::initializer_list<value_type> const &list)
		 : map(std::ranges::begin(list), std::ranges::end(list))
	{
	}

	/*
	 * Map iterator access.
	 */

	[[nodiscard]] auto begin(this map const &self) -> iterator
	{
		return {self.get_ucl_object()};
	}

	[[nodiscard]] auto end(this map const &) -> iterator::sentinel
	{
		return {};
	}

	/*
	 * Reserve space for future insertions.
	 */
	auto reserve(this map &self, size_type nelems) -> void
	{
		::ucl_object_reserve(self.get_ucl_object(), nelems);
	}

	/*
	 * Add an element to the map.
	 */
	auto insert(this map &self, value_type const &v) -> void
	{
		auto uobj = ::ucl_object_ref(v.second.get_ucl_object());

		::ucl_object_insert_key(self.get_ucl_object(), uobj,
					v.first.data(), v.first.size(), true);
	}

	/*
	 * Access a map element by key.
	 */
	[[nodiscard]] auto find(this map const &self, std::string_view key)
		-> std::optional<T>
	{
		auto const *obj = ::ucl_object_lookup_len(
					self.get_ucl_object(),
					key.data(), key.size());
		if (obj == nullptr)
			return {};

		return {T(nihil::ucl::ref, obj)};
	}

	/*
	 * Remove an object from the map.
	 */
	auto remove(this map &self, std::string_view key) -> bool
	{
		return ::ucl_object_delete_keyl(self.get_ucl_object(),
						key.data(), key.size());
	}

	/*
	 * Remove an object from the map and return it.
	 */
	auto pop(this map &self, std::string_view key)
		-> std::optional<T>
	{
		auto *uobj = ::ucl_object_pop_keyl(self.get_ucl_object(),
						   key.data(), key.size());
		if (uobj)
			return T(noref, uobj);
		return {};
	}

	/*
	 * Equivalent to find(), except it throws key_not_found if the key
	 * doesn't exist in the map.
	 */
	[[nodiscard]] auto operator[] (this map const &self,
				       std::string_view key)
		-> T
	{
		auto obj = self.find(key);
		if (obj)
			return *obj;
		throw key_not_found(key);
	}
};

} // namespace nihil::ucl