/*
 *  Created by Phil Nash on 15/6/2018.
 *
 *  Distributed under the Boost Software License, Version 1.0. (See accompanying
 *  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 */
#ifndef TWOBLUECUBES_CATCH_GENERATORS_HPP_INCLUDED
#define TWOBLUECUBES_CATCH_GENERATORS_HPP_INCLUDED

#include "catch_interfaces_generatortracker.h"
#include "catch_common.h"
#include "catch_enforce.h"

#include <memory>
#include <vector>
#include <cassert>

#include <utility>
#include <exception>

namespace Catch {

class GeneratorException : public std::exception {
    const char* const m_msg = "";

public:
    GeneratorException(const char* msg):
        m_msg(msg)
    {}

    const char* what() const noexcept override final;
};

namespace Generators {

    // !TBD move this into its own location?
    namespace pf{
        template<typename T, typename... Args>
        std::unique_ptr<T> make_unique( Args&&... args ) {
            return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
        }
    }

    template<typename T>
    struct IGenerator : GeneratorUntypedBase {
        virtual ~IGenerator() = default;

        // Returns the current element of the generator
        //
        // \Precondition The generator is either freshly constructed,
        // or the last call to `next()` returned true
        virtual T const& get() const = 0;
        using type = T;
    };

    template<typename T>
    class SingleValueGenerator final : public IGenerator<T> {
        T m_value;
    public:
        SingleValueGenerator(T const& value) : m_value( value ) {}
        SingleValueGenerator(T&& value) : m_value(std::move(value)) {}

        T const& get() const override {
            return m_value;
        }
        bool next() override {
            return false;
        }
    };

    template<typename T>
    class FixedValuesGenerator final : public IGenerator<T> {
        std::vector<T> m_values;
        size_t m_idx = 0;
    public:
        FixedValuesGenerator( std::initializer_list<T> values ) : m_values( values ) {}

        T const& get() const override {
            return m_values[m_idx];
        }
        bool next() override {
            ++m_idx;
            return m_idx < m_values.size();
        }
    };

    template <typename T>
    class GeneratorWrapper final {
        std::unique_ptr<IGenerator<T>> m_generator;
    public:
        GeneratorWrapper(std::unique_ptr<IGenerator<T>> generator):
            m_generator(std::move(generator))
        {}
        T const& get() const {
            return m_generator->get();
        }
        bool next() {
            return m_generator->next();
        }
    };

    template <typename T>
    GeneratorWrapper<T> value(T&& value) {
        return GeneratorWrapper<T>(pf::make_unique<SingleValueGenerator<T>>(std::forward<T>(value)));
    }
    template <typename T>
    GeneratorWrapper<T> values(std::initializer_list<T> values) {
        return GeneratorWrapper<T>(pf::make_unique<FixedValuesGenerator<T>>(values));
    }

    template<typename T>
    class Generators : public IGenerator<T> {
        std::vector<GeneratorWrapper<T>> m_generators;
        size_t m_current = 0;

        void populate(GeneratorWrapper<T>&& generator) {
            m_generators.emplace_back(std::move(generator));
        }
        void populate(T&& val) {
            m_generators.emplace_back(value(std::move(val)));
        }
        template<typename U>
        void populate(U&& val) {
            populate(T(std::move(val)));
        }
        template<typename U, typename... Gs>
        void populate(U&& valueOrGenerator, Gs... moreGenerators) {
            populate(std::forward<U>(valueOrGenerator));
            populate(std::forward<Gs>(moreGenerators)...);
        }

    public:
        template <typename... Gs>
        Generators(Gs... moreGenerators) {
            m_generators.reserve(sizeof...(Gs));
            populate(std::forward<Gs>(moreGenerators)...);
        }

        T const& get() const override {
            return m_generators[m_current].get();
        }

        bool next() override {
            if (m_current >= m_generators.size()) {
                return false;
            }
            const bool current_status = m_generators[m_current].next();
            if (!current_status) {
                ++m_current;
            }
            return m_current < m_generators.size();
        }
    };


    template<typename... Ts>
    GeneratorWrapper<std::tuple<Ts...>> table( std::initializer_list<std::tuple<typename std::decay<Ts>::type...>> tuples ) {
        return values<std::tuple<Ts...>>( tuples );
    }

    // Tag type to signal that a generator sequence should convert arguments to a specific type
    template <typename T>
    struct as {};

    template<typename T, typename... Gs>
    auto makeGenerators( GeneratorWrapper<T>&& generator, Gs... moreGenerators ) -> Generators<T> {
        return Generators<T>(std::move(generator), std::forward<Gs>(moreGenerators)...);
    }
    template<typename T>
    auto makeGenerators( GeneratorWrapper<T>&& generator ) -> Generators<T> {
        return Generators<T>(std::move(generator));
    }
    template<typename T, typename... Gs>
    auto makeGenerators( T&& val, Gs... moreGenerators ) -> Generators<T> {
        return makeGenerators( value( std::forward<T>( val ) ), std::forward<Gs>( moreGenerators )... );
    }
    template<typename T, typename U, typename... Gs>
    auto makeGenerators( as<T>, U&& val, Gs... moreGenerators ) -> Generators<T> {
        return makeGenerators( value( T( std::forward<U>( val ) ) ), std::forward<Gs>( moreGenerators )... );
    }

    template <typename T>
    class TakeGenerator : public IGenerator<T> {
        GeneratorWrapper<T> m_generator;
        size_t m_returned = 0;
        size_t m_target;
    public:
        TakeGenerator(size_t target, GeneratorWrapper<T>&& generator):
            m_generator(std::move(generator)),
            m_target(target)
        {
            assert(target != 0 && "Empty generators are not allowed");
        }
        T const& get() const override {
            return m_generator.get();
        }
        bool next() override {
            ++m_returned;
            if (m_returned >= m_target) {
                return false;
            }

            const auto success = m_generator.next();
            // If the underlying generator does not contain enough values
            // then we cut short as well
            if (!success) {
                m_returned = m_target;
            }
            return success;
        }
    };

    template <typename T>
    GeneratorWrapper<T> take(size_t target, GeneratorWrapper<T>&& generator) {
        return GeneratorWrapper<T>(pf::make_unique<TakeGenerator<T>>(target, std::move(generator)));
    }


    template <typename T, typename Predicate>
    class FilterGenerator : public IGenerator<T> {
        GeneratorWrapper<T> m_generator;
        Predicate m_predicate;
    public:
        template <typename P = Predicate>
        FilterGenerator(P&& pred, GeneratorWrapper<T>&& generator):
            m_generator(std::move(generator)),
            m_predicate(std::forward<P>(pred))
        {
            if (!m_predicate(m_generator.get())) {
                // It might happen that there are no values that pass the
                // filter. In that case we throw an exception.
                auto has_initial_value = next();
                if (!has_initial_value) {
                    Catch::throw_exception(GeneratorException("No valid value found in filtered generator"));
                }
            }
        }

        T const& get() const override {
            return m_generator.get();
        }

        bool next() override {
            bool success = m_generator.next();
            if (!success) {
                return false;
            }
            while (!m_predicate(m_generator.get()) && (success = m_generator.next()) == true);
            return success;
        }
    };


    template <typename T, typename Predicate>
    GeneratorWrapper<T> filter(Predicate&& pred, GeneratorWrapper<T>&& generator) {
        return GeneratorWrapper<T>(std::unique_ptr<IGenerator<T>>(pf::make_unique<FilterGenerator<T, Predicate>>(std::forward<Predicate>(pred), std::move(generator))));
    }

    template <typename T>
    class RepeatGenerator : public IGenerator<T> {
        GeneratorWrapper<T> m_generator;
        mutable std::vector<T> m_returned;
        size_t m_target_repeats;
        size_t m_current_repeat = 0;
        size_t m_repeat_index = 0;
    public:
        RepeatGenerator(size_t repeats, GeneratorWrapper<T>&& generator):
            m_generator(std::move(generator)),
            m_target_repeats(repeats)
        {
            assert(m_target_repeats > 0 && "Repeat generator must repeat at least once");
        }

        T const& get() const override {
            if (m_current_repeat == 0) {
                m_returned.push_back(m_generator.get());
                return m_returned.back();
            }
            return m_returned[m_repeat_index];
        }

        bool next() override {
            // There are 2 basic cases:
            // 1) We are still reading the generator
            // 2) We are reading our own cache

            // In the first case, we need to poke the underlying generator.
            // If it happily moves, we are left in that state, otherwise it is time to start reading from our cache
            if (m_current_repeat == 0) {
                const auto success = m_generator.next();
                if (!success) {
                    ++m_current_repeat;
                }
                return m_current_repeat < m_target_repeats;
            }

            // In the second case, we need to move indices forward and check that we haven't run up against the end
            ++m_repeat_index;
            if (m_repeat_index == m_returned.size()) {
                m_repeat_index = 0;
                ++m_current_repeat;
            }
            return m_current_repeat < m_target_repeats;
        }
    };

    template <typename T>
    GeneratorWrapper<T> repeat(size_t repeats, GeneratorWrapper<T>&& generator) {
        return GeneratorWrapper<T>(pf::make_unique<RepeatGenerator<T>>(repeats, std::move(generator)));
    }

    template <typename T, typename U, typename Func>
    class MapGenerator : public IGenerator<T> {
        // TBD: provide static assert for mapping function, for friendly error message
        GeneratorWrapper<U> m_generator;
        Func m_function;
        // To avoid returning dangling reference, we have to save the values
        T m_cache;
    public:
        template <typename F2 = Func>
        MapGenerator(F2&& function, GeneratorWrapper<U>&& generator) :
            m_generator(std::move(generator)),
            m_function(std::forward<F2>(function)),
            m_cache(m_function(m_generator.get()))
        {}

        T const& get() const override {
            return m_cache;
        }
        bool next() override {
            const auto success = m_generator.next();
            if (success) {
                m_cache = m_function(m_generator.get());
            }
            return success;
        }
    };

    template <typename T, typename U, typename Func>
    GeneratorWrapper<T> map(Func&& function, GeneratorWrapper<U>&& generator) {
        return GeneratorWrapper<T>(
            pf::make_unique<MapGenerator<T, U, Func>>(std::forward<Func>(function), std::move(generator))
        );
    }
    template <typename T, typename Func>
    GeneratorWrapper<T> map(Func&& function, GeneratorWrapper<T>&& generator) {
        return GeneratorWrapper<T>(
            pf::make_unique<MapGenerator<T, T, Func>>(std::forward<Func>(function), std::move(generator))
        );
    }

    auto acquireGeneratorTracker( SourceLineInfo const& lineInfo ) -> IGeneratorTracker&;

    template<typename L>
    // Note: The type after -> is weird, because VS2015 cannot parse
    //       the expression used in the typedef inside, when it is in
    //       return type. Yeah, ¯\_(ツ)_/¯
    auto generate( SourceLineInfo const& lineInfo, L const& generatorExpression ) -> decltype(std::declval<decltype(generatorExpression())>().get()) {
        using UnderlyingType = typename decltype(generatorExpression())::type;

        IGeneratorTracker& tracker = acquireGeneratorTracker( lineInfo );
        if (!tracker.hasGenerator()) {
            tracker.setGenerator(pf::make_unique<Generators<UnderlyingType>>(generatorExpression()));
        }

        auto const& generator = static_cast<IGenerator<UnderlyingType> const&>( *tracker.getGenerator() );
        return generator.get();
    }

} // namespace Generators
} // namespace Catch

#define GENERATE( ... ) \
    Catch::Generators::generate( CATCH_INTERNAL_LINEINFO, []{ using namespace Catch::Generators; return makeGenerators( __VA_ARGS__ ); } )


#endif // TWOBLUECUBES_CATCH_GENERATORS_HPP_INCLUDED