Add ChunkGenerator

This generator collects values from the underlying generator until it
has a specified amount of them, and then returns them in one "chunk".
In case the underlying generator does not have enough elements for
a specific chunk, the left-over elements are discarded.

Closes #1538

include/internal/catch_generators_generic.hpp

@@ -0,0 +1,230 @@
+/*
+ *  Created by Martin on 23/2/2019.
+ *
+ *  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_GENERIC_HPP_INCLUDED
+#define TWOBLUECUBES_CATCH_GENERATORS_GENERIC_HPP_INCLUDED
+
+#include "catch_generators.hpp"
+
+namespace Catch {
+namespace Generators {
+
+    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))
+        );
+    }
+
+    template <typename T>
+    class ChunkGenerator final : public IGenerator<std::vector<T>> {
+        std::vector<T> m_chunk;
+        size_t m_chunk_size;
+        GeneratorWrapper<T> m_generator;
+        bool m_used_up = false;
+    public:
+        ChunkGenerator(size_t size, GeneratorWrapper<T> generator) :
+            m_chunk_size(size), m_generator(std::move(generator))
+        {
+            m_chunk.reserve(m_chunk_size);
+            m_chunk.push_back(m_generator.get());
+            for (size_t i = 1; i < m_chunk_size; ++i) {
+                if (!m_generator.next()) {
+                    Catch::throw_exception(GeneratorException("Not enough values to initialize the first chunk"));
+                }
+                m_chunk.push_back(m_generator.get());
+            }
+        }
+        std::vector<T> const& get() const override {
+            return m_chunk;
+        }
+        bool next() override {
+            m_chunk.clear();
+            for (size_t idx = 0; idx < m_chunk_size; ++idx) {
+                if (!m_generator.next()) {
+                    return false;
+                }
+                m_chunk.push_back(m_generator.get());
+            }
+            return true;
+        }
+    };
+
+    template <typename T>
+    GeneratorWrapper<std::vector<T>> chunk(size_t size, GeneratorWrapper<T>&& generator) {
+        return GeneratorWrapper<std::vector<T>>(
+            pf::make_unique<ChunkGenerator<T>>(size, std::move(generator))
+        );
+    }
+
+} // namespace Generators
+} // namespace Catch
+
+
+#endif // TWOBLUECUBES_CATCH_GENERATORS_GENERIC_HPP_INCLUDED