#include "serif/utils/error/errors.hpp"
#include "serif/utils/dependencies/dependencies.hpp"

#include <catch2/catch_test_macros.hpp>
#include <catch2/matchers/catch_matchers_string.hpp>
#include <expected>
#include <memory>
#include <stdexcept>
#include <string>
#include <utility>

namespace {
    namespace dependencies = serif::utils::dependencies;

    struct Source {};
    struct Intermediate {};
    struct Result {};

    struct ThrowingSnapshot {
        /// Simulate a policy failing while it tries to capture replacement state.
        int capture(const int& value) const {
            if (value < 0) {
                serif::utils::errors::serif_error<std::runtime_error, serif::utils::errors::SERiFErrorCode::INVALID_ARGUMENT>("source snapshot unavailable");
            }
            return value;
        }

        /// Compare only successfully captured states.
        bool matches(const int& captured, const int& value) const { return captured == value; }
    };
}

TEST_CASE("Rejected dependency preparation publishes neither candidate results nor snapshots", "[unit][utils][dependencies]") {
    int source = 2;
    int intermediate_calls = 0;
    int result_calls = 0;
    auto context = dependencies::make_dependency_context(dependencies::borrow<Source>(source));
    auto graph = dependencies::make_computation_graph(
        dependencies::make_computation<Result, dependencies::InputList<Intermediate>>([&result_calls](int intermediate) -> std::expected<int, std::string> {
                ++result_calls;
                if (intermediate < 0) { return std::unexpected("input must be nonnegative"); }
                return intermediate + 1;
            }),
        dependencies::make_computation<Intermediate, dependencies::InputList<Source>>([&intermediate_calls](int input) { ++intermediate_calls; return 2 * input; })
    );
    auto cache = dependencies::make_computation_cache(std::move(graph), context);
    REQUIRE(cache.try_prepare(context));
    CHECK(cache.get<Result>() == 5);

    source = -3;
    auto rejected = cache.try_prepare(context);
    REQUIRE_FALSE(rejected);
    CHECK(rejected.error().computation_index == 0);
    CHECK(rejected.error().error == "input must be nonnegative");
    CHECK_FALSE(cache.ready());
    CHECK_FALSE(cache.contains<Intermediate>());
    CHECK_THROWS_AS(cache.get<Result>(), std::logic_error);
    CHECK(cache.report().computed_count() == 0);
    CHECK(cache.report().reused_count() == 0);
    CHECK(intermediate_calls == 2);
    CHECK(result_calls == 2);

    // Retrying rejected inputs must rebuild the prerequisite: its candidate was never committed.
    REQUIRE_FALSE(cache.try_prepare(context));
    CHECK(intermediate_calls == 3);
    CHECK(result_calls == 3);

    // The last accepted cache is still usable when the source returns to its accepted state.
    source = 2;
    const auto recovered = cache.try_prepare(context);
    REQUIRE(recovered);
    CHECK(recovered->reused_count() == 2);
    CHECK(cache.get<Result>() == 5);
    CHECK(intermediate_calls == 3);
    CHECK(result_calls == 3);

    source = 4;
    REQUIRE(cache.try_prepare(context));
    CHECK(cache.get<Result>() == 9);
    CHECK(intermediate_calls == 4);
    CHECK(result_calls == 4);
}

TEST_CASE("Dependency computations can return move-only typed errors", "[unit][utils][dependencies]") {
    using Error = std::unique_ptr<int>;
    int source = -1;
    auto context = dependencies::make_dependency_context(dependencies::borrow<Source>(source));
    auto graph = dependencies::make_computation_graph(dependencies::make_computation<Result, dependencies::InputList<Source>>([](int value) -> std::expected<int, Error> {
            if (value < 0) { return std::unexpected(std::make_unique<int>(value)); }
            return value;
        }));
    auto cache = dependencies::make_computation_cache<Error>(std::move(graph), context);
    const auto rejected = cache.try_prepare(context);
    REQUIRE_FALSE(rejected);
    CHECK(*rejected.error().error == -1);
    source = 3;
    REQUIRE(cache.try_prepare(context));
    CHECK(cache.get<Result>() == 3);
}

TEST_CASE("Exceptions leave dependency results unavailable without replacing the accepted cache", "[unit][utils][dependencies]") {
    int source = 2;
    int calls = 0;
    auto context = dependencies::make_dependency_context(dependencies::borrow<Source>(source, ThrowingSnapshot{}));
    auto graph = dependencies::make_computation_graph(dependencies::make_computation<Result, dependencies::InputList<Source>>([&calls](int value) {
            ++calls;
            if (value == 3) {
                serif::utils::errors::serif_error<std::runtime_error, serif::utils::errors::SERiFErrorCode::INVALID_ARGUMENT>("calculation failed");
            }
            return value;
        }));
    auto cache = dependencies::make_computation_cache(std::move(graph), context);
    REQUIRE(cache.try_prepare(context));
    CHECK(calls == 1);

    SECTION("A source policy throws before evaluation") {
        source = -1;
        CHECK_THROWS_WITH(cache.try_prepare(context), Catch::Matchers::ContainsSubstring("source snapshot unavailable"));
        CHECK(calls == 1);
    }
    SECTION("The calculation throws after snapshot capture") {
        source = 3;
        CHECK_THROWS_WITH(cache.try_prepare(context), Catch::Matchers::ContainsSubstring("calculation failed"));
        CHECK(calls == 2);
    }
    CHECK_FALSE(cache.ready());
    CHECK_THROWS_AS(cache.get<Result>(), std::logic_error);
    source = 2;
    const auto recovered = cache.try_prepare(context);
    REQUIRE(recovered);
    CHECK(recovered->reused_count() == 1);
    CHECK(cache.get<Result>() == 2);
}

TEST_CASE("Preparation counts distinguish successful requests from rejected attempts and survive cache moves", "[unit][utils][dependencies]") {
    int source = 2;
    int evaluations = 0;
    const auto context = dependencies::make_dependency_context(dependencies::borrow<Source>(source));
    const auto computation = dependencies::make_computation<Result, dependencies::InputList<Source>>(
        [&evaluations](int input) -> std::expected<int, std::string> {
            ++evaluations;
            if (input < 0) {
                return std::unexpected("input must be nonnegative");
            }

            return 2 * input;
        }
    );
    auto cache = dependencies::make_computation_cache(context, computation);
    CHECK(cache.preparation_count() == 0);

    const auto computed = cache.try_prepare(context);
    REQUIRE(computed);
    CHECK(computed->status<Result>() == dependencies::PreparationStatus::computed);
    CHECK(cache.preparation_count() == 1);
    CHECK(evaluations == 1);

    const auto reused = cache.try_prepare(context);
    REQUIRE(reused);
    CHECK(reused->status<Result>() == dependencies::PreparationStatus::reused);
    CHECK(cache.preparation_count() == 2);
    CHECK(evaluations == 1);

    source = -1;
    const auto rejected = cache.try_prepare(context);
    REQUIRE_FALSE(rejected);
    CHECK_FALSE(cache.ready());
    CHECK(cache.preparation_count() == 2);
    CHECK(evaluations == 2);

    cache.invalidate();
    CHECK_FALSE(cache.ready());
    CHECK(cache.preparation_count() == 2);
    source = 2;
    const auto recovered = cache.try_prepare(context);
    REQUIRE(recovered);
    CHECK(recovered->status<Result>() == dependencies::PreparationStatus::computed);
    CHECK(cache.preparation_count() == 3);
    CHECK(evaluations == 3);

    auto moved = std::move(cache);
    CHECK(moved.ready());
    CHECK(moved.preparation_count() == 3);
    CHECK(moved.get<Result>() == 4);
    CHECK_FALSE(cache.ready());
    CHECK(cache.preparation_count() == 0);

    const auto moved_report = moved.try_prepare(context);
    REQUIRE(moved_report);
    CHECK(moved_report->status<Result>() == dependencies::PreparationStatus::reused);
    CHECK(moved.preparation_count() == 4);
    CHECK(evaluations == 3);
}