// This file Copyright (C) 2013-2022 Mnemosyne LLC.
// It may be used under GPLv2 (SPDX: GPL-2.0-only), GPLv3 (SPDX: GPL-3.0-only),
// or any future license endorsed by Mnemosyne LLC.
// License text can be found in the licenses/ folder.

#include <array>
#include <cerrno>
#include <cstddef> // size_t
#include <cstdint> // int64_t
#include <map>
#include <string>
#include <string_view>
#include <type_traits>
#include <utility>
#include <vector>

#define LIBTRANSMISSION_VARIANT_MODULE

#include <libtransmission/benc.h>
#include <libtransmission/crypto-utils.h> // tr_rand_buffer(), tr_rand_int()
#include <libtransmission/error.h>
#include <libtransmission/quark.h>
#include <libtransmission/variant.h>

#include "test-fixtures.h"

using VariantTest = ::libtransmission::test::TransmissionTest;
using namespace std::literals;

namespace
{

template<class... Ts>
struct Overloaded : Ts...
{
    using Ts::operator()...;
};

template<class... Ts>
Overloaded(Ts...) -> Overloaded<Ts...>;

} // namespace

#ifndef _WIN32
#define STACK_SMASH_DEPTH (1 * 1000 * 1000)
#else
#define STACK_SMASH_DEPTH (100 * 1000)
#endif

TEST_F(VariantTest, getType)
{
    auto v = tr_variant{};

    v = 30;
    auto i = v.value_if<int64_t>();
    ASSERT_TRUE(i);
    EXPECT_EQ(30, *i);
    auto d = v.value_if<double>();
    ASSERT_TRUE(d);
    EXPECT_EQ(30, static_cast<int>(*d));
    EXPECT_FALSE(v.holds_alternative<bool>());
    EXPECT_FALSE(v.holds_alternative<std::string_view>());

    auto strkey = "foo"sv;
    v = tr_variant{ strkey };
    EXPECT_FALSE(v.holds_alternative<bool>());
    auto sv = v.value_if<std::string_view>();
    ASSERT_TRUE(sv);
    EXPECT_EQ(strkey, *sv);
    EXPECT_NE(std::data(strkey), std::data(*sv));
    EXPECT_EQ(std::size(strkey), std::size(*sv));

    strkey = "anything"sv;
    v = tr_variant::unmanaged_string(strkey);
    sv = v.value_if<std::string_view>();
    ASSERT_TRUE(sv);
    EXPECT_EQ(strkey, *sv);
    EXPECT_EQ(std::data(strkey), std::data(*sv)); // literally the same memory
    EXPECT_EQ(std::size(strkey), std::size(*sv));

    strkey = "true"sv;
    v = tr_variant{ strkey };
    auto b = v.value_if<bool>();
    ASSERT_TRUE(b);
    EXPECT_TRUE(*b);
    sv = v.value_if<std::string_view>();
    ASSERT_TRUE(sv);
    EXPECT_EQ(strkey, *sv);

    strkey = "false"sv;
    v = tr_variant{ strkey };
    b = v.value_if<bool>();
    ASSERT_TRUE(b);
    EXPECT_FALSE(*b);
    sv = v.value_if<std::string_view>();
    ASSERT_TRUE(sv);
    EXPECT_EQ(strkey, *sv);
}

TEST_F(VariantTest, mergeStringsTakesOwnership)
{
    auto const is_equal_string = [](std::string_view const a, std::string_view const b)
    {
        return a == b;
    };

    auto const is_same_address = [](std::string_view const a, std::string_view const b)
    {
        return std::data(a) == std::data(b);
    };

    // set up `src` to hold an unmanaged string
    auto constexpr Original = "this is the string"sv;
    auto const src = tr_variant::unmanaged_string(Original);
    auto src_sv = src.value_if<std::string_view>().value_or(""sv);

    // set up `tgt` to hold another unmanaged string
    auto constexpr WillBeReplaced = "some other string"sv;
    static_assert(Original != WillBeReplaced);
    auto tgt = tr_variant::unmanaged_string(WillBeReplaced);
    auto tgt_sv = tgt.value_if<std::string_view>().value_or(""sv);

    // test that `src` and `tgt` hold unmanaged strings
    EXPECT_TRUE(is_equal_string(Original, src_sv));
    EXPECT_TRUE(is_equal_string(WillBeReplaced, tgt_sv));
    EXPECT_TRUE(is_same_address(Original, src_sv));
    EXPECT_TRUE(is_same_address(WillBeReplaced, tgt_sv));

    tgt.merge(src);

    // test that `tgt` now holds its own copy of `Original`.
    auto const actual = tgt.value_if<std::string_view>().value_or(""sv);
    EXPECT_TRUE(is_equal_string(Original, actual));
    EXPECT_FALSE(is_same_address(Original, actual));
}

TEST_F(VariantTest, parseInt)
{
    static auto constexpr Benc = "i64e"sv;
    static auto constexpr ExpectVal = int64_t{ 64 };

    auto benc = Benc;
    auto const value = transmission::benc::impl::ParseInt(&benc);
    ASSERT_TRUE(value);
    EXPECT_EQ(ExpectVal, *value);
    EXPECT_EQ(std::data(Benc) + std::size(Benc), std::data(benc));
}

TEST_F(VariantTest, parseIntWithMissingEnd)
{
    static auto constexpr Benc = "i64"sv;

    auto benc = Benc;
    EXPECT_FALSE(transmission::benc::impl::ParseInt(&benc));
    EXPECT_EQ(std::data(Benc), std::data(benc));
}

TEST_F(VariantTest, parseIntEmptyBuffer)
{
    static auto constexpr Benc = ""sv;

    auto benc = Benc;
    EXPECT_FALSE(transmission::benc::impl::ParseInt(&benc));
    EXPECT_EQ(std::data(Benc), std::data(benc));
}

TEST_F(VariantTest, parseIntWithBadDigits)
{
    static auto constexpr Benc = "i6z4e"sv;

    auto benc = Benc;
    EXPECT_FALSE(transmission::benc::impl::ParseInt(&benc));
    EXPECT_EQ(std::data(Benc), std::data(benc));
}

TEST_F(VariantTest, parseNegativeInt)
{
    static auto constexpr Benc = "i-3e"sv;
    static auto constexpr Expected = int64_t{ -3 };

    auto benc = Benc;
    auto const value = transmission::benc::impl::ParseInt(&benc);
    ASSERT_TRUE(value);
    EXPECT_EQ(Expected, *value);
    EXPECT_EQ(std::data(Benc) + std::size(Benc), std::data(benc));
}

TEST_F(VariantTest, parseNegativeWithLeadingZero)
{
    static auto constexpr Benc = "i-03e"sv;

    auto benc = Benc;
    EXPECT_FALSE(transmission::benc::impl::ParseInt(&benc));
    EXPECT_EQ(std::data(Benc), std::data(benc));
}

TEST_F(VariantTest, parseIntZero)
{
    static auto constexpr Benc = "i0e"sv;
    static auto constexpr Expected = int64_t{ 0 };

    auto benc = Benc;
    auto const value = transmission::benc::impl::ParseInt(&benc);
    ASSERT_TRUE(value);
    EXPECT_EQ(Expected, *value);
    EXPECT_EQ(std::data(Benc) + std::size(Benc), std::data(benc));
}

TEST_F(VariantTest, parseIntWithLeadingZero)
{
    static auto constexpr Benc = "i04e"sv;

    auto benc = Benc;
    EXPECT_FALSE(transmission::benc::impl::ParseInt(&benc));
    EXPECT_EQ(std::data(Benc), std::data(benc));
}

TEST_F(VariantTest, str)
{
    using namespace transmission::benc::impl;

    // string len is designed to overflow
    auto benc = "99999999999999999999:boat"sv;
    auto inout = benc;
    auto value = ParseString(&inout);
    EXPECT_FALSE(value);
    EXPECT_EQ(benc, inout);

    // good string
    inout = benc = "4:boat";
    value = ParseString(&inout);
    ASSERT_TRUE(value);
    EXPECT_EQ("boat"sv, *value);
    EXPECT_EQ(std::data(benc) + std::size(benc), std::data(inout));

    // string goes past end of buffer
    inout = benc = "4:boa"sv;
    value = ParseString(&inout);
    EXPECT_FALSE(value);
    EXPECT_EQ(benc, inout);

    // empty string
    inout = benc = "0:"sv;
    value = ParseString(&inout);
    ASSERT_TRUE(value);
    EXPECT_EQ(""sv, *value);
    EXPECT_EQ(std::data(benc) + std::size(benc), std::data(inout));

    // short string
    inout = benc = "3:boat";
    value = ParseString(&inout);
    ASSERT_TRUE(value);
    EXPECT_EQ("boa"sv, *value);
    EXPECT_EQ(std::data(benc) + benc.find('t'), std::data(inout));
}

TEST_F(VariantTest, parse)
{
    auto serde = tr_variant_serde::benc();
    serde.inplace();

    auto benc = "i64e"sv;
    auto var = serde.parse(benc).value_or(tr_variant{});
    auto i = var.value_if<int64_t>();
    ASSERT_TRUE(i);
    EXPECT_EQ(64, *i);
    EXPECT_EQ(std::data(benc) + std::size(benc), serde.end());
    var.clear();

    benc = "li64ei32ei16ee"sv;
    var = serde.parse(benc).value_or(tr_variant{});
    auto* l = var.get_if<tr_variant::Vector>();
    ASSERT_NE(l, nullptr);
    EXPECT_EQ(std::data(benc) + std::size(benc), serde.end());
    ASSERT_EQ(3, std::size(*l));
    i = (*l)[0].value_if<int64_t>();
    ASSERT_TRUE(i);
    EXPECT_EQ(64, *i);
    i = (*l)[1].value_if<int64_t>();
    ASSERT_TRUE(i);
    EXPECT_EQ(32, *i);
    i = (*l)[2].value_if<int64_t>();
    ASSERT_TRUE(i);
    EXPECT_EQ(16, *i);
    EXPECT_EQ(benc, serde.to_string(var));
    var.clear();

    benc = "lllee"sv;
    var = serde.parse(benc).value_or(tr_variant{});
    EXPECT_FALSE(var.has_value());
    EXPECT_EQ(std::data(benc) + std::size(benc), serde.end());
    var.clear();

    benc = "le"sv;
    var = serde.parse(benc).value_or(tr_variant{});
    EXPECT_TRUE(var.holds_alternative<tr_variant::Vector>());
    EXPECT_EQ(std::data(benc) + std::size(benc), serde.end());
    EXPECT_EQ(benc, serde.to_string(var));
    var.clear();

    benc = "d20:"sv;
    var = serde.parse(benc).value_or(tr_variant{});
    EXPECT_FALSE(var.has_value());
    EXPECT_EQ(std::data(benc) + 1U, serde.end());
}

TEST_F(VariantTest, bencParseAndReencode)
{
    static auto constexpr Tests = std::array<std::pair<std::string_view, bool>, 9>{ {
        { "llleee"sv, true },
        { "d3:cow3:moo4:spam4:eggse"sv, true },
        { "d4:spaml1:a1:bee"sv, true },
        { "d5:greenli1ei2ei3ee4:spamd1:ai123e3:keyi214eee"sv, true },
        { "d9:publisher3:bob17:publisher-webpage15:www.example.com18:publisher.location4:homee"sv, true },
        { "d8:completei1e8:intervali1800e12:min intervali1800e5:peers0:e"sv, true },
        { "d1:ai0e1:be"sv, false }, // odd number of children
        { ""sv, false },
        { " "sv, false },
    } };

    auto serde = tr_variant_serde::benc();
    serde.inplace();

    for (auto const& [benc, is_good] : Tests)
    {
        auto var = serde.parse(benc);
        EXPECT_EQ(is_good, var.has_value());
        if (var)
        {
            EXPECT_EQ(benc.data() + benc.size(), serde.end());
            EXPECT_EQ(benc, serde.to_string(*var));
        }
    }
}

TEST_F(VariantTest, bencSortWhenSerializing)
{
    static auto constexpr In = "lld1:bi32e1:ai64eeee"sv;
    static auto constexpr ExpectedOut = "lld1:ai64e1:bi32eeee"sv;

    auto serde = tr_variant_serde::benc();
    auto var = serde.inplace().parse(In);
    EXPECT_TRUE(var.has_value());
    EXPECT_EQ(std::data(In) + std::size(In), serde.end());
    EXPECT_EQ(ExpectedOut, serde.to_string(*var));
}

TEST_F(VariantTest, bencMalformedTooManyEndings)
{
    static auto constexpr In = "leee"sv;
    static auto constexpr ExpectedOut = "le"sv;

    auto serde = tr_variant_serde::benc();
    auto var = serde.inplace().parse(In);
    EXPECT_TRUE(var.has_value());
    EXPECT_EQ(std::data(In) + std::size(ExpectedOut), serde.end());
    EXPECT_EQ(ExpectedOut, serde.to_string(*var));
}

TEST_F(VariantTest, bencMalformedNoEnding)
{
    static auto constexpr In = "l1:a1:b1:c"sv;

    auto serde = tr_variant_serde::benc();
    auto const var = serde.inplace().parse(In);
    EXPECT_FALSE(var.has_value());
}

TEST_F(VariantTest, bencMalformedIncompleteString)
{
    static auto constexpr In = "1:"sv;

    auto serde = tr_variant_serde::benc();
    auto const var = serde.inplace().parse(In);
    EXPECT_FALSE(var.has_value());
}

TEST_F(VariantTest, bencToJson)
{
    static auto constexpr Tests = std::array<std::pair<std::string_view, std::string_view>, 5>{
        { { "i6e"sv, "6"sv },
          { "d5:helloi1e5:worldi2ee"sv, R"({"hello":1,"world":2})"sv },
          { "d5:helloi1e5:worldi2e3:fooli1ei2ei3eee"sv, R"({"foo":[1,2,3],"hello":1,"world":2})"sv },
          { "d5:helloi1e5:worldi2e3:fooli1ei2ei3ed1:ai0eeee"sv, R"({"foo":[1,2,3,{"a":0}],"hello":1,"world":2})"sv },
          { "d4:argsd6:statusle7:status2lee6:result7:successe"sv,
            R"({"args":{"status":[],"status2":[]},"result":"success"})"sv } }
    };

    auto benc_serde = tr_variant_serde::benc();
    auto json_serde = tr_variant_serde::json();
    benc_serde.inplace();
    json_serde.compact();

    for (auto const& [benc, expected] : Tests)
    {
        auto top = benc_serde.parse(benc).value_or(tr_variant{});
        EXPECT_EQ(expected, json_serde.to_string(top));
    }
}

TEST_F(VariantTest, mergeMapsCreatesCombinedMap)
{
    auto serde = tr_variant_serde::json();
    serde.compact();
    serde.inplace();

    auto src = serde.parse(R"({"src_key":123})"sv).value_or(tr_variant{});
    auto tgt = serde.parse(R"({"tgt_key":456})"sv).value_or(tr_variant{});
    tgt.merge(src);
    EXPECT_EQ(R"({"src_key":123,"tgt_key":456})"sv, serde.to_string(tgt));
}

TEST_F(VariantTest, mergeMapsOverwritesSrcMapEntries)
{
    auto serde = tr_variant_serde::json();
    serde.compact();
    serde.inplace();

    auto src = serde.parse(R"({"src_key": 123, "dup_key":789})"sv).value_or(tr_variant{});
    auto tgt = serde.parse(R"({"tgt_key": 456, "dup_key":456})"sv).value_or(tr_variant{});
    tgt.merge(src);
    EXPECT_EQ(R"({"dup_key":789,"src_key":123,"tgt_key":456})"sv, serde.to_string(tgt));
}

TEST_F(VariantTest, variantConstructor)
{
    auto const var_none = tr_variant{};
    auto const var_null = tr_variant{ nullptr };
    auto const var_true = tr_variant{ true };
    auto const var_false = tr_variant{ false };
    auto const var_int = tr_variant{ 123 };
    auto const var_real = tr_variant{ 4.5 };
    auto const var_sv = tr_variant{ "foo"sv };
    auto const var_s = tr_variant{ "foo"s };
    auto const var_char_ptr = tr_variant{ "foo" };
    auto const var_char_nullptr = tr_variant{ static_cast<char const*>(nullptr) };

    EXPECT_EQ(var_none.index(), tr_variant::NoneIndex);
    EXPECT_EQ(var_null.index(), tr_variant::NullIndex);
    EXPECT_EQ(var_true.index(), tr_variant::BoolIndex);
    EXPECT_EQ(var_false.index(), tr_variant::BoolIndex);
    EXPECT_EQ(var_int.index(), tr_variant::IntIndex);
    EXPECT_EQ(var_real.index(), tr_variant::DoubleIndex);
    EXPECT_EQ(var_sv.index(), tr_variant::StringIndex);
    EXPECT_EQ(var_s.index(), tr_variant::StringIndex);
    EXPECT_EQ(var_char_ptr.index(), tr_variant::StringIndex);
    EXPECT_EQ(var_char_nullptr.index(), tr_variant::StringIndex);
}

TEST_F(VariantTest, variantAssingmentOperator)
{
    auto var = tr_variant{};

    var = nullptr;
    EXPECT_EQ(var.index(), tr_variant::NullIndex);

    var = true;
    EXPECT_EQ(var.index(), tr_variant::BoolIndex);

    var = false;
    EXPECT_EQ(var.index(), tr_variant::BoolIndex);

    var = 123;
    EXPECT_EQ(var.index(), tr_variant::IntIndex);

    var = 4.5;
    EXPECT_EQ(var.index(), tr_variant::DoubleIndex);

    var = "foo"sv;
    EXPECT_EQ(var.index(), tr_variant::StringIndex);

    var = "foo"s;
    EXPECT_EQ(var.index(), tr_variant::StringIndex);

    var = "foo";
    EXPECT_EQ(var.index(), tr_variant::StringIndex);

    var = static_cast<char const*>(nullptr);
    EXPECT_EQ(var.index(), tr_variant::StringIndex);
}

TEST_F(VariantTest, mergeOverwritesDifferingTypes)
{
    auto const variants = std::array<std::pair<tr_variant, std::string_view>, 7U>{ {
        { tr_variant{ true }, "true" },
        { tr_variant{ int64_t{ 123 } }, "123" },
        { tr_variant{ 4.5 }, "4.5" },
        { tr_variant{ "foo"sv }, R"("foo")"sv },
        { tr_variant{ nullptr }, "null"sv },
        { tr_variant::make_map(0U), "{}"sv },
        { tr_variant::make_vector(), "[]"sv },
    } };

    auto serde = tr_variant_serde::json();
    serde.compact();
    serde.inplace();

    for (auto const& [src, src_expected] : variants)
    {
        for (auto const& [tgt, tgt_expected] : variants)
        {
            if (&src != &tgt)
            {
                // set up `var` to be a copy of `src`
                auto var = src.clone();
                EXPECT_EQ(src_expected, serde.to_string(var));

                var.merge(tgt);

                // test that `var` is now a copy of `tgt`
                EXPECT_EQ(tgt_expected, serde.to_string(var));
            }
        }
    }
}

TEST_F(VariantTest, stackSmashBenc)
{
    // set up a nested list of list of lists.
    static int constexpr Depth = STACK_SMASH_DEPTH;
    std::string const in = std::string(Depth, 'l') + std::string(Depth, 'e');

    // test that parsing fails without crashing
    auto serde = tr_variant_serde::benc();
    auto var = serde.inplace().parse(in);
    EXPECT_FALSE(var.has_value());
    EXPECT_TRUE(serde.error_);
    EXPECT_EQ(E2BIG, serde.error_.code());
}

TEST_F(VariantTest, stackSmashJson)
{
    auto serde = tr_variant_serde::json();
    serde.inplace();

    // set up a nested array of arrays of arrays.
    static auto constexpr Depth = STACK_SMASH_DEPTH;
    auto const in = std::string(Depth, '[') + std::string(Depth, ']');

    // test that parsing fails without crashing
    auto var = serde.inplace().parse(in);
    EXPECT_FALSE(var.has_value());
    EXPECT_TRUE(serde.error_);
    EXPECT_EQ(E2BIG, serde.error_.code());
}

TEST_F(VariantTest, valueIfCanReadBoolsAndIntsInterchangeably)
{
    auto const key1 = tr_quark_new("key1"sv);
    auto const key2 = tr_quark_new("key2"sv);
    auto const key3 = tr_quark_new("key3"sv);
    auto const key4 = tr_quark_new("key4"sv);

    auto top = tr_variant::make_map(4U);
    auto* map = top.get_if<tr_variant::Map>();
    map->try_emplace(key1, false);
    map->try_emplace(key2, 0);
    map->try_emplace(key3, true);
    map->try_emplace(key4, 1);

    // confirm we can read both bools and ints as bools
    auto b = map->value_if<bool>(key1);
    ASSERT_TRUE(b);
    EXPECT_FALSE(*b);
    b = map->value_if<bool>(key2);
    ASSERT_TRUE(b);
    EXPECT_FALSE(*b);
    b = map->value_if<bool>(key3);
    ASSERT_TRUE(b);
    EXPECT_TRUE(*b);
    b = map->value_if<bool>(key4);
    ASSERT_TRUE(b);
    EXPECT_TRUE(*b);

    // confirm we can read both bools and ints as ints
    auto i = map->value_if<int64_t>(key1);
    ASSERT_TRUE(i);
    EXPECT_EQ(0, *i);
    i = map->value_if<int64_t>(key2);
    ASSERT_TRUE(i);
    EXPECT_EQ(0, *i);
    i = map->value_if<int64_t>(key3);
    ASSERT_TRUE(i);
    EXPECT_NE(0, *i);
    i = map->value_if<int64_t>(key4);
    ASSERT_TRUE(i);
    EXPECT_NE(0, *i);
}

TEST_F(VariantTest, dictFindType)
{
    static auto constexpr ExpectedStr = "this-is-a-string"sv;
    static auto constexpr ExpectedBool = true;
    static auto constexpr ExpectedInt = 1234;
    static auto constexpr ExpectedReal = 0.3;

    auto const key_bool = tr_quark_new("this-is-a-bool"sv);
    auto const key_real = tr_quark_new("this-is-a-real"sv);
    auto const key_int = tr_quark_new("this-is-an-int"sv);
    auto const key_str = tr_quark_new("this-is-a-string"sv);
    auto const key_unknown = tr_quark_new("this-is-a-missing-entry"sv);

    // populate a dict
    auto top = tr_variant::make_map(4U);
    auto* map = top.get_if<tr_variant::Map>();
    map->try_emplace(key_bool, ExpectedBool);
    map->try_emplace(key_int, ExpectedInt);
    map->try_emplace(key_real, ExpectedReal);
    map->try_emplace(key_str, ExpectedStr);

    // look up the keys as strings
    EXPECT_FALSE(map->value_if<std::string_view>(key_bool));
    EXPECT_FALSE(map->value_if<std::string_view>(key_real));
    EXPECT_FALSE(map->value_if<std::string_view>(key_int));
    auto sv = map->value_if<std::string_view>(key_str);
    ASSERT_TRUE(sv);
    EXPECT_EQ(ExpectedStr, *sv);
    EXPECT_FALSE(map->value_if<std::string_view>(key_unknown));

    // look up the keys as bools
    EXPECT_FALSE(map->value_if<bool>(key_int));
    EXPECT_FALSE(map->value_if<bool>(key_real));
    EXPECT_FALSE(map->value_if<bool>(key_str));
    auto b = map->value_if<bool>(key_bool);
    ASSERT_TRUE(b);
    EXPECT_EQ(ExpectedBool, b);
    EXPECT_FALSE(map->value_if<bool>(key_unknown));

    // look up the keys as doubles
    EXPECT_FALSE(map->value_if<double>(key_bool));
    auto d = map->value_if<double>(key_int);
    ASSERT_TRUE(d);
    EXPECT_EQ(static_cast<double>(ExpectedInt), *d);
    EXPECT_FALSE(map->value_if<double>(key_str));
    d = map->value_if<double>(key_real);
    ASSERT_TRUE(d);
    EXPECT_EQ(ExpectedReal, *d);

    // look up the keys as ints
    auto i = map->value_if<int64_t>(key_bool);
    ASSERT_TRUE(i);
    EXPECT_EQ(ExpectedBool ? 1 : 0, *i);
    EXPECT_FALSE(map->value_if<int64_t>(key_real));
    EXPECT_FALSE(map->value_if<int64_t>(key_str));
    i = map->value_if<int64_t>(key_int);
    ASSERT_TRUE(i);
    EXPECT_EQ(ExpectedInt, *i);
}

TEST_F(VariantTest, mapContains)
{
    auto serde = tr_variant_serde::json();
    serde.inplace();
    serde.compact();

    // set up a map with some sample entries
    static auto constexpr Input = R"({
        "id": 42,
        "is_finished": true,
        "labels": ["a", "b"],
        "units": { "speed_units": ["KB/s", "MB/s", "GB/s", "TB/s"] },
        "upload_ratio": 4.2,
        "version": "5.0"
    })"sv;
    auto top = serde.parse(Input).value_or(tr_variant{});
    auto* const map = top.get_if<tr_variant::Map>();
    ASSERT_NE(nullptr, map);

    // test that contains() returns true for entries that exist
    EXPECT_TRUE(map->contains(TR_KEY_id));
    EXPECT_TRUE(map->contains(TR_KEY_is_finished));
    EXPECT_TRUE(map->contains(TR_KEY_labels));
    EXPECT_TRUE(map->contains(TR_KEY_units));
    EXPECT_TRUE(map->contains(TR_KEY_upload_ratio));
    EXPECT_TRUE(map->contains(TR_KEY_version));

    // test that contains() returns false for entries that never existed
    EXPECT_FALSE(map->contains(TR_KEY_umask));

    // test that contains() returns false for entries that were removed
    auto const key = TR_KEY_labels;
    EXPECT_TRUE(map->contains(key));
    EXPECT_EQ(1U, map->erase(key));
    EXPECT_FALSE(map->contains(key));
}

TEST_F(VariantTest, visitConstVariant)
{
    auto var = tr_variant::make_vector(1U);
    auto* vec = var.get_if<tr_variant::Vector>();
    ASSERT_NE(vec, nullptr);
    vec->emplace_back(int64_t{ 99 });

    auto const result = std::as_const(var).visit(
        Overloaded{ [](tr_variant::Vector const& values) -> int64_t
                    {
                        EXPECT_EQ(1U, std::size(values));
                        return values[0].value_if<int64_t>().value_or(-1);
                    },
                    [](auto&&) -> int64_t
                    {
                        ADD_FAILURE() << "unexpected alternative";
                        return -1;
                    } });

    EXPECT_EQ(99, result);
}

TEST_F(VariantTest, visitsNodesDepthFirst)
{
    auto serde = tr_variant_serde::json();
    serde.compact();
    serde.inplace();

    // set up a test variant to be visited
    static auto constexpr Input = R"({
        "files": [
            { "name": "file1", "size": 5, "pieces": [1, 2] },
            { "name": "file2", "size": 7, "pieces": [] }
        ],
        "meta": { "active": true }
    })"sv;
    auto const var = serde.parse(Input).value_or(tr_variant{});

    // set up some containers that we'll populate during `var.visit()`
    auto visited_counts = std::map<size_t, size_t>{};
    auto flattened = tr_variant::Vector{};
    flattened.reserve(64U);

    // set up the visitor
    auto flatten = [&](tr_variant const& node, auto const& self) -> void
    {
        ++visited_counts[node.index()];

        node.visit(
            [&](auto const& val)
            {
                // TODO(c++20): use std::remove_cvref_t (P0550R2) when GCC >= 9.1
                using ValueType = std::decay_t<decltype(val)>;

                if constexpr (
                    std::is_same_v<ValueType, bool> || //
                    std::is_same_v<ValueType, double> || //
                    std::is_same_v<ValueType, int64_t> || //
                    std::is_same_v<ValueType, std::monostate> || //
                    std::is_same_v<ValueType, std::nullptr_t> || //
                    std::is_same_v<ValueType, std::string_view> || //
                    std::is_same_v<ValueType, std::string>)
                {
                    flattened.emplace_back(val);
                }
                else if constexpr (std::is_same_v<ValueType, tr_variant::Vector>)
                {
                    for (auto const& child : val)
                    {
                        self(child, self);
                    }
                }
                else if constexpr (std::is_same_v<ValueType, tr_variant::Map>)
                {
                    for (auto const& [key, child] : val)
                    {
                        flattened.emplace_back(tr_variant::unmanaged_string(key));
                        self(child, self);
                    }
                }
            });
    };

    flatten(var, flatten);

    // test that the nodes were visited depth-first
    auto const actual = serde.to_string({ std::move(flattened) });
    auto constexpr Expected =
        R"(["files","name","file1","size",5,"pieces",1,2,"name","file2","size",7,"pieces","meta","active",true])"sv;
    EXPECT_EQ(Expected, actual);

    // test that we visited the expected number of nodes.
    //
    // FIXME(ckerr): `serde.inplace()` doesn't work on JSON right now.
    // RapidJSON always copies strings unless given mutable JSON input.
    // That's why StringViewIndex is missing two counts here.
    auto const expected_visited_count = std::map<size_t, size_t>{
        { tr_variant::BoolIndex, 1U }, //
        { tr_variant::IntIndex, 4U }, //
        { tr_variant::MapIndex, 4U }, //
        { tr_variant::StringIndex, 2U }, //
        { tr_variant::VectorIndex, 3U }, //
    };
    EXPECT_EQ(expected_visited_count, visited_counts);
}

TEST_F(VariantTest, variantFromBufFuzz)
{
    auto benc_serde = tr_variant_serde::json();
    auto json_serde = tr_variant_serde::json();
    auto buf = std::vector<char>{};

    for (size_t i = 0; i < 100000; ++i)
    {
        buf.resize(tr_rand_int(4096U));
        tr_rand_buffer(std::data(buf), std::size(buf));

        (void)benc_serde.inplace().parse(buf);
        (void)json_serde.inplace().parse(buf);
    }
}

TEST_F(VariantTest, serdeEnd)
{
    static auto constexpr TestsJson = std::array{
        std::tuple{ R"({ "json1": 1 }{ "json2": 2 })"sv, '{', 14U },
        std::tuple{ R"({ "json1": 1 })"sv, '\0', 14U },
    };
    static auto constexpr TestsBenc = std::array{
        std::tuple{ "d5:benc1i1eed5:benc2i2ee"sv, 'd', 12U },
        std::tuple{ "d5:benc1i1ee"sv, '\0', 12U },
    };

    for (auto [in, c, pos] : TestsJson)
    {
        auto json_serde = tr_variant_serde::json().inplace();
        auto json_var = json_serde.parse(in).value_or(tr_variant{});
        EXPECT_TRUE(json_var.holds_alternative<tr_variant::Map>()) << json_serde.error_;
        EXPECT_EQ(*json_serde.end(), c);
        EXPECT_EQ(json_serde.end() - std::data(in), pos);
    }

    for (auto [in, c, pos] : TestsBenc)
    {
        auto benc_serde = tr_variant_serde::benc().inplace();
        auto benc_var = benc_serde.parse(in).value_or(tr_variant{});
        EXPECT_TRUE(benc_var.holds_alternative<tr_variant::Map>()) << benc_serde.error_;
        EXPECT_EQ(*benc_serde.end(), c);
        EXPECT_EQ(benc_serde.end() - std::data(in), pos);
    }
}