//     __ _____ _____ _____
//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
// |  |  |__   |  |  | | | |  version 3.12.0
// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
//
// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
// SPDX-License-Identifier: MIT

// This file contains the C++20-only part of unit-user_defined_input.cpp (parsing with
// std::counted_iterator and std::default_sentinel_t). It is kept in a separate translation
// unit so the (much larger) unit-user_defined_input.cpp is built for C++11 only and not
// rebuilt for every C++ standard.

#include "doctest_compatibility.h"

#include <nlohmann/json.hpp>
using nlohmann::json;

#ifdef JSON_HAS_CPP_20
#include <cstddef>
#include <string>
#include <vector>

#if defined(__cpp_lib_concepts)
    #include <iterator>
#endif

#if defined(__cpp_lib_concepts)
TEST_CASE("Parse with std::counted_iterator and std::default_sentinel_t")
{
    using iterator_type = std::string::const_iterator;
    const std::string json_str = R"({"key":"value","array":[1,2,3]})";
    const auto len = static_cast<std::iter_difference_t<iterator_type>>(json_str.size());

    const std::counted_iterator<iterator_type> first(json_str.begin(), len);
    const json j = json::parse(first, std::default_sentinel);
    CHECK(j["key"] == "value");
    CHECK(j["array"].size() == 3);

    const std::counted_iterator<iterator_type> first2(json_str.begin(), len);
    CHECK(json::accept(first2, std::default_sentinel));
}

TEST_CASE("std::counted_iterator reaches the contiguous fast paths")
{
    // A sized sentinel makes the remaining element count computable in O(1), so
    // std::counted_iterator over a contiguous iterator must reach the same bulk
    // string/number scanners as a plain pointer - not just the byte-at-a-time
    // fallback (see #5268 for the equivalent memcpy fast path).
#if JSON_HAS_RANGES
    // JSON_HAS_RANGES is 0 on standard libraries with an incomplete <ranges>
    // (libstdc++ < 11, libc++ < 16), where the adapter deliberately falls back
    // to the byte-at-a-time scanner; everything below still has to work there.
    using adapter_type = nlohmann::detail::iterator_input_adapter<std::counted_iterator<const char*>, std::default_sentinel_t>;
    CHECK(adapter_type::supports_bulk_scan);
    CHECK(adapter_type::supports_seek);
#endif

    // exercise every fast path: long ASCII run, multibyte UTF-8, escapes, and
    // integer/floating-point numbers
    const std::string json_str =
        R"({"ascii":"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",)"
        "\"utf8\":\"\xe4\xb8\xad\xe6\x96\x87\xf0\x9f\x98\x80\xc3\xa9\","
        R"("escaped":"aéb\n\\","ints":[0,-1,18446744073709551615,-9223372036854775808],)"
        R"("floats":[1.5,-2.25e3,0.30000000000000004]})";
    const auto len = static_cast<std::iter_difference_t<const char*>>(json_str.size());

    const std::counted_iterator<const char*> first(json_str.data(), len);
    const json j = json::parse(first, std::default_sentinel);

    // parsing through the pointer adapter must give exactly the same result
    CHECK(j == json::parse(json_str));

#if !defined(JSON_NOEXCEPTION)
    // Diagnostics that quote the offending token are reconstructed from the
    // already-consumed input (supports_seek), a path a sized sentinel only
    // reaches now; check a few that include the "last read" text. Parsing
    // invalid input aborts when exceptions are off, hence the guard.
    // Raw strings and explicit bytes: an escaped literal and two literals
    // written next to each other both read as mistakes to static analysis.
    const auto byte = [](int value)
    {
        return std::string(1, static_cast<char>(value));
    };
    const std::vector<std::string> diagnostic_docs =
    {
        "1\nx",
        "truX",
        "[tru]",
        R"("abc)",
        R"(["\ud834"])",
        R"(["a)" + byte(0x01) + R"(b"])",
        R"([")" + byte(0xC3) + byte(0x28) + R"("])",
        "[1e]",
        R"(["aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaX)"
    };

    for (const auto& text : diagnostic_docs)
    {
        CAPTURE(text)
        const std::counted_iterator<const char*> it(text.data(), static_cast<std::iter_difference_t<const char*>>(text.size()));
        std::string counted_message;
        std::string string_message;
        try
        {
            const json counted_result = json::parse(it, std::default_sentinel);
            static_cast<void>(counted_result);
        }
        catch (const json::parse_error& e)
        {
            counted_message = e.what();
        }
        try
        {
            const json string_result = json::parse(text);
            static_cast<void>(string_result);
        }
        catch (const json::parse_error& e)
        {
            string_message = e.what();
        }
        CHECK_FALSE(counted_message.empty());
        CHECK(counted_message == string_message);
    }

    // and errors must still be reported identically
    const std::string bad = "[01\n]";
    const std::counted_iterator<const char*> bad_first(bad.data(), static_cast<std::iter_difference_t<const char*>>(bad.size()));
    std::string counted_what;
    std::string string_what;
    try
    {
        const json counted_result = json::parse(bad_first, std::default_sentinel);
        static_cast<void>(counted_result);
    }
    catch (const json::parse_error& e)
    {
        counted_what = e.what();
    }
    try
    {
        const json string_result = json::parse(bad);
        static_cast<void>(string_result);
    }
    catch (const json::parse_error& e)
    {
        string_what = e.what();
    }
    CHECK_FALSE(counted_what.empty());
    CHECK(counted_what == string_what);
#endif
}

#if !defined(JSON_NOEXCEPTION)
// several cases below are truncated on purpose, and parsing invalid input
// aborts when exceptions are off
TEST_CASE("std::counted_iterator bulk scanning stops at the counted end")
{
    // The count, not the size of the underlying buffer, is the end of the
    // input: the bulk scanners must never look at the bytes behind it, even
    // though they are readable. Each case is compared against parsing the
    // equivalent prefix as a std::string.
    const auto via_counted = [](const std::string & buf, std::size_t n) -> std::string
    {
        const std::counted_iterator<const char*> first(buf.data(), static_cast<std::iter_difference_t<const char*>>(n));
        try
        {
            const json j = json::parse(first, std::default_sentinel);
            return "OK|" + j.dump();
        }
        catch (const json::parse_error& e)
        {
            return {e.what()};
        }
    };
    const auto via_prefix = [](const std::string & buf, std::size_t n) -> std::string
    {
        try
        {
            const json j = json::parse(buf.substr(0, n));
            return "OK|" + j.dump();
        }
        catch (const json::parse_error& e)
        {
            return {e.what()};
        }
    };

    struct testcase // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init)
    {
        const char* buffer;
        std::size_t count;
    };
    const std::vector<testcase> cases =
    {
        {"[\"abc\"]____TRAILING____", 7},                    // exact fit, tail hidden
        {"[\"abcdefghijklmnop\"]____", 8},                   // cut inside a string
        {"[\"abc\"]____", 6},                                // cut just before the closing quote
        {"[12345]xxxxx", 4},                                 // cut inside a number
        {"[123]999999", 5},                                  // number ends exactly at the count
        {"[\"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\"]", 12},        // closing quote only behind the count
        {"[\"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\"]", 19},      // cut inside an 8-byte SWAR stride
        {"[\"\xe4\xb8\xad\xe6\x96\x87\"]", 5},               // cut inside a UTF-8 sequence
        {"[\"\xe4\xb8\xad\xe6\x96\x87\"]____", 10},          // complete UTF-8, tail hidden
        {"[1.25e3]TRAILINGDIGITS999", 7},                    // number token reaches the count
    };

    for (const auto& tc : cases)
    {
        CAPTURE(tc.buffer)
        CAPTURE(tc.count)
        const std::string buffer = tc.buffer;
        CHECK(via_counted(buffer, tc.count) == via_prefix(buffer, tc.count));
    }
}
#endif
#endif

#endif