#include "graphics/host_gpu/pageManager.h"

#include "graphics/host_gpu/regionDefinitions.h"

#include <algorithm>
#include <array>
#include <atomic>
#include <cstdarg>
#include <cstdio>
#include <cstdlib>
#include <limits>
#include <memory>
#include <mutex>
#include <vector>

#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
#ifndef NOMINMAX
#define NOMINMAX
#endif
#include <windows.h>
#undef min
#undef max
#elif defined(__APPLE__)
#include <mach/mach.h>
#include <mach/mach_vm.h>
#include <pthread.h>
#include <sys/mman.h>
#include <unistd.h>
#else
#include <cerrno>
#include <cstring>
#include <execinfo.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/syscall.h>
#include <unistd.h>
#endif

namespace Libs::Graphics {
namespace {

constexpr uint64_t PAGE_SIZE    = TRACKER_PAGE_SIZE;
constexpr uint64_t REGION_SIZE  = TRACKER_REGION_SIZE;
constexpr uint64_t ADDRESS_SIZE = TRACKER_ADDRESS_SIZE;
constexpr uint64_t REGION_COUNT = ADDRESS_SIZE / REGION_SIZE;

#if KYTY_PLATFORM != KYTY_PLATFORM_WINDOWS
// The tracker reuses Win32 memory-protection tags as internal page-state values (on
// Windows they come from <windows.h> and are what VirtualQuery returns). Mirror the
// canonical Win32 numeric values so the shared state-machine logic is identical.
constexpr uint32_t PAGE_NOACCESS  = 0x01;
constexpr uint32_t PAGE_READONLY  = 0x02;
constexpr uint32_t PAGE_READWRITE = 0x04;
#endif
constexpr uint64_t REGION_PAGES = REGION_SIZE / PAGE_SIZE;

constexpr uint32_t NO_ACCESS_PROTECTION  = PAGE_NOACCESS;
constexpr uint32_t READ_ONLY_PROTECTION  = PAGE_READONLY;
constexpr uint32_t READ_WRITE_PROTECTION = PAGE_READWRITE;

#if defined(__APPLE__)
// Map the tracker's Win32-style protection tags to POSIX mprotect flags.
static int PageProtToPosix(uint32_t protection) {
	switch (protection) {
		case PAGE_NOACCESS: return PROT_NONE;
		case PAGE_READONLY: return PROT_READ;
		case PAGE_READWRITE: return PROT_READ | PROT_WRITE;
		default: return PROT_NONE;
	}
}

// Query the current protection of the page containing vaddr via the Mach VM map and
// collapse it to the tracker's read/write tags (execute is irrelevant to write tracking).
static uint32_t MachQueryPageProt(uint64_t vaddr) {
	auto                           region_addr = static_cast<mach_vm_address_t>(vaddr);
	mach_vm_size_t                 region_size = 0;
	vm_region_basic_info_data_64_t info {};
	mach_msg_type_number_t         count       = VM_REGION_BASIC_INFO_COUNT_64;
	mach_port_t                    object_name = MACH_PORT_NULL;

	kern_return_t kr =
	    mach_vm_region(mach_task_self(), &region_addr, &region_size, VM_REGION_BASIC_INFO_64,
	                   reinterpret_cast<vm_region_info_t>(&info), &count, &object_name);
	if (kr != KERN_SUCCESS || region_addr > vaddr) {
		return PAGE_NOACCESS; // no region covering vaddr
	}
	if ((info.protection & VM_PROT_WRITE) != 0) {
		return PAGE_READWRITE;
	}
	if ((info.protection & VM_PROT_READ) != 0) {
		return PAGE_READONLY;
	}
	return PAGE_NOACCESS;
}
#elif defined(__linux__)
// Zero is the unknown protection sentinel.
constexpr uint32_t UNKNOWN_PROTECTION = 0;
#endif

thread_local bool g_in_fault_resolution = false;

[[noreturn]] void FailFast(const char* reason = nullptr) noexcept {
	std::fputs("PageManager fail-fast: ", stderr);
	std::fputs(reason != nullptr ? reason : "invalid page state", stderr);
	std::fputc('\n', stderr);
#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
	void*      frames[16] {};
	const auto frame_count =
	    CaptureStackBackTrace(0, static_cast<DWORD>(std::size(frames)), frames, nullptr);
	const auto image_base = reinterpret_cast<uintptr_t>(GetModuleHandleW(nullptr));
	for (uint16_t i = 0; i < frame_count; i++) {
		const auto address = reinterpret_cast<uintptr_t>(frames[i]);
		std::fprintf(stderr, "  frame[%u]=0x%016" PRIxPTR " image_rva=0x%016" PRIxPTR "\n", i,
		             address, address >= image_base ? address - image_base : 0);
	}
#elif !defined(__APPLE__)
	void*     frames[16] {};
	const int frame_count = ::backtrace(frames, static_cast<int>(std::size(frames)));
	::backtrace_symbols_fd(frames, frame_count, STDERR_FILENO);
#endif
	std::fflush(stderr);
#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
	TerminateProcess(GetCurrentProcess(), static_cast<UINT>(EXCEPTION_NONCONTINUABLE_EXCEPTION));
#endif
	std::_Exit(322);
}

[[noreturn]] void Fatal(const char* format, ...) {
	std::fputs("PageManager fatal: ", stderr);
	va_list args;
	va_start(args, format);
	std::vfprintf(stderr, format, args);
	va_end(args);
	std::fputc('\n', stderr);
	std::fflush(stderr);
	std::_Exit(322);
}

uint32_t CurrentThread() noexcept {
#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
	return GetCurrentThreadId();
#elif defined(__APPLE__)
	return static_cast<uint32_t>(pthread_mach_thread_np(pthread_self()));
#elif defined(__linux__)
	static thread_local const uint32_t tid = [] {
		const auto raw = static_cast<uint32_t>(::syscall(SYS_gettid));
		if (raw == 0) {
			FailFast("gettid returned the reserved zero owner token");
		}
		return raw;
	}();
	return tid;
#else
	FailFast("page tracking thread identity is unsupported on this platform");
#endif
}

#if defined(__linux__)
int ToHostProtection(uint32_t protection) {
	switch (protection) {
		case NO_ACCESS_PROTECTION: return PROT_NONE;
		case READ_ONLY_PROTECTION: return PROT_READ;
		case READ_WRITE_PROTECTION: return PROT_READ | PROT_WRITE;
		default: Fatal("unmappable protection 0x%08" PRIx32, protection);
	}
}

struct HostMapping {
	uint64_t end        = 0;
	uint32_t protection = UNKNOWN_PROTECTION;
};

// Async-signal-safe lookup in the address-ordered /proc/self/maps.
HostMapping QueryHostMapping(uint64_t vaddr) noexcept {
	int fd = ::open("/proc/self/maps", O_RDONLY | O_CLOEXEC); // NOLINT
	if (fd < 0) {
		return {};
	}

	enum class Field { Start, End, Perms, Rest };

	HostMapping result {};
	auto        field      = Field::Start;
	uint64_t    start      = 0;
	uint64_t    end        = 0;
	char        perms[4]   = {};
	uint32_t    perms_len  = 0;
	bool        line_valid = true;

	char buffer[8192];

	for (bool done = false; !done;) {
		const auto got = ::read(fd, buffer, sizeof(buffer));
		if (got < 0) {
			if (errno == EINTR) {
				continue;
			}
			break;
		}
		if (got == 0) {
			break;
		}

		for (ssize_t i = 0; i < got && !done; i++) {
			const char c = buffer[i];

			if (c == '\n') {
				field      = Field::Start;
				start      = 0;
				end        = 0;
				perms_len  = 0;
				line_valid = true;
				continue;
			}

			if (!line_valid) {
				continue;
			}

			switch (field) {
				case Field::Start:
				case Field::End: {
					uint64_t digit = 0;
					if (c >= '0' && c <= '9') {
						digit = static_cast<uint64_t>(c - '0');
					} else if (c >= 'a' && c <= 'f') {
						digit = static_cast<uint64_t>(c - 'a') + 10;
					} else if (c == '-' && field == Field::Start) {
						field = Field::End;
						break;
					} else if (c == ' ' && field == Field::End) {
						field     = Field::Perms;
						perms_len = 0;
						break;
					} else {
						line_valid = false;
						break;
					}

					auto& value = (field == Field::Start ? start : end);
					value       = (value << 4u) | digit;
					break;
				}

				case Field::Perms: {
					if (c != ' ') {
						if (perms_len < sizeof(perms)) {
							perms[perms_len] = c;
						}
						perms_len++;
						break;
					}

					if (vaddr < start) {
						done = true;
					} else if (vaddr < end && perms_len >= 2) {
						result.end        = end;
						result.protection = perms[1] == 'w'   ? READ_WRITE_PROTECTION
						                    : perms[0] == 'r' ? READ_ONLY_PROTECTION
						                                      : NO_ACCESS_PROTECTION;
						done              = true;
					} else {
						field = Field::Rest;
					}
					break;
				}

				case Field::Rest: break;
			}
		}
	}

	::close(fd);
	return result;
}

uint32_t QueryHostProtection(uint64_t vaddr) noexcept {
	return QueryHostMapping(vaddr).protection;
}
#endif

class SpinGuard final {
public:
	explicit SpinGuard(std::atomic_flag& lock): m_lock(lock) {
		while (m_lock.test_and_set(std::memory_order_acquire)) {
			std::atomic_signal_fence(std::memory_order_seq_cst);
		}
	}
	~SpinGuard() { m_lock.clear(std::memory_order_release); }
	KYTY_CLASS_NO_COPY(SpinGuard);

private:
	std::atomic_flag& m_lock;
};

void ValidateRange(uint64_t vaddr, uint64_t size) {
	if (vaddr == 0 || size == 0 || vaddr >= ADDRESS_SIZE || size > ADDRESS_SIZE - vaddr) {
		Fatal("invalid range vaddr=0x%016" PRIx64 ", size=0x%016" PRIx64, vaddr, size);
	}
}

uint64_t PageStart(uint64_t vaddr) {
	return vaddr & ~(PAGE_SIZE - 1);
}

uint64_t PageEnd(uint64_t vaddr, uint64_t size) {
	ValidateRange(vaddr, size);
	return PageStart(vaddr + size - 1) + PAGE_SIZE;
}

} // namespace

struct PageManager::Impl {
	struct PageState {
		std::atomic_flag lock                = ATOMIC_FLAG_INIT;
		uint32_t         mappings            = 0;
		uint32_t         gpu_read_mappings   = 0;
		uint32_t         gpu_write_mappings  = 0;
		uint32_t         write_watchers      = 0;
		uint32_t         access_watchers     = 0;
		uint32_t         original_protection = 0;
		uint32_t         backing_writer      = 0;
#if defined(__linux__)
		// Shadow the protection applied through Protect().
		uint32_t current_protection = UNKNOWN_PROTECTION;
#endif
		bool resolving            = false;
		bool resolving_read_write = false;
		bool late_read_pending    = false;
		bool late_write_pending   = false;
	};

	struct Region {
		std::array<PageState, REGION_PAGES> pages;
	};

	class PageRangeGuard final {
	public:
		explicit PageRangeGuard(std::span<PageState*> pages): m_pages(pages) {
			for (auto* page: m_pages) {
				while (page->lock.test_and_set(std::memory_order_acquire)) {
					std::atomic_signal_fence(std::memory_order_seq_cst);
				}
			}
		}
		~PageRangeGuard() {
			for (auto it = m_pages.rbegin(); it != m_pages.rend(); ++it) {
				(*it)->lock.clear(std::memory_order_release);
			}
		}
		KYTY_CLASS_NO_COPY(PageRangeGuard);

	private:
		std::span<PageState*> m_pages;
	};

	Impl(PageFaultHandler handler, void* context): fault_handler(handler), fault_context(context) {
		if (fault_handler == nullptr) {
			Fatal("null fault handler");
		}
#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
		SYSTEM_INFO info {};
		GetSystemInfo(&info);
		if (info.dwPageSize != PAGE_SIZE) {
			Fatal("unsupported host page size 0x%08" PRIx32,
			      static_cast<uint32_t>(info.dwPageSize));
		}
#elif defined(__APPLE__)
		// Under Rosetta the host page size is 4 KB, matching TRACKER_PAGE_SIZE.
		if (static_cast<uint64_t>(getpagesize()) != PAGE_SIZE) {
			Fatal("unsupported host page size 0x%08" PRIx32, static_cast<uint32_t>(getpagesize()));
		}
#else
		const auto host_page_size = ::sysconf(_SC_PAGESIZE);
		if (host_page_size < 0 || static_cast<uint64_t>(host_page_size) != PAGE_SIZE) {
			Fatal("unsupported host page size %ld", static_cast<long>(host_page_size));
		}
#endif
		regions = std::make_unique<std::atomic<Region*>[]>(REGION_COUNT);
		for (uint64_t i = 0; i < REGION_COUNT; i++) {
			regions[i].store(nullptr, std::memory_order_relaxed);
		}
	}

	~Impl() {
		for (const auto& region: region_storage) {
			for (auto& page: region->pages) {
				SpinGuard lock(page.lock);
				if (page.mappings != 0 || page.gpu_read_mappings != 0 ||
				    page.gpu_write_mappings != 0 || page.write_watchers != 0 ||
				    page.access_watchers != 0 || page.backing_writer != 0 || page.resolving) {
					FailFast("PageManager destroyed with live page state");
				}
			}
		}
	}

	Region* FindRegion(uint64_t vaddr) const noexcept {
		return vaddr < ADDRESS_SIZE ? regions[vaddr / REGION_SIZE].load(std::memory_order_acquire)
		                            : nullptr;
	}

	Region* GetOrCreateRegion(uint64_t vaddr) {
		const auto index = vaddr / REGION_SIZE;
		if (auto* region = regions[index].load(std::memory_order_acquire); region != nullptr) {
			return region;
		}
		std::lock_guard lock(region_mutex);
		if (auto* region = regions[index].load(std::memory_order_acquire); region != nullptr) {
			return region;
		}
		auto  region = std::make_unique<Region>();
		auto* ptr    = region.get();
		region_storage.push_back(std::move(region));
		regions[index].store(ptr, std::memory_order_release);
		return ptr;
	}

	PageState& GetPage(Region& region, uint64_t vaddr) const {
		return region.pages[(vaddr % REGION_SIZE) / PAGE_SIZE];
	}

	static uint32_t WatcherProtection(const PageState& page) {
		if (page.access_watchers != 0) {
			return NO_ACCESS_PROTECTION;
		}
		if (page.write_watchers != 0) {
			return READ_ONLY_PROTECTION;
		}
		return page.original_protection;
	}

	static void PublishDelayedFaults(PageState& page, uint32_t old_protection,
	                                 uint32_t new_protection) {
		if (old_protection == NO_ACCESS_PROTECTION && new_protection != NO_ACCESS_PROTECTION) {
			page.late_read_pending = true;
		}
		if ((old_protection == NO_ACCESS_PROTECTION || old_protection == READ_ONLY_PROTECTION) &&
		    new_protection == READ_WRITE_PROTECTION) {
			page.late_write_pending = true;
		}
	}

	static void ValidateInitialProtection(std::span<PageState*> pages, uint64_t vaddr) {
		const auto end = vaddr + pages.size() * PAGE_SIZE;
#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
		for (auto address = vaddr; address < end;) {
			MEMORY_BASIC_INFORMATION info {};
			if (VirtualQuery(reinterpret_cast<const void*>(static_cast<uintptr_t>(address)), &info,
			                 sizeof(info)) == 0 ||
			    info.State != MEM_COMMIT || info.Protect != PAGE_READWRITE) {
				Fatal("basic path requires PAGE_READWRITE at 0x%016" PRIx64 " (state=0x%08" PRIx32
				      ", protection=0x%08" PRIx32 ")",
				      address, static_cast<uint32_t>(info.State),
				      static_cast<uint32_t>(info.Protect));
			}
			const auto region_end = reinterpret_cast<uint64_t>(info.BaseAddress) + info.RegionSize;
			if (region_end <= address) {
				Fatal("VirtualQuery returned an invalid region at 0x%016" PRIx64, address);
			}
			address = std::min(end, region_end);
		}
#elif defined(__APPLE__)
		for (auto address = vaddr; address < end; address += PAGE_SIZE) {
			const uint32_t protection = MachQueryPageProt(address);
			if (protection != PAGE_READWRITE) {
				Fatal("basic path requires PAGE_READWRITE at 0x%016" PRIx64
				      " (protection=0x%08" PRIx32 ")",
				      address, protection);
			}
		}
#else
		for (auto address = vaddr; address < end;) {
			const auto mapping = QueryHostMapping(address);
			if (mapping.protection != READ_WRITE_PROTECTION || mapping.end <= address) {
				Fatal("basic path requires a read/write mapping at 0x%016" PRIx64
				      " (protection=0x%08" PRIx32 ")",
				      address, mapping.protection);
			}
			address = std::min(end, mapping.end);
		}
		for (auto* page: pages) {
			page->current_protection = READ_WRITE_PROTECTION;
		}
#endif
		for (auto* page: pages) {
			page->original_protection = READ_WRITE_PROTECTION;
		}
	}

	static bool AllowsAccess([[maybe_unused]] const PageState& page, uint64_t vaddr,
	                         PageFaultAccess access) noexcept {
#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
		MEMORY_BASIC_INFORMATION info {};
		if (VirtualQuery(reinterpret_cast<const void*>(static_cast<uintptr_t>(vaddr)), &info,
		                 sizeof(info)) == 0 ||
		    info.State != MEM_COMMIT) {
			return false;
		}
		switch (access) {
			case PageFaultAccess::Read:
				return info.Protect == PAGE_READONLY || info.Protect == PAGE_READWRITE;
			case PageFaultAccess::Write: return info.Protect == PAGE_READWRITE;
			default: return false;
		}
#elif defined(__APPLE__)
		const uint32_t protection = MachQueryPageProt(vaddr);
		switch (access) {
			case PageFaultAccess::Read:
				return protection == PAGE_READONLY || protection == PAGE_READWRITE;
			case PageFaultAccess::Write: return protection == PAGE_READWRITE;
			default: return false;
		}
#else
		const auto permitted = [](uint32_t protection, PageFaultAccess wanted) {
			switch (wanted) {
				case PageFaultAccess::Read:
					return protection == READ_ONLY_PROTECTION ||
					       protection == READ_WRITE_PROTECTION;
				case PageFaultAccess::Write: return protection == READ_WRITE_PROTECTION;
				default: return false;
			}
		};

		if (!permitted(page.current_protection, access)) {
			return false;
		}
		return permitted(QueryHostProtection(vaddr), access);
#endif
	}

	static void ProtectRange(std::span<PageState*> pages, uint64_t vaddr, uint32_t protection,
	                         std::span<const uint32_t> expected_old, bool fault_path) noexcept {
		const auto size = pages.size() * PAGE_SIZE;
		if (pages.size() != expected_old.size()) {
			FailFast("protection range state size mismatch");
		}
#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
		struct HostRange {
			uint64_t begin = 0;
			uint64_t end   = 0;
		};
		std::vector<HostRange> host_ranges;
		const auto             end = vaddr + size;
		for (auto address = vaddr; address < end;) {
			MEMORY_BASIC_INFORMATION info {};
			if (VirtualQuery(reinterpret_cast<const void*>(static_cast<uintptr_t>(address)), &info,
			                 sizeof(info)) == 0 ||
			    info.State != MEM_COMMIT) {
				if (fault_path) {
					FailFast("VirtualProtect fault transition did not match expected protection");
				}
				Fatal("invalid protection transition at 0x%016" PRIx64 ", state=0x%08" PRIx32
				      ", new=0x%08" PRIx32,
				      address, static_cast<uint32_t>(info.State), protection);
			}
			const auto region_end = reinterpret_cast<uint64_t>(info.BaseAddress) + info.RegionSize;
			const auto query_end  = std::min(end, region_end);
			if (query_end <= address) {
				if (fault_path) {
					FailFast("VirtualQuery returned an invalid fault transition region");
				}
				Fatal("VirtualQuery returned an invalid region at 0x%016" PRIx64, address);
			}
			const auto first_page = static_cast<size_t>((address - vaddr) / PAGE_SIZE);
			const auto last_page =
			    static_cast<size_t>((query_end - vaddr + PAGE_SIZE - 1) / PAGE_SIZE);
			for (auto page = first_page; page < last_page; page++) {
				if (info.Protect != expected_old[page]) {
					if (fault_path) {
						FailFast(
						    "VirtualProtect fault transition did not match expected protection");
					}
					Fatal("invalid protection transition at 0x%016" PRIx64 ", actual=0x%08" PRIx32
					      ", expected=0x%08" PRIx32 ", new=0x%08" PRIx32,
					      vaddr + page * PAGE_SIZE, static_cast<uint32_t>(info.Protect),
					      expected_old[page], protection);
				}
			}
			const auto allocation = reinterpret_cast<uint64_t>(info.AllocationBase);
			if (host_ranges.empty() || allocation != host_ranges.back().begin) {
				host_ranges.push_back({allocation, query_end});
			} else {
				host_ranges.back().end = query_end;
			}
			address = query_end;
		}
		for (auto range: host_ranges) {
			range.begin               = std::max(range.begin, vaddr);
			DWORD      old_protection = 0;
			const auto first_page     = static_cast<size_t>((range.begin - vaddr) / PAGE_SIZE);
			if (VirtualProtect(reinterpret_cast<void*>(static_cast<uintptr_t>(range.begin)),
			                   range.end - range.begin, protection, &old_protection) == 0 ||
			    old_protection != expected_old[first_page]) {
				if (fault_path) {
					FailFast("VirtualProtect fault transition did not match expected protection");
				}
				Fatal("invalid protection transition at 0x%016" PRIx64 ", old=0x%08" PRIx32
				      ", expected=0x%08" PRIx32 ", new=0x%08" PRIx32,
				      range.begin, static_cast<uint32_t>(old_protection), expected_old[first_page],
				      protection);
			}
		}
#elif defined(__APPLE__)
		// mprotect cannot report the previous protection, so the expected_old comparison
		// is dropped; the tracker is the sole mutator of these pages and drives the
		// transition from its own shadow state.
		(void)expected_old;
		if (mprotect(reinterpret_cast<void*>(static_cast<uintptr_t>(vaddr)), size,
		             PageProtToPosix(protection)) != 0) {
			if (fault_path) {
				FailFast("mprotect fault transition failed");
			}
			Fatal("mprotect failed at 0x%016" PRIx64 ", new=0x%08" PRIx32, vaddr, protection);
		}
#else
		for (size_t i = 0; i < pages.size(); i++) {
			const auto actual = pages[i]->current_protection;
			if (actual != UNKNOWN_PROTECTION && actual != expected_old[i]) {
				if (fault_path) {
					FailFast("mprotect fault transition did not match expected protection");
				}
				Fatal("invalid protection transition at 0x%016" PRIx64 ", old=0x%08" PRIx32
				      ", expected=0x%08" PRIx32 ", new=0x%08" PRIx32,
				      vaddr + i * PAGE_SIZE, actual, expected_old[i], protection);
			}
		}
		if (::mprotect(reinterpret_cast<void*>(static_cast<uintptr_t>(vaddr)), size,
		               ToHostProtection(protection)) != 0) {
			if (fault_path) {
				FailFast("mprotect failed on the fault path");
			}
			Fatal("mprotect failed at 0x%016" PRIx64 ", new=0x%08" PRIx32 " (%s)", vaddr,
			      protection, std::strerror(errno));
		}
		for (auto* page: pages) {
			page->current_protection = protection;
		}
#endif
	}

	static void Protect(PageState& page, uint64_t vaddr, uint32_t protection, uint32_t expected_old,
	                    bool fault_path) noexcept {
		PageState* pages[]    = {&page};
		uint32_t   expected[] = {expected_old};
		ProtectRange(pages, vaddr, protection, expected, fault_path);
	}

	std::unique_ptr<std::atomic<Region*>[]> regions;
	std::vector<std::unique_ptr<Region>>    region_storage;
	std::mutex                              region_mutex;
	PageFaultHandler                        fault_handler = nullptr;
	void*                                   fault_context = nullptr;
};

static_assert(std::atomic<void*>::is_always_lock_free);

PageManager::PageManager(PageFaultHandler fault_handler, void* fault_context)
    : m_impl(std::make_unique<Impl>(fault_handler, fault_context)) {}

PageManager::~PageManager() = default;

uint64_t PageManager::GetPageSize() const {
	if (g_in_fault_resolution) {
		FailFast("nested page fault while resolving a watched page");
	}
	return PAGE_SIZE;
}

bool PageManager::IsTracked(uint64_t vaddr) const noexcept {
	if (g_in_fault_resolution) {
		FailFast("IsTracked called during fault resolution");
	}
	auto* region = m_impl->FindRegion(vaddr);
	if (region == nullptr) {
		return false;
	}
	auto&     page = m_impl->GetPage(*region, vaddr);
	SpinGuard lock(page.lock);
	return page.write_watchers != 0 || page.access_watchers != 0;
}

bool PageManager::IsMapped(uint64_t vaddr, uint64_t size) const noexcept {
	if (vaddr == 0 || size == 0 || vaddr >= ADDRESS_SIZE || size > ADDRESS_SIZE - vaddr) {
		return false;
	}
	const auto end = PageStart(vaddr + size - 1) + PAGE_SIZE;
	for (auto page_vaddr = PageStart(vaddr); page_vaddr < end; page_vaddr += PAGE_SIZE) {
		auto* region = m_impl->FindRegion(page_vaddr);
		if (region == nullptr) {
			return false;
		}
		auto&     page = m_impl->GetPage(*region, page_vaddr);
		SpinGuard lock(page.lock);
		if (page.mappings == 0) {
			return false;
		}
	}
	return true;
}

bool PageManager::HasGpuAccess(uint64_t vaddr, uint64_t size, GpuAccess access) const noexcept {
	if (access != GpuAccess::Read && access != GpuAccess::Write && access != GpuAccess::ReadWrite) {
		FailFast("HasGpuAccess received an invalid GPU access mode");
	}
	const bool need_read  = access == GpuAccess::Read || access == GpuAccess::ReadWrite;
	const bool need_write = access == GpuAccess::Write || access == GpuAccess::ReadWrite;
	if (vaddr == 0 || size == 0 || vaddr >= ADDRESS_SIZE || size > ADDRESS_SIZE - vaddr) {
		return false;
	}
	const auto end = PageEnd(vaddr, size);
	for (auto addr = PageStart(vaddr); addr < end; addr += PAGE_SIZE) {
		auto* region = m_impl->FindRegion(addr);
		if (region == nullptr) {
			return false;
		}
		auto&     page = m_impl->GetPage(*region, addr);
		SpinGuard lock(page.lock);
		if ((need_read && page.gpu_read_mappings == 0) ||
		    (need_write && page.gpu_write_mappings == 0)) {
			return false;
		}
	}
	return true;
}

void PageManager::UpdatePageWatchers(bool track, uint64_t vaddr, uint64_t size,
                                     PageWatchMode mode) {
	if (mode != PageWatchMode::Write && mode != PageWatchMode::ReadWrite) {
		Fatal("invalid watcher mode");
	}
	const auto begin = PageStart(vaddr);
	const auto end   = PageEnd(vaddr, size);
	for (auto chunk_begin = begin; chunk_begin < end;) {
		const auto chunk_end = std::min(end, (chunk_begin / REGION_SIZE + 1) * REGION_SIZE);
		auto*      region =
		    track ? m_impl->GetOrCreateRegion(chunk_begin) : m_impl->FindRegion(chunk_begin);
		if (region == nullptr) {
			Fatal("untracking unknown page 0x%016" PRIx64, chunk_begin);
		}

		const auto page_count = static_cast<size_t>((chunk_end - chunk_begin) / PAGE_SIZE);
		std::vector<Impl::PageState*> pages;
		pages.reserve(page_count);
		for (auto address = chunk_begin; address < chunk_end; address += PAGE_SIZE) {
			pages.push_back(&m_impl->GetPage(*region, address));
		}
		Impl::PageRangeGuard lock(pages);

		std::vector<uint8_t> first_watchers(page_count);
		for (size_t i = 0; i < page_count; i++) {
			auto&      page    = *pages[i];
			const auto address = chunk_begin + i * PAGE_SIZE;
			if (page.resolving && track) {
				FailFast("new page watcher raced active fault resolution");
			}
			if (page.mappings == 0) {
				Fatal("watching unmapped page 0x%016" PRIx64, address);
			}
			auto& watchers =
			    (mode == PageWatchMode::ReadWrite ? page.access_watchers : page.write_watchers);
			if (track) {
				if (watchers == std::numeric_limits<uint32_t>::max()) {
					Fatal("watcher overflow at 0x%016" PRIx64, address);
				}
				first_watchers[i] = page.write_watchers == 0 && page.access_watchers == 0;
			} else {
				if (watchers == 0) {
					Fatal("watcher underflow at 0x%016" PRIx64, address);
				}
				if (page.backing_writer != 0 && page.backing_writer != CurrentThread()) {
					Fatal("backing write ownership changed at 0x%016" PRIx64, address);
				}
			}
		}

		if (track) {
			for (size_t first = 0; first < page_count;) {
				while (first < page_count && first_watchers[first] == 0) {
					first++;
				}
				auto last = first;
				while (last < page_count && first_watchers[last] != 0) {
					last++;
				}
				if (first != last) {
					Impl::ValidateInitialProtection(std::span {pages}.subspan(first, last - first),
					                                chunk_begin + first * PAGE_SIZE);
				}
				first = last;
			}
		}

		std::vector<uint32_t> old_protections(page_count);
		std::vector<uint32_t> new_protections(page_count);
		std::vector<uint8_t>  transitions(page_count);
		for (size_t i = 0; i < page_count; i++) {
			auto& page = *pages[i];
			auto& watchers =
			    (mode == PageWatchMode::ReadWrite ? page.access_watchers : page.write_watchers);
			const auto old_protection = Impl::WatcherProtection(page);
			if (track) {
				watchers++;
			} else {
				watchers--;
			}
			const auto new_protection = Impl::WatcherProtection(page);
			old_protections[i]        = old_protection;
			new_protections[i]        = new_protection;
			if (new_protection != old_protection && (track || page.backing_writer == 0)) {
				transitions[i] = 1;
			}
		}

		for (size_t first = 0; first < page_count;) {
			while (first < page_count && transitions[first] == 0) {
				first++;
			}
			if (first == page_count) {
				break;
			}
			const auto protection = new_protections[first];
			auto       current    = first + 1;
			auto       last       = current;
			for (; current < page_count && new_protections[current] == protection; current++) {
				if (old_protections[current] != new_protections[current] &&
				    transitions[current] == 0) {
					break;
				}
				if (transitions[current] != 0) {
					last = current + 1;
				}
			}
			Impl::ProtectRange(std::span {pages}.subspan(first, last - first),
			                   chunk_begin + first * PAGE_SIZE, protection,
			                   std::span {old_protections}.subspan(first, last - first), false);
			first = current;
		}

		for (size_t i = 0; i < page_count; i++) {
			auto&      page       = *pages[i];
			const auto protection = new_protections[i];
			if (track) {
				switch (protection) {
					case NO_ACCESS_PROTECTION:
						page.late_read_pending  = false;
						page.late_write_pending = false;
						break;
					case READ_ONLY_PROTECTION: page.late_write_pending = false; break;
					default: break;
				}
			} else if (page.backing_writer == 0) {
				Impl::PublishDelayedFaults(page, old_protections[i], protection);
				if (page.write_watchers == 0 && page.access_watchers == 0) {
					page.original_protection = 0;
				}
			}
		}
		chunk_begin = chunk_end;
	}
}

void PageManager::OnGpuMap(uint64_t vaddr, uint64_t size, GpuAccess access) {
	if (g_in_fault_resolution) {
		FailFast("GPU mapping changed during fault resolution");
	}
	if (access != GpuAccess::Read && access != GpuAccess::Write && access != GpuAccess::ReadWrite) {
		FailFast("GPU map received an invalid access mode");
	}
	const bool gpu_read  = access == GpuAccess::Read || access == GpuAccess::ReadWrite;
	const bool gpu_write = access == GpuAccess::Write || access == GpuAccess::ReadWrite;
	const auto end       = PageEnd(vaddr, size);
	for (auto addr = PageStart(vaddr); addr < end; addr += PAGE_SIZE) {
		auto&     page = m_impl->GetPage(*m_impl->GetOrCreateRegion(addr), addr);
		SpinGuard lock(page.lock);
		if (page.resolving || page.mappings == std::numeric_limits<uint32_t>::max() ||
		    (gpu_read && page.gpu_read_mappings == std::numeric_limits<uint32_t>::max()) ||
		    (gpu_write && page.gpu_write_mappings == std::numeric_limits<uint32_t>::max())) {
			Fatal("invalid map state at 0x%016" PRIx64, addr);
		}
		page.mappings++;
		page.gpu_read_mappings += gpu_read ? 1u : 0u;
		page.gpu_write_mappings += gpu_write ? 1u : 0u;
#if defined(__linux__)
		// New guest mappings start read/write.
		if (page.current_protection == UNKNOWN_PROTECTION) {
			page.current_protection = READ_WRITE_PROTECTION;
		}
#endif
	}
}

void PageManager::OnGpuUnmap(uint64_t vaddr, uint64_t size, GpuAccess access) {
	if (g_in_fault_resolution) {
		FailFast("GPU unmapping changed during fault resolution");
	}
	if (access != GpuAccess::Read && access != GpuAccess::Write && access != GpuAccess::ReadWrite) {
		FailFast("GPU unmap received an invalid access mode");
	}
	const bool gpu_read  = access == GpuAccess::Read || access == GpuAccess::ReadWrite;
	const bool gpu_write = access == GpuAccess::Write || access == GpuAccess::ReadWrite;
	const auto end       = PageEnd(vaddr, size);
	for (auto page_vaddr = PageStart(vaddr); page_vaddr < end; page_vaddr += PAGE_SIZE) {
		auto* region = m_impl->FindRegion(page_vaddr);
		if (region == nullptr) {
			Fatal("unmapping unknown page 0x%016" PRIx64, page_vaddr);
		}
		auto&     page = m_impl->GetPage(*region, page_vaddr);
		SpinGuard lock(page.lock);
		if (page.resolving || page.mappings == 0 || (gpu_read && page.gpu_read_mappings == 0) ||
		    (gpu_write && page.gpu_write_mappings == 0) ||
		    (page.mappings == 1 && (page.write_watchers != 0 || page.access_watchers != 0))) {
			Fatal("invalid unmap state at 0x%016" PRIx64, page_vaddr);
		}
		page.mappings--;
		page.gpu_read_mappings -= gpu_read ? 1u : 0u;
		page.gpu_write_mappings -= gpu_write ? 1u : 0u;
		if (page.mappings == 0) {
			if (page.gpu_read_mappings != 0 || page.gpu_write_mappings != 0) {
				FailFast("GPU unmap left nonzero GPU mapping counts");
			}
			page.late_read_pending  = false;
			page.late_write_pending = false;
		}
	}
}

PageManager::BackingWrite::BackingWrite(PageManager& manager, uint64_t vaddr,
                                        uint64_t size) noexcept
    : m_manager(manager), m_vaddr(vaddr), m_size(size) {
	m_manager.BeginBackingWrite(vaddr, size);
}

PageManager::BackingWrite::~BackingWrite() {
	m_manager.EndBackingWrite(m_vaddr, m_size);
}

std::vector<std::unique_ptr<PageManager::BackingWrite>>
PageManager::ReserveBackingWrites(std::span<const RangeSet::Range> ranges) {
	if (ranges.empty()) {
		Fatal("cannot reserve empty backing-write ranges");
	}
	std::vector<std::unique_ptr<BackingWrite>> writes;
	writes.reserve(ranges.size());
	uint64_t begin = 0;
	uint64_t end   = 0;
	for (const auto& range: ranges) {
		if (range.address == 0 || range.size == 0 || range.size > UINT64_MAX - range.address ||
		    range.address + range.size > UINT64_MAX - (PAGE_SIZE - 1)) {
			Fatal("invalid backing-write range");
		}
		const auto page_begin = PageStart(range.address);
		const auto page_end   = PageStart(range.address + range.size + PAGE_SIZE - 1);
		if (begin != 0 && page_begin > end) {
			writes.push_back(std::make_unique<BackingWrite>(*this, begin, end - begin));
			begin = 0;
		}
		if (begin == 0) {
			begin = page_begin;
			end   = page_end;
		} else {
			end = std::max(end, page_end);
		}
	}
	writes.push_back(std::make_unique<BackingWrite>(*this, begin, end - begin));
	return writes;
}

void PageManager::BeginBackingWrite(uint64_t vaddr, uint64_t size) noexcept {
	if (g_in_fault_resolution) {
		FailFast("backing write began during fault resolution");
	}
	const auto end    = PageEnd(vaddr, size);
	const auto writer = CurrentThread();
	for (auto address = PageStart(vaddr); address < end; address += PAGE_SIZE) {
		auto* region = m_impl->FindRegion(address);
		if (region == nullptr) {
			Fatal("backing write reserves an unknown page at 0x%016" PRIx64, address);
		}
		auto&     page = m_impl->GetPage(*region, address);
		SpinGuard lock(page.lock);
		if (page.mappings == 0 || page.resolving || page.backing_writer != 0 ||
		    page.access_watchers == 0) {
			Fatal("backing write races page resolution at 0x%016" PRIx64, address);
		}
		page.resolving            = true;
		page.resolving_read_write = true;
		page.backing_writer       = writer;
	}
}

void PageManager::EndBackingWrite(uint64_t vaddr, uint64_t size) noexcept {
	if (g_in_fault_resolution) {
		FailFast("backing write ended during fault resolution");
	}
	const auto end    = PageEnd(vaddr, size);
	const auto writer = CurrentThread();
	for (auto address = PageStart(vaddr); address < end; address += PAGE_SIZE) {
		auto* region = m_impl->FindRegion(address);
		if (region == nullptr) {
			FailFast("backing write ended for an unknown page");
		}
		auto&     page = m_impl->GetPage(*region, address);
		SpinGuard lock(page.lock);
		if (!page.resolving || page.backing_writer != writer) {
			FailFast("backing write ended without matching owner and resolving state");
		}
		const auto old_protection = NO_ACCESS_PROTECTION;
		const auto new_protection = Impl::WatcherProtection(page);
		if (new_protection != old_protection) {
			Impl::Protect(page, address, new_protection, old_protection, false);
		}
		Impl::PublishDelayedFaults(page, old_protection, new_protection);
		if (page.write_watchers == 0 && page.access_watchers == 0) {
			page.original_protection = 0;
		}
		page.backing_writer       = 0;
		page.resolving            = false;
		page.resolving_read_write = false;
	}
}

bool PageManager::HandleFault(PageFaultAccess access, uint64_t fault_vaddr) noexcept {
	if (g_in_fault_resolution) {
		FailFast("nested HandleFault call");
	}
	auto* region = m_impl->FindRegion(fault_vaddr);
	if (region == nullptr) {
		return false;
	}
	auto& page   = m_impl->GetPage(*region, fault_vaddr);
	bool  waited = false;
	while (true) {
		SpinGuard lock(page.lock);
		if (access == PageFaultAccess::Read && page.late_read_pending &&
		    Impl::AllowsAccess(page, fault_vaddr, access)) {
			page.late_read_pending = false;
			return true;
		}
		if (access == PageFaultAccess::Write && page.late_write_pending &&
		    Impl::AllowsAccess(page, fault_vaddr, access)) {
			page.late_write_pending = false;
			return true;
		}
		if (page.resolving) {
			if (page.backing_writer == CurrentThread()) {
				FailFast("backing writer faulted on its own reserved page");
			}
			if ((!page.resolving_read_write && access != PageFaultAccess::Write) ||
			    (page.resolving_read_write && access != PageFaultAccess::Read &&
			     access != PageFaultAccess::Write)) {
				FailFast("fault access is incompatible with the active resolver");
			}
			waited = true;
			continue;
		}
		if (page.write_watchers == 0 && page.access_watchers == 0) {
			if (access != PageFaultAccess::Read && access != PageFaultAccess::Write) {
				return false;
			}
			bool&      pending = (access == PageFaultAccess::Read ? page.late_read_pending
			                                                      : page.late_write_pending);
			const bool allowed = Impl::AllowsAccess(page, fault_vaddr, access);
			pending            = false;
			if (waited && !allowed) {
				FailFast("page remained inaccessible after waiting for its resolver");
			}
			// More than one CPU can fault before a protection transition becomes visible. The first
			// delayed fault consumes the hint bit; later faults must also resume once the mapped
			// page already permits the requested access. A genuinely read-only/no-access page still
			// falls through to the guest exception path.
			return allowed;
		}
		if ((access != PageFaultAccess::Read && access != PageFaultAccess::Write) ||
		    (access == PageFaultAccess::Read && page.access_watchers == 0)) {
			FailFast("fault access is incompatible with active page watchers");
		}
		page.resolving            = true;
		page.resolving_read_write = page.access_watchers != 0;
		break;
	}
	g_in_fault_resolution = true;
	const bool handled    = m_impl->fault_handler(m_impl->fault_context, access, fault_vaddr, 1,
	                                              PageFaultPhase::Invalidate);
	g_in_fault_resolution = false;
	{
		SpinGuard lock(page.lock);
		if (!handled || !page.resolving) {
			FailFast("fault invalidation did not preserve the resolving state");
		}
	}
	g_in_fault_resolution = true;
	const bool completed  = m_impl->fault_handler(m_impl->fault_context, access, fault_vaddr, 1,
	                                              PageFaultPhase::Complete);
	g_in_fault_resolution = false;
	{
		SpinGuard lock(page.lock);
		if (!completed || !page.resolving) {
			FailFast("fault completion did not preserve the resolving state");
		}
		if (page.write_watchers != 0 || page.access_watchers != 0) {
			const auto old_protection  = Impl::WatcherProtection(page);
			const bool read_only_fault = access == PageFaultAccess::Read;
			if (read_only_fault && page.access_watchers == 0) {
				FailFast("read fault completed without a read/write watcher");
			}
			page.access_watchers = 0;
			if (!read_only_fault) {
				page.write_watchers = 0;
			}
			const auto restored_protection = Impl::WatcherProtection(page);
			Impl::Protect(page, PageStart(fault_vaddr), restored_protection, old_protection, true);
			if (page.write_watchers == 0) {
				page.original_protection = 0;
			}
			Impl::PublishDelayedFaults(page, old_protection, restored_protection);
		} else if (!Impl::AllowsAccess(page, fault_vaddr, access)) {
			FailFast("fault completion left the page inaccessible");
		}
		page.resolving            = false;
		page.resolving_read_write = false;
	}
	g_in_fault_resolution = true;
	const bool released   = m_impl->fault_handler(m_impl->fault_context, access, fault_vaddr, 1,
	                                              PageFaultPhase::Release);
	g_in_fault_resolution = false;
	if (!released) {
		FailFast("fault release callback failed");
	}
	return true;
}

} // namespace Libs::Graphics