//go:build windows

// deathwatch: reads Elden Ring's death counter read-only, straight from
// the process (the same byte pattern / offset used by LiveSplit's
// "eldenring_boss_timer.asl" ASL script, verified by hand on this PC).
// Writes nothing to the game's memory.
//
// Exposes:
//
//	GET  /            -> status panel (HTML)
//	GET  /?view=overlay -> transparent version for OBS Browser Source
//	GET  /deaths      -> {"deaths":N,"players":[...],"character":"...","slot":N,...}
package main

import (
	"crypto/tls"
	_ "embed"
	"encoding/binary"
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"os"
	"strconv"
	"strings"
	"syscall"
	"time"
	"unicode/utf16"
	"unsafe"
)

//go:embed overlay.html
var overlayHTML []byte

const (
	processName = "eldenring.exe"

	processQueryInformation = 0x0400
	processVMRead           = 0x0010
	th32csSnapProcess       = 0x00000002
	th32csSnapModule        = 0x00000008
	th32csSnapModule32      = 0x00000010
	maxPath                 = 260
)

var (
	kernel32                     = syscall.NewLazyDLL("kernel32.dll")
	procOpenProcess              = kernel32.NewProc("OpenProcess")
	procCloseHandle              = kernel32.NewProc("CloseHandle")
	procReadProcessMemory        = kernel32.NewProc("ReadProcessMemory")
	procCreateToolhelp32Snapshot = kernel32.NewProc("CreateToolhelp32Snapshot")
	procModule32FirstW           = kernel32.NewProc("Module32FirstW")
	procModule32NextW            = kernel32.NewProc("Module32NextW")
	procProcess32FirstW          = kernel32.NewProc("Process32FirstW")
	procProcess32NextW           = kernel32.NewProc("Process32NextW")

	versionDLL                  = syscall.NewLazyDLL("version.dll")
	procGetFileVersionInfoSizeW = versionDLL.NewProc("GetFileVersionInfoSizeW")
	procGetFileVersionInfoW     = versionDLL.NewProc("GetFileVersionInfoW")
	procVerQueryValueW          = versionDLL.NewProc("VerQueryValueW")
)

// vsFixedFileInfo is Windows's VS_FIXEDFILEINFO struct: used to pull the
// game's version straight from eldenring.exe, same as SoulMemory (which
// reads MainModule.FileVersionInfo.ProductVersion).
type vsFixedFileInfo struct {
	Signature        uint32
	StrucVersion     uint32
	FileVersionMS    uint32
	FileVersionLS    uint32
	ProductVersionMS uint32
	ProductVersionLS uint32
	FileFlagsMask    uint32
	FileFlags        uint32
	FileOS           uint32
	FileType         uint32
	FileSubtype      uint32
	FileDateMS       uint32
	FileDateLS       uint32
}

type processEntry32 struct {
	Size              uint32
	CntUsage          uint32
	ProcessID         uint32
	DefaultHeapID     uintptr
	ModuleID          uint32
	CntThreads        uint32
	ParentProcessID   uint32
	PriorityClassBase int32
	Flags             uint32
	ExeFile           [maxPath]uint16
}

type moduleEntry32 struct {
	Size         uint32
	ModuleID     uint32
	ProcessID    uint32
	GlblcntUsage uint32
	ProccntUsage uint32
	ModBaseAddr  uintptr
	ModBaseSize  uint32
	HModule      syscall.Handle
	ModuleName   [256]uint16
	ExePath      [maxPath]uint16
}

// ---------------------------- Windows API helpers ----------------------------

func findProcessID(name string) (uint32, error) {
	snap, _, _ := procCreateToolhelp32Snapshot.Call(uintptr(th32csSnapProcess), 0)
	if snap == 0 || snap == uintptr(^uintptr(0)) {
		return 0, fmt.Errorf("couldn't take a process snapshot")
	}
	defer procCloseHandle.Call(snap)

	var pe processEntry32
	pe.Size = uint32(unsafe.Sizeof(pe))
	r, _, _ := procProcess32FirstW.Call(snap, uintptr(unsafe.Pointer(&pe)))
	if r == 0 {
		return 0, fmt.Errorf("Process32First failed")
	}
	for {
		exe := syscall.UTF16ToString(pe.ExeFile[:])
		if strings.EqualFold(exe, name) {
			return pe.ProcessID, nil
		}
		r, _, _ := procProcess32NextW.Call(snap, uintptr(unsafe.Pointer(&pe)))
		if r == 0 {
			break
		}
	}
	return 0, fmt.Errorf("process not found: %s", name)
}

func findModuleBase(pid uint32, name string) (uintptr, uint32, string, error) {
	snap, _, _ := procCreateToolhelp32Snapshot.Call(uintptr(th32csSnapModule|th32csSnapModule32), uintptr(pid))
	if snap == 0 || snap == uintptr(^uintptr(0)) {
		return 0, 0, "", fmt.Errorf("couldn't take a module snapshot")
	}
	defer procCloseHandle.Call(snap)

	var me moduleEntry32
	me.Size = uint32(unsafe.Sizeof(me))
	r, _, _ := procModule32FirstW.Call(snap, uintptr(unsafe.Pointer(&me)))
	if r == 0 {
		return 0, 0, "", fmt.Errorf("Module32First failed")
	}
	for {
		mname := syscall.UTF16ToString(me.ModuleName[:])
		if strings.EqualFold(mname, name) {
			return me.ModBaseAddr, me.ModBaseSize, syscall.UTF16ToString(me.ExePath[:]), nil
		}
		r, _, _ := procModule32NextW.Call(snap, uintptr(unsafe.Pointer(&me)))
		if r == 0 {
			break
		}
	}
	return 0, 0, "", fmt.Errorf("module not found: %s", name)
}

// productVersion reads the game executable's version. label carries both
// full version numbers (product and file) because they don't always
// match, which helps diagnose whether the PlayerIns offset ever needs
// adjusting.
func productVersion(path string) (major, minor uint16, label string, ok bool) {
	if path == "" {
		return 0, 0, "", false
	}
	p, err := syscall.UTF16PtrFromString(path)
	if err != nil {
		return 0, 0, "", false
	}
	size, _, _ := procGetFileVersionInfoSizeW.Call(uintptr(unsafe.Pointer(p)), 0)
	if size == 0 {
		return 0, 0, "", false
	}
	buf := make([]byte, size)
	r, _, _ := procGetFileVersionInfoW.Call(uintptr(unsafe.Pointer(p)), 0, size, uintptr(unsafe.Pointer(&buf[0])))
	if r == 0 {
		return 0, 0, "", false
	}
	sub, err := syscall.UTF16PtrFromString(`\`)
	if err != nil {
		return 0, 0, "", false
	}
	var info *vsFixedFileInfo
	var infoLen uint32
	r, _, _ = procVerQueryValueW.Call(
		uintptr(unsafe.Pointer(&buf[0])),
		uintptr(unsafe.Pointer(sub)),
		uintptr(unsafe.Pointer(&info)),
		uintptr(unsafe.Pointer(&infoLen)),
	)
	if r == 0 || info == nil || infoLen == 0 {
		return 0, 0, "", false
	}
	quad := func(ms, ls uint32) string {
		return fmt.Sprintf("%d.%d.%d.%d", ms>>16, ms&0xFFFF, ls>>16, ls&0xFFFF)
	}
	label = fmt.Sprintf("product %s / file %s",
		quad(info.ProductVersionMS, info.ProductVersionLS),
		quad(info.FileVersionMS, info.FileVersionLS))
	return uint16(info.ProductVersionMS >> 16), uint16(info.ProductVersionMS & 0xFFFF), label, true
}

// playerInsOffsetForVersion mirrors SoulMemory's table (InitializeOffsets):
// up to 1.06 the PlayerIns offset inside WorldChrMan is 0x18468, from
// 1.07 onward it's 0x1E508.
//
// WATCH OUT: the version the exe reports is NOT what the game shows on
// screen (the exe can say 2.7.1.0 while the game says 1.17.1), and
// SoulMemory's table is written with the game's own numbers. So this is
// only a HUNCH for deciding which one to try first: what actually
// decides is playerInsCandidates plus the in-memory verification.
func playerInsOffsetForVersion(major, minor uint16, ok bool) uintptr {
	if ok && major == 1 && minor <= 6 {
		return 0x18468
	}
	return 0x1E508
}

// playerInsCandidates returns the known offsets to try, with the one the
// version suggests listed first.
func playerInsCandidates(major, minor uint16, ok bool) []uintptr {
	if playerInsOffsetForVersion(major, minor, ok) == 0x18468 {
		return []uintptr{0x18468, 0x1E508}
	}
	return []uintptr{0x1E508, 0x18468}
}

func openProcessHandle(pid uint32) (syscall.Handle, error) {
	h, _, err := procOpenProcess.Call(uintptr(processQueryInformation|processVMRead), 0, uintptr(pid))
	if h == 0 {
		return 0, err
	}
	return syscall.Handle(h), nil
}

func readMemory(h syscall.Handle, addr uintptr, size int) ([]byte, bool) {
	if addr == 0 {
		return nil, false
	}
	buf := make([]byte, size)
	var n uintptr
	r, _, _ := procReadProcessMemory.Call(uintptr(h), addr, uintptr(unsafe.Pointer(&buf[0])), uintptr(size), uintptr(unsafe.Pointer(&n)))
	if r == 0 || int(n) != size {
		return nil, false
	}
	return buf, true
}

// ------------------------- signature scans -------------------------
//
// Two signatures, both the same shape: a 7-byte "mov reg,[rip+disp32]"
// instruction, where the first 3 bytes are the opcode and the next 4 are
// the displacement. The resolved static slot holds the pointer to the
// object (one more dereference needed).
//
//	GameDataMan  -> holds the death counter (+0x94) and the boss-fight flag
//	              (+0xC0). Same pattern eldenring_boss_timer.asl (LiveSplit)
//	              uses.
//	WorldChrMan  -> holds the pointer to PlayerIns (+playerInsOffset). If
//	              that pointer is null, there's no character in the world:
//	              you're at the main menu or on a loading screen. Exactly
//	              what SoulMemory.IsPlayerLoaded() does.

type patByte struct {
	val      byte
	wildcard bool
}

// parsePattern accepts "48 8B 05 ?? ?? ?? ??" (?? = wildcard).
func parsePattern(s string) []patByte {
	var out []patByte
	for _, tok := range strings.Fields(s) {
		if strings.HasPrefix(tok, "?") {
			out = append(out, patByte{wildcard: true})
			continue
		}
		v, err := strconv.ParseUint(tok, 16, 8)
		if err != nil {
			panic("invalid pattern: " + tok)
		}
		out = append(out, patByte{val: byte(v)})
	}
	return out
}

var (
	// mov rax,[rip+disp32]; test rax,rax; jz +5; mov rax,[rax+58]; ret; ret
	gameDataManPattern = parsePattern("48 8B 05 ?? ?? ?? ?? 48 85 C0 74 05 48 8B 40 58 C3 C3")
	// mov rsi,[rip+disp32]; test rsi,rsi; ...  (WorldChrManImp, same as SoulMemory)
	worldChrManPattern = parsePattern("48 8B 35 ?? ?? ?? ?? 48 85 F6 ?? ?? BB 01 00 00 00 89 5C 24 20 48 8B B6")
	// mov rax,[rip+disp32]; cmp byte ptr [rax+disp32],0D; sete al; ret
	// (GameMan: +0xAC0 holds the loaded character's save slot)
	gameManPattern = parsePattern("48 8B 05 ?? ?? ?? ?? 80 B8 ?? ?? ?? ?? 0D 0F 94 C0 C3")
)

// saveSlotOffset: where GameMan stores the save-slot index (0-9) of the
// loaded game. This is a character's REAL identity: it doesn't depend on
// the name, so two characters sharing a name never mix.
const saveSlotOffset = 0xAC0

func matchAt(buf []byte, i int, pattern []patByte) bool {
	if i+len(pattern) > len(buf) {
		return false
	}
	for j, p := range pattern {
		if !p.wildcard && buf[i+j] != p.val {
			return false
		}
	}
	return true
}

// scanModule looks for several patterns in a single pass over the module,
// reading it in chunks (with overlap, in case a pattern straddles a chunk
// boundary). Returns, for each pattern, the match address or 0.
func scanModule(h syscall.Handle, base uintptr, size uint32, patterns [][]patByte) []uintptr {
	const chunk = 1 << 20 // 1 MiB
	const overlap = 64

	found := make([]uintptr, len(patterns))
	remaining := len(patterns)

	var pos uint32
	for pos < size && remaining > 0 {
		readSize := chunk
		if rem := int(size - pos); readSize > rem {
			readSize = rem
		}
		buf, ok := readMemory(h, base+uintptr(pos), readSize)
		if ok {
			for i := 0; i < len(buf); i++ {
				for p := range patterns {
					if found[p] != 0 {
						continue
					}
					if matchAt(buf, i, patterns[p]) {
						found[p] = base + uintptr(pos) + uintptr(i)
						remaining--
					}
				}
			}
		}
		if uint32(readSize) <= overlap {
			break
		}
		pos += uint32(readSize) - overlap
	}
	return found
}

// ripSlot turns the address of a 7-byte "mov reg,[rip+disp32]"
// instruction into the address of the static slot it points to.
func ripSlot(h syscall.Handle, matchAddr uintptr) (uintptr, error) {
	if matchAddr == 0 {
		return 0, fmt.Errorf("pattern not found")
	}
	codeLocation := matchAddr + 3 // the first 3 bytes are the opcode
	dispBytes, ok := readMemory(h, codeLocation, 4)
	if !ok {
		return 0, fmt.Errorf("couldn't read the RIP-relative displacement")
	}
	disp := int32(binary.LittleEndian.Uint32(dispBytes))
	return codeLocation + 4 + uintptr(int64(disp)), nil
}

// gamePointers gathers everything resolved just once per process session:
// the static slots (which don't move) and the game's version.
type gamePointers struct {
	gameDataManSlot uintptr
	worldChrManSlot uintptr // 0 if the pattern wasn't found (we keep going without the menu check)
	gameManSlot     uintptr // 0 if not found: falls back to identifying by name
	playerInsOffset uintptr // the one currently in use (or the preferred candidate)
	playerInsTried  []uintptr
	offsetConfirmed bool // true once verified by actually reading memory
	versionLabel    string

	nameChain     nameCandidate // how we got to the character's name
	nameConfirmed bool
	namePending   string // candidate waiting to repeat (see resolveCharName)
	namePendingOf nameCandidate
}

// resolvePointers does the signature scans (expensive: walks the whole
// module) just once per process session. Deliberately does NOT return
// the resolved objects themselves: those pointers get re-read every tick,
// because the game can destroy and recreate GameDataMan (e.g. going back
// to the main menu and loading again). If we cached a stale address,
// we'd keep reading it successfully (the memory page is still valid) but
// its contents would belong to something else entirely — the most likely
// cause of a counter that "goes up on its own" without an actual death.
// SoulMemory does the same: its Pointer class resolves the whole chain on
// every read, never caching the final address.
func resolvePointers(h syscall.Handle, pid uint32) (gamePointers, error) {
	var gp gamePointers

	base, size, exePath, err := findModuleBase(pid, processName)
	if err != nil {
		return gp, err
	}

	major, minor, label, okVer := productVersion(exePath)
	gp.playerInsTried = playerInsCandidates(major, minor, okVer)
	gp.playerInsOffset = gp.playerInsTried[0]
	gp.versionLabel = label
	if !okVer {
		gp.versionLabel = "unknown"
	}

	matches := scanModule(h, base, size, [][]patByte{gameDataManPattern, worldChrManPattern, gameManPattern})

	gp.gameDataManSlot, err = ripSlot(h, matches[0])
	if err != nil {
		return gp, fmt.Errorf("GameDataMan's pattern wasn't found (did the game update?)")
	}

	// WorldChrMan is optional: if it's missing, we keep counting deaths,
	// we just lose menu/loading-screen detection.
	if slot, werr := ripSlot(h, matches[1]); werr == nil {
		gp.worldChrManSlot = slot
	}
	// GameMan is optional too: without it, we identify by name.
	if slot, gerr := ripSlot(h, matches[2]); gerr == nil {
		gp.gameManSlot = slot
	}
	return gp, nil
}

// derefPointer reads a static slot (cheap: 8 bytes) and returns the
// object's CURRENT address. Called every tick, not just once.
func derefPointer(h syscall.Handle, slot uintptr) (uintptr, bool) {
	if slot == 0 {
		return 0, false
	}
	buf, ok := readMemory(h, slot, 8)
	if !ok {
		return 0, false
	}
	return uintptr(binary.LittleEndian.Uint64(buf)), true
}

// ------------------------- character name -------------------------
//
// Sourced from a Cheat Engine table: "GameDataMan +0C +9C, unicode,
// length 19". That notation allows more than one reading (is 0x0C a
// pointer to dereference, or do the two offsets just add up?), and on
// top of that the community/the ASL use GameDataMan+0x08 to reach
// PlayerGameData. So instead of picking one, all three get tried, and
// whichever gives back something that looks like a real name wins.

type nameCandidate struct {
	ptrOffset  uintptr // offset where the pointer lives (0 = no dereference)
	nameOffset uintptr // offset of the text within the object
	label      string
}

var nameCandidates = []nameCandidate{
	{0x08, 0x9C, "[GameDataMan+0x08]+0x9C (PlayerGameData)"},
	{0x0C, 0x9C, "[GameDataMan+0x0C]+0x9C"},
	{0x00, 0xA8, "GameDataMan+0xA8 (0x0C and 0x9C added together)"},
}

// looksLikeName (and charNameMaxChars) live in names.go: they don't
// depend on Windows, so they're kept out of this file to be testable
// without a PC with the game open.

func readCharName(h syscall.Handle, gameDataMan uintptr, c nameCandidate) (string, bool) {
	base := gameDataMan
	if c.ptrOffset != 0 {
		p, ok := derefPointer(h, gameDataMan+c.ptrOffset)
		if !ok || p == 0 {
			return "", false
		}
		base = p
	}
	buf, ok := readMemory(h, base+c.nameOffset, charNameMaxChars*2)
	if !ok {
		return "", false
	}
	u16 := make([]uint16, 0, charNameMaxChars)
	for i := 0; i+1 < len(buf); i += 2 {
		ch := binary.LittleEndian.Uint16(buf[i : i+2])
		if ch == 0 {
			break
		}
		u16 = append(u16, ch)
	}
	s := strings.TrimSpace(string(utf16.Decode(u16)))
	if !looksLikeName(s) {
		return "", false
	}
	return s, true
}

// resolveCharName returns the character's name. Before locking in a
// variant, it requires seeing it give the SAME text on two readings in a
// row: the real name doesn't change from one second to the next, but a
// chunk of memory that happens to pass the filter is far less likely to
// repeat.
func resolveCharName(h syscall.Handle, gameDataMan uintptr, gp *gamePointers) (string, bool) {
	if gp.nameConfirmed {
		return readCharName(h, gameDataMan, gp.nameChain)
	}
	for _, c := range nameCandidates {
		s, ok := readCharName(h, gameDataMan, c)
		if !ok {
			continue
		}
		if gp.namePending == s && gp.namePendingOf == c {
			gp.nameChain = c
			gp.nameConfirmed = true
			gp.namePending = ""
			log.Printf("character name: \"%s\" (read via %s)", s, c.label)
			return s, true
		}
		gp.namePending = s
		gp.namePendingOf = c
		return "", false
	}
	gp.namePending = ""
	return "", false
}

// readSaveSlot returns the loaded game's slot index (0-9), or -1 if it
// couldn't be read. Elden Ring has 10 slots, so any other value is
// garbage and gets discarded.
func readSaveSlot(h syscall.Handle, gp gamePointers) int {
	if gp.gameManSlot == 0 {
		return -1
	}
	gameMan, ok := derefPointer(h, gp.gameManSlot)
	if !ok || gameMan == 0 {
		return -1
	}
	buf, ok := readMemory(h, gameMan+saveSlotOffset, 1)
	if !ok {
		return -1
	}
	slot := int(buf[0])
	if slot < 0 || slot > 9 {
		return -1
	}
	return slot
}

// isPlayerLoaded mirrors SoulMemory.IsPlayerLoaded(): resolves
// WorldChrMan and reads the pointer to PlayerIns; if it's null, there's
// no character in the world. The second return value says whether we
// were able to evaluate it at all.
//
// Until the offset is confirmed, instead of trusting the version number
// (which in Elden Ring doesn't match what the game displays), the known
// offsets are tried and whichever one first points at genuinely readable
// memory wins. That's decided by the machine, not by a table that can
// age badly.
func isPlayerLoaded(h syscall.Handle, gp *gamePointers) (loaded bool, known bool) {
	if gp.worldChrManSlot == 0 {
		return true, false
	}
	worldChrMan, ok := derefPointer(h, gp.worldChrManSlot)
	if !ok {
		return true, false
	}
	if worldChrMan == 0 {
		return false, true
	}

	if gp.offsetConfirmed {
		playerIns, ok := derefPointer(h, worldChrMan+gp.playerInsOffset)
		if !ok {
			return true, false
		}
		return playerIns != 0, true
	}

	for _, cand := range gp.playerInsTried {
		playerIns, ok := derefPointer(h, worldChrMan+cand)
		if !ok || playerIns == 0 {
			continue
		}
		// A real pointer points at mapped memory; a garbage one almost
		// never survives this read.
		if _, ok := readMemory(h, playerIns, 8); !ok {
			continue
		}
		gp.playerInsOffset = cand
		gp.offsetConfirmed = true
		log.Printf("PlayerIns confirmed at +0x%X (verified by reading the object, not by version number)", cand)
		return true, true
	}
	return false, true
}

// -------------------------------- poller loop --------------------------------

// maxPlausibleDeltaPerTick: between two readings ~1s apart, with the
// character loaded the whole time, the real death counter can't go up by
// more than this (and never goes down). A bigger jump almost always
// means we grabbed memory that's no longer GameDataMan (a stale/invalid
// address), not an actual death.
const maxPlausibleDeltaPerTick = 3

func pollLoop() {
	var (
		handle       syscall.Handle
		pid          uint32
		gp           gamePointers
		resolved     bool
		lastRaw      int32
		haveLastRaw  bool
		sawUnloaded  bool
		warnedNoWCM  bool
		lastBossRead bool

		// Menu-detection watchdog: while we believe no character is
		// loaded, we still peek at the death counter. If it climbs the
		// way a real death does, our detection is lying (you were
		// actually playing) and we turn it off.
		unloadedRaw      int32
		unloadedRawFirst int32
		haveUnloadedRaw  bool
	)

	closeHandle := func() {
		if handle != 0 {
			procCloseHandle.Call(uintptr(handle))
			handle = 0
		}
		pid = 0
		gp = gamePointers{}
		resolved = false
		haveLastRaw = false
		sawUnloaded = false
		haveUnloadedRaw = false
	}

	for {
		if handle == 0 {
			newPid, err := findProcessID(processName)
			if err != nil {
				st.setDisconnected("waiting for eldenring.exe")
				time.Sleep(3 * time.Second)
				continue
			}
			h, err := openProcessHandle(newPid)
			if err != nil {
				st.setDisconnected("couldn't open the process (permissions?): " + err.Error())
				time.Sleep(3 * time.Second)
				continue
			}
			pid = newPid
			handle = h
			log.Printf("eldenring.exe found (PID %d), scanning signatures...", pid)
		}

		if !resolved {
			p, err := resolvePointers(handle, pid)
			if err != nil {
				st.setDisconnected(err.Error())
				time.Sleep(2 * time.Second)
				// if the process died, release the handle to retry from scratch
				if _, ferr := findProcessID(processName); ferr != nil {
					closeHandle()
				}
				continue
			}
			gp = p
			resolved = true
			haveLastRaw = false
			log.Printf("game version: %s | GameDataMan slot 0x%X", gp.versionLabel, gp.gameDataManSlot)
			if gp.gameManSlot != 0 {
				log.Printf("GameMan slot 0x%X (identifying characters by their save slot)", gp.gameManSlot)
			} else {
				log.Printf("warning: GameMan's pattern wasn't found; identifying characters by name")
			}
			if gp.worldChrManSlot != 0 {
				log.Printf("WorldChrMan slot 0x%X | PlayerIns: trying +0x%X and confirming against memory", gp.worldChrManSlot, gp.playerInsOffset)
			} else if !warnedNoWCM {
				warnedNoWCM = true
				log.Printf("warning: WorldChrMan's pattern wasn't found; still counting deaths but without menu/loading-screen detection")
			}
		}

		// Same as LiveSplit's ASL, which does "if (!IsPlayerLoaded) return;":
		// with no character in the world, nothing gets read. The total
		// stays frozen on screen (no dash shown) so it doesn't flicker on
		// every loading screen.
		if loaded, known := isPlayerLoaded(handle, &gp); known && !loaded {
			// Safety net. The PlayerIns offset depends on the game's
			// version: if a patch ever moves it, we'd read null forever
			// and the counter would freeze mid-stream.
			//
			// The only judge we can trust is the death counter itself:
			// at the start menu it NEVER goes up. So the raw value gets
			// peeked at without being used, and if it climbs the way a
			// real death does (+1, +2, +3), you were actually playing
			// and our detection was lying. Unlike a timeout, this can't
			// fire just from leaving the game sitting at the menu a while.
			if gdm, ok := derefPointer(handle, gp.gameDataManSlot); ok && gdm != 0 {
				if buf, ok := readMemory(handle, gdm+0x94, 4); ok {
					raw := int32(binary.LittleEndian.Uint32(buf))
					if raw >= 0 && raw < 1_000_000 {
						if haveUnloadedRaw {
							if d := raw - unloadedRaw; d >= 1 && d <= maxPlausibleDeltaPerTick {
								log.Printf("the death counter went from %d to %d while I thought no character was loaded: menu detection is wrong on this version, turning it off and continuing to count", unloadedRaw, raw)
								gp.worldChrManSlot = 0
								// Recover what happened during the confused
								// stretch: keep the reference at that
								// period's first reading so the "crossed a
								// loading screen" logic can credit the
								// deaths if there weren't many.
								lastRaw = unloadedRawFirst
								haveLastRaw = true
								sawUnloaded = true
								haveUnloadedRaw = false
								continue
							}
						} else {
							unloadedRawFirst = raw
						}
						unloadedRaw = raw
						haveUnloadedRaw = true
					}
				}
			}
			// Careful: haveLastRaw/lastRaw are NOT touched, precisely so
			// they can be compared against the last good reading once
			// the world comes back.
			st.setPlayerUnloaded("main menu or loading screen")
			sawUnloaded = true
			time.Sleep(1 * time.Second)
			continue
		}
		haveUnloadedRaw = false

		// Re-dereference the slot on EVERY tick (not just on connect) to
		// never end up stuck with a stale GameDataMan address.
		gameDataMan, ok := derefPointer(handle, gp.gameDataManSlot)
		if !ok {
			st.setDisconnected("lost the memory reading (the game closed or restarted)")
			closeHandle()
			time.Sleep(2 * time.Second)
			continue
		}
		if gameDataMan == 0 {
			st.setPlayerUnloaded("no game loaded")
			sawUnloaded = true
			time.Sleep(1 * time.Second)
			continue
		}

		deathsBuf, ok1 := readMemory(handle, gameDataMan+0x94, 4)
		bossBuf, ok2 := readMemory(handle, gameDataMan+0xC0, 1)
		if !ok1 {
			st.setDisconnected("lost the memory reading (the game closed or restarted)")
			closeHandle()
			time.Sleep(2 * time.Second)
			continue
		}
		raw := int32(binary.LittleEndian.Uint32(deathsBuf))
		boss := lastBossRead
		if ok2 {
			boss = bossBuf[0] != 0
			lastBossRead = boss
		}
		if raw < 0 || raw > 1_000_000 {
			log.Printf("discarding an impossible reading (raw %d) - rescanning signatures", raw)
			resolved = false
			haveLastRaw = false
			time.Sleep(1 * time.Second)
			continue
		}

		// Within the same save, the counter never goes down or jumps: if
		// it does, it's memory that's no longer GameDataMan. Crossing a
		// load, on the other hand, can change to anything, since it might
		// be a different character — and setCharacter handles that case.
		if haveLastRaw && !sawUnloaded {
			delta := int64(raw) - int64(lastRaw)
			if delta < 0 || delta > maxPlausibleDeltaPerTick {
				log.Printf("discarding a suspicious reading (raw %d, previous %d) - rescanning signatures", raw, lastRaw)
				resolved = false
				haveLastRaw = false
				time.Sleep(1 * time.Second)
				continue
			}
		}

		// Which character this is gets resolved BEFORE recording the
		// reading: if you switched characters, the total jumps to theirs
		// on this very pass, with no need to wait for a death.
		name, _ := resolveCharName(handle, gameDataMan, &gp)
		st.setCharacter(readSaveSlot(handle, gp), name, raw)

		st.setReading(raw, boss)

		lastRaw = raw
		haveLastRaw = true
		sawUnloaded = false

		time.Sleep(1 * time.Second)
	}
}

// ---------------------------------- HTTP ----------------------------------

// portOf pulls the port out of an address like "0.0.0.0:47822", so your
// partner can be told exactly what to put in their config.
func portOf(addr string) string {
	if _, port, ok := strings.Cut(addr, ":"); ok {
		return port
	}
	return addr
}

func withCORS(w http.ResponseWriter) {
	w.Header().Set("Access-Control-Allow-Origin", "*")
	w.Header().Set("Cache-Control", "no-store")
}

func main() {
	log.SetFlags(log.Ltime)
	log.Println("=== Elden Ring Death Counter (local, read-only) ===")

	loadLocales()
	cfg := loadConfig()
	writeSampleConfig()
	isPeer := cfg.Mode == "peer"

	lang := resolveLang(cfg.Language)
	log.Printf("version: %s | PID %d | mode %s | language %s (available: %s)",
		buildTag, os.Getpid(), cfg.Mode, lang, strings.Join(availableLangs(), ", "))

	totals = newTotalsStore()
	st.init(totals)

	go pollLoop()

	registry := newPeerRegistry()

	// The token is required on both ends: without it, anyone who can
	// reach the port could inject data into the overlay. The hub also
	// generates its own TLS certificate the first time: the peer pins it
	// by fingerprint (pin.go), not by certificate-authority trust, which
	// doesn't exist for a Tailscale or LAN address anyway.
	var token string
	var hubCert tls.Certificate
	var certFingerprint string
	if !isPeer {
		t, generated, err := resolveToken(cfg)
		if err != nil {
			log.Fatalf("couldn't prepare the token: %v", err)
		}
		token = t
		logTokenBanner(token, generated)

		cert, fp, certGenerated, err := loadOrCreateHubCert()
		if err != nil {
			log.Fatalf("couldn't prepare the TLS certificate for the peer link: %v", err)
		}
		if certGenerated {
			log.Println("generated a new TLS certificate for the peer link")
		}
		hubCert, certFingerprint = cert, fp

		candidates := candidateIPv4s()
		host := pickBestHost(candidates)
		if len(candidates) > 0 {
			log.Printf("detected network addresses: %s", strings.Join(candidates, ", "))
		}
		peerPort := portOf(cfg.PeerListen)
		if host != "" {
			invite := encodeInvite(inviteCode{Host: host, Port: peerPort, Fingerprint: certFingerprint, Token: token})
			log.Println("invite code for your co-op partner — paste it as invite = \"...\" in their config.toml:")
			log.Println(invite)
			log.Printf("(wrong address? they can override just the host with hub = \"<the right IP>:%s\")", peerPort)
		} else {
			log.Println("couldn't auto-detect a network address to build an invite code with.")
			log.Printf("have your partner set these by hand in their config.toml: hub = \"<your IP>:%s\", token = \"%s\", fingerprint = \"%s\"", peerPort, token, certFingerprint)
		}
	}

	var peerHub string
	if isPeer {
		hub, tok, fp, ok, err := resolvePeerConn(cfg)
		if err != nil {
			log.Fatalf("peer config problem: %v", err)
		}
		if ok {
			peerHub = hub
			go peerLoop(cfg, hub, tok, fp)
		} else {
			log.Println("peer mode with nothing configured yet (no 'invite', no 'hub'+'token'+'fingerprint'): running as a local-only overlay for now")
		}
	} else {
		registry.declare(cfg.Partner)
	}

	mux := http.NewServeMux()

	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "text/html; charset=utf-8")
		w.Header().Set("X-Build", buildTag)
		w.Write(overlayHTML)
	})

	// The UI's text: the page requests it once on load. ?lang= lets you
	// force a language without touching the config, handy for having the
	// overlay in one language and the panel in another.
	mux.HandleFunc("/strings.json", func(w http.ResponseWriter, r *http.Request) {
		withCORS(w)
		want := lang
		if q := r.URL.Query().Get("lang"); q != "" {
			want = resolveLang(q)
		}
		w.Header().Set("Content-Type", "application/json; charset=utf-8")
		json.NewEncoder(w).Encode(stringsFor(want))
	})

	mux.HandleFunc("/deaths", func(w http.ResponseWriter, r *http.Request) {
		withCORS(w)
		snap := st.snapshot()

		// This player first, then partners in order of appearance.
		players := []playerView{{
			Name:         displayName(cfg),
			Deaths:       snap.Total,
			BossFight:    snap.BossFight,
			PlayerLoaded: snap.PlayerLoaded,
			Connected:    snap.Connected,
			Self:         true,
		}}
		// Co-op mode only when a partner is (or was just recently) connected.
		if registry.coopMode() {
			players = append(players, registry.views()...)
		}

		var combined int64
		for _, p := range players {
			combined += p.Deaths
		}

		resp := map[string]interface{}{
			"players":  players,
			"combined": combined,
			"build":    buildTag,
			// Single-player-version fields: kept so nothing already
			// pointing at them breaks.
			"deaths":       snap.Total,
			"rawDeaths":    snap.RawDeaths,
			"character":    snap.CharName,
			"slot":         snap.Slot,
			"bossFight":    snap.BossFight,
			"connected":    snap.Connected,
			"playerLoaded": snap.PlayerLoaded,
		}
		w.Header().Set("Content-Type", "application/json")
		json.NewEncoder(w).Encode(resp)
	})

	log.Printf("Panel:   http://%s/", cfg.Listen)
	if isPeer {
		if peerHub != "" {
			log.Printf("Pushing the counter to the hub %s. This window needs to stay open while you play.", peerHub)
		}
		if err := http.ListenAndServe(cfg.Listen, mux); err != nil {
			log.Fatalf("couldn't start the local server: %v", err)
		}
		return
	}

	log.Printf("OBS URL: http://%s/?view=overlay", cfg.Listen)
	log.Println("Keep this window open while you stream. Ctrl+C to close.")

	// Panel/overlay in plain HTTP, in the background; the peer server
	// (TLS, with the certificate from above) blocks in the foreground as
	// the process's main server.
	go func() {
		if err := http.ListenAndServe(cfg.Listen, mux); err != nil {
			log.Fatalf("couldn't start the local server: %v", err)
		}
	}()

	peerMux := http.NewServeMux()
	peerMux.HandleFunc("/ws", registry.wsHandler(token))
	peerSrv := &http.Server{
		Addr:      cfg.PeerListen,
		Handler:   peerMux,
		TLSConfig: hubServerTLSConfig(hubCert),
	}
	log.Printf("Peer link: %s (TLS, certificate pinned)", cfg.PeerListen)
	if err := peerSrv.ListenAndServeTLS("", ""); err != nil {
		log.Fatalf("couldn't start the peer server: %v", err)
	}
}