// process.go: everything about finding the death counter in the game's
// memory that does NOT depend on which OS is doing the reading — AOB
// signature scanning, pointer resolution, character-name reading, and the
// poll loop that ties it all together.
//
// The actual reading is behind procHandle and a handful of functions
// (findProcessID, openProcess, closeProcessHandle, readMemory,
// findModuleBase, productVersion, systemLang) implemented once per
// platform in process_windows.go/process_linux.go. Elden Ring under
// Proton on Linux is the exact same Windows binary Wine is running, so
// every signature and offset below is identical on both platforms — only
// how the process gets found and read differs.
package main

import (
	"encoding/binary"
	"fmt"
	"log"
	"strconv"
	"strings"
	"time"
	"unicode/utf16"
)

const processName = "eldenring.exe"

// procHandle is an opaque reference to an open process, produced by
// openProcess and consumed by readMemory/closeProcessHandle. What it
// actually holds is platform-specific: a real Windows HANDLE value, or
// just a pid on Linux (which needs no persistent OS resource — see
// process_linux.go).
type procHandle uintptr

// Boundary functions as package variables, defaulting to the platform
// implementation compiled into process_windows.go/process_linux.go.
// Tests (process_test.go) swap these for a fake in-memory reader — same
// pattern as testExeDir in totals.go, not a new interface.
var (
	findProcessIDFn      = findProcessID
	openProcessFn        = openProcess
	closeProcessHandleFn = closeProcessHandle
	readMemoryFn         = readMemory
	findModuleBaseFn     = findModuleBase
	productVersionFn     = productVersion
)

// ------------------------- 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 procHandle, 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 := readMemoryFn(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 procHandle, 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 := readMemoryFn(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 procHandle, pid uint32) (gamePointers, error) {
	var gp gamePointers

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

	major, minor, label, okVer := productVersionFn(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 procHandle, slot uintptr) (uintptr, bool) {
	if slot == 0 {
		return 0, false
	}
	buf, ok := readMemoryFn(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 the OS at all, let alone Windows vs. Linux, so they're kept
// out of this file to be testable without a PC with the game open.

func readCharName(h procHandle, 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 := readMemoryFn(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 procHandle, 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 procHandle, gp gamePointers) int {
	if gp.gameManSlot == 0 {
		return -1
	}
	gameMan, ok := derefPointer(h, gp.gameManSlot)
	if !ok || gameMan == 0 {
		return -1
	}
	buf, ok := readMemoryFn(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, and on
// Linux isn't available at all — see productVersion), 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
// or an OS that can't report a version at all.
func isPlayerLoaded(h procHandle, 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 := readMemoryFn(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
}

// 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 in
// isPlayerLoaded. On Linux, where productVersion always reports ok=false,
// this hunch is simply skipped — the in-memory verification still nails
// it down.
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}
}

// -------------------------------- 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       procHandle
		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 {
			closeProcessHandleFn(handle)
			handle = 0
		}
		pid = 0
		gp = gamePointers{}
		resolved = false
		haveLastRaw = false
		sawUnloaded = false
		haveUnloadedRaw = false
	}

	for {
		if handle == 0 {
			newPid, err := findProcessIDFn(processName)
			if err != nil {
				st.setDisconnected("waiting for eldenring.exe")
				time.Sleep(3 * time.Second)
				continue
			}
			h, err := openProcessFn(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 := findProcessIDFn(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 := readMemoryFn(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 := readMemoryFn(handle, gameDataMan+0x94, 4)
		bossBuf, ok2 := readMemoryFn(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)
	}
}