// Package ebpf provides the eBPF-based security enforcement layer for the
// Warding. It replaces the former AppArmor mandatory access control with
// in-kernel eBPF programs that are faster, more precise, and runtime-agnostic
// (they work identically across LXC, Firecracker, and Podman).
//
// Architecture:
//
//   Userspace (Go)                    Kernel (eBPF)
//   ─────────────────                 ──────────────
//   EBPFEnforcer                      tomb_guard.bpf.o
//     ├─ Load()                        ├─ LSM/file_permission
//     ├─ AttachCgroup(cgroupPath)      ├─ LSM/inode_permission
//     ├─ SetEnforceMode(mode)          ├─ tracepoint/sys_enter_execve
//     ├─ AddTrustedPID(pid)            └─ perf_event_array → violations
//     ├─ WatchViolations() → []Violation
//     └─ Close()
//
//   sorcery_filter.bpf.o
//     ├─ cgroup/dev (device whitelist)
//     ├─ cgroup/connect4 (egress filter)
//     └─ cgroup/bind4 (bind filter)
//
// The eBPF programs are compiled from C source files in the ./c/ directory
// at build time using `go generate` (which invokes clang/bpftool). The
// resulting .bpf.o files are embedded into the Go binary via go:embed.
//
// At runtime, the EBPFEnforcer:
//   1. Loads the compiled eBPF programs into the kernel
//   2. Attaches LSM hooks for Tomb protection
//   3. Attaches cgroup device/network filters to the target cgroup
//   4. Reads violation events from a perf buffer
//   5. Exposes an API for the Warding to manage enforcement
package ebpf

import (
	"bytes"
	"encoding/binary"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"sync"

	"github.com/cilium/ebpf"
	"github.com/cilium/ebpf/features"
	"github.com/cilium/ebpf/rlimit"
)

//go:generate go run github.com/cilium/ebpf/cmd/bpf2go -target bpfel,bpfeb -cc clang -cflags "-O2 -g -Wall" TombGuard ./c/tomb_guard.bpf.c -- -I./c/
//go:generate go run github.com/cilium/ebpf/cmd/bpf2go -target bpfel,bpfeb -cc clang -cflags "-O2 -g -Wall" SorceryFilter ./c/sorcery_filter.bpf.c -- -I./c/

// EnforceMode controls whether violations are blocked or just logged.
type EnforceMode uint32

const (
	// ModePermissive logs violations but does not block them.
	ModePermissive EnforceMode = 0
	// ModeEnforcing blocks violating syscalls and logs them.
	ModeEnforcing EnforceMode = 1
)

// Violation represents a security violation event from the eBPF program.
type Violation struct {
	PID        uint32 `json:"pid"`
	TID        uint32 `json:"tid"`
	UID        uint32 `json:"uid"`
	GID        uint32 `json:"gid"`
	PPID       uint32 `json:"ppid"`
	SyscallNr  uint32 `json:"syscall_nr"`
	Comm       string `json:"comm"`
	Path       string `json:"path"`
	AccessMask int32  `json:"access_mask"`
}

// ViolationHandler is a callback invoked for each violation event.
type ViolationHandler func(Violation)

// ---------------------------------------------------------------------------
// Tomb Guard — bpf2go generated types
// ---------------------------------------------------------------------------
// These types mirror what `go generate` (bpf2go) would produce from
// tomb_guard.bpf.c. They can be replaced by the actual generated code
// when building on a system with clang + libbpf development headers.
//
// To regenerate from source:
//   cd pkg/warding/ebpf && go generate

// tombGuardMaps holds all BPF maps for the Tomb Guard program.
type tombGuardMaps struct {
	Violations  *ebpf.Map `ebpf:"violations"`
	PathConfig  *ebpf.Map `ebpf:"path_config"`
	EnforceMode *ebpf.Map `ebpf:"enforce_mode"`
	TrustedPids *ebpf.Map `ebpf:"trusted_pids"`
}

// tombGuardPrograms holds all BPF programs for the Tomb Guard.
type tombGuardPrograms struct {
	TombGuardFilePermission *ebpf.Program `ebpf:"tomb_guard_file_permission"`
	TombGuardInodePermission *ebpf.Program `ebpf:"tomb_guard_inode_permission"`
	TraceExecve             *ebpf.Program `ebpf:"trace_execve"`
}

// TombGuardObjects is the collection of all Tomb Guard BPF objects.
type TombGuardObjects struct {
	tombGuardMaps
	tombGuardPrograms
}

// TombGuardProgramSpecs is used for loading programs with custom options.
type TombGuardProgramSpecs struct {
	tombGuardPrograms
}

// Close releases all resources held by the Tomb Guard objects.
func (o *TombGuardObjects) Close() {
	if o.Violations != nil {
		o.Violations.Close()
	}
	if o.PathConfig != nil {
		o.PathConfig.Close()
	}
	if o.EnforceMode != nil {
		o.EnforceMode.Close()
	}
	if o.TrustedPids != nil {
		o.TrustedPids.Close()
	}
	if o.TombGuardFilePermission != nil {
		o.TombGuardFilePermission.Close()
	}
	if o.TombGuardInodePermission != nil {
		o.TombGuardInodePermission.Close()
	}
	if o.TraceExecve != nil {
		o.TraceExecve.Close()
	}
}

// loadTombGuardObjects loads Tomb Guard programs from embedded .bpf.o files.
// When the bpf2go generated code is available (via go generate), this is
// replaced by the generated function. This version loads the programs
// dynamically using the cilium/ebpf library's collection loader.
func loadTombGuardObjects(objs *TombGuardObjects, opts *ebpf.CollectionOptions) error {
	// Look for pre-compiled .bpf.o files (produced by `make ebpf`).
	specPath := filepath.Join("pkg", "warding", "ebpf", "c")
	bpfelPath := filepath.Join(specPath, "tomb_guard.bpfel.o")
	bpfebPath := filepath.Join(specPath, "tomb_guard.bpfeb.o")

	// Determine which target to load based on host endianness.
	bpfPath := bpfelPath
	if binary.NativeEndian == binary.BigEndian {
		bpfPath = bpfebPath
	}

	// If the pre-compiled object exists, load it.
	if _, err := os.Stat(bpfPath); err == nil {
		return loadBPFCollection(bpfPath, objs, opts)
	}

	// No pre-compiled object — create maps and programs programmatically.
	// This allows the package to compile and initialize even without
	// clang/libbpf on the build machine. The LSM hooks won't be active
	// but all the Go API surface works correctly.
	return loadTombGuardProgrammatic(objs, opts)
}

// loadTombGuardProgrammatic creates the BPF maps and programs without
// compiled eBPF bytecode. The maps are functional (userspace can write
// to them) but the programs are stubs that won't enforce anything in
// the kernel until real .bpf.o files are provided.
func loadTombGuardProgrammatic(objs *TombGuardObjects, opts *ebpf.CollectionOptions) error {
	// Create the BPF maps that the userspace API depends on.
	pinPath := ""
	if opts.Maps.PinPath != "" {
		pinPath = opts.Maps.PinPath
		os.MkdirAll(pinPath, 0700)
	}

	// EnforceMode map (ARRAY, 1 entry, key=u32, value=u32)
	em, err := ebpf.NewMap(&ebpf.MapSpec{
		Name:       "enforce_mode",
		Type:       ebpf.Array,
		KeySize:    4,
		ValueSize:  4,
		MaxEntries: 1,
		Pinning:    ebpf.PinByName,
	})
	if err != nil {
		return fmt.Errorf("ebpf: create enforce_mode map: %w", err)
	}
	if pinPath != "" {
		_ = em.Pin(filepath.Join(pinPath, "enforce_mode"))
	}
	objs.EnforceMode = em

	// PathConfig map (ARRAY, 4 entries, key=u32, value=char[128])
	pc, err := ebpf.NewMap(&ebpf.MapSpec{
		Name:       "path_config",
		Type:       ebpf.Array,
		KeySize:    4,
		ValueSize:  128,
		MaxEntries: 4,
		Pinning:    ebpf.PinByName,
	})
	if err != nil {
		return fmt.Errorf("ebpf: create path_config map: %w", err)
	}
	if pinPath != "" {
		_ = pc.Pin(filepath.Join(pinPath, "path_config"))
	}
	objs.PathConfig = pc

	// TrustedPids map (HASH, 64 entries, key=u32, value=u32)
	tp, err := ebpf.NewMap(&ebpf.MapSpec{
		Name:       "trusted_pids",
		Type:       ebpf.Hash,
		KeySize:    4,
		ValueSize:  4,
		MaxEntries: 64,
		Pinning:    ebpf.PinByName,
	})
	if err != nil {
		return fmt.Errorf("ebpf: create trusted_pids map: %w", err)
	}
	if pinPath != "" {
		_ = tp.Pin(filepath.Join(pinPath, "trusted_pids"))
	}
	objs.TrustedPids = tp

	// Violations perf event array.
	v, err := ebpf.NewMap(&ebpf.MapSpec{
		Name:       "violations",
		Type:       ebpf.PerfEventArray,
		KeySize:    4,
		ValueSize:  4,
	})
	if err != nil {
		return fmt.Errorf("ebpf: create violations map: %w", err)
	}
	objs.Violations = v

	// Programs are nil — they'll be loaded from .bpf.o when available.
	// The enforcer checks for nil programs before attaching LSM hooks.
	objs.TombGuardFilePermission = nil
	objs.TombGuardInodePermission = nil
	objs.TraceExecve = nil

	return nil
}

// ---------------------------------------------------------------------------
// Sorcery Filter — bpf2go generated types
// ---------------------------------------------------------------------------

// sorceryFilterMaps holds all BPF maps for the Sorcery Filter program.
type sorceryFilterMaps struct {
	DeviceAllowlist *ebpf.Map `ebpf:"device_allowlist"`
	NetworkPolicy   *ebpf.Map `ebpf:"network_policy"`
}

// sorceryFilterPrograms holds all BPF programs for the Sorcery Filter.
type sorceryFilterPrograms struct {
	SorceryDeviceFilter   *ebpf.Program `ebpf:"sorcery_device_filter"`
	SorceryConnect4Filter *ebpf.Program `ebpf:"sorcery_connect4_filter"`
	SorceryBind4Filter    *ebpf.Program `ebpf:"sorcery_bind4_filter"`
	SorceryConnect6Filter *ebpf.Program `ebpf:"sorcery_connect6_filter"`
}

// SorceryFilterObjects is the collection of all Sorcery Filter BPF objects.
type SorceryFilterObjects struct {
	sorceryFilterMaps
	sorceryFilterPrograms
}

// SorceryFilterProgramSpecs is used for loading programs with custom options.
type SorceryFilterProgramSpecs struct {
	sorceryFilterPrograms
}

// Close releases all resources held by the Sorcery Filter objects.
func (o *SorceryFilterObjects) Close() {
	if o.DeviceAllowlist != nil {
		o.DeviceAllowlist.Close()
	}
	if o.NetworkPolicy != nil {
		o.NetworkPolicy.Close()
	}
	if o.SorceryDeviceFilter != nil {
		o.SorceryDeviceFilter.Close()
	}
	if o.SorceryConnect4Filter != nil {
		o.SorceryConnect4Filter.Close()
	}
	if o.SorceryBind4Filter != nil {
		o.SorceryBind4Filter.Close()
	}
	if o.SorceryConnect6Filter != nil {
		o.SorceryConnect6Filter.Close()
	}
}

// loadSorceryFilterObjects loads Sorcery Filter programs from embedded .bpf.o.
func loadSorceryFilterObjects(objs *SorceryFilterObjects, opts *ebpf.CollectionOptions) error {
	specPath := filepath.Join("pkg", "warding", "ebpf", "c")
	bpfelPath := filepath.Join(specPath, "sorcery_filter.bpfel.o")
	bpfebPath := filepath.Join(specPath, "sorcery_filter.bpfeb.o")

	bpfPath := bpfelPath
	if binary.NativeEndian == binary.BigEndian {
		bpfPath = bpfebPath
	}

	if _, err := os.Stat(bpfPath); err == nil {
		return loadBPFCollection(bpfPath, objs, opts)
	}

	return loadSorceryFilterProgrammatic(objs, opts)
}

// loadSorceryFilterProgrammatic creates the cgroup filter maps without
// compiled eBPF bytecode. Maps are functional; programs are nil stubs.
func loadSorceryFilterProgrammatic(objs *SorceryFilterObjects, opts *ebpf.CollectionOptions) error {
	pinPath := ""
	if opts.Maps.PinPath != "" {
		pinPath = opts.Maps.PinPath
		os.MkdirAll(pinPath, 0700)
	}

	// DeviceAllowlist (HASH, 128 entries, key=u32, value=u32)
	da, err := ebpf.NewMap(&ebpf.MapSpec{
		Name:       "device_allowlist",
		Type:       ebpf.Hash,
		KeySize:    4,
		ValueSize:  4,
		MaxEntries: 128,
		Pinning:    ebpf.PinByName,
	})
	if err != nil {
		return fmt.Errorf("ebpf: create device_allowlist map: %w", err)
	}
	if pinPath != "" {
		_ = da.Pin(filepath.Join(pinPath, "device_allowlist"))
	}
	objs.DeviceAllowlist = da

	// NetworkPolicy (HASH, 64 entries, key=u32, value=network_rule{12 bytes})
	np, err := ebpf.NewMap(&ebpf.MapSpec{
		Name:       "network_policy",
		Type:       ebpf.Hash,
		KeySize:    4,
		ValueSize:  12, // u32 ip + u32 mask + u16 port + u16 protocol
		MaxEntries: 64,
		Pinning:    ebpf.PinByName,
	})
	if err != nil {
		return fmt.Errorf("ebpf: create network_policy map: %w", err)
	}
	if pinPath != "" {
		_ = np.Pin(filepath.Join(pinPath, "network_policy"))
	}
	objs.NetworkPolicy = np

	// Programs are nil — loaded from .bpf.o when available.
	objs.SorceryDeviceFilter = nil
	objs.SorceryConnect4Filter = nil
	objs.SorceryBind4Filter = nil
	objs.SorceryConnect6Filter = nil

	return nil
}

// ---------------------------------------------------------------------------
// Generic BPF collection loader
// ---------------------------------------------------------------------------

// loadBPFCollection loads a .bpf.o file into the kernel using cilium/ebpf's
// CollectionSpec loader. This is used when pre-compiled objects are available.
func loadBPFCollection(bpfPath string, target interface{}, opts *ebpf.CollectionOptions) error {
	spec, err := ebpf.LoadCollectionSpec(bpfPath)
	if err != nil {
		return fmt.Errorf("ebpf: load spec from %s: %w", bpfPath, err)
	}

	var coll *ebpf.Collection
	if opts != nil {
		coll, err = ebpf.NewCollectionWithOptions(spec, *opts)
	} else {
		coll, err = ebpf.NewCollection(spec)
	}
	if err != nil {
		return fmt.Errorf("ebpf: load collection: %w", err)
	}

	// Map the loaded collection onto the target struct.
	switch t := target.(type) {
	case *TombGuardObjects:
		t.Violations = coll.Maps["violations"]
		t.PathConfig = coll.Maps["path_config"]
		t.EnforceMode = coll.Maps["enforce_mode"]
		t.TrustedPids = coll.Maps["trusted_pids"]
		t.TombGuardFilePermission = coll.Programs["tomb_guard_file_permission"]
		t.TombGuardInodePermission = coll.Programs["tomb_guard_inode_permission"]
		t.TraceExecve = coll.Programs["trace_execve"]
	case *SorceryFilterObjects:
		t.DeviceAllowlist = coll.Maps["device_allowlist"]
		t.NetworkPolicy = coll.Maps["network_policy"]
		t.SorceryDeviceFilter = coll.Programs["sorcery_device_filter"]
		t.SorceryConnect4Filter = coll.Programs["sorcery_connect4_filter"]
		t.SorceryBind4Filter = coll.Programs["sorcery_bind4_filter"]
		t.SorceryConnect6Filter = coll.Programs["sorcery_connect6_filter"]
	}

	return nil
}

// ---------------------------------------------------------------------------
// EBPFEnforcer
// ---------------------------------------------------------------------------

// EBPFEnforcer manages the lifecycle of the eBPF security programs.
type EBPFEnforcer struct {
	mu sync.Mutex

	// Tomb guard (LSM + tracepoint)
	tombGuardObjs  TombGuardObjects
	tombGuardSpecs *TombGuardPrograms

	// Cgroup filter (device + network)
	cgroupFilterObjs  SorceryFilterObjects
	cgroupFilterSpecs *SorceryFilterPrograms

	// Attached links (for cleanup)
	links       []ebpf.Link
	cgroupLinks []ebpf.Link

	// Perf reader for violation events
	violationReader *ebpf.PerfReader
	violationHandler ViolationHandler
	stopCh          chan struct{}

	// State
	loaded        bool
	cgroupAttached bool
}

// NewEnforcer creates a new EBPFEnforcer. Call Load() to compile and load
// the programs into the kernel.
func NewEnforcer() *EBPFEnforcer {
	return &EBPFEnforcer{
		stopCh: make(chan struct{}),
	}
}

// Load compiles (if needed) and loads the eBPF programs into the kernel.
// This must be called before AttachCgroup().
func (e *EBPFEnforcer) Load() error {
	e.mu.Lock()
	defer e.mu.Unlock()

	if e.loaded {
		return nil
	}

	// Remove memory lock limit (required for eBPF map creation).
	if err := rlimit.RemoveMemlock(); err != nil {
		return fmt.Errorf("ebpf: failed to remove memlock: %w", err)
	}

	rootDir := os.Getenv("SORCERY_GO_ROOT")
	if rootDir == "" {
		rootDir = "/var/lib/sorcery-go"
	}
	mapPinPath := filepath.Join(rootDir, "ebpf", "maps")

	opts := &ebpf.CollectionOptions{
		Maps: ebpf.MapOptions{
			PinPath: mapPinPath,
		},
	}

	// Load Tomb Guard programs.
	if err := loadTombGuardObjects(&e.tombGuardObjs, opts); err != nil {
		return fmt.Errorf("ebpf: failed to load tomb guard: %w", err)
	}

	// Load Cgroup Filter programs.
	if err := loadSorceryFilterObjects(&e.cgroupFilterObjs, opts); err != nil {
		// Cgroup filter is optional (not all systems support it).
		// Log but don't fail.
		fmt.Fprintf(os.Stderr, "ebpf: warning: cgroup filter not available: %v\n", err)
	}

	e.loaded = true
	return nil
}

// AttachCgroup attaches the cgroup device and network filter programs to
// the given cgroup path. This is the primary attachment point for LXC and
// Podman containers. Firecracker manages its own isolation.
func (e *EBPFEnforcer) AttachCgroup(cgroupPath string) error {
	e.mu.Lock()
	defer e.mu.Unlock()

	if !e.loaded {
		return errors.New("ebpf: not loaded — call Load() first")
	}

	if _, err := os.Stat(cgroupPath); os.IsNotExist(err) {
		return fmt.Errorf("ebpf: cgroup %s does not exist", cgroupPath)
	}

	// Attach device filter.
	if e.cgroupFilterObjs.SorceryDeviceFilter != nil {
		link, err := ebpf.AttachCgroup(ebpf.AttachCgroupOpts{
			Path:    cgroupPath,
			Attach:  ebpf.AttachCgroupDev,
			Program: e.cgroupFilterObjs.SorceryDeviceFilter,
		})
		if err != nil {
			return fmt.Errorf("ebpf: attach device filter: %w", err)
		}
		e.cgroupLinks = append(e.cgroupLinks, link)
	}

	// Attach connect4 filter (egress network).
	if e.cgroupFilterObjs.SorceryConnect4Filter != nil {
		link, err := ebpf.AttachCgroup(ebpf.AttachCgroupOpts{
			Path:    cgroupPath,
			Attach:  ebpf.AttachCgroupInet4Connect,
			Program: e.cgroupFilterObjs.SorceryConnect4Filter,
		})
		if err != nil {
			return fmt.Errorf("ebpf: attach connect4 filter: %w", err)
		}
		e.cgroupLinks = append(e.cgroupLinks, link)
	}

	e.cgroupAttached = true
	return nil
}

// SetEnforceMode sets the enforcement mode for the Tomb guard.
// ModePermissive (0) = log only, ModeEnforcing (1) = deny + log.
func (e *EBPFEnforcer) SetEnforceMode(mode EnforceMode) error {
	e.mu.Lock()
	defer e.mu.Unlock()

	if !e.loaded {
		return errors.New("ebpf: not loaded")
	}

	key := uint32(0)
	val := uint32(mode)
	return e.tombGuardObjs.EnforceMode.Update(key, val, ebpf.UpdateAny)
}

// GetEnforceMode returns the current enforcement mode.
func (e *EBPFEnforcer) GetEnforceMode() (EnforceMode, error) {
	e.mu.Lock()
	defer e.mu.Unlock()

	if !e.loaded {
		return ModePermissive, errors.New("ebpf: not loaded")
	}

	key := uint32(0)
	var val uint32
	if err := e.tombGuardObjs.EnforceMode.Lookup(key, &val); err != nil {
		return ModePermissive, err
	}
	return EnforceMode(val), nil
}

// SetTombPath updates the protected Tomb path prefix at runtime.
func (e *EBPFEnforcer) SetTombPath(path string) error {
	e.mu.Lock()
	defer e.mu.Unlock()

	if !e.loaded {
		return errors.New("ebpf: not loaded")
	}

	if len(path) >= 128 {
		return fmt.Errorf("ebpf: path too long (max 127 chars)")
	}

	buf := make([]byte, 128)
	copy(buf, path)
	key := uint32(0)
	return e.tombGuardObjs.PathConfig.Update(key, buf, ebpf.UpdateAny)
}

// SetStatePath updates the protected State path prefix at runtime.
func (e *EBPFEnforcer) SetStatePath(path string) error {
	e.mu.Lock()
	defer e.mu.Unlock()

	if !e.loaded {
		return errors.New("ebpf: not loaded")
	}

	if len(path) >= 128 {
		return fmt.Errorf("ebpf: path too long (max 127 chars)")
	}

	buf := make([]byte, 128)
	copy(buf, path)
	key := uint32(1)
	return e.tombGuardObjs.PathConfig.Update(key, buf, ebpf.UpdateAny)
}

// AddTrustedPID adds a PID to the trusted allowlist. Trusted processes
// bypass all Tomb protection enforcement (they are the sorcery engine itself).
func (e *EBPFEnforcer) AddTrustedPID(pid uint32) error {
	e.mu.Lock()
	defer e.mu.Unlock()

	if !e.loaded {
		return errors.New("ebpf: not loaded")
	}

	return e.tombGuardObjs.TrustedPids.Update(pid, uint32(1), ebpf.UpdateAny)
}

// RemoveTrustedPID removes a PID from the trusted allowlist.
func (e *EBPFEnforcer) RemoveTrustedPID(pid uint32) error {
	e.mu.Lock()
	defer e.mu.Unlock()

	if !e.loaded {
		return errors.New("ebpf: not loaded")
	}

	return e.tombGuardObjs.TrustedPids.Delete(pid)
}

// AllowDevice adds a device to the cgroup device allowlist.
// major/minor of 0xFFFF means "any" for that field.
func (e *EBPFEnforcer) AllowDevice(major, minor, access uint32) error {
	e.mu.Lock()
	defer e.mu.Unlock()

	if !e.loaded || e.cgroupFilterObjs.DeviceAllowlist == nil {
		return errors.New("ebpf: not loaded or cgroup filter unavailable")
	}

	key := (major << 16) | (minor & 0xFFFF)
	return e.cgroupFilterObjs.DeviceAllowlist.Update(key, access, ebpf.UpdateAny)
}

// AddNetworkRule adds a network policy rule for egress filtering.
func (e *EBPFEnforcer) AddNetworkRule(index uint32, ip, mask uint32, port uint16, protocol uint16) error {
	e.mu.Lock()
	defer e.mu.Unlock()

	if !e.loaded || e.cgroupFilterObjs.NetworkPolicy == nil {
		return errors.New("ebpf: not loaded or cgroup filter unavailable")
	}

	rule := struct {
		IP       uint32
		Mask     uint32
		Port     uint16
		Protocol uint16
	}{IP: ip, Mask: mask, Port: port, Protocol: protocol}

	return e.cgroupFilterObjs.NetworkPolicy.Update(index, rule, ebpf.UpdateAny)
}

// WatchViolations starts reading violation events from the perf buffer.
// The handler callback is invoked for each event. This blocks until
// StopWatching() is called.
func (e *EBPFEnforcer) WatchViolations(handler ViolationHandler) error {
	e.mu.Lock()
	defer e.mu.Unlock()

	if !e.loaded {
		return errors.New("ebpf: not loaded")
	}

	reader, err := ebpf.NewPerfReader(ebpf.PerfReaderOptions{
		Map:      e.tombGuardObjs.Violations,
		ReadSize: 4096,
	})
	if err != nil {
		return fmt.Errorf("ebpf: create perf reader: %w", err)
	}

	e.violationReader = reader
	e.violationHandler = handler

	go e.readLoop()
	return nil
}

// readLoop continuously reads from the perf buffer.
func (e *EBPFEnforcer) readLoop() {
	buf := make([]byte, 4096)
	for {
		select {
		case <-e.stopCh:
			return
		default:
		}

		n, err := e.violationReader.Read(buf)
		if err != nil {
			if errors.Is(err, ebpf.ErrClosed) {
				return
			}
			continue
		}
		if n == 0 {
			continue
		}

		e.parseAndHandle(buf[:n])
	}
}

// parseAndHandle parses raw perf event data and invokes the handler.
func (e *EBPFEnforcer) parseAndHandle(data []byte) {
	// Perf event format: [header (8 bytes)][payload]
	for len(data) >= 8+280 {
		payload := data[8:]

		r := bytes.NewReader(payload)

		var pid, tid, uid, gid, syscallNr, ppid uint32
		binary.Read(r, binary.LittleEndian, &pid)
		binary.Read(r, binary.LittleEndian, &tid)
		binary.Read(r, binary.LittleEndian, &uid)
		binary.Read(r, binary.LittleEndian, &gid)
		binary.Read(r, binary.LittleEndian, &syscallNr)
		binary.Read(r, binary.LittleEndian, &ppid)

		var comm [16]byte
		r.Read(comm[:])

		var path [256]byte
		r.Read(path[:])

		var accessMask int32
		binary.Read(r, binary.LittleEndian, &accessMask)

		v := Violation{
			PID:        pid,
			TID:        tid,
			UID:        uid,
			GID:        gid,
			PPID:       ppid,
			SyscallNr:  syscallNr,
			Comm:       string(bytes.TrimRight(comm[:], "\x00")),
			Path:       string(bytes.TrimRight(path[:], "\x00")),
			AccessMask: accessMask,
		}

		if e.violationHandler != nil {
			e.violationHandler(v)
		}

		recordSize := 24 + 16 + 256 + 4
		aligned := (recordSize + 7) & ^7
		if int(aligned) > len(data) {
			break
		}
		data = data[aligned:]
	}
}

// StopWatching stops the violation watch loop.
func (e *EBPFEnforcer) StopWatching() {
	select {
	case <-e.stopCh:
		// Already closed.
	default:
		close(e.stopCh)
	}
	if e.violationReader != nil {
		e.violationReader.Close()
		e.violationReader = nil
	}
}

// Close detaches all programs and releases all kernel resources.
func (e *EBPFEnforcer) Close() {
	e.StopWatching()

	for _, link := range e.cgroupLinks {
		link.Close()
	}
	e.cgroupLinks = nil

	for _, link := range e.links {
		link.Close()
	}
	e.links = nil

	if e.loaded {
		e.tombGuardObjs.Close()
		e.cgroupFilterObjs.Close()
		e.loaded = false
		e.cgroupAttached = false
	}
}

// IsLoaded reports whether the eBPF programs are loaded into the kernel.
func (e *EBPFEnforcer) IsLoaded() bool {
	e.mu.Lock()
	defer e.mu.Unlock()
	return e.loaded
}

// IsCgroupAttached reports whether the cgroup filters are attached.
func (e *EBPFEnforcer) IsCgroupAttached() bool {
	e.mu.Lock()
	defer e.mu.Unlock()
	return e.cgroupAttached
}

// SelfTrustedPID adds the current process PID to the trusted allowlist.
func (e *EBPFEnforcer) SelfTrustedPID() error {
	return e.AddTrustedPID(uint32(os.Getpid()))
}

// Status returns a human-readable summary of the enforcer state.
func (e *EBPFEnforcer) Status() string {
	e.mu.Lock()
	defer e.mu.Unlock()

	if !e.loaded {
		return "eBPF: not loaded"
	}

	mode, _ := e.GetEnforceMode()
	modeStr := "permissive (log only)"
	if mode == ModeEnforcing {
		modeStr = "enforcing (deny + log)"
	}

	cgroupStr := "not attached"
	if e.cgroupAttached {
		cgroupStr = "attached"
	}

	// Detect if programs were loaded from .bpf.o or are programmatic stubs.
	programStr := "maps only (no .bpf.o — compile with clang for full enforcement)"
	if e.tombGuardObjs.TombGuardFilePermission != nil {
		programStr = "LSM + cgroup filters active"
	}

	return fmt.Sprintf("eBPF: loaded | mode: %s | cgroup filter: %s | programs: %s",
		modeStr, cgroupStr, programStr)
}

// ProbeCapabilities checks if the system supports the required eBPF features.
// Returns a list of available features and any errors.
func ProbeCapabilities() (lsm, cgroupDev, cgroupNet bool, err error) {
	// Check LSM support.
	lsm = features.HaveLSM() == nil

	// Check cgroup BPF support (device + network).
	cgroupDev = false
	cgroupNet = false

	if _, err := os.Stat("/sys/fs/cgroup"); err == nil {
		cgroupDev = true
		cgroupNet = true
	}

	return lsm, cgroupDev, cgroupNet, nil
}