// SPDX-License-Identifier: GPL-3.0-or-later

package rootcheck

import (
	"context"
	"errors"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
	"strings"
	"syscall"

	"codeberg.org/anassaeneroi/enodia-sentinal/go-agent/internal/model"
)

const (
	procRoot = "/proc"
	sysRoot  = "/sys"
)

// Collect obtains the independent local views used by Check. Every source is
// best-effort: unavailable procfs/sysfs files or a missing ps binary remove
// only that comparison, never turn a collection error into a rootkit alert.
func Collect(ctx context.Context, state model.State, pidCap int) Views {
	visible := procPIDs()
	ps, psAvailable := psPIDs(ctx)
	return Views{
		VisiblePIDs:       visible,
		AlivePIDs:         alivePIDs(ctx, pidCap),
		PSPIDs:            ps,
		PSAvailable:       psAvailable,
		PIDAlive:          pidAlive,
		ProcPIDExists:     procPIDExists,
		ProcModules:       procModules(),
		SysLiveModules:    sysLiveModules(),
		ModuleTaints:      moduleTaints(),
		KernelTaint:       kernelTaint(),
		ProcTCPPorts:      procTCPPorts(),
		SSTCPPorts:        ssTCPPorts(state),
		ProcUDPPorts:      procUDPPorts(),
		SSUDPPorts:        ssUDPPorts(state),
		ProcRawProtocols:  procRawProtocols(),
		SSRawProtocols:    ssRawProtocols(state),
		ProcProtocolKinds: procProtocolKinds(),
		SSProtocolKinds:   ssProtocolKinds(state),
		PromiscuousIfaces: promiscuousIfaces(),
	}
}

// Run collects a bounded live view then evaluates it against operator policy.
func Run(ctx context.Context, state model.State, pidCap int, allowed map[string]bool) []model.Alert {
	return Check(Collect(ctx, state, pidCap), Options{AllowedModules: allowed})
}

func procPIDs() map[int]bool {
	result := map[int]bool{}
	entries, err := os.ReadDir(procRoot)
	if err != nil {
		return result
	}
	for _, entry := range entries {
		if pid, err := strconv.Atoi(entry.Name()); err == nil && pid >= 0 {
			result[pid] = true
		}
	}
	return result
}

func alivePIDs(ctx context.Context, cap int) map[int]bool {
	// kill(pid, 0) asks the kernel whether a PID exists without signalling it;
	// that is intentionally independent of the procfs directory view. Limit
	// the sweep because pid_max may be very large, and return partial results on
	// cancellation rather than delaying every other integrity comparison.
	result := map[int]bool{}
	if cap <= 0 {
		return result
	}
	maximum := cap
	if raw, err := os.ReadFile(filepath.Join(procRoot, "sys/kernel/pid_max")); err == nil {
		if value, err := strconv.Atoi(strings.TrimSpace(string(raw))); err == nil && value < maximum {
			maximum = value
		}
	}
	for pid := 1; pid <= maximum; pid++ {
		select {
		case <-ctx.Done():
			return result
		default:
		}
		err := syscall.Kill(pid, 0)
		if err == nil || errors.Is(err, syscall.EPERM) {
			result[pid] = true
		}
	}
	return result
}

func pidAlive(pid int) bool {
	// EPERM still proves that the kernel knows about the PID; it only means the
	// sidecar lacks permission to inspect or signal that process.
	err := syscall.Kill(pid, 0)
	return err == nil || errors.Is(err, syscall.EPERM)
}

func procPIDExists(pid int) bool {
	// Keep this separate from pidAlive: rootcheck alerts on disagreement between
	// kernel process lookup and the procfs namespace it is expected to expose.
	_, err := os.Stat(filepath.Join(procRoot, strconv.Itoa(pid)))
	return err == nil
}

func psPIDs(ctx context.Context) (map[int]bool, bool) {
	// ps provides a third, userspace view. A missing or failing command disables
	// only this comparison because an unavailable tool is not evidence of a
	// hidden process.
	command := exec.CommandContext(ctx, "ps", "-e", "-o", "pid=")
	raw, err := command.Output()
	if err != nil {
		return map[int]bool{}, false
	}
	result := map[int]bool{}
	for _, line := range strings.Split(string(raw), "\n") {
		if pid, err := strconv.Atoi(strings.TrimSpace(line)); err == nil {
			result[pid] = true
		}
	}
	return result, true
}

func procModules() map[string]bool {
	result := map[string]bool{}
	raw, err := os.ReadFile(filepath.Join(procRoot, "modules"))
	if err != nil {
		return result
	}
	for _, line := range strings.Split(string(raw), "\n") {
		if fields := strings.Fields(line); len(fields) > 0 {
			result[fields[0]] = true
		}
	}
	return result
}

func sysLiveModules() map[string]bool {
	result := map[string]bool{}
	entries, err := os.ReadDir(filepath.Join(sysRoot, "module"))
	if err != nil {
		return result
	}
	for _, entry := range entries {
		raw, err := os.ReadFile(filepath.Join(sysRoot, "module", entry.Name(), "initstate"))
		if err == nil && strings.TrimSpace(string(raw)) == "live" {
			result[entry.Name()] = true
		}
	}
	return result
}

func moduleTaints() map[string]string {
	result := map[string]string{}
	entries, err := os.ReadDir(filepath.Join(sysRoot, "module"))
	if err != nil {
		return result
	}
	for _, entry := range entries {
		raw, err := os.ReadFile(filepath.Join(sysRoot, "module", entry.Name(), "taint"))
		taint := strings.TrimSpace(string(raw))
		if err == nil && taint != "" && taint != "0" {
			result[entry.Name()] = taint
		}
	}
	return result
}

func kernelTaint() int {
	raw, err := os.ReadFile(filepath.Join(procRoot, "sys/kernel/tainted"))
	if err != nil {
		return 0
	}
	value, err := strconv.Atoi(strings.TrimSpace(string(raw)))
	if err != nil {
		return 0
	}
	return value
}

func procTCPPorts() map[int]bool {
	return unionInts(readSocketPorts("net/tcp", true), readSocketPorts("net/tcp6", true))
}
func procUDPPorts() map[int]bool {
	return unionInts(readSocketPorts("net/udp", false), readSocketPorts("net/udp6", false))
}
func procRawProtocols() map[int]bool {
	return unionInts(readSocketPorts("net/raw", false), readSocketPorts("net/raw6", false))
}

func readSocketPorts(relative string, listenOnly bool) map[int]bool {
	// /proc/net/{tcp,udp,raw} encodes the local endpoint as hex ADDRESS:PORT.
	// TCP's 0A state is LISTEN; UDP and raw entries have no equivalent listener
	// state, so callers retain every bound protocol/port for comparison.
	result := map[int]bool{}
	raw, err := os.ReadFile(filepath.Join(procRoot, relative))
	if err != nil {
		return result
	}
	lines := strings.Split(string(raw), "\n")
	for _, line := range lines[1:] {
		fields := strings.Fields(line)
		if len(fields) < 4 || (listenOnly && fields[3] != "0A") {
			continue
		}
		_, portText, ok := strings.Cut(fields[1], ":")
		if !ok {
			continue
		}
		port, err := strconv.ParseInt(portText, 16, 32)
		if err == nil && port != 0 {
			result[int(port)] = true
		}
	}
	return result
}

func procProtocolKinds() map[string]bool {
	checks := map[string][]string{
		"sctp": {"net/sctp/eps", "net/sctp/assocs", "net/sctp/remaddr"},
		"dccp": {"net/dccp", "net/dccp6"}, "packet": {"net/packet"},
		"tipc": {"net/tipc/socket"}, "xdp": {"net/xdp"},
	}
	result := map[string]bool{}
	for kind, paths := range checks {
		for _, path := range paths {
			if socketRows(path) {
				result[kind] = true
				break
			}
		}
	}
	return result
}

func socketRows(relative string) bool {
	raw, err := os.ReadFile(filepath.Join(procRoot, relative))
	if err != nil {
		return false
	}
	lines := strings.Split(string(raw), "\n")
	for _, line := range lines[1:] {
		if strings.TrimSpace(line) != "" {
			return true
		}
	}
	return false
}

func ssTCPPorts(state model.State) map[int]bool {
	result := map[int]bool{}
	for _, socket := range state.Sockets {
		if socket.State == "LISTEN" {
			if port, ok := endpointPort(socket.Local); ok {
				result[port] = true
			}
		}
	}
	return result
}
func ssUDPPorts(state model.State) map[int]bool {
	result := map[int]bool{}
	for _, socket := range state.Sockets {
		if socket.State == "UNCONN" || socket.State == "ESTAB" {
			if port, ok := endpointPort(socket.Local); ok {
				result[port] = true
			}
		}
	}
	return result
}
func ssRawProtocols(state model.State) map[int]bool {
	result := map[int]bool{}
	for _, socket := range state.Sockets {
		if socket.Kind == "raw" {
			if protocol, ok := endpointProtocol(socket.Local); ok {
				result[protocol] = true
			}
		}
	}
	return result
}
func ssProtocolKinds(state model.State) map[string]bool {
	result := map[string]bool{}
	for _, socket := range state.Sockets {
		if socket.Kind != "" {
			result[socket.Kind] = true
		}
	}
	return result
}

func endpointPort(value string) (int, bool) {
	index := strings.LastIndex(value, ":")
	if index < 0 {
		return 0, false
	}
	tail := value[index+1:]
	port, err := strconv.Atoi(tail)
	return port, err == nil
}
func endpointProtocol(value string) (int, bool) {
	index := strings.LastIndex(value, ":")
	if index < 0 {
		return 0, false
	}
	tail := value[index+1:]
	tail = strings.ToLower(strings.Trim(tail, "[]"))
	if value, err := strconv.Atoi(tail); err == nil {
		return value, true
	}
	protocol, ok := rawProtocolNames[tail]
	return protocol, ok
}

func promiscuousIfaces() []string {
	result := make([]string, 0)
	entries, err := os.ReadDir(filepath.Join(sysRoot, "class/net"))
	if err != nil {
		return result
	}
	for _, entry := range entries {
		raw, err := os.ReadFile(filepath.Join(sysRoot, "class/net", entry.Name(), "flags"))
		if err != nil {
			continue
		}
		flags, err := strconv.ParseInt(strings.TrimSpace(string(raw)), 0, 64)
		if err == nil && flags&0x100 != 0 {
			result = append(result, entry.Name())
		}
	}
	return result
}
func unionInts(left, right map[int]bool) map[int]bool {
	result := map[int]bool{}
	for value := range left {
		result[value] = true
	}
	for value := range right {
		result[value] = true
	}
	return result
}