// Cgroup-based quarantine with multi-runtime support.
//
// When the Warding detects a high-severity threat it freezes the offending
// container or VM. This uses the most appropriate mechanism for each runtime:
//
//   - LXC: cgroup v2 freezer (preferred), then lxc-freeze, then systemctl
//   - Podman: cgroup v2 freezer (preferred), then podman pause
//   - Firecracker: VMM process SIGSTOP (no cgroup involvement)
//   - BareMetal: cgroup v2 freezer if applicable, otherwise SIGSTOP
//
// On cgroup v2 systems (kernel >= 4.15, systemd >= 244) the freezer is at
// /sys/fs/cgroup/<container-path>/cgroup.freeze. Writing "1" freezes every
// process in the cgroup atomically.
package warding

import (
        "fmt"
        "os"
        "os/exec"
        "path/filepath"
        "strings"
        "sync"
)

// RuntimeAdapter is a minimal interface for runtime-specific freeze/thaw
// operations. This avoids importing the full runtime package from warding.
type RuntimeAdapter interface {
        // Freeze suspends all processes in the named container/sanctum.
        Freeze(nodeID string) error
        // Thaw resumes a frozen container/sanctum.
        Thaw(nodeID string) error
        // CgroupPath returns the cgroup v2 path for the container.
        CgroupPath(nodeID string) string
}

// validateNodeID rejects nodeID values that contain path traversal
// characters, preventing abuse of cgroup path construction.
func validateNodeID(nodeID string) error {
        if nodeID == "" {
                return fmt.Errorf("warding: nodeID must not be empty")
        }
        if strings.ContainsAny(nodeID, "/\\..") {
                return fmt.Errorf("warding: nodeID contains invalid characters: %q", nodeID)
        }
        return nil
}

// freezeContainer freezes a container or VM by name using the configured
// runtime adapter. If no adapter is set, falls back to generic cgroup v2
// detection (for backward compatibility).
func freezeContainer(nodeID string) error {
        if err := validateNodeID(nodeID); err != nil {
                return err
        }
        // If a runtime adapter is configured, use it.
        runtimeAdapterMu.RLock()
        adapter := globalRuntimeAdapter
        runtimeAdapterMu.RUnlock()
        if adapter != nil {
                return adapter.Freeze(nodeID)
        }
        return genericFreeze(nodeID)
}

// thawContainer thaws a frozen container or VM by name.
func thawContainer(nodeID string) error {
        if err := validateNodeID(nodeID); err != nil {
                return err
        }
        runtimeAdapterMu.RLock()
        adapter := globalRuntimeAdapter
        runtimeAdapterMu.RUnlock()
        if adapter != nil {
                return adapter.Thaw(nodeID)
        }
        return genericThaw(nodeID)
}

var (
        // globalRuntimeAdapter is the runtime-specific freeze/thaw implementation.
        // Set via SetRuntimeAdapter(). Protected by runtimeAdapterMu.
        globalRuntimeAdapter RuntimeAdapter
        runtimeAdapterMu  sync.RWMutex
)

// SetRuntimeAdapter configures the runtime-specific freeze/thaw handler.
// Called by the CLI layer when the runtime is initialized.
func SetRuntimeAdapter(adapter RuntimeAdapter) {
        runtimeAdapterMu.Lock()
        defer runtimeAdapterMu.Unlock()
        globalRuntimeAdapter = adapter
}

// genericFreeze is the fallback freeze mechanism that tries multiple
// approaches in order of preference.
func genericFreeze(nodeID string) error {
        // 1. Try cgroup v2 freezer (preferred — works for LXC, Podman, any cgroup-managed process).
        if v2Path := cgroupV2Path(nodeID); v2Path != "" {
                if err := os.WriteFile(filepath.Join(v2Path, "cgroup.freeze"),
                        []byte("1"), 0644); err == nil {
                        return nil
                }
        }

        // 2. Try runtime-specific CLIs (ordered by detection).
        freezeCommands := []struct {
                binary string
                args   []string
        }{
                {"lxc-freeze", []string{"-n", nodeID}},
                {"podman", []string{"pause", nodeID}},
                {"systemctl", []string{"freeze", nodeID}},
        }

        for _, fc := range freezeCommands {
                if _, err := exec.LookPath(fc.binary); err == nil {
                        if out, err := exec.Command(fc.binary, fc.args...).CombinedOutput(); err == nil {
                                return nil
                        } else {
                                return fmt.Errorf("%s: %w (%s)", fc.binary, err, string(out))
                        }
                }
        }

        return fmt.Errorf("no freezer available (tried cgroup v2, lxc-freeze, podman pause, systemctl)")
}

// genericThaw is the fallback thaw mechanism.
func genericThaw(nodeID string) error {
        // 1. Try cgroup v2.
        if v2Path := cgroupV2Path(nodeID); v2Path != "" {
                if err := os.WriteFile(filepath.Join(v2Path, "cgroup.freeze"),
                        []byte("0"), 0644); err == nil {
                        return nil
                }
        }

        // 2. Try runtime-specific CLIs.
        thawCommands := []struct {
                binary string
                args   []string
        }{
                {"lxc-unfreeze", []string{"-n", nodeID}},
                {"podman", []string{"unpause", nodeID}},
                {"systemctl", []string{"thaw", nodeID}},
        }

        for _, tc := range thawCommands {
                if _, err := exec.LookPath(tc.binary); err == nil {
                        if out, err := exec.Command(tc.binary, tc.args...).CombinedOutput(); err == nil {
                                return nil
                        } else {
                                return fmt.Errorf("%s: %w (%s)", tc.binary, err, string(out))
                        }
                }
        }

        return fmt.Errorf("no thaw mechanism available")
}

// cgroupV2Path tries to locate the cgroup v2 path for a container.
// It checks common locations for LXC, Podman, and systemd-managed containers.
func cgroupV2Path(nodeID string) string {
        candidates := []string{
                // LXC paths.
                filepath.Join("/sys/fs/cgroup/lxc", nodeID),
                filepath.Join("/sys/fs/cgroup/lxc.payload", nodeID),
                filepath.Join("/sys/fs/cgroup/system.slice", "lxc-"+nodeID+".service"),
                filepath.Join("/sys/fs/cgroup/machine.slice", "lxc-"+nodeID+".service"),
                // Podman paths.
                filepath.Join("/sys/fs/cgroup/machine.slice", "libpod-"+nodeID+".scope"),
                filepath.Join("/sys/fs/cgroup/machine.slice", "podman-"+nodeID+".scope"),
                // Generic systemd scope.
                filepath.Join("/sys/fs/cgroup/system.slice", nodeID+".scope"),
                filepath.Join("/sys/fs/cgroup/machine.slice", nodeID+".scope"),
        }
        for _, p := range candidates {
                if _, err := os.Stat(filepath.Join(p, "cgroup.freeze")); err == nil {
                        return p
                }
        }
        return ""
}