/*
Hybrid Isolation - Security and resource isolation for Volt hybrid-native containers.

Configures:
  - Landlock LSM policy generation (NEVER AppArmor)
  - Seccomp profile selection (strict/default/unconfined)
  - Cgroups v2 resource limits (memory, CPU, I/O, PIDs)
  - Network namespace setup (private network stack)

Copyright (c) Armored Gates LLC. All rights reserved.
*/
package hybrid

import (
	"fmt"
	"path/filepath"
	"strings"
)

// ── Seccomp Profiles ─────────────────────────────────────────────────────────

// SeccompProfile selects the syscall filtering level for a container.
type SeccompProfile string

const (
	// SeccompStrict blocks dangerous syscalls and limits the container to a
	// safe subset. Suitable for untrusted workloads.
	SeccompStrict SeccompProfile = "strict"

	// SeccompDefault applies the systemd-nspawn default seccomp filter which
	// blocks mount, reboot, kexec, and other admin syscalls.
	SeccompDefault SeccompProfile = "default"

	// SeccompUnconfined disables seccomp filtering entirely. Use only for
	// trusted workloads that need full syscall access (e.g. nested containers).
	SeccompUnconfined SeccompProfile = "unconfined"
)

// ── Landlock Policy ──────────────────────────────────────────────────────────

// LandlockAccess defines the bitfield of allowed filesystem operations.
// These mirror the LANDLOCK_ACCESS_FS_* constants from the kernel ABI.
type LandlockAccess uint64

const (
	LandlockAccessFSExecute    LandlockAccess = 1 << 0
	LandlockAccessFSWriteFile  LandlockAccess = 1 << 1
	LandlockAccessFSReadFile   LandlockAccess = 1 << 2
	LandlockAccessFSReadDir    LandlockAccess = 1 << 3
	LandlockAccessFSRemoveDir  LandlockAccess = 1 << 4
	LandlockAccessFSRemoveFile LandlockAccess = 1 << 5
	LandlockAccessFSMakeChar   LandlockAccess = 1 << 6
	LandlockAccessFSMakeDir    LandlockAccess = 1 << 7
	LandlockAccessFSMakeReg    LandlockAccess = 1 << 8
	LandlockAccessFSMakeSock   LandlockAccess = 1 << 9
	LandlockAccessFSMakeFifo   LandlockAccess = 1 << 10
	LandlockAccessFSMakeBlock  LandlockAccess = 1 << 11
	LandlockAccessFSMakeSym    LandlockAccess = 1 << 12
	LandlockAccessFSRefer      LandlockAccess = 1 << 13
	LandlockAccessFSTruncate   LandlockAccess = 1 << 14

	// Convenience combinations.
	LandlockReadOnly  = LandlockAccessFSReadFile | LandlockAccessFSReadDir
	LandlockReadWrite = LandlockReadOnly | LandlockAccessFSWriteFile |
		LandlockAccessFSMakeReg | LandlockAccessFSMakeDir |
		LandlockAccessFSRemoveFile | LandlockAccessFSRemoveDir |
		LandlockAccessFSTruncate
	LandlockReadExec = LandlockReadOnly | LandlockAccessFSExecute
)

// LandlockRule maps a filesystem path to the permitted access mask.
type LandlockRule struct {
	Path   string
	Access LandlockAccess
}

// LandlockPolicy is an ordered set of Landlock rules for a container.
type LandlockPolicy struct {
	Rules []LandlockRule
}

// ServerPolicy returns a Landlock policy for server/service workloads.
// Allows execution from /usr and /lib, read-write to /app, /tmp, /var.
func ServerPolicy(rootfs string) *LandlockPolicy {
	return &LandlockPolicy{
		Rules: []LandlockRule{
			{Path: filepath.Join(rootfs, "usr"), Access: LandlockReadExec},
			{Path: filepath.Join(rootfs, "lib"), Access: LandlockReadOnly | LandlockAccessFSExecute},
			{Path: filepath.Join(rootfs, "lib64"), Access: LandlockReadOnly | LandlockAccessFSExecute},
			{Path: filepath.Join(rootfs, "bin"), Access: LandlockReadExec},
			{Path: filepath.Join(rootfs, "sbin"), Access: LandlockReadExec},
			{Path: filepath.Join(rootfs, "etc"), Access: LandlockReadOnly},
			{Path: filepath.Join(rootfs, "app"), Access: LandlockReadWrite},
			{Path: filepath.Join(rootfs, "tmp"), Access: LandlockReadWrite},
			{Path: filepath.Join(rootfs, "var"), Access: LandlockReadWrite},
			{Path: filepath.Join(rootfs, "run"), Access: LandlockReadWrite},
		},
	}
}

// DesktopPolicy returns a Landlock policy for desktop/interactive workloads.
// More permissive than ServerPolicy: full home access, /var write access.
func DesktopPolicy(rootfs string) *LandlockPolicy {
	return &LandlockPolicy{
		Rules: []LandlockRule{
			{Path: filepath.Join(rootfs, "usr"), Access: LandlockReadExec},
			{Path: filepath.Join(rootfs, "lib"), Access: LandlockReadOnly | LandlockAccessFSExecute},
			{Path: filepath.Join(rootfs, "lib64"), Access: LandlockReadOnly | LandlockAccessFSExecute},
			{Path: filepath.Join(rootfs, "bin"), Access: LandlockReadExec},
			{Path: filepath.Join(rootfs, "sbin"), Access: LandlockReadExec},
			{Path: filepath.Join(rootfs, "etc"), Access: LandlockReadWrite},
			{Path: filepath.Join(rootfs, "home"), Access: LandlockReadWrite | LandlockAccessFSExecute},
			{Path: filepath.Join(rootfs, "tmp"), Access: LandlockReadWrite},
			{Path: filepath.Join(rootfs, "var"), Access: LandlockReadWrite},
			{Path: filepath.Join(rootfs, "run"), Access: LandlockReadWrite},
			{Path: filepath.Join(rootfs, "opt"), Access: LandlockReadExec},
		},
	}
}

// ── Cgroups v2 Resource Limits ───────────────────────────────────────────────

// ResourceLimits configures cgroups v2 resource constraints for a container.
type ResourceLimits struct {
	// Memory limits (e.g. "512M", "2G"). Empty means unlimited.
	MemoryHard string // memory.max — hard limit, OOM kill above this
	MemorySoft string // memory.high — throttle above this (soft pressure)

	// CPU limits.
	CPUWeight int    // cpu.weight (1-10000, default 100). Proportional share.
	CPUSet    string // cpuset.cpus (e.g. "0-3", "0,2"). Pin to specific cores.

	// I/O limits.
	IOWeight int // io.weight (1-10000, default 100). Proportional share.

	// PID limit.
	PIDsMax int // pids.max — maximum number of processes. 0 means unlimited.
}

// DefaultResourceLimits returns conservative defaults suitable for most workloads.
func DefaultResourceLimits() *ResourceLimits {
	return &ResourceLimits{
		MemoryHard: "2G",
		MemorySoft: "1G",
		CPUWeight:  100,
		CPUSet:     "",   // no pinning
		IOWeight:   100,
		PIDsMax:    4096,
	}
}

// SystemdProperties converts ResourceLimits into systemd unit properties
// suitable for passing to systemd-run or systemd-nspawn via --property=.
func (r *ResourceLimits) SystemdProperties() []string {
	var props []string

	// Cgroups v2 delegation is always enabled for hybrid containers.
	props = append(props, "Delegate=yes")

	if r.MemoryHard != "" {
		props = append(props, fmt.Sprintf("MemoryMax=%s", r.MemoryHard))
	}
	if r.MemorySoft != "" {
		props = append(props, fmt.Sprintf("MemoryHigh=%s", r.MemorySoft))
	}
	if r.CPUWeight > 0 {
		props = append(props, fmt.Sprintf("CPUWeight=%d", r.CPUWeight))
	}
	if r.CPUSet != "" {
		props = append(props, fmt.Sprintf("AllowedCPUs=%s", r.CPUSet))
	}
	if r.IOWeight > 0 {
		props = append(props, fmt.Sprintf("IOWeight=%d", r.IOWeight))
	}
	if r.PIDsMax > 0 {
		props = append(props, fmt.Sprintf("TasksMax=%d", r.PIDsMax))
	}

	return props
}

// ── Network Isolation ────────────────────────────────────────────────────────

// NetworkMode selects the container network configuration.
type NetworkMode string

const (
	// NetworkPrivate creates a fully isolated network namespace with a veth
	// pair connected to the host bridge (voltbr0). The container gets its own
	// IP stack, routing table, and firewall rules.
	NetworkPrivate NetworkMode = "private"

	// NetworkHost shares the host network namespace. The container sees all
	// host interfaces and ports. Use only for trusted system services.
	NetworkHost NetworkMode = "host"

	// NetworkNone creates an isolated network namespace with no external
	// connectivity. Loopback only.
	NetworkNone NetworkMode = "none"
)

// NetworkConfig holds the network isolation settings for a container.
type NetworkConfig struct {
	Mode   NetworkMode
	Bridge string // bridge name for private mode (default: "voltbr0")

	// PortForwards maps host ports to container ports when Mode is NetworkPrivate.
	PortForwards []PortForward

	// DNS servers to inject into the container's resolv.conf.
	DNS []string
}

// PortForward maps a single host port to a container port.
type PortForward struct {
	HostPort      int
	ContainerPort int
	Protocol      string // "tcp" or "udp"
}

// DefaultNetworkConfig returns a private-network configuration with the
// standard Volt bridge.
func DefaultNetworkConfig() *NetworkConfig {
	return &NetworkConfig{
		Mode:   NetworkPrivate,
		Bridge: "voltbr0",
		DNS:    []string{"1.1.1.1", "1.0.0.1"},
	}
}

// NspawnNetworkArgs returns the systemd-nspawn arguments for this network
// configuration.
func (n *NetworkConfig) NspawnNetworkArgs() []string {
	switch n.Mode {
	case NetworkPrivate:
		args := []string{"--network-bridge=" + n.Bridge}
		for _, pf := range n.PortForwards {
			proto := pf.Protocol
			if proto == "" {
				proto = "tcp"
			}
			args = append(args, fmt.Sprintf("--port=%s:%d:%d", proto, pf.HostPort, pf.ContainerPort))
		}
		return args
	case NetworkHost:
		return nil // no network flags = share host namespace
	case NetworkNone:
		return []string{"--private-network"}
	default:
		return []string{"--network-bridge=voltbr0"}
	}
}

// ── Isolation Profile ────────────────────────────────────────────────────────

// IsolationConfig combines all isolation settings for a hybrid container.
type IsolationConfig struct {
	Landlock  *LandlockPolicy
	Seccomp   SeccompProfile
	Resources *ResourceLimits
	Network   *NetworkConfig

	// PrivateUsers enables user namespace isolation (--private-users).
	PrivateUsers bool

	// ReadOnlyFS mounts the rootfs as read-only (--read-only).
	ReadOnlyFS bool
}

// DefaultIsolation returns a security-first isolation configuration suitable
// for production workloads.
func DefaultIsolation(rootfs string) *IsolationConfig {
	return &IsolationConfig{
		Landlock:     ServerPolicy(rootfs),
		Seccomp:      SeccompDefault,
		Resources:    DefaultResourceLimits(),
		Network:      DefaultNetworkConfig(),
		PrivateUsers: true,
		ReadOnlyFS:   false,
	}
}

// NspawnArgs returns the complete set of systemd-nspawn arguments for this
// isolation configuration. These are appended to the base nspawn command.
func (iso *IsolationConfig) NspawnArgs() []string {
	var args []string

	// Resource limits and cgroup delegation via --property.
	for _, prop := range iso.Resources.SystemdProperties() {
		args = append(args, "--property="+prop)
	}

	// Seccomp profile.
	switch iso.Seccomp {
	case SeccompStrict:
		// systemd-nspawn applies its default filter automatically.
		// For strict mode we add --capability=drop-all to further limit.
		args = append(args, "--drop-capability=all")
	case SeccompDefault:
		// Use nspawn's built-in seccomp filter — no extra flags needed.
	case SeccompUnconfined:
		// Disable the built-in seccomp filter for trusted workloads.
		args = append(args, "--system-call-filter=~")
	}

	// Network isolation.
	args = append(args, iso.Network.NspawnNetworkArgs()...)

	// User namespace isolation.
	if iso.PrivateUsers {
		args = append(args, "--private-users=pick")
	}

	// Read-only rootfs.
	if iso.ReadOnlyFS {
		args = append(args, "--read-only")
	}

	return args
}

// NspawnConfigBlock returns the .nspawn file content sections for this
// isolation configuration. Written to /etc/systemd/nspawn/<name>.nspawn.
func (iso *IsolationConfig) NspawnConfigBlock(name string) string {
	var b strings.Builder

	// [Exec] section
	b.WriteString("[Exec]\n")
	b.WriteString("Boot=yes\n")
	b.WriteString("PrivateUsers=")
	if iso.PrivateUsers {
		b.WriteString("pick\n")
	} else {
		b.WriteString("no\n")
	}

	// Environment setup.
	b.WriteString(fmt.Sprintf("Environment=VOLT_CONTAINER=%s\n", name))
	b.WriteString("Environment=VOLT_RUNTIME=hybrid\n")

	b.WriteString("\n")

	// [Network] section
	b.WriteString("[Network]\n")
	switch iso.Network.Mode {
	case NetworkPrivate:
		b.WriteString(fmt.Sprintf("Bridge=%s\n", iso.Network.Bridge))
	case NetworkNone:
		b.WriteString("Private=yes\n")
	case NetworkHost:
		// No network section needed for host mode.
	}

	b.WriteString("\n")

	// [ResourceControl] section (selected limits for the .nspawn file).
	b.WriteString("[ResourceControl]\n")
	if iso.Resources.MemoryHard != "" {
		b.WriteString(fmt.Sprintf("MemoryMax=%s\n", iso.Resources.MemoryHard))
	}
	if iso.Resources.PIDsMax > 0 {
		b.WriteString(fmt.Sprintf("TasksMax=%d\n", iso.Resources.PIDsMax))
	}

	return b.String()
}