// Package runtime provides a unified abstraction over container runtimes.
//
// Sorcery-Go can deploy Essences into different execution environments
// (called "Sanctums"). This package defines the Runtime interface that
// decouples the Warding, Coven, and Reanimation logic from any specific
// container technology.
//
// Supported runtimes:
//   - LXC: Traditional system containers (lxc-tools CLI)
//   - Podman: OCI containers (podman CLI / REST API)
//   - Firecracker: Lightweight microVMs (Firecracker VMM API via Unix socket)
//   - BareMetal: Direct filesystem deployment (no container)
//
// The active runtime is selected at startup via SORCERY_GO_RUNTIME env var
// or the Runtime field in the Config struct. Each runtime adapter implements
// the Runtime interface, providing a consistent API for container lifecycle
// management, process execution, freeze/thaw, and status queries.
package runtime

import (
        "context"
        "fmt"
        "time"
)

// Type identifies the container runtime backend.
type Type string

const (
        // RuntimeLXC uses the LXC system container tools (lxc-create, lxc-start, etc.)
        RuntimeLXC Type = "lxc"
        // RuntimePodman uses the Podman OCI container engine.
        RuntimePodman Type = "podman"
        // RuntimeFirecracker uses Firecracker microVMs.
        RuntimeFirecracker Type = "firecracker"
        // RuntimeBareMetal deploys directly to the host filesystem (no container).
        RuntimeBareMetal Type = "baremetal"
)

// SanctumStatus describes the current state of a container/sanctum.
type SanctumStatus string

const (
        StatusRunning   SanctumStatus = "running"
        StatusStopped   SanctumStatus = "stopped"
        StatusFrozen    SanctumStatus = "frozen"
        StatusCreating  SanctumStatus = "creating"
        StatusDestroyed SanctumStatus = "destroyed"
        StatusUnknown   SanctumStatus = "unknown"
)

// SanctumInfo provides runtime-specific information about a sanctum.
type SanctumInfo struct {
        ID       string        `json:"id"`
        Name     string        `json:"name"`
        Runtime  Type          `json:"runtime"`
        Status   SanctumStatus `json:"status"`
        Arch     string        `json:"arch"`
        IP       string        `json:"ip,omitempty"`
        PID      uint32        `json:"pid,omitempty"`
        Cgroup   string        `json:"cgroup,omitempty"`
        Created  time.Time     `json:"created"`
        RootFS   string        `json:"rootfs,omitempty"`
        Metadata map[string]string `json:"metadata,omitempty"`
}

// CreateOpts holds the parameters for creating a new sanctum.
type CreateOpts struct {
        // Name is the human-readable container name.
        Name string

        // Image is the base image or template (LXC template, OCI image, rootfs path).
        Image string

        // Arch is the target architecture (x86_64, aarch64).
        Arch string

        // RootFS is the path to the root filesystem (for baremetal or custom rootfs).
        RootFS string

        // NetworkConfig specifies the network attachment.
        NetworkConfig *NetworkConfig

        // BindMounts are host paths to bind-mount into the container.
        BindMounts []BindMount

        // EnvVars are environment variables to set inside the container.
        EnvVars map[string]string

        // Caps is the set of Linux capabilities to retain (empty = drop all).
        Caps []string

        // MemoryMB is the memory limit in megabytes (0 = unlimited).
        MemoryMB uint64

        // VCPUs is the number of virtual CPUs (for Firecracker).
        VCPUs uint32

        // KernelPath is the host kernel image path (for Firecracker).
        KernelPath string

        // RootDrivePath is the root block device path (for Firecracker).
        RootDrivePath string

        // ExtraConfig passes runtime-specific configuration as key-value pairs.
        ExtraConfig map[string]string
}

// NetworkConfig specifies network attachment for a sanctum.
type NetworkConfig struct {
        // Type is the network mode (bridge, none, host).
        Type string // "bridge", "none", "host"

        // Bridge is the host bridge interface name (e.g., "br0").
        Bridge string

        // MACAddress is the desired MAC address (empty = auto-generate).
        MACAddress string

        // IP is the desired IP address (empty = DHCP/auto).
        IP string
}

// BindMount represents a host-to-container bind mount.
type BindMount struct {
        // HostPath is the path on the host.
        HostPath string
        // ContainerPath is the path inside the container.
        ContainerPath string
        // ReadOnly makes the mount read-only.
        ReadOnly bool
}

// ExecResult captures the output of a command executed inside a sanctum.
type ExecResult struct {
        ExitCode int
        Stdout   []byte
        Stderr   []byte
}

// Runtime is the interface that all container runtime backends must implement.
//
// It provides a unified API for the full lifecycle of a Sanctum:
// create, start, stop, freeze/thaw, exec, and destroy. The Warding uses
// this interface to manage containers without knowing the underlying runtime.
type Runtime interface {
        // Type returns the runtime type identifier (lxc, podman, firecracker, baremetal).
        Type() Type

        // Name returns a human-readable name for this runtime instance.
        Name() string

        // Probe checks whether this runtime is available on the host.
        // Returns nil if the runtime tools/API are accessible.
        Probe() error

        // Create provisions a new sanctum with the given options.
        // Returns the sanctum ID on success.
        Create(ctx context.Context, opts CreateOpts) (string, error)

        // Start boots or starts a stopped sanctum.
        Start(ctx context.Context, sanctumID string) error

        // Stop gracefully stops a running sanctum.
        Stop(ctx context.Context, sanctumID string) error

        // Freeze suspends all processes in a running sanctum (cgroup freezer).
        Freeze(ctx context.Context, sanctumID string) error

        // Thaw resumes a frozen sanctum.
        Thaw(ctx context.Context, sanctumID string) error

        // Destroy removes a sanctum and all its resources.
        Destroy(ctx context.Context, sanctumID string) error

        // Exec runs a command inside a running sanctum and returns the output.
        Exec(ctx context.Context, sanctumID string, command []string, stdin []byte) (*ExecResult, error)

        // Status returns the current state and info about a sanctum.
        Status(ctx context.Context, sanctumID string) (*SanctumInfo, error)

        // List returns all sanctums managed by this runtime.
        List(ctx context.Context) ([]*SanctumInfo, error)

        // CgroupPath returns the cgroup v2 path for a sanctum.
        // This is used by the eBPF enforcer to attach cgroup filters.
        // Returns "" if the runtime does not use cgroups (e.g., Firecracker).
        CgroupPath(sanctumID string) string
}

// Factory creates a Runtime instance for the given type.
// Returns an error if the runtime type is unknown or unavailable.
func Factory(rtType Type) (Runtime, error) {
        switch rtType {
        case RuntimeLXC:
                r := NewLXCRuntime()
                if err := r.Probe(); err != nil {
                        return nil, err
                }
                return r, nil
        case RuntimePodman:
                r := NewPodmanRuntime()
                if err := r.Probe(); err != nil {
                        return nil, err
                }
                return r, nil
        case RuntimeFirecracker:
                r := NewFirecrackerRuntime()
                if err := r.Probe(); err != nil {
                        return nil, err
                }
                return r, nil
        case RuntimeBareMetal:
                return NewBareMetalRuntime(), nil
        default:
                return nil, fmt.Errorf("runtime: unknown runtime type %q (supported: lxc, podman, firecracker, baremetal)", rtType)
        }
}

// AutoDetect tries to find an available runtime on the host.
// It probes LXC first, then Podman, then Firecracker, and falls back
// to baremetal if none are found.
func AutoDetect() (Runtime, error) {
        candidates := []Type{RuntimeLXC, RuntimePodman, RuntimeFirecracker, RuntimeBareMetal}
        for _, t := range candidates {
                r, err := Factory(t)
                if err == nil {
                        return r, nil
                }
        }
        return NewBareMetalRuntime(), nil
}