mvm-core 0.13.0

use anyhow::{Result, bail};
use serde::{Deserialize, Serialize};

use crate::idle_metrics::IdleMetrics;
use crate::pool::Role;

/// Instance lifecycle status. Only instances have runtime state.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum InstanceStatus {
    Created,
    Ready,
    Running,
    Warm,
    Sleeping,
    Stopped,
    Destroyed,
}

impl std::fmt::Display for InstanceStatus {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Created => write!(f, "created"),
            Self::Ready => write!(f, "ready"),
            Self::Running => write!(f, "running"),
            Self::Warm => write!(f, "warm"),
            Self::Sleeping => write!(f, "sleeping"),
            Self::Stopped => write!(f, "stopped"),
            Self::Destroyed => write!(f, "destroyed"),
        }
    }
}

/// Per-instance network configuration.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct InstanceNet {
    /// TAP device name: "tn<net_id>i<offset>"
    pub tap_dev: String,
    /// Deterministic MAC: "02:xx:xx:xx:xx:xx"
    pub mac: String,
    /// Guest IP within tenant subnet, e.g. "10.240.3.5"
    pub guest_ip: String,
    /// Tenant gateway, e.g. "10.240.3.1"
    pub gateway_ip: String,
    /// CIDR prefix length from tenant subnet, e.g. 24
    pub cidr: u8,
}

/// Full instance state, persisted at instances/<id>/instance.json.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct InstanceState {
    pub instance_id: String,
    pub pool_id: String,
    pub tenant_id: String,
    pub status: InstanceStatus,
    pub net: InstanceNet,
    /// Role inherited from pool at creation time.
    #[serde(default)]
    pub role: Role,
    pub revision_hash: Option<String>,
    pub firecracker_pid: Option<u32>,
    pub last_started_at: Option<String>,
    pub last_stopped_at: Option<String>,
    #[serde(default)]
    pub idle_metrics: IdleMetrics,
    pub healthy: Option<bool>,
    pub last_health_check_at: Option<String>,
    pub manual_override_until: Option<String>,
    /// Config drive version currently mounted.
    #[serde(default)]
    pub config_version: Option<u64>,
    /// Secrets epoch currently mounted.
    #[serde(default)]
    pub secrets_epoch: Option<u64>,
    /// Timestamp when instance entered Running status.
    #[serde(default)]
    pub entered_running_at: Option<String>,
    /// Timestamp when instance entered Warm status.
    #[serde(default)]
    pub entered_warm_at: Option<String>,
    /// Timestamp of last work activity (from guest agent or metrics).
    #[serde(default)]
    pub last_busy_at: Option<String>,
}

/// Validate that a state transition is allowed.
///
/// Returns Ok(()) if the transition is valid, Err with explanation otherwise.
/// Enforces the state machine defined in the spec.
pub fn validate_transition(from: InstanceStatus, to: InstanceStatus) -> Result<()> {
    // Any state -> Destroyed is always allowed
    if to == InstanceStatus::Destroyed {
        return Ok(());
    }

    let valid = matches!(
        (from, to),
        // Build completes
        (InstanceStatus::Created, InstanceStatus::Ready)
        // Start
        | (InstanceStatus::Ready, InstanceStatus::Running)
        // Pause vCPUs
        | (InstanceStatus::Running, InstanceStatus::Warm)
        // Stop from running
        | (InstanceStatus::Running, InstanceStatus::Stopped)
        // Resume from warm
        | (InstanceStatus::Warm, InstanceStatus::Running)
        // Snapshot + shutdown
        | (InstanceStatus::Warm, InstanceStatus::Sleeping)
        // Stop from warm
        | (InstanceStatus::Warm, InstanceStatus::Stopped)
        // Wake from snapshot
        | (InstanceStatus::Sleeping, InstanceStatus::Running)
        // Stop from sleeping (discard snapshot)
        | (InstanceStatus::Sleeping, InstanceStatus::Stopped)
        // Fresh boot from stopped
        | (InstanceStatus::Stopped, InstanceStatus::Running)
        // Rebuild
        | (InstanceStatus::Ready, InstanceStatus::Ready)
    );

    if valid {
        Ok(())
    } else {
        bail!("Invalid state transition: {} -> {}", from, to)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_valid_transitions() {
        assert!(validate_transition(InstanceStatus::Created, InstanceStatus::Ready).is_ok());
        assert!(validate_transition(InstanceStatus::Ready, InstanceStatus::Running).is_ok());
        assert!(validate_transition(InstanceStatus::Running, InstanceStatus::Warm).is_ok());
        assert!(validate_transition(InstanceStatus::Running, InstanceStatus::Stopped).is_ok());
        assert!(validate_transition(InstanceStatus::Warm, InstanceStatus::Running).is_ok());
        assert!(validate_transition(InstanceStatus::Warm, InstanceStatus::Sleeping).is_ok());
        assert!(validate_transition(InstanceStatus::Warm, InstanceStatus::Stopped).is_ok());
        assert!(validate_transition(InstanceStatus::Sleeping, InstanceStatus::Running).is_ok());
        assert!(validate_transition(InstanceStatus::Sleeping, InstanceStatus::Stopped).is_ok());
        assert!(validate_transition(InstanceStatus::Stopped, InstanceStatus::Running).is_ok());
        assert!(validate_transition(InstanceStatus::Ready, InstanceStatus::Ready).is_ok());
    }

    #[test]
    fn test_destroyed_from_any() {
        for status in [
            InstanceStatus::Created,
            InstanceStatus::Ready,
            InstanceStatus::Running,
            InstanceStatus::Warm,
            InstanceStatus::Sleeping,
            InstanceStatus::Stopped,
        ] {
            assert!(
                validate_transition(status, InstanceStatus::Destroyed).is_ok(),
                "{} -> Destroyed should be valid",
                status,
            );
        }
    }

    #[test]
    fn test_invalid_transitions() {
        assert!(validate_transition(InstanceStatus::Created, InstanceStatus::Running).is_err());
        assert!(validate_transition(InstanceStatus::Created, InstanceStatus::Warm).is_err());
        assert!(validate_transition(InstanceStatus::Running, InstanceStatus::Sleeping).is_err());
        assert!(validate_transition(InstanceStatus::Sleeping, InstanceStatus::Warm).is_err());
        assert!(validate_transition(InstanceStatus::Stopped, InstanceStatus::Warm).is_err());
        assert!(validate_transition(InstanceStatus::Stopped, InstanceStatus::Sleeping).is_err());
    }

    #[test]
    fn test_instance_state_json_roundtrip() {
        let state = InstanceState {
            instance_id: "i-a3f7b2c1".to_string(),
            pool_id: "workers".to_string(),
            tenant_id: "acme".to_string(),
            status: InstanceStatus::Running,
            net: InstanceNet {
                tap_dev: "tn3i5".to_string(),
                mac: "02:fc:00:03:00:05".to_string(),
                guest_ip: "10.240.3.5".to_string(),
                gateway_ip: "10.240.3.1".to_string(),
                cidr: 24,
            },
            role: Role::Gateway,
            revision_hash: Some("abc123".to_string()),
            firecracker_pid: Some(12345),
            last_started_at: Some("2025-01-01T00:00:00Z".to_string()),
            last_stopped_at: None,
            idle_metrics: IdleMetrics::default(),
            healthy: Some(true),
            last_health_check_at: None,
            manual_override_until: None,
            config_version: Some(3),
            secrets_epoch: Some(1),
            entered_running_at: Some("2025-01-01T00:00:00Z".to_string()),
            entered_warm_at: None,
            last_busy_at: None,
        };

        let json = serde_json::to_string_pretty(&state).unwrap();
        let parsed: InstanceState = serde_json::from_str(&json).unwrap();
        assert_eq!(parsed.instance_id, "i-a3f7b2c1");
        assert_eq!(parsed.status, InstanceStatus::Running);
        assert_eq!(parsed.net.tap_dev, "tn3i5");
        assert_eq!(parsed.role, Role::Gateway);
        assert_eq!(parsed.config_version, Some(3));
        assert_eq!(
            parsed.entered_running_at.as_deref(),
            Some("2025-01-01T00:00:00Z")
        );
    }

    #[test]
    fn test_instance_state_backward_compat() {
        // JSON without new fields should deserialize with defaults
        let json = r#"{
            "instance_id": "i-test",
            "pool_id": "workers",
            "tenant_id": "acme",
            "status": "running",
            "net": {
                "tap_dev": "tn3i5",
                "mac": "02:fc:00:03:00:05",
                "guest_ip": "10.240.3.5",
                "gateway_ip": "10.240.3.1",
                "cidr": 24
            },
            "revision_hash": null,
            "firecracker_pid": null,
            "last_started_at": null,
            "last_stopped_at": null,
            "healthy": null,
            "last_health_check_at": null,
            "manual_override_until": null
        }"#;
        let parsed: InstanceState = serde_json::from_str(json).unwrap();
        assert_eq!(parsed.role, Role::Worker);
        assert_eq!(parsed.config_version, None);
        assert_eq!(parsed.secrets_epoch, None);
        assert_eq!(parsed.entered_running_at, None);
        assert_eq!(parsed.entered_warm_at, None);
        assert_eq!(parsed.last_busy_at, None);
    }

    #[test]
    fn test_status_display() {
        assert_eq!(InstanceStatus::Running.to_string(), "running");
        assert_eq!(InstanceStatus::Sleeping.to_string(), "sleeping");
        assert_eq!(InstanceStatus::Destroyed.to_string(), "destroyed");
    }
}