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// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Commercial
// See LICENSE-AGPL and LICENSE-COMMERCIAL in this repository for license terms.
//! The resource lifecycle state machine every `cloud-forge` resource
//! goes through, and the transition table that governs it.
//!
//! This directly implements the roadmap's invariant
//! **CLOUD-I003: deleted resources cannot silently reappear** --
//! [`Lifecycle::Deleted`] has no outgoing transitions at all, checked
//! exhaustively below rather than left to convention.
#![forbid(unsafe_code)]
use cloud_errors::CloudError;
/// A resource's lifecycle state.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum Lifecycle {
Creating,
Active,
Updating,
Deleting,
Deleted,
Failed,
}
impl Lifecycle {
fn name(self) -> &'static str {
match self {
Lifecycle::Creating => "Creating",
Lifecycle::Active => "Active",
Lifecycle::Updating => "Updating",
Lifecycle::Deleting => "Deleting",
Lifecycle::Deleted => "Deleted",
Lifecycle::Failed => "Failed",
}
}
/// Whether moving from `self` to `to` is allowed.
///
/// The table, spelled out rather than computed, so it is the
/// single place anyone auditing this crate needs to read:
///
/// - `Creating` -> `Active`, `Failed`
/// - `Active` -> `Updating`, `Deleting`, `Failed`
/// - `Updating` -> `Active`, `Failed`
/// - `Deleting` -> `Deleted`, `Failed`
/// - `Failed` -> `Deleting` (so a failed resource can still be torn down)
/// - `Deleted` -> nothing; terminal.
pub fn can_transition_to(self, to: Lifecycle) -> bool {
use Lifecycle::*;
matches!(
(self, to),
(Creating, Active)
| (Creating, Failed)
| (Active, Updating)
| (Active, Deleting)
| (Active, Failed)
| (Updating, Active)
| (Updating, Failed)
| (Deleting, Deleted)
| (Deleting, Failed)
| (Failed, Deleting)
)
}
/// Attempts the transition, returning [`CloudError::InvalidTransition`]
/// if it isn't allowed.
pub fn transition_to(self, to: Lifecycle) -> Result<Lifecycle, CloudError> {
if self.can_transition_to(to) {
Ok(to)
} else {
Err(CloudError::InvalidTransition {
what: "lifecycle",
from: self.name().to_string(),
to: to.name().to_string(),
})
}
}
/// A terminal state has no outgoing transitions at all.
pub fn is_terminal(self) -> bool {
self == Lifecycle::Deleted
}
}
#[cfg(test)]
mod tests {
use super::*;
use Lifecycle::*;
const ALL: [Lifecycle; 6] = [Creating, Active, Updating, Deleting, Deleted, Failed];
#[test]
fn deleted_is_the_only_terminal_state() {
for state in ALL {
assert_eq!(state.is_terminal(), state == Deleted);
}
}
#[test]
fn deleted_has_no_outgoing_transitions() {
for target in ALL {
assert!(
!Deleted.can_transition_to(target),
"Deleted -> {target:?} should be rejected"
);
}
}
#[test]
fn the_happy_path_creating_through_deleted_is_allowed() {
let mut state = Creating;
for next in [Active, Updating, Active, Deleting, Deleted] {
state = state.transition_to(next).unwrap();
}
assert_eq!(state, Deleted);
}
#[test]
fn a_failed_resource_can_still_be_torn_down() {
assert!(Creating.can_transition_to(Failed));
assert!(Failed.can_transition_to(Deleting));
assert!(Deleting.can_transition_to(Deleted));
}
#[test]
fn creating_cannot_skip_straight_to_deleting_or_deleted() {
assert!(!Creating.can_transition_to(Deleting));
assert!(!Creating.can_transition_to(Deleted));
}
#[test]
fn active_cannot_go_back_to_creating() {
assert!(!Active.can_transition_to(Creating));
}
#[test]
fn transition_to_returns_a_descriptive_error_on_rejection() {
let err = Deleted.transition_to(Active).unwrap_err();
let message = err.to_string();
assert!(message.contains("Deleted"));
assert!(message.contains("Active"));
}
#[test]
fn no_state_can_transition_to_itself() {
for state in ALL {
assert!(
!state.can_transition_to(state),
"{state:?} -> itself should not be a no-op transition"
);
}
}
}
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