| 1 | package idear |
| 2 | |
| 3 | import ( |
| 4 | "errors" |
| 5 | "fmt" |
| 6 | ) |
| 7 | |
| 8 | // ErrForbidden is the sentinel every MayActOn refusal wraps. Callers |
| 9 | // that only need the yes/no answer use errors.Is; the wrapped text |
| 10 | // carries the reason for logs and error pages. |
| 11 | var ErrForbidden = errors.New("idear: forbidden") |
| 12 | |
| 13 | // MayActOn reports whether actor may manage target — change target's |
| 14 | // role, deactivate, or reactivate them. It is a pure function so the |
| 15 | // full role matrix can be exhausted in a table test with no database |
| 16 | // and no HTTP server. |
| 17 | // |
| 18 | // Four rules, in order, each closing a specific hole: |
| 19 | // |
| 20 | // 1. actor must be non-nil and active — a deactivated admin keeps |
| 21 | // their row (removal is never a delete) but loses every privilege |
| 22 | // the row once carried. |
| 23 | // 2. actor must be at least Admin — a Member can see the roster but |
| 24 | // never act on it. |
| 25 | // 3. actor and target must be different people, compared by ID — an |
| 26 | // Owner deactivating or demoting themselves is exactly how an |
| 27 | // instance ends up with no one able to administer it. |
| 28 | // 4. target's rank must be strictly below actor's — Admin manages |
| 29 | // Member only, Owner manages Admin and Member, and nobody at any |
| 30 | // rank manages an Owner. Equal rank is refused, not just higher |
| 31 | // rank: two Owners or two Admins may never act on one another. |
| 32 | func MayActOn(actor, target *Member) error { |
| 33 | if err := mayManage(actor); err != nil { |
| 34 | return err |
| 35 | } |
| 36 | if target == nil { |
| 37 | return fmt.Errorf("%w: no target", ErrForbidden) |
| 38 | } |
| 39 | if actor.ID == target.ID { |
| 40 | return fmt.Errorf("%w: cannot act on self", ErrForbidden) |
| 41 | } |
| 42 | if rank(target.Role) >= rank(actor.Role) { |
| 43 | return fmt.Errorf("%w: target's rank is not below actor's", ErrForbidden) |
| 44 | } |
| 45 | return nil |
| 46 | } |
| 47 | |
| 48 | // mayManage is rules 1 and 2 of MayActOn on their own: the authority |
| 49 | // FLOOR, with no target in it. It answers "is this actor allowed to |
| 50 | // manage anything at all" — which is the question Invite and Revoke |
| 51 | // ask (they have no target Member), and the question the store's other |
| 52 | // mutations must ask FIRST, before any invariant check that names the |
| 53 | // target. |
| 54 | // |
| 55 | // That ordering is what keeps ErrLastOwner from becoming a membership |
| 56 | // oracle. Deactivate and SetRole refuse an Owner target with |
| 57 | // ErrLastOwner rather than ErrForbidden, because "the owner cannot be |
| 58 | // removed" is true for every actor and ErrForbidden would imply some |
| 59 | // higher rank could do it. But a plain Member must still be refused |
| 60 | // for lacking authority, not told which row is the Owner's — so the |
| 61 | // floor is checked first and the target-shaped invariant second. |
| 62 | func mayManage(actor *Member) error { |
| 63 | if actor == nil || !actor.Active() { |
| 64 | return fmt.Errorf("%w: actor is not an active member", ErrForbidden) |
| 65 | } |
| 66 | if !actor.Role.AtLeast(RoleAdmin) { |
| 67 | return fmt.Errorf("%w: actor must be at least admin", ErrForbidden) |
| 68 | } |
| 69 | return nil |
| 70 | } |
| 71 | |
amadan