| 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 | // Five 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 must not be the Owner — nobody at any rank manages an |
| 29 | // Owner, in either PeerGrants mode. Ownership moves only by |
| 30 | // Transfer. |
| 31 | // 5. target must be within actor's reach (see reaches). By default |
| 32 | // that is strictly below: Admin manages Member only, Owner manages |
| 33 | // Admin and Member, and two Admins may never act on one another. |
| 34 | // Built with PeerGrants, equal rank is within reach too, so an |
| 35 | // Admin manages other Admins. |
| 36 | func MayActOn(actor, target *Member) error { |
| 37 | if err := mayManage(actor); err != nil { |
| 38 | return err |
| 39 | } |
| 40 | if target == nil { |
| 41 | return fmt.Errorf("%w: no target", ErrForbidden) |
| 42 | } |
| 43 | if actor.ID == target.ID { |
| 44 | return fmt.Errorf("%w: cannot act on self", ErrForbidden) |
| 45 | } |
| 46 | if target.Role == RoleOwner { |
| 47 | return fmt.Errorf("%w: nobody acts on the owner", ErrForbidden) |
| 48 | } |
| 49 | if !reaches(actor.Role, target.Role) { |
| 50 | return fmt.Errorf("%w: target's rank is beyond actor's reach", ErrForbidden) |
| 51 | } |
| 52 | return nil |
| 53 | } |
| 54 | |
| 55 | // reaches is the ONE rank comparison behind both halves of authority: |
| 56 | // who an actor may manage (MayActOn) and what role they may grant |
| 57 | // (checkInviteRole). Keeping them on one predicate is what stops the |
| 58 | // two drifting apart — an actor who could grant a rank they could not |
| 59 | // then manage would mint someone beyond their own reach, and one who |
| 60 | // could manage a rank they could not grant would be left demoting |
| 61 | // people they could never promote back. |
| 62 | // |
| 63 | // Strictly below by default; at or below when built with PeerGrants. |
| 64 | // It says nothing about RoleOwner — both callers refuse that |
| 65 | // outright, before asking. |
| 66 | func reaches(actor, other Role) bool { |
| 67 | if PeerGrants { |
| 68 | return rank(other) <= rank(actor) |
| 69 | } |
| 70 | return rank(other) < rank(actor) |
| 71 | } |
| 72 | |
| 73 | // mayManage is rules 1 and 2 of MayActOn on their own: the authority |
| 74 | // FLOOR, with no target in it. It answers "is this actor allowed to |
| 75 | // manage anything at all" — which is the question Invite and Revoke |
| 76 | // ask (they have no target Member), and the question the store's other |
| 77 | // mutations must ask FIRST, before any invariant check that names the |
| 78 | // target. |
| 79 | // |
| 80 | // That ordering is what keeps ErrLastOwner from becoming a membership |
| 81 | // oracle. Deactivate and SetRole refuse an Owner target with |
| 82 | // ErrLastOwner rather than ErrForbidden, because "the owner cannot be |
| 83 | // removed" is true for every actor and ErrForbidden would imply some |
| 84 | // higher rank could do it. But a plain Member must still be refused |
| 85 | // for lacking authority, not told which row is the Owner's — so the |
| 86 | // floor is checked first and the target-shaped invariant second. |
| 87 | func mayManage(actor *Member) error { |
| 88 | if actor == nil || !actor.Active() { |
| 89 | return fmt.Errorf("%w: actor is not an active member", ErrForbidden) |
| 90 | } |
| 91 | if !actor.Role.AtLeast(RoleAdmin) { |
| 92 | return fmt.Errorf("%w: actor must be at least admin", ErrForbidden) |
| 93 | } |
| 94 | return nil |
| 95 | } |
| 96 | |
amadan