Permit — a building permit that cannot skip a review

permit.cell

// ============================================================================
// PERMIT — a building permit that cannot skip a review
// ============================================================================
// New York's self-certification program let architects stamp their own
// permits "to speed things up" — DOB audits later found buildings approved
// with zoning and structural reviews simply skipped, and the city spent a
// decade revoking permits for occupied buildings. The skip is possible when
// "reviewed" is a checkbox. Here the approval chain is the state machine
// itself: `issued` is only reachable THROUGH zoning, structural, and fire
// review, soma verify proves it, and `denied` and `issued` are terminal.
// The fee ledger is a second wall: a permit cannot be charged twice.
// ============================================================================

cell BuildingPermit {
    face {
        signal pay_fee(id: String) -> Map
        signal pass_zoning(id: String) -> Map
        signal pass_structural(id: String) -> Map
        signal pass_fire(id: String) -> Map
        signal issue(id: String) -> Map
        signal deny(id: String) -> Map
        signal permit_state(id: String) -> String
    }

    memory {
        // permit -> fee payments. Double-billing is unrepresentable.
        fees: Map<String, Int> [persistent, consistent]
        invariant fees >= 0 && fees <= 1
    }

    // The chain. There is NO edge from filed to issued: every issued
    // permit passed all three reviews, by construction.
    state permit {
        initial: filed
        filed -> zoning_ok
        zoning_ok -> structural_ok
        structural_ok -> fire_ok
        fire_ok -> issued
        filed -> denied
        zoning_ok -> denied
        structural_ok -> denied
        fire_ok -> denied
    }

    on permit_state(id: String) { return get_status(id) }

    on pay_fee(id: String) {
        let prior = fees.get(id) ?? 0
        let w = try { fees.set(id, prior + 1) }
        if w.error != () {
            return map("ok", false, "reason", "fee already collected for {id}")
        }
        return map("ok", true, "permit", id)
    }

    on pass_zoning(id: String) {
        let r = try { transition(id, "zoning_ok") }
        if r.error != () { return map("ok", false, "reason", "{r.error}") }
        return map("ok", true, "stage", permit_state(id))
    }

    on pass_structural(id: String) {
        let r = try { transition(id, "structural_ok") }
        if r.error != () { return map("ok", false, "reason", "{r.error}") }
        return map("ok", true, "stage", permit_state(id))
    }

    on pass_fire(id: String) {
        let r = try { transition(id, "fire_ok") }
        if r.error != () { return map("ok", false, "reason", "{r.error}") }
        return map("ok", true, "stage", permit_state(id))
    }

    on issue(id: String) {
        if (fees.get(id) ?? 0) == 0 {
            return map("ok", false, "reason", "fee unpaid for {id}")
        }
        let r = try { transition(id, "issued") }
        if r.error != () { return map("ok", false, "reason", "{r.error}") }
        return map("ok", true, "permit", id)
    }

    on deny(id: String) {
        let r = try { transition(id, "denied") }
        if r.error != () { return map("ok", false, "reason", "{r.error}") }
        return map("ok", true, "permit", id)
    }
}

cell test PermitTests {
    rules {
        // the self-certification shortcut does not exist
        assert pay_fee("p1").ok == true
        assert issue("p1").ok == false                    // filed -> issued: no edge
        assert_fails transition("p1", "issued")
        assert_fails transition("p1", "fire_ok")          // and no skipping ahead

        // the only road is through every review
        assert pass_zoning("p1").ok == true
        assert pass_structural("p1").ok == true
        assert pass_fire("p1").ok == true
        assert issue("p1").ok == true
        assert permit_state("p1") == "issued"
        assert_fails transition("p1", "filed")            // issued is forever
        assert_fails fees.set("p1", 2)                    // no double-billing

        // an unpaid permit stalls at the cashier even after reviews
        assert pass_zoning("p2").ok == true
        assert pass_structural("p2").ok == true
        assert pass_fire("p2").ok == true
        assert issue("p2").ok == false                    // fee unpaid

        // a denial is terminal too
        assert deny("p3").ok == true
        assert_fails transition("p3", "zoning_ok")
    }
}