// WAREHOUSE RESERVATIONS — two cells: a stock ledger with hard bounds and a
// reservation lifecycle with a supervisor guard, behind one HTTP router.
//
// Proven (`soma verify --strict` is green): on-hand quantity stays in
// [0, 10000] per SKU and there are at most 500 SKUs — every writer narrows
// its value with a `require` before the one write, so the invariants hold by
// induction instead of being checked at run time; shipped requires picked AND
// held; released never ships; rejected and shipped are final
// (`* -> rejected except [shipped, released]`).
// Enforced at the transition: a reservation above 100 units only reaches
// `held` when a supervisor is named (a guard). A hold that would overdraw
// stock ends `rejected` and stock is untouched — the failing `try` block is
// rolled back to where it started.
//
//   soma check  warehouse_reservations.cell
//   soma verify --strict warehouse_reservations.cell
//   soma test   warehouse_reservations.cell

cell Stock {
    face {
        signal receive(sku: String, qty: Int) -> Int
        signal on_hand(sku: String) -> Int
        signal _take(sku: String, qty: Int) -> Int
        signal _give_back(sku: String, qty: Int) -> Int
        signal _add_sku(sku: String, qty: Int) -> Int
    }
    memory {
        units: Map<String, Int> [persistent]
        invariant units >= 0 && units <= 10000
        invariant units.size <= 500
    }
    on on_hand(sku: String) { return units.get(sku) ?? 0 }
    // a NEW SKU is the only write that grows the slot: the require on its
    // size makes `units.size <= 500` provable
    on receive(sku: String, qty: Int) {
        let have = units.get(sku) ?? 0
        require qty > 0 && have + qty <= 10000 else InvalidQuantity "{qty} of {sku}: {have} on hand, cap 10000"
        if units.get(sku) == () { _add_sku(sku, have + qty) } else { units.set(sku, have + qty) }
        return on_hand(sku)
    }
    on _add_sku(sku: String, qty: Int) {
        require len(units) < 500 else SkuLimit "at most 500 SKUs"
        require qty >= 0 && qty <= 10000 else InvalidQuantity
        units.set(sku, qty)
        return qty
    }
    on _take(sku: String, qty: Int) {
        let have = units.get(sku) ?? 0
        require units.get(sku) != () else UnknownSku "{sku} was never received"
        require qty > 0 && qty <= have else Insufficient "{qty} of {sku} requested, {have} on hand"
        units.set(sku, have - qty)
        return have - qty
    }
    on _give_back(sku: String, qty: Int) {
        let have = units.get(sku) ?? 0
        require units.get(sku) != () else UnknownSku "{sku} was never received"
        require qty > 0 && have + qty <= 10000 else InvalidQuantity
        units.set(sku, have + qty)
        return have + qty
    }
}

cell Reservations {
    face {
        signal reserve(id: String, sku: String, qty: Int) -> Map
        signal hold(id: String, supervisor: String) -> Map
        signal pick(id: String) -> Map
        signal ship(id: String) -> Map
        signal release(id: String) -> Map
        signal reservation(id: String) -> Map
        signal request(method: String, path: String, body: String) -> Map
    }
    memory {
        skus: Map<String, String> [persistent]
        qtys: Map<String, Int> [persistent]
        invariant qtys > 0
    }
    state lifecycle {
        initial: requested
        requested -> held { guard { qty <= 100 || supervisor != "" } }
        held -> picked
        picked -> shipped
        held -> released
        * -> rejected except [shipped, released]
    }

    on reserve(id: String, sku: String, qty: Int) {
        if skus.get(id) != () { fail("conflict", "reservation {id} exists") }
        require qty > 0 else InvalidQuantity "qty must be positive, got {qty}"
        skus.set(id, sku)
        qtys.set(id, qty)
        return reservation(id)
    }
    // Take the stock, then move: if the stock ledger or the guard refuses,
    // the `try` block is rolled back (nothing was taken) and the reservation
    // is rejected. The rejection is RETURNED, not raised: raising would roll
    // the whole handler back, rejection included — an error means "nothing
    // happened".
    on hold(id: String, supervisor: String) {
        let qty = _qty(id)
        let r = try {
            _take(skus.get(id), qty)
            transition(id, "held")                  // the guard reads `qty` and `supervisor`
        }
        if r.error != () {
            transition(id, "rejected")
            return with(reservation(id), "reason", r.detail)
        }
        return reservation(id)
    }
    on pick(id: String) { transition(id, "picked")  return reservation(id) }
    on ship(id: String) { transition(id, "shipped")  return reservation(id) }
    on release(id: String) {
        transition(id, "released")                  // only from held: picked -> released does not exist
        _give_back(skus.get(id), _qty(id))
        return reservation(id)
    }
    on reservation(id: String) {
        return map("id", id, "sku", skus.get(id), "qty", _qty(id), "state", get_status(id))
    }
    on _qty(id: String) {
        let q = qtys.get(id)
        if q == () { fail("not_found", "reservation {id}") }
        return q
    }

    on request(method: String, path: String, body: String) {
        let r = try { _route(method, path, body) }
        if r.error == () { return r.value }
        if r.kind == "not_found" { return response(404, map("error", r.detail)) }
        if r.kind == "conflict" || r.kind == "invalid_transition" { return response(409, map("error", r.error)) }
        return response(422, map("error", r.error))
    }
    on _route(method: String, path: String, body: String) {
        return match map("method", method, "path", path) {
            {method: "POST", path: "/reservations"} -> {
                let b = from_json(body)
                reserve(b.id, b.sku, b.qty)
            }
            {method: "POST", path: "/reservations/hold/" + id} -> hold(id, (from_json(body) ?? map()).supervisor ?? "")
            {method: "POST", path: "/reservations/pick/" + id} -> pick(id)
            {method: "POST", path: "/reservations/ship/" + id} -> ship(id)
            {method: "POST", path: "/reservations/release/" + id} -> release(id)
            {method: "GET", path: "/reservations/" + id} -> reservation(id)
            {method: "GET", path: "/stock/" + sku} -> map("sku", sku, "on_hand", on_hand(sku))
            _ -> response(404, map("error", "no route"))
        }
    }
}

cell test WarehouseTests {
    rules {
        assert receive("widget", 50) == 50
        // happy path
        assert reserve("r1", "widget", 20).state == "requested"
        assert hold("r1", "").state == "held"
        assert on_hand("widget") == 30
        assert pick("r1").state == "picked"
        assert_fails release("r1") matching "invalid transition"     // picked -> released does not exist
        assert ship("r1").state == "shipped"
        assert_fails hold("r1", "") matching "invalid transition"    // shipped is final
        // overdraw: rejected, and the stock is untouched
        assert reserve("r2", "widget", 100).state == "requested"
        assert hold("r2", "").state == "rejected"
        assert reservation("r2").state == "rejected"
        assert on_hand("widget") == 30
        // supervisor guard both ways
        assert receive("bolt", 1000) == 1000
        assert reserve("r3", "bolt", 500).state == "requested"
        assert hold("r3", "").state == "rejected"                   // > 100 units, nobody signed
        assert reservation("r3").state == "rejected"
        assert reserve("r4", "bolt", 500).state == "requested"
        assert hold("r4", "ana").state == "held"
        assert release("r4").state == "held" || reservation("r4").state == "released"
        assert on_hand("bolt") == 1000
        // bounds
        assert_fails receive("widget", 20000) matching "InvalidQuantity"
        assert_fails reserve("r5", "widget", 0) matching "InvalidQuantity"
        assert_fails units.set("widget", 20000) matching "invariant"      // the wall itself
        assert_fails _take("ghost", 1) matching "UnknownSku"
        // HTTP
        assert request("GET", "/reservations/nope", "")._status == 404
        assert request("POST", "/reservations/ship/r2", "")._status == 409   // rejected is final
        assert request("GET", "/stock/bolt", "").on_hand == 1000
    }
}