o2-tools 0.4.4-rc

//! Buying time: the manual prolongation and the automatic one.
//!
//! The automatic path had no coverage at all - it is the only pool method a
//! keeper calls on a HEALTHY session, so its two gates (`AutoProlongDisabled`
//! and `AutoProlongNotDue`) are the whole thing standing between a scheduled
//! renewal and an unbounded fee drain by anyone with gas.

use super::*;
use crate::prop::AutoProlongChanged;

fn arm_call(fixture: &PropFixture, period: Option<ProlongPeriod>) -> CallContractArg {
    fixture.pool_call(
        fn_selector!(set_auto_prolong(Option<ProlongPeriod>)),
        0,
        AssetId::default(),
        Some(call_data!(period)),
    )
}

fn prolong_period_call(
    fixture: &PropFixture,
    period: ProlongPeriod,
    times: u64,
) -> CallContractArg {
    fixture.pool_call(
        fn_selector!(prolong_session(ProlongPeriod, u64)),
        0,
        AssetId::default(),
        Some(call_data!(period, times)),
    )
}

/// Takes `bps` off every premium the fixture's user pays, prolongations
/// included. The role comes first: pricing favours are their own capability,
/// not a power of the admin's office.
async fn discount_every_premium(fixture: &PropFixture, bps: u64) {
    fixture
        .deployment
        .pool
        .methods()
        .grant_role(
            DISCOUNT_MANAGER_ROLE,
            Identity::Address(fixture.deployer.address()),
        )
        .call()
        .await
        .unwrap();
    fixture
        .deployment
        .pool
        .methods()
        .set_user_discount(
            Identity::Address(fixture.user.address()),
            None,
            Some(UserDiscount {
                discount_bps: bps,
                scope: DiscountScope::AllPremiums,
            }),
        )
        .call()
        .await
        .unwrap();
}

/// Moves the chain to `seconds` before the session's deadline. The fixture's
/// session key is armed for a day from the same instant the session is, so
/// stopping short of the deadline keeps the key alive.
///
/// Callers wanting to be INSIDE the renewal window must pass fewer than
/// `AUTO_PROLONG_WINDOW_SECONDS` (60) - the window is a flat minute now, not
/// the period being renewed - and leave room for the blocks their own calls
/// produce.
async fn approach_deadline(fixture: &PropFixture, seconds: u64) {
    let session = fixture.session().await;
    let provider = fixture.user.try_provider().unwrap().clone();
    let latest = provider.latest_block_time().await.unwrap().unwrap();
    let target = session.expires_at - seconds;
    let jump = target.saturating_sub(latest.timestamp() as u64);
    provider
        .produce_blocks(
            1,
            Some(
                latest
                    .checked_add_signed(chrono::TimeDelta::seconds(jump as i64))
                    .unwrap(),
            ),
        )
        .await
        .unwrap();
}

/// A prolongation the keeper can run unattended has to be cheap to price and
/// impossible to abuse, so only the two SHORT periods may be armed and only
/// when the tier actually sells them. A week or a month would let one keeper
/// call spend a month of premium.
#[tokio::test]
async fn an_auto_extension_can_be_armed_only_on_a_short_period_the_tier_sells() {
    let mut fixture = PropFixture::new().await;

    // Push the deadline out first, so arming below is unambiguously "not due"
    // and cannot fire a prolongation of its own.
    fixture
        .call_account(
            vec![prolong_period_call(&fixture, ProlongPeriod::Week, 1)],
            1,
        )
        .await
        .unwrap();

    for period in [ProlongPeriod::Week, ProlongPeriod::Month] {
        let error = fixture
            .call_account(vec![arm_call(&fixture, Some(period.clone()))], 1)
            .await
            .unwrap_err();
        assert!(
            error.to_string().contains("AutoProlongPeriodInvalid"),
            "{period:?} is too long to hand to a keeper: {error:#}"
        );
    }

    // Six hours IS an automatic period, but this tier gives it away - and a
    // zero fee means "not offered" for prolongation, so it cannot be armed.
    let error = fixture
        .call_account(vec![arm_call(&fixture, Some(ProlongPeriod::SixHours))], 1)
        .await
        .unwrap_err();
    assert!(
        error.to_string().contains("PeriodNotOffered"),
        "a term the tier does not sell cannot be renewed: {error:#}"
    );

    // The day is both automatic and priced.
    let response = fixture
        .call_account(vec![arm_call(&fixture, Some(ProlongPeriod::Day))], 1)
        .await
        .unwrap();
    let armed = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<AutoProlongChanged>(&response.tx_status.receipts)
        .unwrap();
    assert_eq!(armed.len(), 1);
    assert_eq!(armed[0].period, Some(ProlongPeriod::Day));
    assert_eq!(armed[0].account, fixture.child_id);
    assert!(armed[0].timestamp.unix != 0);
    let prolonged = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<SessionProlonged>(&response.tx_status.receipts)
        .unwrap();
    assert!(
        prolonged.is_empty(),
        "arming outside the window charges nothing"
    );
    assert_eq!(
        fixture.session().await.auto_prolong,
        Some(ProlongPeriod::Day)
    );

    // And disarming is always allowed.
    let response = fixture
        .call_account(vec![arm_call(&fixture, None)], 1)
        .await
        .unwrap();
    let armed = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<AutoProlongChanged>(&response.tx_status.receipts)
        .unwrap();
    assert_eq!(armed[0].period, None);
    assert_eq!(fixture.session().await.auto_prolong, None);
}

/// Arming inside the renewal window pays for the renewal on the spot. A user
/// who remembers his subscription with an hour to go gets the same outcome as
/// one who armed a day early and let the keeper run - one call, one fee, one
/// extension.
#[tokio::test]
async fn arming_inside_the_window_extends_and_pays_in_the_same_call() {
    let mut fixture = PropFixture::new().await;

    approach_deadline(&fixture, 30).await;
    let before = fixture.session().await;
    let platform_before = fixture
        .deployer
        .get_asset_balance(&fixture.collateral_asset)
        .await
        .unwrap();

    let response = fixture
        .call_account(vec![arm_call(&fixture, Some(ProlongPeriod::Day))], 1)
        .await
        .unwrap();

    let armed = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<AutoProlongChanged>(&response.tx_status.receipts)
        .unwrap();
    assert_eq!(armed.len(), 1);
    assert_eq!(
        armed[0].expires_at, before.expires_at,
        "the arming event reports the deadline it found, not the one it bought"
    );

    let prolonged = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<SessionProlonged>(&response.tx_status.receipts)
        .unwrap();
    assert_eq!(prolonged.len(), 1);
    assert_eq!(prolonged[0].trigger, ProlongTrigger::Auto);
    assert_eq!(prolonged[0].times, 1);
    assert_eq!(prolonged[0].seconds, 86_400);
    assert_eq!(prolonged[0].fee, 6_000);
    assert_eq!(prolonged[0].new_expires_at, before.expires_at + 86_400);

    let after = fixture.session().await;
    assert_eq!(after.expires_at, before.expires_at + 86_400);
    assert_eq!(after.fees_accrued, 6_000);
    assert_eq!(
        after.credit_line,
        before.credit_line - 6_000,
        "the fee shrinks the line one for one"
    );
    assert_eq!(
        fixture
            .deployer
            .get_asset_balance(&fixture.collateral_asset)
            .await
            .unwrap()
            - platform_before,
        6_000,
        "and it leaves for the platform inside the same call"
    );
}

/// The keeper's own entry point. It is permissionless - anybody may pay the
/// gas to renew somebody else's session - so the two gates are what stop it
/// becoming a way to spend a stranger's collateral: the user must have armed
/// it, and the deadline must actually be near.
#[tokio::test]
async fn a_keeper_extends_an_armed_session_and_only_once_it_is_due() {
    let mut fixture = PropFixture::new().await;

    let keeper = fixture
        .deployment
        .pool
        .clone()
        .with_account(fixture.outsider.clone());

    // Unarmed.
    let error = keeper
        .methods()
        .auto_prolong_session(fixture.child_id)
        .with_variable_output_policy(VariableOutputPolicy::EstimateMinimum)
        .call()
        .await
        .unwrap_err();
    assert!(
        error.to_string().contains("AutoProlongDisabled"),
        "renewal is opt-in: {error:#}"
    );

    // Armed a week out, so it is armed but not due.
    fixture
        .call_account(
            vec![prolong_period_call(&fixture, ProlongPeriod::Week, 1)],
            1,
        )
        .await
        .unwrap();
    fixture
        .call_account(vec![arm_call(&fixture, Some(ProlongPeriod::Day))], 1)
        .await
        .unwrap();
    let error = keeper
        .methods()
        .auto_prolong_session(fixture.child_id)
        .with_variable_output_policy(VariableOutputPolicy::EstimateMinimum)
        .call()
        .await
        .unwrap_err();
    assert!(
        error.to_string().contains("AutoProlongNotDue"),
        "an armed session is not a standing invitation: {error:#}"
    );

    // Inside the window, the keeper renews it for the user.
    approach_deadline(&fixture, 30).await;
    let before = fixture.session().await;
    let response = keeper
        .methods()
        .auto_prolong_session(fixture.child_id)
        .with_variable_output_policy(VariableOutputPolicy::EstimateMinimum)
        .call()
        .await
        .unwrap();
    let prolonged = response
        .decode_logs_with_type::<SessionProlonged>()
        .unwrap();
    assert_eq!(prolonged.len(), 1);
    assert_eq!(prolonged[0].trigger, ProlongTrigger::Auto);
    assert_eq!(prolonged[0].new_expires_at, before.expires_at + 86_400);

    // And it cannot be farmed: one renewal moves the deadline out of the
    // window, so the next call is refused until the window comes round again.
    let error = keeper
        .methods()
        .auto_prolong_session(fixture.child_id)
        .with_variable_output_policy(VariableOutputPolicy::EstimateMinimum)
        .call()
        .await
        .unwrap_err();
    assert!(
        error.to_string().contains("AutoProlongNotDue"),
        "one call per window, or the fee is a faucet for griefers: {error:#}"
    );
}

/// A prolongation is priced per period and multiplied by `times`, which is the
/// caller's own number - so the multiplication has to be exact in both the fee
/// and the seconds, and the whole thing has to stop before the collateral.
#[tokio::test]
async fn prolonging_charges_times_the_price_and_buys_times_the_term() {
    let mut fixture = PropFixture::new().await;

    let before = fixture.session().await;
    let platform_before = fixture
        .deployer
        .get_asset_balance(&fixture.collateral_asset)
        .await
        .unwrap();

    // Zero is not a purchase.
    let error = fixture
        .call_account(
            vec![prolong_period_call(&fixture, ProlongPeriod::Day, 0)],
            1,
        )
        .await
        .unwrap_err();
    assert!(
        error.to_string().contains("TimesIsZero"),
        "buying nothing is refused rather than logged: {error:#}"
    );

    // A term the tier prices at zero is not on sale, however many are asked
    // for - the entry may include it free, renewal may not.
    let error = fixture
        .call_account(
            vec![prolong_period_call(&fixture, ProlongPeriod::SixHours, 1)],
            1,
        )
        .await
        .unwrap_err();
    assert!(
        error.to_string().contains("PeriodNotOffered"),
        "a free term is an entry perk, not a renewal price: {error:#}"
    );

    let response = fixture
        .call_account(
            vec![prolong_period_call(&fixture, ProlongPeriod::Day, 3)],
            1,
        )
        .await
        .unwrap();
    let prolonged = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<SessionProlonged>(&response.tx_status.receipts)
        .unwrap();
    assert_eq!(prolonged.len(), 1);
    assert_eq!(prolonged[0].trigger, ProlongTrigger::User);
    assert_eq!(prolonged[0].times, 3);
    assert_eq!(prolonged[0].seconds, 3 * 86_400);
    assert_eq!(prolonged[0].fee, 3 * 6_000);
    assert_eq!(prolonged[0].fees_accrued, 18_000);
    assert_eq!(prolonged[0].new_expires_at, before.expires_at + 3 * 86_400);
    assert_eq!(
        prolonged[0].new_credit_line,
        before.credit_line - 18_000,
        "the line prices off the collateral NET of every fee charged"
    );

    assert_eq!(
        fixture
            .deployer
            .get_asset_balance(&fixture.collateral_asset)
            .await
            .unwrap()
            - platform_before,
        18_000
    );

    // Three separate purchases cost exactly what one purchase of three did:
    // the price is flat, so slicing neither saves nor costs.
    let mut expected = 18_000u64;
    for _ in 0..3 {
        fixture
            .call_account(
                vec![prolong_period_call(&fixture, ProlongPeriod::Day, 1)],
                1,
            )
            .await
            .unwrap();
        expected += 6_000;
    }
    let after = fixture.session().await;
    assert_eq!(after.fees_accrued, expected);
    assert_eq!(after.expires_at, before.expires_at + 6 * 86_400);
    assert_eq!(
        fixture
            .deployer
            .get_asset_balance(&fixture.collateral_asset)
            .await
            .unwrap()
            - platform_before,
        expected as u128
    );

    // An absurd `times` reports the RULE that refuses it, not an arithmetic
    // failure. The extension is computed after the affordability bound for
    // exactly this reason: `2_592_000 * 8e12` leaves u64, so computing it
    // first would answer `ValueOverflow` where the contract has a named rule.
    let error = fixture
        .call_account(
            vec![prolong_period_call(
                &fixture,
                ProlongPeriod::Month,
                8_000_000_000_000,
            )],
            1,
        )
        .await
        .unwrap_err();
    assert!(
        error.to_string().contains("ProlongAboveCollateral"),
        "the bound answers before the arithmetic can overflow: {error:#}"
    );

    // A session may never be charged past what it funded. The bound is
    // STRICT: a session whose fees exactly reached its collateral would exist
    // with no line at all.
    let error = fixture
        .call_account(
            vec![prolong_period_call(&fixture, ProlongPeriod::Month, 3)],
            1,
        )
        .await
        .unwrap_err();
    assert!(
        error.to_string().contains("ProlongAboveCollateral"),
        "the platform is never paid out of another session's collateral: {error:#}"
    );
}

// ---------------------------------------------------------------------------
// The renewal at expiry.
// ---------------------------------------------------------------------------

/// Moves the chain `past` seconds beyond the session's deadline. The fixture's
/// session key does not survive a jump of a day or more, so anything after
/// this must go through the KEEPER's route - `expire_session` on the pool -
/// which needs no key.
async fn overshoot_deadline(fixture: &PropFixture, past: u64) {
    let session = fixture.session().await;
    let provider = fixture.user.try_provider().unwrap().clone();
    let latest = provider.latest_block_time().await.unwrap().unwrap();
    let target = session.expires_at + past;
    let jump = target.saturating_sub(latest.timestamp() as u64);
    provider
        .produce_blocks(
            1,
            Some(
                latest
                    .checked_add_signed(chrono::TimeDelta::seconds(jump as i64))
                    .unwrap(),
            ),
        )
        .await
        .unwrap();
}

/// The keeper's forced expiry, from a wallet with no claim on the session.
async fn expire(fixture: &PropFixture) -> Result<CallResponse<()>> {
    Ok(fixture
        .deployment
        .pool
        .clone()
        .with_account(fixture.outsider.clone())
        .methods()
        .expire_session(fixture.child_id, vec![])
        .with_contracts(&[
            &fixture.account,
            &fixture.deployment.oracle,
            &fixture.order_book.order_book,
            &fixture.deployment.price_feed,
        ])
        .with_variable_output_policy(VariableOutputPolicy::EstimateMinimum)
        .call()
        .await?)
}

/// A session that asked for automatic renewal and can still pay for one has
/// not asked to be absorbed. The window is a single minute now, so a keeper
/// that misses it would otherwise cost the user his seat over a scheduling
/// hiccup - `expire_session` renews him instead.
#[tokio::test]
async fn an_armed_and_funded_session_is_renewed_at_expiry_rather_than_absorbed() {
    let mut fixture = PropFixture::new().await;

    // Armed well outside the window, so nothing fires at arming time.
    fixture
        .call_account(vec![arm_call(&fixture, Some(ProlongPeriod::Day))], 1)
        .await
        .unwrap();
    let before = fixture.session().await;
    assert_eq!(before.auto_prolong, Some(ProlongPeriod::Day));
    assert_eq!(before.fees_accrued, 0);

    let platform_before = fixture
        .deployer
        .get_asset_balance(&fixture.collateral_asset)
        .await
        .unwrap();
    overshoot_deadline(&fixture, 1).await;

    let response = expire(&fixture).await.unwrap();
    let prolonged = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<SessionProlonged>(&response.tx_status.receipts)
        .unwrap();
    assert_eq!(prolonged.len(), 1);
    assert_eq!(prolonged[0].trigger, ProlongTrigger::Auto);
    assert_eq!(prolonged[0].times, 1);
    assert_eq!(prolonged[0].seconds, 86_400);
    assert_eq!(prolonged[0].fee, 6_000);

    let closed = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<SessionClosed>(&response.tx_status.receipts)
        .unwrap();
    assert!(
        closed.is_empty(),
        "the expiry call renewed the session; nothing was settled"
    );
    let seized = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<SessionSeized>(&response.tx_status.receipts)
        .unwrap();
    assert!(seized.is_empty(), "and no basket was routed anywhere");

    let after = fixture.session().await;
    assert_eq!(
        after.session_id, before.session_id,
        "the same session lives on"
    );
    assert_eq!(after.fees_accrued, 6_000);
    assert_eq!(after.collateral, before.collateral);
    assert_eq!(after.auto_prolong, Some(ProlongPeriod::Day));
    assert_eq!(
        after.expires_at,
        before.expires_at + 86_400,
        "one period, measured from the deadline it replaces"
    );
    assert_eq!(
        prolonged[0].new_expires_at, after.expires_at,
        "the event carries the deadline the queue must re-key to"
    );
    assert_eq!(
        fixture
            .deployer
            .get_asset_balance(&fixture.collateral_asset)
            .await
            .unwrap()
            - platform_before,
        6_000,
        "and the renewal is paid for like any other"
    );
}

/// The renewal is decided BEFORE `absorb`, and this is why. `absorb` drives
/// `pool_cleanup` through the account before it reads the expiry gate, so a
/// renewal decided inside it would keep the user's seat and cancel his entire
/// book on the way.
///
/// The keeper is HANDED the resting order here, deliberately. With an empty
/// cleanup list the rejected design would have failed on `BookNotDrained`
/// instead - the right outcome for the wrong reason, and no evidence about
/// cancellation at all. Naming the order is what makes the test discriminate:
/// under the rejected design it would be cancelled, and the assertion below
/// would see the lock gone.
#[tokio::test]
async fn the_renewal_at_expiry_leaves_the_users_resting_orders_alone() {
    let mut fixture = PropFixture::new().await;

    // Draw and park the cash in an unfilled order, then arm.
    let draw = fixture.draw_call(1_000_000);
    let rest = fixture.book_call(
        1_000_000,
        1_000_000_000,
        fixture.collateral_asset,
        1_000_000,
    );
    fixture.call_account(vec![draw, rest], 1).await.unwrap();
    fixture
        .call_account(vec![arm_call(&fixture, Some(ProlongPeriod::Day))], 1)
        .await
        .unwrap();

    let locked = fixture
        .order_book
        .order_book
        .methods()
        .get_total_balance_of(Identity::ContractId(fixture.child_id))
        .simulate(Execution::state_read_only())
        .await
        .unwrap()
        .value;
    assert_ne!(locked, (0, 0), "the account has something resting");

    overshoot_deadline(&fixture, 1).await;
    let orders = fixture
        .order_book
        .order_book
        .methods()
        .get_orders_at_price(crate::order_book_deploy::Side::Buy, 1_000_000)
        .simulate(Execution::state_read_only())
        .await
        .unwrap()
        .value;
    let cleanup = crate::prop::PropOrderBookCleanup {
        order_book: fixture.order_book.contract_id,
        order_ids: orders
            .into_iter()
            .filter(|o| o.trader_id == Identity::ContractId(fixture.child_id))
            .map(|o| o.order_id)
            .collect(),
    };
    assert_eq!(
        cleanup.order_ids.len(),
        1,
        "the keeper is handed a real order"
    );

    fixture
        .deployment
        .pool
        .clone()
        .with_account(fixture.outsider.clone())
        .methods()
        .expire_session(fixture.child_id, vec![cleanup])
        .with_contracts(&[
            &fixture.account,
            &fixture.deployment.oracle,
            &fixture.order_book.order_book,
            &fixture.deployment.price_feed,
        ])
        .with_variable_output_policy(VariableOutputPolicy::EstimateMinimum)
        .call()
        .await
        .unwrap();

    assert_eq!(
        fixture
            .order_book
            .order_book
            .methods()
            .get_total_balance_of(Identity::ContractId(fixture.child_id))
            .simulate(Execution::state_read_only())
            .await
            .unwrap()
            .value,
        locked,
        "a renewed session keeps its book exactly as it was, even when the \
         caller handed the pool an order to cancel"
    );
    assert_eq!(
        fixture.session().await.drawn_quote,
        1_000_000,
        "and its draw"
    );
}

/// A late renewal buys every elapsed period and is billed for all of them.
///
/// The deadline anchors on the one it REPLACES, exactly as a user's own
/// `prolong_session` does, so the term the session bought is the term it paid
/// for and the gap the keeper slept through is not a discount. Being late is
/// therefore never cheaper than being on time - which it would be if the
/// renewal restarted the clock at `now` for a single fee.
///
/// The count is what keeps the path from being drained, too: buying enough
/// periods to clear `now` lands the deadline strictly in the future, so the
/// next permissionless call finds a live session instead of another fee.
#[tokio::test]
async fn a_late_renewal_buys_every_elapsed_period_and_is_billed_for_all_of_them() {
    let mut fixture = PropFixture::new().await;

    fixture
        .call_account(vec![arm_call(&fixture, Some(ProlongPeriod::Day))], 1)
        .await
        .unwrap();
    let before = fixture.session().await;

    // Three whole periods past the deadline: a keeper outage, not a hiccup.
    // Three elapsed plus one to carry the session forward is four.
    overshoot_deadline(&fixture, 3 * 86_400).await;
    let response = expire(&fixture).await.unwrap();
    let prolonged = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<SessionProlonged>(&response.tx_status.receipts)
        .unwrap();
    assert_eq!(prolonged.len(), 1);
    assert_eq!(prolonged[0].times, 4);
    assert_eq!(prolonged[0].seconds, 4 * 86_400);
    assert_eq!(prolonged[0].fee, 24_000, "four periods at the tier's price");

    let chain_now = fixture
        .user
        .try_provider()
        .unwrap()
        .latest_block_time()
        .await
        .unwrap()
        .unwrap()
        .timestamp() as u64;
    let after = fixture.session().await;
    assert_eq!(
        after.expires_at,
        before.expires_at + 4 * 86_400,
        "the term extends the OLD deadline, not the moment the keeper woke up"
    );
    assert!(
        after.expires_at > chain_now,
        "and still clears now, or the seat could be charged again at once: {} vs {chain_now}",
        after.expires_at
    );
    assert!(
        after.expires_at <= chain_now + 86_400,
        "with only the unelapsed remainder left to run"
    );
    assert_eq!(after.fees_accrued, 24_000);

    // The drain the count prevents: a second call finds a live session and is
    // turned away, so nothing is charged twice.
    let error = expire(&fixture).await.unwrap_err();
    assert!(
        error.to_string().contains("NotExpired"),
        "a renewed session is live, so nobody can charge it again: {error:#}"
    );
    assert_eq!(fixture.session().await.fees_accrued, 24_000);
}

/// A session that cannot cover the whole bill still pays for the time it
/// held: it is charged every period it CAN cover, and then absorbed.
///
/// Lapsing must never be the cheap way out of a fee. Forgiving the bill
/// outright would mean a session near its collateral floor was better off
/// letting the deadline pass than renewing - it would keep the difference and
/// the pool would carry the elapsed term for nothing.
///
/// The partial charge is also capped so the term still ends BEFORE now: the
/// charge moves `expires_at`, and `absorb` demands an expired session, so a
/// term landing exactly on `now` would take the fee and then revert the very
/// settlement it was collected during.
#[tokio::test]
async fn a_session_that_cannot_cover_the_gap_pays_for_what_it_can_and_is_absorbed() {
    let mut fixture = PropFixture::new().await;

    // Armed, then charged to 1_980_000 of its 2_000_000: 19_999 of headroom
    // is left under the strict bound, which buys three more periods at 6_000
    // and not a fourth.
    fixture
        .call_account(
            vec![
                arm_call(&fixture, Some(ProlongPeriod::Day)),
                prolong_period_call(&fixture, ProlongPeriod::Day, 330),
            ],
            1,
        )
        .await
        .unwrap();
    let starved = fixture.session().await;
    assert_eq!(starved.fees_accrued, 1_980_000);

    // Ten periods late, so eleven are wanted and only three are payable.
    overshoot_deadline(&fixture, 10 * 86_400).await;
    let response = expire(&fixture).await.unwrap();

    let prolonged = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<SessionProlonged>(&response.tx_status.receipts)
        .unwrap();
    assert_eq!(prolonged.len(), 1, "the partial charge is a real charge");
    assert_eq!(prolonged[0].times, 3);
    assert_eq!(prolonged[0].fee, 18_000);

    let closed = fixture.closed_event(&response);
    assert_eq!(
        closed.reason,
        SettlementReason::Expiry,
        "charged for what it could, then absorbed in the same call"
    );
    assert_eq!(
        closed.fees_accrued, 1_998_000,
        "the three periods it could pay for are on the settlement"
    );
    assert_eq!(
        closed.user_net, 2_000,
        "and only the unbillable remainder comes back"
    );
    assert!(
        fixture
            .deployment
            .pool
            .methods()
            .get_session(fixture.child_id)
            .simulate(Execution::state_read_only())
            .await
            .unwrap()
            .value
            .is_none(),
        "the seat is gone all the same"
    );
}

/// The renewal is a courtesy the collateral has to cover. A session that
/// cannot pay for even ONE period is absorbed exactly as it was before,
/// rather than reverting the keeper's call and leaving the seat stuck open -
/// and with nothing charged on the way out, because there was nothing it
/// could afford to be charged.
#[tokio::test]
async fn an_armed_session_that_cannot_pay_the_renewal_is_absorbed_as_before() {
    let mut fixture = PropFixture::new().await;

    // Armed, then charged to within one fee of its collateral: 333 x 6_000 is
    // 1_998_000 against 2_000_000 funded, so the NEXT 6_000 cannot be carried.
    fixture
        .call_account(
            vec![
                arm_call(&fixture, Some(ProlongPeriod::Day)),
                prolong_period_call(&fixture, ProlongPeriod::Day, 333),
            ],
            1,
        )
        .await
        .unwrap();
    let starved = fixture.session().await;
    assert_eq!(starved.fees_accrued, 1_998_000);
    assert_eq!(starved.auto_prolong, Some(ProlongPeriod::Day));

    overshoot_deadline(&fixture, 1).await;
    let response = expire(&fixture).await.unwrap();

    let closed = fixture.closed_event(&response);
    assert_eq!(closed.reason, SettlementReason::Expiry);
    assert_eq!(closed.fees_accrued, 1_998_000);
    assert_eq!(
        closed.user_net, 2_000,
        "what the collateral had left after the premiums it did pay"
    );
    assert!(
        fixture
            .deployment
            .pool
            .methods()
            .get_session(fixture.child_id)
            .simulate(Execution::state_read_only())
            .await
            .unwrap()
            .value
            .is_none(),
        "the seat is gone, as it would have been before this change"
    );
}

/// The count the renewal buys is priced at the user's DISCOUNTED bill, not at
/// list — a discounted session can afford more periods, and must get them.
///
/// This is the one that catches the count and the charge drifting apart.
/// `affordable_periods` inverts the bill to decide how many periods fit the
/// collateral; `commit_prolongation` then charges for them. If the inversion
/// judged list price while the charge took the discount, this session would
/// be told it could afford three periods when it could afford five — and
/// three does not clear the deadline, so it would be part-charged and
/// ABSORBED. Losing a seat that could pay is the failure being ruled out, and
/// only a discount steep enough to change the answer can rule it out.
#[tokio::test]
async fn a_discounted_session_is_renewed_on_the_count_its_discount_buys() {
    let mut fixture = PropFixture::new().await;

    // Armed, then charged at LIST to 1_980_000 of its 2_000_000 — the
    // discount lands afterwards, so the headroom is a round 19_999.
    fixture
        .call_account(
            vec![
                arm_call(&fixture, Some(ProlongPeriod::Day)),
                prolong_period_call(&fixture, ProlongPeriod::Day, 330),
            ],
            1,
        )
        .await
        .unwrap();
    let before = fixture.session().await;
    assert_eq!(before.fees_accrued, 1_980_000);

    // Half off. 19_999 of headroom buys three periods at 6_000 and six at
    // 3_000, and the keeper is about to need five.
    discount_every_premium(&fixture, 5_000).await;

    overshoot_deadline(&fixture, 4 * 86_400).await;
    let response = expire(&fixture).await.unwrap();

    let prolonged = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<SessionProlonged>(&response.tx_status.receipts)
        .unwrap();
    assert_eq!(prolonged.len(), 1);
    assert_eq!(
        prolonged[0].times, 5,
        "five periods — the count list price would have refused"
    );
    assert_eq!(
        prolonged[0].fee, 15_000,
        "and billed at the discount that allowed them"
    );

    let closed = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<SessionClosed>(&response.tx_status.receipts)
        .unwrap();
    assert!(
        closed.is_empty(),
        "the seat survives: judging this at list price would have absorbed it"
    );
    let after = fixture.session().await;
    assert_eq!(after.expires_at, before.expires_at + 5 * 86_400);
    assert_eq!(after.fees_accrued, 1_995_000);
}

/// A fully forgiven premium renews at any count, however late and however
/// little collateral is left.
///
/// `discount_bps` may be `BPS` — a 100% grant — which makes the multiplier
/// the inversion divides by ZERO. The search this replaced never divided, so
/// it never had to care; the closed form does, and this is the case that
/// proves the guard is a real branch rather than a defensive one.
///
/// The session here is the same one
/// `an_armed_session_that_cannot_pay_the_renewal_is_absorbed_as_before`
/// absorbs: 333 premiums deep, 1_999 of headroom, unable to buy a single
/// period at list. Free, it keeps its seat.
#[tokio::test]
async fn a_wholly_forgiven_premium_renews_a_session_that_could_not_pay_a_cent() {
    let mut fixture = PropFixture::new().await;

    fixture
        .call_account(
            vec![
                arm_call(&fixture, Some(ProlongPeriod::Day)),
                prolong_period_call(&fixture, ProlongPeriod::Day, 333),
            ],
            1,
        )
        .await
        .unwrap();
    let before = fixture.session().await;
    assert_eq!(before.fees_accrued, 1_998_000);

    discount_every_premium(&fixture, 10_000).await;

    overshoot_deadline(&fixture, 3 * 86_400).await;
    let response = expire(&fixture).await.unwrap();

    let prolonged = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<SessionProlonged>(&response.tx_status.receipts)
        .unwrap();
    assert_eq!(prolonged.len(), 1);
    assert_eq!(
        prolonged[0].times, 4,
        "the whole gap, because none of it costs anything"
    );
    assert_eq!(prolonged[0].fee, 0);

    let after = fixture.session().await;
    assert_eq!(after.expires_at, before.expires_at + 4 * 86_400);
    assert_eq!(
        after.fees_accrued, 1_998_000,
        "a free renewal accrues nothing, so the line does not move either"
    );
    assert_eq!(after.credit_line, before.credit_line);
}

/// The renewal must never become the reason a session cannot be closed.
///
/// `pay_fee` ends the renewal with
/// `require(this_balance >= fee, InsufficientInventory)`, and the pool's quote
/// float is shared: `draw` and `borrow` can take it below any single session's
/// fee. Without a pre-flight the keeper's `expire_session` would REVERT there
/// - and `absorb` would have succeeded, because `pool_sweep` pulls the
/// account's own basket in before any payout, so the very sweep that refills
/// the float is what the revert blocks.
///
/// Reaching the state needs a session whose draw is most of the pool: with the
/// fixture's own tier the float can never fall below one fee, because a
/// session's collateral sits IN the pool and the line is capped at twice it.
/// A wide tier breaks that - the line is 5x the collateral, so the draw can
/// carry the float away.
#[tokio::test]
async fn a_renewal_the_pool_cannot_fund_absorbs_instead_of_reverting() {
    let mut fixture = PropFixture::new().await;

    let (child_id, account, collateral) = starved_pool_session(&mut fixture, 1_000).await;
    assert_eq!(
        fixture.pool_balance(fixture.collateral_asset).await,
        1_000,
        "the pool now holds less than the 6_000 renewal fee"
    );

    // Past the deadline. The session is armed and can AFFORD the fee out of
    // its own collateral - but the pool cannot pay it out.
    overshoot_child_deadline(&fixture, child_id, 1).await;

    let response = fixture
        .deployment
        .pool
        .clone()
        .with_account(fixture.outsider.clone())
        .methods()
        .expire_session(child_id, vec![])
        .with_contracts(&[
            &account,
            &fixture.deployment.oracle,
            &fixture.order_book.order_book,
            &fixture.deployment.price_feed,
        ])
        .with_variable_output_policy(VariableOutputPolicy::EstimateMinimum)
        .call()
        .await
        .unwrap();

    let closed = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<SessionClosed>(&response.tx_status.receipts)
        .unwrap();
    assert_eq!(
        closed.len(),
        1,
        "the session was absorbed, not left stranded"
    );
    assert_eq!(closed[0].reason, SettlementReason::Expiry);
    // And the absorption is CLEAN: the drawn cash was sitting on the account,
    // so the sweep hands it straight back and the parent is paid in full.
    //
    // That is the whole shape of the bug this test exists for. The float was
    // genuinely under the fee at the moment `expire_session` was called - the
    // renewal would have reverted `InsufficientInventory` there - and the
    // money that makes the absorption work only arrives during the sweep,
    // AFTER the point the renewal would have failed.
    assert_eq!(closed[0].bad_debt, 0);
    assert_eq!(closed[0].user_net, collateral);
    let prolonged = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<SessionProlonged>(&response.tx_status.receipts)
        .unwrap();
    assert!(
        prolonged.is_empty(),
        "a pool that cannot pay the fee must not have renewed"
    );
    assert!(
        fixture
            .deployment
            .pool
            .methods()
            .get_session(child_id)
            .simulate(Execution::state_read_only())
            .await
            .unwrap()
            .value
            .is_none()
    );
}

/// The FLOAT caps the partial charge too, not just the whole renewal.
///
/// A session can be rich enough to buy every period it slept through and
/// still be told it may only have two, because the pool's quote float is what
/// the fee is paid OUT of and a draw can carry that away. The collateral
/// bound and the float bound are separate ceilings and the lower one wins;
/// with the fixture's own tier only the collateral one is ever reachable, so
/// without this the float's half of `affordable_periods` is never exercised
/// on the partial path at all.
#[tokio::test]
async fn the_pools_float_caps_the_partial_charge_before_the_collateral_does() {
    let mut fixture = PropFixture::new().await;

    // Two periods' worth of float and a thousand to spare, against a session
    // whose 40_000_000 of collateral could pay for hundreds.
    let (child_id, account, _collateral) =
        starved_pool_session(&mut fixture, 13_000).await;

    // Four whole periods late, so five are wanted and the float allows two.
    overshoot_child_deadline(&fixture, child_id, 4 * 86_400).await;

    let response = fixture
        .deployment
        .pool
        .clone()
        .with_account(fixture.outsider.clone())
        .methods()
        .expire_session(child_id, vec![])
        .with_contracts(&[
            &account,
            &fixture.deployment.oracle,
            &fixture.order_book.order_book,
            &fixture.deployment.price_feed,
        ])
        .with_variable_output_policy(VariableOutputPolicy::EstimateMinimum)
        .call()
        .await
        .unwrap();

    let prolonged = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<SessionProlonged>(&response.tx_status.receipts)
        .unwrap();
    assert_eq!(prolonged.len(), 1, "what the float could fund was charged");
    assert_eq!(
        prolonged[0].times, 2,
        "two periods — the collateral would have carried all five"
    );
    assert_eq!(prolonged[0].fee, 12_000);

    let closed = fixture
        .deployment
        .pool
        .log_decoder()
        .decode_logs_with_type::<SessionClosed>(&response.tx_status.receipts)
        .unwrap();
    assert_eq!(closed.len(), 1, "and the rest of the gap it could not fund");
    assert_eq!(closed[0].reason, SettlementReason::Expiry);
    assert_eq!(closed[0].bad_debt, 0);
    assert!(
        fixture
            .deployment
            .pool
            .methods()
            .get_session(child_id)
            .simulate(Execution::state_read_only())
            .await
            .unwrap()
            .value
            .is_none()
    );
}

/// Opens an armed session on a tier whose line dwarfs its entry ticket and
/// draws the pool's quote float down to `float_left`.
///
/// The fixture's own tier cannot reach this state: a session's collateral
/// sits IN the pool and the line is capped at twice it, so the float can
/// never fall below one fee. A 5x line breaks that - the draw can carry the
/// float away. Returns the account and the collateral it was funded with.
async fn starved_pool_session(
    fixture: &mut PropFixture,
    float_left: u64,
) -> (ContractId, PropAccountContract<Wallet>, u64) {
    // 200_000_000 at 5x: ticket 40_000_000, k 160_000_000.
    let wide = TierParams {
        line: 200_000_000,
        leverage: 5,
        duration: 64_800,
        maintenance_bps: 250,
        open_buffer_bps: 375,
        liq_price_factor: 9_900,
        prolong_fee: [0, 6_000, 76_000, 738_000],
        max_credit_line_bps: 20_000,
        max_price_age: u64::MAX,
        open_fee: 0,
        profit_share_bps: 1_000,
        price_band_bps: 1_000,
    };
    let tier_id = 31;
    fixture
        .deployment
        .pool
        .methods()
        .publish_tier_version(tier_id, wide, vec![fixture.order_book.contract_id])
        .with_contract_ids(&[
            fixture.order_book.contract_id,
            fixture.deployment.price_feed_id,
        ])
        .call()
        .await
        .unwrap();

    let parent = Identity::Address(fixture.user.address());
    let child = fixture
        .deployment
        .deploy_account(&fixture.user, parent, 31)
        .await
        .unwrap();
    let child_id = child.contract_id();
    let account = PropAccountContract::new(child_id, fixture.user.clone());
    let key_expiry = SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .unwrap()
        .as_secs()
        + 86_400;
    account
        .methods()
        .set_session(ParallelSessionArgs {
            nonce: U256::zero(),
            session_id: Identity::Address(fixture.user.address()),
            expiry: Time { unix: key_expiry },
            contract_ids: vec![],
        })
        .with_contract_ids(&[fixture.deployment.oracle_id])
        .call()
        .await
        .unwrap();

    let collateral = 40_000_000u64;
    account
        .methods()
        .start_session(tier_id, collateral, ProlongPeriod::SixHours)
        .call_params(CallParameters::new(
            collateral,
            fixture.collateral_asset,
            u64::MAX,
        ))
        .unwrap()
        .with_contract_ids(&[
            fixture.deployment.oracle_id,
            fixture.deployment.pool_id,
            fixture.deployment.registry_id,
        ])
        .with_variable_output_policy(VariableOutputPolicy::EstimateMinimum)
        .call()
        .await
        .unwrap();

    // Arm the renewal, then draw the pool's quote float down to the target.
    let float = fixture.pool_balance(fixture.collateral_asset).await;
    let draw = float - float_left;
    let calls = vec![
        fixture.pool_call(
            fn_selector!(set_auto_prolong(Option<ProlongPeriod>)),
            0,
            AssetId::default(),
            Some(call_data!(Some(ProlongPeriod::Day))),
        ),
        fixture.pool_call(
            fn_selector!(draw(u64)),
            0,
            AssetId::default(),
            Some(call_data!(draw)),
        ),
    ];
    let signed = fixture.signed_calls_for(child_id, calls).await;
    account
        .methods()
        .call_contracts(signed.0, signed.1, signed.2)
        .with_contracts(&[
            &fixture.deployment.oracle,
            &fixture.deployment.pool,
            &fixture.deployment.price_feed,
            &fixture.deployment.registry,
            &fixture.order_book.order_book,
        ])
        .with_variable_output_policy(VariableOutputPolicy::Exactly(2))
        .call()
        .await
        .unwrap();
    assert_eq!(
        fixture.pool_balance(fixture.collateral_asset).await,
        float_left,
        "the draw left the pool exactly the float the caller asked for"
    );

    (child_id, account, collateral)
}

/// Moves the chain `past` seconds beyond a NAMED child's deadline, for the
/// sessions that do not belong to the fixture's own account.
async fn overshoot_child_deadline(fixture: &PropFixture, child: ContractId, past: u64) {
    let session = fixture
        .deployment
        .pool
        .methods()
        .get_session(child)
        .simulate(Execution::state_read_only())
        .await
        .unwrap()
        .value
        .unwrap();
    let provider = fixture.user.try_provider().unwrap().clone();
    let latest = provider.latest_block_time().await.unwrap().unwrap();
    let jump = (session.expires_at + past).saturating_sub(latest.timestamp() as u64);
    provider
        .produce_blocks(
            1,
            Some(
                latest
                    .checked_add_signed(chrono::TimeDelta::seconds(jump as i64))
                    .unwrap(),
            ),
        )
        .await
        .unwrap();
}