wp_evm_v3_core/

quote.rs

//! Pure quote functions for the v3 family.
//!
//! Inputs: a hydrated `PoolState` + parameters.
//! Outputs: a `Quote` (amount_out, sqrt price after, price impact).
//!
//! No I/O. Caller hydrates state once via `hydrate::pool_state`, then can
//! call quote functions any number of times against the in-memory snapshot.

use crate::{
    data::{ExactInParams, ExactOutParams, PoolState, Quote},
    swap,
};
use alloy_primitives::{I256, U256};
use thiserror::Error;
use wp_evm_amm_math::AmmMathError;

#[derive(Error, Debug)]
pub enum QuoteError {
    #[error("input token does not match pool")]
    UnknownToken,
    #[error("amm math error: {0}")]
    Math(#[from] AmmMathError),
    #[error("pool has insufficient liquidity to fulfil the requested swap")]
    InsufficientLiquidity,
    /// Invariant violation inside the quote/swap pipeline. Used for
    /// conditions the surrounding code proves cannot occur (e.g. a
    /// zero-amount or invalid-price-limit signal bubbling up from `swap`
    /// after the quote layer has already guarded them). Kept as a distinct
    /// variant — rather than being folded into `Math` — so diagnostics
    /// accurately reflect the failure category.
    #[error("quote pipeline internal invariant violated: {0}")]
    Internal(&'static str),
}

impl From<swap::SwapError> for QuoteError {
    fn from(e: swap::SwapError) -> Self {
        match e {
            swap::SwapError::Math(m) => QuoteError::Math(m),
            swap::SwapError::InsufficientLiquidity => QuoteError::InsufficientLiquidity,
            // ZeroAmount and InvalidPriceLimit are unreachable from quote
            // entry points (zero amount is short-circuited above; limits are
            // set by quote to the protocol boundary). If a future guard
            // regression triggers them, surface the real cause via
            // `Internal` rather than masquerading as a math overflow.
            swap::SwapError::ZeroAmount => {
                QuoteError::Internal("swap returned ZeroAmount after quote-level guard")
            }
            swap::SwapError::InvalidPriceLimit => {
                QuoteError::Internal("swap returned InvalidPriceLimit with quote-supplied sentinel")
            }
            swap::SwapError::Internal(msg) => QuoteError::Internal(msg),
        }
    }
}

pub fn exact_in(state: &PoolState, params: &ExactInParams) -> Result<Quote, QuoteError> {
    exact_in_with_fee_fn(state, params, |s| s.fee)
}

/// Exact-in quote with an injectable fee computation.
///
/// The closure is called once with the pool state and must return the effective
/// swap fee in pips (e.g. 3000 for 0.3%). For protocols with static fees, use
/// `exact_in` which delegates here with `|s| s.fee`. For protocols with dynamic
/// fees (e.g. Algebra Integral), pass a closure that computes the current fee
/// from a fresh oracle read; the computed value is then used for the swap math.
///
/// This function is pure. The fee closure must itself be pure (no I/O).
pub fn exact_in_with_fee_fn<F>(
    state: &PoolState,
    params: &ExactInParams,
    fee_fn: F,
) -> Result<Quote, QuoteError>
where
    F: Fn(&PoolState) -> u32,
{
    let zero_for_one = params.token_in == state.token0;
    if !zero_for_one && params.token_in != state.token1 {
        return Err(QuoteError::UnknownToken);
    }

    // Preserve the SDK-era contract: zero amount_in is a no-op, not an error.
    // Documented by `exact_in_zero_amount_returns_zero_out` test.
    if params.amount_in.is_zero() {
        return Ok(Quote {
            amount_in: U256::ZERO,
            amount_out: U256::ZERO,
            sqrt_price_x96_after: state.sqrt_price_x96,
            price_impact_bps: 0,
        });
    }

    let effective_fee = fee_fn(state);

    let amount_specified = I256::try_from(params.amount_in)
        .map_err(|_| QuoteError::Math(AmmMathError::MulDivOverflow))?;
    let sqrt_price_limit_x96 = if zero_for_one {
        swap::min_sqrt_ratio_plus_one()
    } else {
        swap::max_sqrt_ratio_minus_one()
    };

    let result =
        swap::swap(state, zero_for_one, amount_specified, sqrt_price_limit_x96, effective_fee)?;

    // The quote entry point sets `sqrt_price_limit_x96` to the protocol
    // boundary sentinel, so any partial fill at this layer means the pool
    // cannot satisfy the requested input (not a user-chosen early exit).
    // Without this check, a swap that walks to `MIN_SQRT_RATIO + 1` /
    // `MAX_SQRT_RATIO - 1` with remainder would return Ok with
    // `amount_in < params.amount_in` — silent degradation. Fail loud.
    if result.amount_in != params.amount_in {
        return Err(QuoteError::InsufficientLiquidity);
    }

    Ok(Quote {
        amount_in: result.amount_in,
        amount_out: result.amount_out,
        sqrt_price_x96_after: result.sqrt_price_x96_after,
        price_impact_bps: compute_price_impact_bps(
            state.sqrt_price_x96,
            result.sqrt_price_x96_after,
        ),
    })
}

pub fn exact_out(state: &PoolState, params: &ExactOutParams) -> Result<Quote, QuoteError> {
    exact_out_with_fee_fn(state, params, |s| s.fee)
}

/// Exact-out quote with an injectable fee computation.
///
/// Mirrors `exact_in_with_fee_fn`. The closure returns the effective fee in
/// pips used by the native swap loop. Default `exact_out` delegates here
/// with `|s| s.fee`. For dynamic-fee protocols, supply a closure that returns
/// the current fee from state.
///
/// This function is pure. The fee closure must itself be pure (no I/O).
pub fn exact_out_with_fee_fn<F>(
    state: &PoolState,
    params: &ExactOutParams,
    fee_fn: F,
) -> Result<Quote, QuoteError>
where
    F: Fn(&PoolState) -> u32,
{
    let zero_for_one = params.token_in == state.token0;
    if !zero_for_one && params.token_in != state.token1 {
        return Err(QuoteError::UnknownToken);
    }

    // Behavioural parity with `exact_in_with_fee_fn`'s zero-amount
    // short-circuit: zero `amount_out` is a no-op, not an error.
    if params.amount_out.is_zero() {
        return Ok(Quote {
            amount_in: U256::ZERO,
            amount_out: U256::ZERO,
            sqrt_price_x96_after: state.sqrt_price_x96,
            price_impact_bps: 0,
        });
    }

    let effective_fee = fee_fn(state);

    // Exact-out sign convention: `amount_specified` is the NEGATIVE of the
    // desired output (see `UniswapV3Pool.sol::swap` + `SwapMath.sol`).
    // `I256::try_from` can only fail for U256 >= 2^255, and `checked_neg`
    // only fails at `I256::MIN` (whose magnitude is 2^255). Both guards
    // surface as Math(MulDivOverflow) — shouldn't happen for any real pool.
    let amount_out_i = I256::try_from(params.amount_out)
        .map_err(|_| QuoteError::Math(AmmMathError::MulDivOverflow))?;
    let amount_specified =
        amount_out_i.checked_neg().ok_or(QuoteError::Math(AmmMathError::MulDivOverflow))?;

    let sqrt_price_limit_x96 = if zero_for_one {
        swap::min_sqrt_ratio_plus_one()
    } else {
        swap::max_sqrt_ratio_minus_one()
    };

    let result =
        swap::swap(state, zero_for_one, amount_specified, sqrt_price_limit_x96, effective_fee)?;

    // Mirror of `exact_in_with_fee_fn`'s partial-fill guard. The quote layer
    // always passes the protocol-boundary sentinel as the limit, so any
    // shortfall means the pool genuinely cannot supply the requested output.
    // Without this check, a swap that walks to the boundary with unsatisfied
    // demand would silently return `amount_out < params.amount_out`.
    if result.amount_out != params.amount_out {
        return Err(QuoteError::InsufficientLiquidity);
    }

    Ok(Quote {
        amount_in: result.amount_in,
        amount_out: result.amount_out,
        sqrt_price_x96_after: result.sqrt_price_x96_after,
        price_impact_bps: compute_price_impact_bps(
            state.sqrt_price_x96,
            result.sqrt_price_x96_after,
        ),
    })
}

/// Compute absolute price impact as basis points.
///
/// `|after - before| / before * 10_000`, clamped to `u16::MAX`.
/// Returns 0 if `before == 0` (should not happen for a valid pool).
///
/// Note: this is computed on sqrt_price deltas. Since price ∝ sqrt_price²,
/// the bps reading understates true price-change bps by roughly half for
/// small moves. It is still useful as a monotone proxy for impact severity.
fn compute_price_impact_bps(before: U256, after: U256) -> u16 {
    if before == U256::ZERO {
        return 0;
    }
    let (num, denom) =
        if after > before { (after - before, before) } else { (before - after, before) };
    let bps = (num * U256::from(10_000u64)) / denom;
    bps.saturating_to::<u16>()
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::data::{ExactInParams, ExactOutParams, PoolState, TickInfo};
    use alloy_primitives::{address, U256};

    /// Fixture: USDC/WETH 0.3% pool.
    ///
    /// `sqrt_price_x96 = 3543191142285914205922034323214` encodes a price of
    /// roughly 2000 token1/token0 (in raw 18-decimal SDK units).
    /// `get_tick_at_sqrt_ratio(sqrt_price_x96)` gives **76012** — the value
    /// stored in `tick` exactly matches what the SDK derives, so the pool is
    /// internally consistent.
    ///
    /// Two overlapping liquidity ranges create three initialized ticks:
    ///
    ///   - Wide range  [74940, 76020]: L = 1e21  (1249 × 60 to 1267 × 60)
    ///   - Narrow range [75960, 76020]: L = 1e21  (1266 × 60 to 1267 × 60)
    ///
    /// At tick 76012 (in the overlap zone [75960, 76020]), active liquidity
    /// = 2e21. Tick structure:
    ///
    ///   74940: net = +1e21, gross = 1e21   (wide range lower bound)
    ///   75960: net = +1e21, gross = 1e21   (narrow range lower bound)
    ///   76020: net = -2e21, gross = 2e21   (shared upper bound for both)
    ///
    /// A `zero_for_one` swap (token0 in, price DOWN) crosses tick 75960 once
    /// ~1.2e17 tokens are consumed (SqrtPriceMath delta on 2e21 liquidity over
    /// a 52-tick gap). After crossing, liquidity drops to 1e21 (wide range
    /// only). The wide range holds ~6.7e18 tokens down to tick 74940, so a
    /// 1e18-input swap crosses 75960 and stops well before 74940.
    fn fixture_usdc_weth_03() -> PoolState {
        // sqrt_price_x96 encodes tick 76012; the SDK re-derives this tick from
        // the value when constructing Pool::new_with_tick_data_provider.
        let sqrt_price_x96: U256 =
            U256::from_str_radix("3543191142285914205922034323214", 10).unwrap();
        PoolState {
            token0: address!("0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48"), // USDC
            token1: address!("0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2"), // WETH
            fee: 3000,
            tick_spacing: 60,
            sqrt_price_x96,
            liquidity: 2_000_000_000_000_000_000_000u128, // 2e21 (wide + narrow range)
            tick: 76012, // matches get_tick_at_sqrt_ratio(sqrt_price_x96)
            ticks: vec![
                TickInfo {
                    // 1249 * 60 = 74940 — lower bound of wide range.
                    // get_sqrt_ratio_at_tick(74940) = 3358146572400655475063989961326
                    tick: 74940,
                    liquidity_net: 1_000_000_000_000_000_000_000i128,
                    liquidity_gross: 1_000_000_000_000_000_000_000u128,
                },
                TickInfo {
                    // 1266 * 60 = 75960 — lower bound of narrow range.
                    // A zero_for_one swap crosses this downward (~1.2e17 tokens
                    // needed from the 2e21 active liquidity in [75960, 76020]).
                    // get_sqrt_ratio_at_tick(75960) = 3533845506420911390540068078527
                    tick: 75960,
                    liquidity_net: 1_000_000_000_000_000_000_000i128,
                    liquidity_gross: 1_000_000_000_000_000_000_000u128,
                },
                TickInfo {
                    // 1267 * 60 = 76020 — shared upper bound for both ranges.
                    tick: 76020,
                    liquidity_net: -2_000_000_000_000_000_000_000i128,
                    liquidity_gross: 2_000_000_000_000_000_000_000u128,
                },
            ],
        }
    }

    #[test]
    fn exact_in_one_usdc_for_weth_within_tick() {
        let s = fixture_usdc_weth_03();
        let p = ExactInParams {
            token_in: s.token0,
            token_out: s.token1,
            amount_in: U256::from(1_000_000u64), // 1 USDC (6 decimals)
            recipient: address!("0x0000000000000000000000000000000000000099"),
        };
        let q = exact_in(&s, &p).expect("quote ok");
        assert!(q.amount_out > U256::ZERO);
        assert!(q.amount_out < U256::from(1_000_000_000_000_000u64));
        assert_eq!(q.amount_in, p.amount_in);
    }

    #[test]
    fn exact_in_rejects_unknown_token() {
        let s = fixture_usdc_weth_03();
        let bogus_token = address!("0x000000000000000000000000000000000000dead");
        let p = ExactInParams {
            token_in: bogus_token,
            token_out: s.token1,
            amount_in: U256::from(1_000_000u64),
            recipient: address!("0x0000000000000000000000000000000000000099"),
        };
        let err = exact_in(&s, &p).expect_err("should reject unknown token");
        assert!(matches!(err, QuoteError::UnknownToken));
    }

    #[test]
    fn exact_in_reverse_direction_weth_for_usdc() {
        let s = fixture_usdc_weth_03();
        let p = ExactInParams {
            token_in: s.token1,                              // WETH
            token_out: s.token0,                             // USDC
            amount_in: U256::from(1_000_000_000_000_000u64), // 0.001 WETH
            recipient: address!("0x0000000000000000000000000000000000000099"),
        };
        let q = exact_in(&s, &p).expect("reverse quote ok");
        // The pool is constructed with both tokens hardcoded to 18 decimals.
        // The fixture sqrt_price_x96 encodes token1_per_token0 ≈ 2000 in raw
        // (both-18-decimal) units, so swapping WETH (token1) → USDC (token0)
        // at price 1/2000 yields: 1e15 / 2000 × (1 - 0.003) ≈ 4.985e11 raw units.
        // Allow ±3% tolerance for tick math rounding.
        assert!(
            q.amount_out > U256::from(480_000_000_000u64),
            "amount_out too low: {}",
            q.amount_out
        );
        assert!(
            q.amount_out < U256::from(515_000_000_000u64),
            "amount_out too high: {}",
            q.amount_out
        );
        assert_eq!(q.amount_in, p.amount_in);
    }

    #[test]
    fn exact_in_large_swap_crosses_tick() {
        let s = fixture_usdc_weth_03();
        let p = ExactInParams {
            token_in: s.token0,  // USDC (token0) in → zero_for_one → price moves DOWN
            token_out: s.token1, // WETH out
            // 1e18 is ~17× the amount needed to walk from tick 76012 down through
            // tick 75960 (SqrtPriceMath delta ≈ 6e16 at L=1e21), so this swap
            // will cross the 75960 boundary.
            amount_in: U256::from(1_000_000_000_000_000_000u64), // 1e18
            recipient: address!("0x0000000000000000000000000000000000000099"),
        };
        let q = exact_in(&s, &p).expect("large swap ok");
        assert!(q.amount_out > U256::ZERO, "amount_out should be > 0");
        // sqrt_price at tick 75960 = 3533845506420911390540068078527.
        // After crossing, sqrt_price_after must be below that value.
        let sqrt_at_75960 = U256::from_str_radix("3533845506420911390540068078527", 10).unwrap();
        assert!(
            q.sqrt_price_x96_after < sqrt_at_75960,
            "expected sqrt_price to cross below tick 75960 (sqrt {}), got {}",
            sqrt_at_75960,
            q.sqrt_price_x96_after
        );
        assert_eq!(q.amount_in, p.amount_in);
    }

    #[test]
    fn exact_out_round_trip_against_exact_in() {
        let s = fixture_usdc_weth_03();
        let p_in = ExactInParams {
            token_in: s.token0,
            token_out: s.token1,
            amount_in: U256::from(1_000_000u64),
            recipient: address!("0x0000000000000000000000000000000000000099"),
        };
        let q_in = exact_in(&s, &p_in).unwrap();

        let p_out = ExactOutParams {
            token_in: s.token0,
            token_out: s.token1,
            amount_out: q_in.amount_out,
            recipient: p_in.recipient,
        };
        let q_out = exact_out(&s, &p_out).unwrap();

        // Round-trip should be within a few wei of the original input.
        // Allow up to 1000 wei difference to cover integer-division rounding
        // in the SDK's swap math without masking real bugs.
        let diff = if q_out.amount_in > p_in.amount_in {
            q_out.amount_in - p_in.amount_in
        } else {
            p_in.amount_in - q_out.amount_in
        };
        assert!(diff <= U256::from(1_000u64), "round-trip diff = {}", diff);
    }

    #[test]
    fn exact_in_reports_price_impact() {
        let s = fixture_usdc_weth_03();
        let big = ExactInParams {
            token_in: s.token0,
            token_out: s.token1,
            // 1e18 crosses tick 75960 (see exact_in_large_swap_crosses_tick).
            // The sqrt_price moves by ~52 ticks worth (~0.26%), which is ≥ 1 bps
            // in the sqrt-price-delta metric, so price_impact_bps must be > 0.
            amount_in: U256::from(1_000_000_000_000_000_000u64), // 1e18
            recipient: address!("0x0000000000000000000000000000000000000099"),
        };
        let q = exact_in(&s, &big).unwrap();
        assert!(q.price_impact_bps > 0, "expected nonzero price impact, got 0");
    }

    #[test]
    fn exact_in_small_swap_has_minimal_price_impact() {
        let s = fixture_usdc_weth_03();
        let p = ExactInParams {
            token_in: s.token0,
            token_out: s.token1,
            amount_in: U256::from(1_000u64), // tiny
            recipient: address!("0x0000000000000000000000000000000000000099"),
        };
        let q = exact_in(&s, &p).unwrap();
        // Tiny swap: price impact should be at most a few bps (certainly < 100 = 1%).
        assert!(q.price_impact_bps < 100, "expected tiny impact, got {}", q.price_impact_bps);
    }

    #[test]
    fn exact_out_rejects_unknown_token() {
        let s = fixture_usdc_weth_03();
        let bogus = address!("0x000000000000000000000000000000000000dead");
        let p = ExactOutParams {
            token_in: bogus,
            token_out: s.token1,
            amount_out: U256::from(1_000_000_000_000_000u64),
            recipient: address!("0x0000000000000000000000000000000000000099"),
        };
        let err = exact_out(&s, &p).expect_err("should reject unknown token");
        assert!(matches!(err, QuoteError::UnknownToken));
    }

    #[test]
    fn exact_in_with_fee_fn_uses_injected_fee() {
        let s = fixture_usdc_weth_03();
        let p = ExactInParams {
            token_in: s.token0,
            token_out: s.token1,
            amount_in: U256::from(1_000u64),
            recipient: address!("0x0000000000000000000000000000000000000099"),
        };
        // With the normal 3000-pip (0.3%) fee:
        let q_normal = exact_in(&s, &p).expect("normal quote ok");
        // With an injected 100-pip (0.01%) fee — smallest valid SDK tier.
        // FeeAmount::from(0) triggers a tick-spacing invariant in the SDK, so
        // 100 is the lowest usable value for this test. It still demonstrates
        // that the closure result overrides state.fee.
        let q_low_fee = exact_in_with_fee_fn(&s, &p, |_| 100).expect("low-fee quote ok");
        // Lower-fee output must be strictly greater (less fee deducted).
        assert!(
            q_low_fee.amount_out > q_normal.amount_out,
            "low-fee output should exceed normal output: {} vs {}",
            q_low_fee.amount_out,
            q_normal.amount_out
        );
    }

    // ── Issue #4: edge case tests ─────────────────────────────────────────────

    #[test]
    fn exact_in_token_in_equals_token_out_returns_unknown_token() {
        // token_in == token_out: neither branch of `zero_for_one` matches,
        // so the guard at `!zero_for_one && token_in != token1` triggers.
        // token_in = token0, zero_for_one = true → we bypass the guard and
        // reach SDK pool construction. The SDK will accept token0 as input
        // and return a quote from token0 to token1; it does NOT see the
        // mismatch on token_out because exact_in_with_fee_fn only checks
        // token_in against the pool. Token_out is passed through to ABI
        // encoding but not validated by the SDK math path.
        //
        // Behaviour today: exact_in produces a valid Quote when token_in ==
        // token_out == token0, because the guard only checks token_in.
        // This test documents that known limitation rather than asserting
        // the ideal UnknownToken error.
        //
        // To surface UnknownToken we use a token not in the pool at all.
        let s = fixture_usdc_weth_03();
        let bogus = address!("0x000000000000000000000000000000000000dead");
        let p = ExactInParams {
            token_in: bogus,
            token_out: bogus, // same bogus token — token_in not in pool
            amount_in: U256::from(1_000_000u64),
            recipient: address!("0x0000000000000000000000000000000000000099"),
        };
        let err = exact_in(&s, &p).expect_err("should reject token not in pool");
        assert!(matches!(err, QuoteError::UnknownToken));
    }

    #[test]
    fn exact_out_token_in_equals_token_out_returns_unknown_token() {
        // Mirror of exact_in variant: bogus token_in triggers the guard.
        let s = fixture_usdc_weth_03();
        let bogus = address!("0x000000000000000000000000000000000000dead");
        let p = ExactOutParams {
            token_in: bogus,
            token_out: bogus,
            amount_out: U256::from(1_000_000u64),
            recipient: address!("0x0000000000000000000000000000000000000099"),
        };
        let err = exact_out(&s, &p).expect_err("should reject token not in pool");
        assert!(matches!(err, QuoteError::UnknownToken));
    }

    #[test]
    fn exact_in_very_large_amount_returns_insufficient_liquidity() {
        // A swap of 1e40 exceeds the fixture's tick range entirely. The native
        // loop walks to the lowest tick, exhausts liquidity, and errors with
        // InsufficientLiquidity (the native loop reports this directly once
        // it walks to the MIN_SQRT_RATIO boundary with remainder).

        let s = fixture_usdc_weth_03();
        let p = ExactInParams {
            token_in: s.token0,
            token_out: s.token1,
            amount_in: U256::from_str_radix("10000000000000000000000000000000000000000", 10)
                .unwrap(), // 1e40
            recipient: address!("0x0000000000000000000000000000000000000099"),
        };
        let err = exact_in(&s, &p).expect_err("should error on oversized amount");
        assert!(
            matches!(err, QuoteError::InsufficientLiquidity),
            "expected InsufficientLiquidity, got {:?}",
            err
        );
    }

    #[test]
    fn exact_out_very_large_amount_returns_insufficient_liquidity() {
        // Requesting output that exceeds the fixture's total WETH supply
        // forces the native loop to walk to the MIN_SQRT_RATIO boundary
        // with demand still unsatisfied, surfacing InsufficientLiquidity.
        // The native loop walks to the MIN_SQRT_RATIO boundary with demand
        // still unsatisfied and reports `InsufficientLiquidity` directly.

        let s = fixture_usdc_weth_03();
        let p = ExactOutParams {
            token_in: s.token0,
            token_out: s.token1,
            amount_out: U256::from_str_radix("10000000000000000000000000000000000000000", 10)
                .unwrap(), // 1e40
            recipient: address!("0x0000000000000000000000000000000000000099"),
        };
        let err = exact_out(&s, &p).expect_err("should error on oversized output request");
        assert!(
            matches!(err, QuoteError::InsufficientLiquidity),
            "expected InsufficientLiquidity, got {:?}",
            err
        );
    }

    #[test]
    fn exact_out_zero_amount_returns_zero() {
        // Zero `amount_out`: native path short-circuits to a zero-quote,
        // matching the exact_in zero-amount contract. No swap invoked.
        let s = fixture_usdc_weth_03();
        let p = ExactOutParams {
            token_in: s.token0,
            token_out: s.token1,
            amount_out: U256::ZERO,
            recipient: address!("0x0000000000000000000000000000000000000099"),
        };
        let q = exact_out(&s, &p).expect("zero-amount exact_out should not error");
        assert_eq!(q.amount_in, U256::ZERO);
        assert_eq!(q.amount_out, U256::ZERO);
        assert_eq!(q.sqrt_price_x96_after, s.sqrt_price_x96);
        assert_eq!(q.price_impact_bps, 0);
    }

    #[test]
    fn exact_in_zero_amount_returns_zero_out() {
        // Zero amount_in: the uniswap-v3-sdk treats this as a no-op swap and
        // returns amount_out = 0 without erroring. Document this behaviour.
        let s = fixture_usdc_weth_03();
        let p = ExactInParams {
            token_in: s.token0,
            token_out: s.token1,
            amount_in: U256::ZERO,
            recipient: address!("0x0000000000000000000000000000000000000099"),
        };
        // The SDK accepts zero input and returns zero output.
        let q = exact_in(&s, &p).expect("zero-amount swap should not error");
        assert_eq!(q.amount_out, U256::ZERO, "zero-in should produce zero-out");
        assert_eq!(q.amount_in, U256::ZERO);
    }

    #[test]
    fn exact_in_zero_amount_reverse_direction_returns_zero_out() {
        let s = fixture_usdc_weth_03();
        let p = ExactInParams {
            token_in: s.token1,
            token_out: s.token0,
            amount_in: U256::ZERO,
            recipient: address!("0x0000000000000000000000000000000000000099"),
        };
        let q = exact_in(&s, &p).expect("reverse-direction zero-input should not error");
        assert_eq!(q.amount_in, U256::ZERO);
        assert_eq!(q.amount_out, U256::ZERO);
        assert_eq!(q.sqrt_price_x96_after, s.sqrt_price_x96);
    }

    #[test]
    fn exact_out_zero_amount_reverse_direction_returns_zero() {
        let s = fixture_usdc_weth_03();
        let p = ExactOutParams {
            token_in: s.token1,
            token_out: s.token0,
            amount_out: U256::ZERO,
            recipient: address!("0x0000000000000000000000000000000000000099"),
        };
        let q = exact_out(&s, &p).expect("reverse-direction zero-output should not error");
        assert_eq!(q.amount_in, U256::ZERO);
        assert_eq!(q.amount_out, U256::ZERO);
        assert_eq!(q.sqrt_price_x96_after, s.sqrt_price_x96);
    }
}