rustrade-execution 0.1.0

use derive_more::{Display, From};
use rand::prelude::IndexedRandom;
use serde::{Deserialize, Serialize};
use smol_str::SmolStr;

#[derive(
    Debug, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Deserialize, Serialize, Display, From,
)]
pub struct ClientOrderId<T = SmolStr>(pub T);

impl ClientOrderId<SmolStr> {
    /// Construct a `ClientOrderId` from the specified string.
    ///
    /// Use [`Self::random`] to generate a random stack-allocated `ClientOrderId`.
    pub fn new<S: Into<SmolStr>>(id: S) -> Self {
        Self(id.into())
    }

    /// Construct a stack-allocated `ClientOrderId` backed by a 23 byte [`SmolStr`].
    pub fn random() -> Self {
        const LEN_URL_SAFE_SYMBOLS: usize = 64;
        const URL_SAFE_SYMBOLS: [char; LEN_URL_SAFE_SYMBOLS] = [
            '_', '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e',
            'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
            'w', 'x', 'y', 'z', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
            'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
        ];
        // SmolStr can be up to 23 bytes long without allocating
        const LEN_NON_ALLOCATING_CID: usize = 23;

        let mut thread_rng = rand::rng();

        #[allow(clippy::expect_used)] // Invariant: URL_SAFE_SYMBOLS is a const 64-element array
        let random_utf8: [u8; LEN_NON_ALLOCATING_CID] = std::array::from_fn(|_| {
            let symbol = URL_SAFE_SYMBOLS
                .choose(&mut thread_rng)
                .expect("URL_SAFE_SYMBOLS slice is not empty");

            *symbol as u8
        });

        #[allow(clippy::expect_used)] // Invariant: all URL_SAFE_SYMBOLS chars are ASCII
        let random_utf8_str =
            std::str::from_utf8(&random_utf8).expect("URL_SAFE_SYMBOLS are valid utf8");

        Self(SmolStr::new_inline(random_utf8_str))
    }
}

impl Default for ClientOrderId<SmolStr> {
    fn default() -> Self {
        Self::random()
    }
}

#[derive(
    Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Deserialize, Serialize, Display, From,
)]
pub struct OrderId<T = SmolStr>(pub T);

impl OrderId {
    pub fn new<S: AsRef<str>>(id: S) -> Self {
        Self(SmolStr::new(id))
    }
}

#[derive(
    Debug, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Deserialize, Serialize, Display, From,
)]
pub struct StrategyId(pub SmolStr);

impl StrategyId {
    pub fn new<S: AsRef<str>>(id: S) -> Self {
        Self(SmolStr::new(id))
    }

    pub fn unknown() -> Self {
        // "unknown" is 7 bytes — always inline; new_inline avoids the heap-allocation
        // branch in SmolStr::new and is safe because the literal fits.
        Self(SmolStr::new_inline("unknown"))
    }

    /// The fixed `StrategyId` used for synthetic settlement trades generated by the engine
    /// on `ContractExpiry`. Using a `pub const` prevents bypassing any future validation.
    ///
    /// Note: conceptually this constant belongs to `rustrade::engine` (it is used exclusively
    /// by the engine's contract lifecycle logic). It lives here because `StrategyId` is
    /// defined in `rustrade-execution`; moving it to `rustrade::engine` would add a `smol_str`
    /// import to that crate for a single constant.
    pub const ENGINE_EXPIRY: StrategyId = StrategyId(SmolStr::new_static("__engine_expiry__"));
}

/// Opaque identifier for a tracked position.
///
/// In `OmsMode::Netting` this is always `"netting"` (at most one position per instrument).
/// In `OmsMode::Hedging` this is derived from the `ClientOrderId` of the opening order,
/// specified via [`crate::order::request::RequestOpen::position_id`] at order submission.
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Deserialize, Serialize)]
pub struct PositionId(pub SmolStr);

impl PositionId {
    pub fn new(id: impl Into<SmolStr>) -> Self {
        Self(id.into())
    }

    /// The fixed `PositionId` used for all netting-mode positions.
    pub const NETTING: PositionId = PositionId(SmolStr::new_static("netting"));
}

impl Default for PositionId {
    fn default() -> Self {
        Self::NETTING
    }
}

impl std::fmt::Display for PositionId {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        self.0.fmt(f)
    }
}