Deterministic
order matching.

use ferromatch_core::{Order, OrderBook, OrderType,
                       Side, TimeInForce};

let mut book = OrderBook::new(/* symbol_id */ 1);

// Resting bid at $100.50 for 200 shares
let order = Order::new(
    /* id */ 42,
    /* price */ 100_500_000,  // $100.50
    /* quantity */ 200,
    Side::Buy,
    OrderType::Limit,
    TimeInForce::GoodTilCancel,
    /* timestamp */ ts_ns,
);

let result = book.submit(order)?;
// result.fills    — empty (resting)
// result.status   — OrderStatus::Resting

use ferromatch_core::{OrderBook, MatchError};

// Order 42 is somewhere in the book — we don't track
// its price or side, just the ID we got back at submit
let cancelled = book.cancel(42)?;
// cancelled.remaining_quantity — unfilled portion

// Idempotent retry pattern:
match book.cancel(9999) {
    Err(MatchError::OrderNotFound) => {},  // gone
    Ok(order) => audit(order),
    Err(e) => return Err(e),
}

use ferromatch_journal::{EventJournal,
                          JournalConsumer,
                          EVENT_ORDER_STATUS, EVENT_TRADE};

// Open the journal that survived the crash
let journal = EventJournal::open(
    "ferromatch.journal",
    1 << 20,
)?;

let mut consumer = JournalConsumer::new(&journal);
while let Some(entry) = consumer.read_next() {
    match entry.event_kind {
        EVENT_ORDER_STATUS => replay_submit(&entry),
        EVENT_TRADE        => replay_fill(&entry),
        _ => {}
    }
}
// book is now consistent with the on-disk record