Emrin Yaşam Döngüsü — İptal Ettim Sandım, Borsa Neden Doldurdu?

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package com.bank.oms.order;
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import java.util.EnumSet;
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import java.util.Set;
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public enum OrderStatus {
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    PENDING_NEW, NEW, PARTIALLY_FILLED, PENDING_CANCEL, FILLED, CANCELED, REJECTED;
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    public boolean isTerminal() {
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        return this == FILLED || this == CANCELED || this == REJECTED;
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    }
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    /** States a report may move this one to. A terminal state never moves again. */
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    public Set<OrderStatus> next() {
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        return switch (this) {
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            case PENDING_NEW -> EnumSet.of(NEW, REJECTED);
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            case NEW, PARTIALLY_FILLED -> EnumSet.of(PARTIALLY_FILLED, FILLED, PENDING_CANCEL, CANCELED);
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            case PENDING_CANCEL -> EnumSet.of(PENDING_CANCEL, PARTIALLY_FILLED, FILLED, CANCELED);
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            case FILLED, CANCELED, REJECTED -> EnumSet.noneOf(OrderStatus.class);
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        };
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    }
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}

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package com.bank.oms.order;
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public record ExecutionReport(String execId, String orderId, Type type, long lastQty, long lastPriceKurus) {
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    public enum Type { ACK, FILL, CANCELED, CANCEL_REJECT, REJECTED }
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}

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package com.bank.oms.order;
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import java.util.HashSet;
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import java.util.Set;
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public final class Order {
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    private final String id;
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    private final long quantity;
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    private long filled;
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    private OrderStatus status = OrderStatus.PENDING_NEW;
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    private final Set<String> seenExecIds = new HashSet<>();
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    public Order(String id, long quantity) {
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        this.id = id;
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        this.quantity = quantity;
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    }
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    /** Sending a cancel only asks. The exchange decides. */
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    public void cancelRequested() {
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        moveTo(OrderStatus.PENDING_CANCEL);
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    }
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    public void on(ExecutionReport report) {
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        if (!seenExecIds.add(report.execId())) {
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            return; // a resent report: already counted
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        }
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        switch (report.type()) {
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            case ACK -> moveTo(OrderStatus.NEW);
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            case FILL -> {
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                filled += report.lastQty();
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                if (filled == quantity) {
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                    moveTo(OrderStatus.FILLED);
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                } else if (status != OrderStatus.PENDING_CANCEL) {
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                    moveTo(OrderStatus.PARTIALLY_FILLED);
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                }
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            }
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            case CANCELED -> moveTo(OrderStatus.CANCELED);
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            case CANCEL_REJECT -> {
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                // Too late: the fills decide what the order is now.
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                if (status == OrderStatus.PENDING_CANCEL) {
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                    status = filled == 0 ? OrderStatus.NEW : OrderStatus.PARTIALLY_FILLED;
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                }
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            }
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            case REJECTED -> moveTo(OrderStatus.REJECTED);
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        }
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    }
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    private void moveTo(OrderStatus target) {
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        if (!status.next().contains(target)) {
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            throw new IllegalStateException(id + ": " + status + " cannot become " + target);
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        }
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        status = target;
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    }
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    public OrderStatus status() {
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        return status;
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    }
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    public long filled() {
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        return filled;
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    }
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}