1 files changed, 78 insertions, 0 deletions
diff --git a/src/order_watcher/event_watcher.ts b/src/order_watcher/event_watcher.ts
new file mode 100644
index 000000000..205885f96
--- /dev/null
+++ b/src/order_watcher/event_watcher.ts
@@ -0,0 +1,78 @@
+import * as Web3 from 'web3';
+import * as _ from 'lodash';
+import {Web3Wrapper} from '../web3_wrapper';
+import {BlockParamLiteral, EventCallback, MempoolEventCallback} from '../types';
+import {AbiDecoder} from '../utils/abi_decoder';
+import {intervalUtils} from '../utils/interval_utils';
+
+const DEFAULT_EVENT_POLLING_INTERVAL = 200;
+
+export class EventWatcher {
+    private _web3Wrapper: Web3Wrapper;
+    private _pollingIntervalMs: number;
+    private _intervalId: NodeJS.Timer;
+    private _lastEvents: Web3.LogEntry[] = [];
+    private _callbackAsync?: MempoolEventCallback;
+    constructor(web3Wrapper: Web3Wrapper, pollingIntervalMs: undefined|number) {
+        this._web3Wrapper = web3Wrapper;
+        this._pollingIntervalMs = _.isUndefined(pollingIntervalMs) ?
+                                  DEFAULT_EVENT_POLLING_INTERVAL :
+                                  pollingIntervalMs;
+    }
+    public subscribe(callback: MempoolEventCallback, numConfirmations: number): void {
+        this._callbackAsync = callback;
+        this._intervalId = intervalUtils.setAsyncExcludingInterval(
+            this._pollForMempoolEventsAsync.bind(this, numConfirmations), this._pollingIntervalMs,
+        );
+    }
+    public unsubscribe(): void {
+        delete this._callbackAsync;
+        this._lastEvents = [];
+        intervalUtils.clearAsyncExcludingInterval(this._intervalId);
+    }
+    private async _pollForMempoolEventsAsync(numConfirmations: number): Promise<void> {
+        const pendingEvents = await this._getMempoolEventsAsync(numConfirmations);
+        if (pendingEvents.length === 0) {
+            // HACK: Sometimes when node rebuilds the pending block we get back the empty result.
+            // We don't want to emit a lot of removal events and bring them back after a couple of miliseconds,
+            // that's why we just ignore those cases.
+            return;
+        }
+        const removedEvents = _.differenceBy(this._lastEvents, pendingEvents, JSON.stringify);
+        const newEvents = _.differenceBy(pendingEvents, this._lastEvents, JSON.stringify);
+        let isRemoved = true;
+        await this._emitDifferencesAsync(removedEvents, isRemoved);
+        isRemoved = false;
+        await this._emitDifferencesAsync(newEvents, isRemoved);
+        this._lastEvents = pendingEvents;
+    }
+    private async _getMempoolEventsAsync(numConfirmations: number): Promise<Web3.LogEntry[]> {
+        let fromBlock: BlockParamLiteral|number;
+        let toBlock: BlockParamLiteral|number;
+        if (numConfirmations === 0) {
+            fromBlock = BlockParamLiteral.Pending;
+            toBlock = BlockParamLiteral.Pending;
+        } else {
+            toBlock = await this._web3Wrapper.getBlockNumberAsync();
+            fromBlock = toBlock - numConfirmations;
+        }
+        const mempoolFilter = {
+            fromBlock,
+            toBlock,
+        };
+        const pendingEvents = await this._web3Wrapper.getLogsAsync(mempoolFilter);
+        return pendingEvents;
+    }
+    // TODO: Let's emit out own LogEntry type that has property isRemoved rather then removed
+    private async _emitDifferencesAsync(logs: Web3.LogEntry[], isRemoved: boolean): Promise<void> {
+        for (const log of logs) {
+            const logEvent = {
+                removed: isRemoved,
+                ...log,
+            };
+            if (!_.isUndefined(this._callbackAsync)) {
+                await this._callbackAsync(logEvent);
+            }
+        }
+    }
+}