3 files changed, 79 insertions, 15 deletions

diff --git a/src/0x.ts b/src/0x.ts
index 0af164b1e..ff3220757 100644
--- a/src/0x.ts
+++ b/src/0x.ts
@@ -12,6 +12,7 @@ import {constants} from './utils/constants';
 import {utils} from './utils/utils';
 import {signatureUtils} from './utils/signature_utils';
 import {assert} from './utils/assert';
+import {AbiDecoder} from './utils/abi_decoder';
 import {artifacts} from './artifacts';
 import {ExchangeWrapper} from './contract_wrappers/exchange_wrapper';
 import {TokenRegistryWrapper} from './contract_wrappers/token_registry_wrapper';
@@ -70,6 +71,7 @@ export class ZeroEx {
      */
     public proxy: TokenTransferProxyWrapper;
     private _web3Wrapper: Web3Wrapper;
+    private _abiDecoder: AbiDecoder;
     /**
      * Verifies that the elliptic curve signature `signature` was generated
      * by signing `data` with the private key corresponding to the `signerAddress` address.
@@ -183,7 +185,9 @@ export class ZeroEx {
             // We re-assign the send method so that Web3@1.0 providers work with 0x.js
             (provider as any).sendAsync = (provider as any).send;
         }
-        this._registerArtifactsWithinABIDecoder();
+        const artifactJSONs = _.values(artifacts);
+        const abiArrays = _.map(artifactJSONs, artifact => artifact.abi);
+        this._abiDecoder = new AbiDecoder(abiArrays);
         const gasPrice = _.isUndefined(config) ? undefined : config.gasPrice;
         const defaults = {
             gasPrice,
@@ -281,16 +285,13 @@ export class ZeroEx {
                 if (!_.isNull(transactionReceipt)) {
                     clearInterval(intervalId);
                     const logsWithDecodedArgs = _.map(transactionReceipt.logs, (log: Web3.LogEntry) => {
-                        const decodedLog = abiDecoder.decodeLogs([log])[0];
-                        const decodedArgs = decodedLog.events;
-                        const args: DecodedLogArgs = {};
-                        _.forEach(decodedArgs, arg => {
-                            args[arg.name] = arg.value;
-                        });
+                        const decodedLog = this._abiDecoder.decodeLog(log);
+                        if (_.isUndefined(decodedLog)) {
+                            throw new Error('Unknown log');
+                        }
                         const logWithDecodedArgs: LogWithDecodedArgs = {
                             ...log,
-                            args,
-                            event: decodedLog.name,
+                            ...decodedLog,
                         };
                         return logWithDecodedArgs;
                     });
@@ -304,9 +305,4 @@ export class ZeroEx {
         });
         return txReceiptPromise;
     }
-    private _registerArtifactsWithinABIDecoder(): void {
-        for (const artifact of _.values(artifacts)) {
-            abiDecoder.addABI(artifact.abi);
-        }
-    }
 }
diff --git a/src/types.ts b/src/types.ts
index 9d3f77127..4f9c6714d 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -402,11 +402,13 @@ export interface DecodedLogArgs {
     [argName: string]: ContractEventArg;
 }
 
-export interface LogWithDecodedArgs extends Web3.LogEntry {
+export interface DecodedArgs {
     args: DecodedLogArgs;
     event: string;
 }
 
+export interface LogWithDecodedArgs extends Web3.LogEntry, DecodedArgs {}
+
 export interface TransactionReceiptWithDecodedLogs extends Web3.TransactionReceipt {
     logs: LogWithDecodedArgs[];
 }
diff --git a/src/utils/abi_decoder.ts b/src/utils/abi_decoder.ts
new file mode 100644
index 000000000..0600f86f2
--- /dev/null
+++ b/src/utils/abi_decoder.ts
@@ -0,0 +1,66 @@
+import * as Web3 from 'web3';
+import * as _ from 'lodash';
+import {AbiType, DecodedLogArgs, DecodedArgs} from '../types';
+import * as SolidityCoder from 'web3/lib/solidity/coder.js';
+
+export class AbiDecoder {
+    private savedABIs: Web3.AbiDefinition[] = [];
+    private methodIDs: {[signatureHash: string]: Web3.EventAbi} = {};
+    constructor(abiArrays: Web3.AbiDefinition[][]) {
+        _.map(abiArrays, this.addABI.bind(this));
+    }
+    public decodeLog(logItem: Web3.LogEntry): DecodedArgs|undefined {
+        const methodID = logItem.topics[0];
+        const event = this.methodIDs[methodID];
+        if (!_.isUndefined(event)) {
+            const logData = logItem.data;
+            const decodedParams: DecodedLogArgs = {};
+            let dataIndex = 0;
+            let topicsIndex = 1;
+
+            const nonIndexedInputs = _.filter(event.inputs, input => !input.indexed);
+            const dataTypes = _.map(nonIndexedInputs, input => input.type);
+            const decodedData = SolidityCoder.decodeParams(dataTypes, logData.slice(2));
+            _.map(event.inputs, (param: Web3.EventParameter) => {
+                let value;
+                if (param.indexed) {
+                    value = logItem.topics[topicsIndex];
+                    topicsIndex++;
+                } else {
+                    value = decodedData[dataIndex];
+                    dataIndex++;
+                }
+                if (param.type === 'address') {
+                    value = this.padZeros(new Web3().toBigNumber(value).toString(16));
+                } else if (param.type === 'uint256' || param.type === 'uint8' || param.type === 'int' ) {
+                    value = new Web3().toBigNumber(value).toString(10);
+                }
+                decodedParams[param.name] = value;
+            });
+
+            return {
+                event: event.name,
+                args: decodedParams,
+            };
+        }
+    }
+    private addABI(abiArray: Web3.AbiDefinition[]): void {
+        _.map(abiArray, (abi: Web3.AbiDefinition) => {
+            if (abi.type === AbiType.Event) {
+                const signature = `${abi.name}(${_.map(abi.inputs, input => input.type).join(',')})`;
+                const signatureHash = new Web3().sha3(signature);
+                this.methodIDs[signatureHash] = abi;
+            }
+        });
+        this.savedABIs = this.savedABIs.concat(abiArray);
+    }
+    private padZeros(address: string) {
+      let formatted = address;
+      if (formatted.indexOf('0x') !== -1) {
+        formatted = formatted.slice(2);
+      }
+
+      formatted = _.padStart(formatted, 40, '0');
+      return '0x' + formatted;
+    }
+}