Decode contract events (#2763)

* Decode contract events

* Untable marker

packages/api-contract/src/Abi.ts

@@ -1,9 +1,9 @@
 // Copyright 2017-2020 @polkadot/api-contract authors & contributors
 // SPDX-License-Identifier: Apache-2.0
 
-import { AnyJson } from '@polkadot/types/types';
-import { ChainProperties, ContractConstructorSpec, ContractMessageSpec, ContractProject } from '@polkadot/types/interfaces';
-import { AbiConstructor, AbiMessage, AbiMessageParam } from './types';
+import { AnyJson, Codec } from '@polkadot/types/types';
+import { ChainProperties, ContractConstructorSpec, ContractEventSpec, ContractMessageSpec, ContractMessageParamSpec, ContractProject } from '@polkadot/types/interfaces';
+import { AbiConstructor, AbiEvent, AbiMessage, AbiParam, DecodedEvent } from './types';
 
 import { assert, isNumber, isObject, isString, stringCamelCase } from '@polkadot/util';
 
@@ -22,6 +22,8 @@ function findMessage <T extends AbiMessage> (list: T[], messageOrId: T | string
 }
 
 export default class Abi {
+  readonly #events: AbiEvent[];
+
   public readonly constructors: AbiConstructor[];
 
   public readonly json: AnyJson;
@@ -47,14 +49,17 @@ export default class Abi {
 
     this.project.types.forEach((_, index) => this.registry.getMetaTypeDef(this.registry.createType('SiLookupTypeId', index + 1)));
     this.constructors = this.project.spec.constructors.map((spec: ContractConstructorSpec, index) =>
-      this.#createBase(spec, index, {
+      this.#createMessage(spec, index, {
         isConstructor: true
       })
     );
+    this.#events = this.project.spec.events.map((spec: ContractEventSpec, index) =>
+      this.#createEvent(spec, index)
+    );
     this.messages = this.project.spec.messages.map((spec: ContractMessageSpec, index): AbiMessage => {
       const typeSpec = spec.returnType.unwrapOr(null);
 
-      return this.#createBase(spec, index, {
+      return this.#createMessage(spec, index, {
         isMutating: spec.mutates.isTrue,
         isPayable: spec.payable.isTrue,
         returnType: typeSpec
@@ -64,6 +69,29 @@ export default class Abi {
     });
   }
 
+  /**
+   * Warning: Unstable API, bound to change
+   */
+  public decodeEvent (eventU8a: Uint8Array): DecodedEvent {
+    const index = eventU8a[0];
+    const event = this.#events[index];
+
+    assert(event, `Unable to find event with index ${index}`);
+
+    let offset = 1;
+
+    return {
+      args: event.args.map(({ type }): Codec => {
+        const value = this.registry.createType(type.type as 'Text', eventU8a.subarray(offset));
+
+        offset += value.encodedLength;
+
+        return value;
+      }),
+      event
+    };
+  }
+
   public findConstructor (constructorOrId: AbiConstructor | string | number): AbiConstructor {
     return findMessage(this.constructors, constructorOrId);
   }
@@ -72,9 +100,8 @@ export default class Abi {
     return findMessage(this.messages, messageOrId);
   }
 
-  #createBase = (spec: ContractMessageSpec | ContractConstructorSpec, index: number, add: Partial<AbiMessage> = {}): AbiMessage => {
-    const identifier = spec.name.toString();
-    const args = spec.args.map((arg, index): AbiMessageParam => {
+  #createArgs = (args: ContractMessageParamSpec[], spec: unknown): AbiParam[] => {
+    return args.map((arg, index): AbiParam => {
       try {
         assert(isObject(arg.type), 'Invalid type definition found');
 
@@ -88,12 +115,23 @@ export default class Abi {
         throw error;
       }
     });
+  }
 
+  #createEvent = (spec: ContractEventSpec, index: number): AbiEvent => {
+    return {
+      args: this.#createArgs(spec.args, spec),
+      docs: spec.docs.map((doc) => doc.toString()),
+      identifier: spec.name.toString(),
+      index
+    };
+  }
+
+  #createMessage = (spec: ContractMessageSpec | ContractConstructorSpec, index: number, add: Partial<AbiMessage> = {}): AbiMessage => {
     return {
       ...add,
-      args,
+      args: this.#createArgs(spec.args, spec),
       docs: spec.docs.map((doc) => doc.toString()),
-      identifier,
+      identifier: spec.name.toString(),
       index,
       selector: spec.selector
     };

packages/api-contract/src/types.ts

@@ -16,13 +16,25 @@ export interface ContractBase<ApiType extends ApiTypes> {
   messages: AbiMessage[];
 }
 
-export interface AbiMessageParam {
+export interface AbiParam {
   name: string;
   type: TypeDef;
 }
 
+export interface AbiEvent {
+  args: AbiParam[];
+  docs: string[];
+  identifier: string;
+  index: number;
+}
+
+export interface DecodedEvent {
+  args: Codec[];
+  event: AbiEvent;
+}
+
 export interface AbiMessage {
-  args: AbiMessageParam[];
+  args: AbiParam[];
   docs: string[];
   identifier: string;
   index: number;