feat(@embark/plugins): introduce API to register a contract factory

This commit introduces two new plugin APIs `registerTestContractFactory()` and
`registerCustomContractGenerator()`, which can be used to register a factory function
for the creation of web3 contract instances within tests, and custom code generation
  for `embark console` respectively.

Example:

```
// some.plugin.js

module.exports = function (embark) {
  embark.registerTestContractFactory(function (contractRecipe, web3) {
    // do something with web3 and contractRecipe and return contract instance here
  });
};
```

**Notice that**:

- This factory function is used for contract instance creation within tests.
  A `contractRecipe` and a `web3` instance is accessible within the factory.

Example:

```
// some.plugin.js

module.exports = function (embark) {
  embark.registerCustomContractGenerator(function (contractRecipe) {
    // returns code string that will be eval'ed
  });
};
```

**Notice that**:

- Once registered, this generator will be used for **all** contract instances
  that will be created for `embark console`, including built-in once like
  ENSRegistry.

- While this does affect contract creation in client-side code, it doesn't
  actually affect the instances created for deployment hooks **if** deployment
  hooks are written as functions.

Closes #1066

Always use custom generator and fallback to vanilla

src/lib/core/plugin.js

@@ -13,6 +13,8 @@ var Plugin = function(options) {
   this.clientWeb3Providers = [];
   this.beforeDeploy = [];
   this.contractsGenerators = [];
+  this.generateCustomContractCode = null;
+  this.testContractFactory = null;
   this.pipeline = [];
   this.pipelineFiles = [];
   this.console = [];
@@ -120,6 +122,16 @@ Plugin.prototype.registerContractsGeneration = function(cb) {
   this.addPluginType('contractGeneration');
 };
 
+Plugin.prototype.registerCustomContractGenerator = function (cb) {
+  this.generateCustomContractCode = cb;
+  this.addPluginType('customContractGeneration');
+};
+
+Plugin.prototype.registerTestContractFactory = function(cb) {
+  this.testContractFactory = cb;
+  this.addPluginType('testContractFactory');
+};
+
 Plugin.prototype.registerPipeline = function(matcthingFiles, cb) {
   // TODO: generate error for more than one pipeline per plugin
   this.pipeline.push({matcthingFiles: matcthingFiles, cb: cb});

src/lib/modules/code_generator/index.js

@@ -69,6 +69,18 @@ class CodeGenerator {
       cb(self.generateContractCode(contract, gasLimit));
     });
 
+    self.events.setCommandHandler('code-generator:contract:custom', (contract, cb) => {
+      const customCode = self.generateCustomContractCode(contract);
+      if (!customCode) {
+        // Fallback to generate code from vanilla contract generator.
+        //
+        // TODO: can be moved into a afterDeploy event
+        // just need to figure out the gasLimit coupling issue
+        return cb(self.generateContractCode(contract, contract._gasLimit || false));
+      }
+      cb(customCode);
+    });
+
     self.events.setCommandHandler('code-generator:embarkjs:provider-code', (cb) => {
       cb(self.getEmbarkJsProviderCode());
     });
@@ -171,6 +183,14 @@ class CodeGenerator {
     return block;
   }
 
+  generateCustomContractCode(contract) {
+    const customContractGeneratorPlugin = this.plugins.getPluginsFor('customContractGeneration').splice(-1)[0];
+    if (!customContractGeneratorPlugin) {
+      return null;
+    }
+    return customContractGeneratorPlugin.generateCustomContractCode(contract);
+  }
+
   generateNamesInitialization(useEmbarkJS) {
     if (!useEmbarkJS || this.namesystemConfig === {}) return "";
 

src/lib/modules/deployment/contract_deployer.js

@@ -193,9 +193,7 @@ class ContractDeployer {
     contract.deployedAddress = trackedContract.address;
     self.events.emit("deploy:contract:deployed", contract);
 
-    // TODO: can be moved into a afterDeploy event
-    // just need to figure out the gasLimit coupling issue
-    self.events.request('code-generator:contract:vanilla', contract, contract._gasLimit || false, (contractCode) => {
+    self.events.request('code-generator:contract:custom', contract, (contractCode) => {
       self.events.request('runcode:eval', contractCode, () => {}, true);
       return callback();
     });
@@ -306,9 +304,8 @@ class ContractDeployer {
           self.events.emit("deploy:contract:receipt", receipt);
           self.events.emit("deploy:contract:deployed", contract);
 
-          // TODO: can be moved into a afterDeploy event
-          // just need to figure out the gasLimit coupling issue
-          self.events.request('code-generator:contract:vanilla', contract, contract._gasLimit || false, (contractCode) => {
+
+          self.events.request('code-generator:contract:custom', contract, (contractCode) => {
             self.events.request('runcode:eval', contractCode, () => {}, true);
             self.plugins.runActionsForEvent('deploy:contract:deployed', {contract: contract}, () => {
               return next(null, receipt);

src/lib/modules/tests/test.js

@@ -11,6 +11,7 @@ class Test {
     this.options = options || {};
     this.simOptions = {};
     this.events = options.events;
+    this.plugins = options.config.plugins;
     this.logger = options.logger;
     this.ipc = options.ipc;
     this.configObj = options.config;
@@ -268,7 +269,9 @@ class Test {
               self.contracts[contract.className] = {};
             }
 
-            const newContract = Test.getWeb3Contract(contract, web3);
+            const testContractFactoryPlugin = self.plugins.getPluginsFor('testContractFactory').slice(-1)[0];
+
+            const newContract = testContractFactoryPlugin ? testContractFactoryPlugin.testContractFactory(contract, web3) : Test.getWeb3Contract(contract, web3);
             Object.setPrototypeOf(self.contracts[contract.className], newContract);
 
             eachCb();