feat(pipeline): Add advanced extensibility support

Adds the ability to extend the pipeline through `before` and
`after` extension points in `pre.js`

src/defaults/html.pipe.js

@@ -61,6 +61,10 @@ const htmlpipe = (cont, payload, action) => {
     .when(esi) // flag ESI when there is ESI in the response
     .error(selectStatus(production()));
 
+
+  // pipe.attach.before(foo, 'fetch');
+  // pipe.attach.after(bar, 'flag');
+
   action.logger.log('debug', 'Running HTML pipeline');
   return pipe.run(payload);
 };

src/pipeline.js

@@ -94,6 +94,37 @@ class Pipeline {
     this._posts = [];
     // functions that are executed before each step
     this._taps = [];
+
+    this.attach = function attach(ext) {
+      if (this.sealed) {
+        return;
+      }
+      if (ext && ext.before && typeof ext.before === 'object') {
+        Object.keys(ext.before).map(key => this.before(ext.before[key], key));
+      }
+      if (ext && ext.after && typeof ext.after === 'object') {
+        Object.keys(ext.after).map(key => this.after(ext.after[key], key));
+      }
+      this.sealed = true;
+    };
+
+    this.attach.generic = (f, name, offset = 0) => {
+      const re = new RegExp(`^.*\\:${name} from `);
+      const foundpres = this._pres
+        .filter(pre => pre.alias)
+        .findIndex(pre => re.test(pre.alias));
+      const foundposts = this._posts
+        .filter(post => post.alias)
+        .findIndex(post => re.test(post.alias));
+      if (foundpres !== -1) {
+        this._pres.splice(foundpres + offset, 0, f);
+      } else if (foundposts !== -1) {
+        this._posts.splice(foundpres + offset, 0, f);
+      }
+    };
+    this.attach.before = (f, name) => this.attach.generic(f, name, 0);
+
+    this.attach.after = (f, name) => this.attach.generic(f, name, 1);
   }
 
   /**
@@ -159,6 +190,7 @@ class Pipeline {
         }
         return args[0];
       };
+      wrappedfunc.alias = lastfunc.alias;
       this._last.push(wrappedfunc);
     } else {
       throw new Error('when() needs function to operate on.');
@@ -215,14 +247,8 @@ class Pipeline {
    * - the name and code location of the function that called the function before
    * @param {Function} f
    */
+  // eslint-disable-next-line class-methods-use-this
   describe(f) {
-    if (!this._action
-        || !this._action.logger
-        || !this._action.logger.level
-        || this._action.logger.level !== 'silly') {
-      // skip capturing the stack trace when it is mever read
-      return 'anonymous';
-    }
     if (f.alias) {
       return f.alias;
     }
@@ -250,6 +276,8 @@ class Pipeline {
    * context.
    */
   async run(context = {}) {
+    // register all custom attachers to the pipeline
+    this.attach(this._oncef);
     /**
      * Reduction function used to process the pipeline functions and merge the context parameters.
      * @param {Object} currContext Accumulated context

test/testHTML.js

@@ -156,9 +156,33 @@ describe('Testing HTML Pipeline', () => {
     assert.equal(result.response.body, '<p>Hello World</p>');
   });
 
-  it('html.pipe detects ESI in response body', async () => {
-    const result = await pipe(
-      ({ content }) => ({ response: { body: `${content.document.body.innerHTML}<esi:include src="foo.html">` } }),
+  it('html.pipe can be extended', async () => {
+    const myfunc = ({ content }) => ({ response: { body: `${content.document.body.innerHTML}<esi:include src="foo.html">` } });
+
+    let calledfoo = false;
+    let calledbar = false;
+    function foo() {
+      assert.equal(calledfoo, false, 'foo has not yet been called');
+      assert.equal(calledbar, false, 'bar has not yet been called');
+      calledfoo = true;
+    }
+
+    function bar() {
+      assert.equal(calledfoo, true, 'foo has been called');
+      assert.equal(calledbar, false, 'bar has not yet been called');
+      calledbar = true;
+    }
+
+    myfunc.before = {
+      fetch: foo,
+    };
+
+    myfunc.after = {
+      flag: bar,
+    };
+
+    await pipe(
+      myfunc,
       {
         content: {
           body: 'Hello World',
@@ -171,9 +195,8 @@ describe('Testing HTML Pipeline', () => {
       },
     );
 
-    assert.equal(result.response.headers['X-ESI'], 'enabled');
-    assert.equal(result.response.headers['Content-Type'], 'text/html');
-    assert.equal(result.response.body, '<p>Hello World</p><esi:include src="foo.html">');
+    assert.equal(calledfoo, true, 'foo has been called');
+    assert.equal(calledbar, true, 'bar has been called');
   });
 
   it('html.pipe renders index.md from helix-cli correctly', async () => {