From f5309a3219fdad197a763451b961fa9f23637c6d Mon Sep 17 00:00:00 2001
From: Michael Kelly <mkelly@mozilla.com>
Date: Mon, 8 Oct 2018 11:02:20 -0700
Subject: [PATCH] Split extraction methods and ensure they return null when no
 match is found.

Open Graph and selector-based extraction are now separate forms of extraction
instead of a single, "fallback" extraction method.
---
 src/extraction/index.js                       | 36 +++++++++++++++----
 src/extraction/open_graph.js                  | 33 +++++++++++++++++
 .../{fallback => selector}/index.js           | 30 +++++++---------
 .../{fallback => selector}/selectors.js       |  0
 4 files changed, 75 insertions(+), 24 deletions(-)
 create mode 100644 src/extraction/open_graph.js
 rename src/extraction/{fallback => selector}/index.js (72%)
 rename src/extraction/{fallback => selector}/selectors.js (100%)

diff --git a/src/extraction/index.js b/src/extraction/index.js
index 1391a9a..046f383 100644
--- a/src/extraction/index.js
+++ b/src/extraction/index.js
@@ -10,18 +10,42 @@
 
 import config from 'commerce/config/content';
 import extractProductWithFathom from 'commerce/extraction/fathom';
-import extractProductWithFallback from 'commerce/extraction/fallback';
+import extractProductWithFallback from 'commerce/extraction/selector';
+import extractProductWithOpenGraph from 'commerce/extraction/open_graph';
+
+/**
+ * Extraction methods are given the document object for the page, and must
+ * return either a valid ExtractedProduct, or null if a valid product could not
+ * be found.
+ */
+const EXTRACTION_METHODS = [
+  extractProductWithFathom,
+  extractProductWithFallback,
+  extractProductWithOpenGraph,
+];
+
+/**
+ * Perform product extraction, trying each method from EXTRACTION_METHODS in
+ * order until one of them returns a truthy result.
+ * @return {ExtractedProduct|null}
+ */
+function extractProduct() {
+  for (const extract of EXTRACTION_METHODS) {
+    const extractedProduct = extract(window.document);
+    if (extractedProduct) {
+      return extractedProduct;
+    }
+  }
+
+  return null;
+}
 
 /**
  * Checks to see if any product information for the page was found,
  * and if so, sends it to the background script.
  */
 async function attemptExtraction() {
-  const extractedProduct = (
-    extractProductWithFathom(window.document)
-    || extractProductWithFallback()
-  );
-
+  const extractedProduct = extractProduct();
   if (extractedProduct) {
     await browser.runtime.sendMessage({
       from: 'content',
diff --git a/src/extraction/open_graph.js b/src/extraction/open_graph.js
new file mode 100644
index 0000000..144f7fc
--- /dev/null
+++ b/src/extraction/open_graph.js
@@ -0,0 +1,33 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * Product extraction via Open Graph tags.
+ */
+
+const OPEN_GRAPH_PROPERTY_VALUES = {
+  title: 'og:title',
+  image: 'og:image',
+  price: 'og:price:amount',
+};
+
+/**
+ * Returns any product information available on the page from Open Graph <meta>
+ * tags.
+ */
+export default function extractProduct() {
+  const extractedProduct = {};
+  for (const [feature, propertyValue] of Object.entries(OPEN_GRAPH_PROPERTY_VALUES)) {
+    const metaEle = document.querySelector(`meta[property='${propertyValue}']`);
+
+    // Fail early if any required tags aren't found.
+    if (!metaEle) {
+      return null;
+    }
+
+    extractedProduct[feature] = metaEle.getAttribute('content');
+  }
+
+  return extractedProduct;
+}
diff --git a/src/extraction/fallback/index.js b/src/extraction/selector/index.js
similarity index 72%
rename from src/extraction/fallback/index.js
rename to src/extraction/selector/index.js
index 6dee32d..ccd87bb 100644
--- a/src/extraction/fallback/index.js
+++ b/src/extraction/selector/index.js
@@ -10,14 +10,7 @@
 * Features: title, image, price
 */
 
-import extractionData from 'commerce/extraction/fallback/selectors';
-
-
-const OPEN_GRAPH_PROPERTY_VALUES = {
-  title: 'og:title',
-  image: 'og:image',
-  price: 'og:price:amount',
-};
+import extractionData from 'commerce/extraction/selector/selectors';
 
 /**
  * Returns any extraction data found for the vendor based on the URL
@@ -54,22 +47,23 @@ function findValue(extractors) {
 
 /**
  * Returns any product information available on the page from CSS
- * selectors if they exist, otherwise from Open Graph <meta> tags.
+ * selectors if they exist.
  */
 export default function extractProduct() {
-  const extractedProduct = {};
   const featureInfo = getFeatureInfo();
   if (featureInfo) {
+    const extractedProduct = {};
     for (const [feature, extractors] of Object.entries(featureInfo)) {
-      extractedProduct[feature] = findValue(extractors);
-    }
-  } else {
-    for (const [feature, propertyValue] of Object.entries(OPEN_GRAPH_PROPERTY_VALUES)) {
-      const metaEle = document.querySelector(`meta[property='${propertyValue}']`);
-      if (metaEle) {
-        extractedProduct[feature] = metaEle.getAttribute('content');
+      const featureValue = findValue(extractors);
+      if (!featureValue) {
+        return null;
       }
+
+      extractedProduct[feature] = featureValue;
     }
+
+    return extractedProduct;
   }
-  return extractedProduct;
+
+  return null;
 }
diff --git a/src/extraction/fallback/selectors.js b/src/extraction/selector/selectors.js
similarity index 100%
rename from src/extraction/fallback/selectors.js
rename to src/extraction/selector/selectors.js