Added a plugin system for looking up products against external services by barcode (references #6)

data/plugins/DemoBarcodeLookupPlugin.php

@@ -0,0 +1,78 @@
+<?php
+
+use \Grocy\Helpers\BaseBarcodeLookupPlugin;
+
+/*
+	This class must extend BaseBarcodeLookupPlugin (in namespace \Grocy\Helpers)
+*/
+class DemoBarcodeLookupPlugin extends BaseBarcodeLookupPlugin
+{
+	/*
+		To use this plugin, configure it in data/config.php like this:
+		define('STOCK_BARCODE_LOOKUP_PLUGIN', 'DemoBarcodeLookupPlugin');
+	*/
+
+	/*
+		To try it:
+		Call the API function at /api/stock/external-barcode-lookup/{barcode}
+
+		When you also add ?add=true as a query parameter to the API call,
+		on a successful lookup the product is added to the database and in the output
+		the new product id is included (automatically, nothing to do here in the plugin)
+	*/
+
+	/*
+		Provided references:
+
+		$this->Locations contains all locations
+		$this->QuantityUnits contains all quantity units
+	*/
+
+	/*
+		Useful hints:
+
+		Get a quantity unit by name:
+		$quantityUnit = FindObjectInArrayByPropertyValue($this->QuantityUnits, 'name', 'Piece');
+
+		Get a location by name:
+		$location = FindObjectInArrayByPropertyValue($this->Locations, 'name', 'Fridge');
+	*/
+
+	/*
+		This class must implement the protected abstract function ExecuteLookup($barcode),
+		which is called with the barcode that needs to be looked up and must return an
+		associative array of the product model or null, when nothing was found for the barcode.
+
+		The returned array must contain at least these properties:
+		array(
+			'name' => '',
+			'location_id' => 1, // A valid id of a location object, check against $this->Locations
+			'qu_id_purchase' => 1, // A valid id of quantity unit object, check against $this->QuantityUnits
+			'qu_id_stock' => 1, // A valid id of quantity unit object, check against $this->QuantityUnits
+			'qu_factor_purchase_to_stock' => 1, // Normally 1 when quantity unit stock and purchase is the same
+			'barcode' => $barcode // The barcode of the product, maybe just pass through $barcode or manipulate it if necessary
+		)
+	*/
+	protected function ExecuteLookup($barcode)
+	{
+		if ($barcode === 'x') // Demonstration when nothing is found
+		{
+			return null;
+		}
+		elseif ($barcode === 'e') // Demonstration when an error occurred
+		{
+			throw new \Exception('This is the error message from the plugin...');
+		}
+		else
+		{
+			return array(
+				'name' => 'LookedUpProduct_' . RandomString(5),
+				'location_id' => $this->Locations[0]->id,
+				'qu_id_purchase' => $this->QuantityUnits[0]->id,
+				'qu_id_stock' => $this->QuantityUnits[0]->id,
+				'qu_factor_purchase_to_stock' => 1,
+				'barcode' => $barcode
+			);
+		}
+	}
+}