Removing Dependency from SDK Core Project

- Copied files required for Rest API SDK
- Removed PPApiContext and directly connected APIContext with PPConfigManager
- Removed duplicate data storage of configuration and credentials.
- Code Style Fixes
- Remove build.xml file as it is not required anymore
- Updated the samples
- Updated the documentations

lib/PayPal/Core/PPCredentialManager.php

@@ -0,0 +1,167 @@
+<?php
+
+namespace PayPal\Core;
+
+use PayPal\Auth\OAuthTokenCredential;
+use PayPal\Exception\PPInvalidCredentialException;
+
+/**
+ * Class PPCredentialManager
+ *
+ * PPCredentialManager holds all the credential information in one place.
+ *
+ * @package PayPal\Core
+ */
+class PPCredentialManager
+{
+    /**
+     * Singleton Object
+     *
+     * @var self
+     */
+    private static $instance;
+
+    /**
+     * Hashmap to contain credentials for accounts.
+     *
+     * @var array
+     */
+    private $credentialHashmap = array();
+
+    /**
+     * Contains the API username of the default account to use
+     * when authenticating API calls
+     *
+     * @var string
+     */
+    private $defaultAccountName;
+
+    /**
+     * Constructor initialize credential for multiple accounts specified in property file
+     *
+     * @param $config
+     * @throws \Exception
+     */
+    private function __construct($config)
+    {
+        try {
+            $this->initCredential($config);
+        } catch (\Exception $e) {
+            $this->credentialHashmap = array();
+            throw $e;
+        }
+    }
+
+    /**
+     * Create singleton instance for this class.
+     *
+     * @param array|null $config
+     * @return PPCredentialManager
+     */
+    public static function getInstance($config = null)
+    {
+        if (!self::$instance) {
+            self::$instance = new self($config == null ? PPConfigManager::getInstance()->getConfigHashmap() : $config);
+        }
+        return self::$instance;
+    }
+
+    /**
+     * Load credentials for multiple accounts, with priority given to Signature credential.
+     *
+     * @param [] $config
+     */
+    private function initCredential($config)
+    {
+        $suffix = 1;
+        $prefix = "acct";
+
+        $arr = array();
+        foreach ($config as $k => $v) {
+            if (strstr($k, $prefix)) {
+                $arr[$k] = $v;
+            }
+        }
+        $credArr = $arr;
+
+        $arr = array();
+        foreach ($config as $key => $value) {
+            $pos = strpos($key, '.');
+            if (strstr($key, "acct")) {
+                $arr[] = substr($key, 0, $pos);
+            }
+        }
+        $arrayPartKeys = array_unique($arr);
+
+        $key = $prefix . $suffix;
+        $userName = null;
+        while (in_array($key, $arrayPartKeys)) {
+            if (isset($credArr[$key . ".ClientId"]) && isset($credArr[$key . ".ClientId"])) {
+                $userName = $key;
+                $this->credentialHashmap[$userName] = new OAuthTokenCredential(
+                    $credArr[$key . ".ClientId"],
+                    $credArr[$key . ".ClientSecret"]
+                );
+            }
+            if ($userName && $this->defaultAccountName == null) {
+                if (array_key_exists($key . '.UserName', $credArr)) {
+                    $this->defaultAccountName = $credArr[$key . '.UserName'];
+                } else {
+                    $this->defaultAccountName = $key;
+                }
+            }
+            $suffix++;
+            $key = $prefix . $suffix;
+        }
+
+    }
+
+    /**
+     * Sets credential object for users
+     *
+     * @param \PayPal\Auth\OAuthTokenCredential $credential
+     * @param string|null   $userId  User Id associated with the account
+     * @param bool $default If set, it would make it as a default credential for all requests
+     *
+     * @return $this
+     */
+    public function setCredentialObject(OAuthTokenCredential $credential, $userId = null, $default = true)
+    {
+        $key = $userId == null ? 'default' : $userId;
+        $this->credentialHashmap[$key] = $credential;
+        if ($default) {
+            $this->defaultAccountName = $key;
+        }
+        return $this;
+    }
+
+    /**
+     * Obtain Credential Object based on UserId provided.
+     *
+     * @param null $userId
+     * @return OAuthTokenCredential
+     * @throws PPInvalidCredentialException
+     */
+    public function getCredentialObject($userId = null)
+    {
+        if ($userId == null) {
+            $credObj = $this->credentialHashmap[$this->defaultAccountName];
+        } else if (array_key_exists($userId, $this->credentialHashmap)) {
+            $credObj = $this->credentialHashmap[$userId];
+        }
+
+        if (empty($credObj)) {
+            throw new PPInvalidCredentialException("Invalid userId $userId");
+        }
+        return $credObj;
+    }
+
+    /**
+     * Disabling __clone call
+     */
+    public function __clone()
+    {
+        trigger_error('Clone is not allowed.', E_USER_ERROR);
+    }
+
+}