fix(email-composer): Aligned function calls with Cordova plugin

Co-authored-by: ChelloApps<name@example.com>

closes: #3220

src/@ionic-native/plugins/email-composer/index.ts

@@ -70,9 +70,27 @@ export interface EmailComposerOptions {
  * ...
  *
  *
- * this.emailComposer.isAvailable().then((available: boolean) =>{
+ * this.emailComposer.getClients().then((apps: []) => {
+ *    // Returns an array of configured email clients for the device
+ * });
+ *
+ * this.emailComposer.hasClient().then(app, (isValid: boolean) => {
+ *  if (isValid) {
+ *    // Now we know we have a valid email client configured
+ *    // Not specifying an app will return true if at least one email client is configured
+ *  }
+ * });
+ *
+ * this.emailComposer.hasAccount().then((isValid: boolean) => {
+ *  if (isValid) {
+ *    // Now we know we have a valid email account configured
+ *  }
+ * });
+ *
+ * this.emailComposer.isAvailable().then(app, (available: boolean) => {
  *  if(available) {
- *    //Now we know we can send
+ *    // Now we know we can send an email, calls hasClient and hasAccount
+ *    // Not specifying an app will return true if at least one email client is configured
  *  }
  * });
  *
@@ -143,34 +161,83 @@ export class EmailComposer extends IonicNativePlugin {
   }
 
   /**
-   * Verifies if sending emails is supported on the device.
+   * Verifies if an email account is configured on the device.
+   *
+   * @returns {Promise<any>} Resolves if available, rejects if not available
+   */
+  @CordovaCheck()
+  hasAccount(): Promise<any> {
+    return getPromise<boolean>((resolve) => {
+      EmailComposer.getPlugin().hasAccount((result: boolean) => {
+        if (result) {
+          resolve(true);
+        } else {
+          resolve(false);
+        }
+      });
+    });
+  }
+
+  /**
+   * Verifies if a specific email client is installed on the device.
    *
    * @param {string} [app] App id or uri scheme.
    * @returns {Promise<any>} Resolves if available, rejects if not available
    */
+
   @CordovaCheck()
-  isAvailable(app?: string): Promise<any> {
-    return getPromise<boolean>((resolve, reject) => {
+  hasClient(app?: string): Promise<any> {
+    return getPromise<boolean>((resolve) => {
       if (app) {
-        EmailComposer.getPlugin().isAvailable(app, (isAvailable: boolean) => {
-          if (isAvailable) {
-            resolve();
+        EmailComposer.getPlugin().hasClient(app, (result: boolean) => {
+          if (result) {
+            resolve(true);
           } else {
-            reject();
+            resolve(false);
           }
         });
       } else {
-        EmailComposer.getPlugin().isAvailable((isAvailable: boolean) => {
-          if (isAvailable) {
-            resolve();
-          } else {
-            reject();
-          }
+        EmailComposer.getPlugin().getClients((apps: string[]) => {
+          resolve(apps.length && apps.length > 0);
         });
       }
     });
   }
 
+  /**
+   * Returns an array of email clients installed on the device.
+   *
+   * @returns {Promise<string[]>} Resolves if available, rejects if not available
+   */
+  @CordovaCheck()
+  @Cordova({ platforms: ['Android'] })
+  getClients(): Promise<string[]> {
+    return getPromise<string[]>(resolve => {
+      EmailComposer.getPlugin().getClients((apps: any) => {
+        if (Object.prototype.toString.call(apps) === '[object String]') {
+          apps = [apps];
+      }
+        resolve(apps);
+      });
+    });
+  }
+
+  /**
+   * Verifies if sending emails is supported on the device.
+   *
+   * @param {string} [app] App id or uri scheme.
+   * @returns {Promise<any>} Resolves if available, rejects if not available
+   */
+  @CordovaCheck()
+  isAvailable(app?: string): Promise<any> {
+    return getPromise<boolean>((resolve) => {
+      Promise.all([this.hasAccount, this.hasClient(app)])
+        .then((results) => {
+          return resolve(results.length === 2 && results[0] && results[1]);
+        });
+    });
+  }
+
   /**
    * Displays the email composer pre-filled with data.
    *