Add a new function deleteIfExists -> Bool

Closes #208

Author: brunoocasali

Sources/MeiliSearch/Indexes.swift

@@ -230,6 +230,24 @@ public struct Indexes {
     }
   }
 
+  /**
+   Delete the index only if it exists.
+
+  - parameter completion: The completion closure used to notify when the server
+   completes the delete request, it returns a `Bool` that is `true`
+   If the request sucessfully deleted an existent index or `false` if a failure occured or the index do not exist.
+   */
+  public func deleteIfExists(_ completion: @escaping (Bool) -> Void) {
+    self.request.delete(api: "/indexes/\(self.uid)") { result in
+      switch result {
+      case .success:
+        completion(true)
+      default:
+        completion(false)
+      }
+    }
+  }
+
     // MARK: Document
 
   /**

Tests/MeiliSearchUnitTests/IndexesTests.swift

@@ -277,6 +277,45 @@ class IndexesTests: XCTestCase {
     self.wait(for: [expectation], timeout: 10.0)
   }
 
+  func testDeleteIndexIfExists() {
+    // Prepare the mock server
+    session.pushEmpty(code: 204)
+
+    // Start the test with the mocked server
+    let expectation = XCTestExpectation(description: "Delete Movies index")
+
+    self.index.deleteIfExists { result in
+      if result {
+        XCTAssertTrue(result)
+        expectation.fulfill()
+      } else {
+        XCTFail("Failed to delete Movies index, it was not present on the server")
+      }
+      expectation.fulfill()
+    }
+
+    self.wait(for: [expectation], timeout: 10.0)
+  }
+
+  func testDeleteIndexIfExistsWhenIsnt() {
+    // Prepare the mock server
+    session.pushEmpty(code: 404)
+
+    // Start the test with the mocked server
+    let expectation = XCTestExpectation(description: "Delete Movies index only if exists")
+
+    self.index.deleteIfExists { result in
+      if !result {
+        XCTAssertFalse(result)
+        expectation.fulfill()
+      } else {
+        XCTFail("Deleting the index should have returned false as the index does not exist on the server")
+      }
+      expectation.fulfill()
+    }
+
+    self.wait(for: [expectation], timeout: 10.0)
+  }
 }
 // swiftlint:enable force_unwrapping
 // swiftlint:enable force_try