Created proper error logging (#55)

* changes in the evaluation of sessionInfo

* added Errors struct

* changed error handling if FFmpeg not present

* fixed error loggin thanks to the new Errors struct

* minor fix after changes in sanitizeUrls

* fix for succsesful execution and unknown code

Types.ts

@@ -4,9 +4,32 @@ export type Session = {
     ApiGatewayVersion: string;
 }
 
+
 export type Metadata = {
     date: string;
     title: string;
     playbackUrl: string;
     posterImage: string;
-}
+}
+
+
+interface Errors {
+    [key: number]: string
+}
+
+// I didn't use an enum because there is no real advantage that i can find and
+// we can't use multiline string for long errors
+// TODO: create better errors descriptions
+export const Errors: Errors = {
+    22: 'FFmpeg is missing. \n' +
+        'Destreamer requires a fairly recent release of FFmpeg to work properly. \n' +
+        'Please install it with your preferred package manager or copy FFmpeg binary in destreamer root directory. \n',
+
+    33: 'cannot split videoID from videUrl \n',
+
+    44: 'couldn\'t evaluate sessionInfo in the page \n',
+
+    55: 'running in an elevated shell \n',
+
+    66: 'no valid URL in the input \n'
+}