colloquial language - Is 「やってもた」 the same as 「やってしまった」? What is the grammatical rule behind this?

I have recently seen 「やってもた」 used in a Japanese conversation, I don't remember the context exactly, but it was something like：

久々にやってもた。

After asking my Japanese friend, it turns out to be some kind of Osaka-ben expression used instead of 「やってしまった」, where the 「も」 stands for 「しまう」. My friend couldn't give me another use of this so I'm here asking two questions:

1. 
   

   Is my explanation of 「やってもた」 accurate?

   
   


2. 
   
   

   Can we extract from this example a generic grammatical rule that can be applied to most situation?

   
   

I seek to learn Osaka-ben and I'm trying to replace my old habits, so I would be very grateful if you can provide some external resources about this or at least mention your sources.

Answer

1) It is "やってもうた" or "やってしもた".
2) The form "もうた" or "しもた" are shortened forms of "しもうた". The (auxiliary) verb "しまう" has a stem ending with the glide "w": "simaw-", and underwent different developments in Kansai and Kantoo regarding inflection. In Kantoo, the "w" was interpreted as a consonant, and was used to trigger gemination (a.k.a. [促]{そく}[音]{おん}[便]{びん}) in past tense:

simaw-ta → simatta

On the other hand, in Kansai, the "w" (back glide) was turned into "u" (high back vowel), and then underwent further change of vowels (k.a. ウ音便):

simaw-ta → simauta → simouta

If you are expecting external materials on these sound changes, you may want to study about ウ音便 and 促音便.