fading multiple leds

I have a Jeep with DIY yellow led side markers. They are always on when my stock markers are on and flash once my turn singal or hazards flash. My question is i want to make the flashing "flow" from center to outsides. I found a digital rgb led strip i can use and use arduino. Just bump down the 12v trigger to 5v and I'll be good... but the coding is not my strong suit. I know the very basics and have not a clue how to start it.

Basically 12v trigger (blinking will this effect the program?) Turn on a flow pattern on my rgb leds and stop "flowing" once trigger is off. Would love for the "flow" to finish its pattern then fade back up to on after trigger is off. Thats it. Could anyone help me set up? Is this possible?

Sounds like you need a variable to keep track of which thing the LEDs are currently. Traditionally this is called the "state". Each state is represented by an integer value and you can use a switch/case statement to execute the code for the current state.

Sounds like you have at least four states:

Solid Off. Solid On. Flowing. Transition from Flowing to On.

Are there any other states? Maybe blinking between dim for side marker and bright for turn signal? If so you probably also want a solid dim state for when the side markers are on but the turn signal for that side is not. LIST THEM ALL.