Immediate Actions count as swift actions on your turn.
I think in this case Character A has committed to an attack on Enemy A.
The ready action goes off when the attack starts. Wording of the readied action trigger may matter here.
Is there a rule that lets Character A interrupt his own attack and perform a different action?
Well here's the thing, Character A declared Windy Escape as a Swift Action for his turn, whereas the actual spell states that it's an Immediate Action.
That is not a problem at all. Check the rules for immediate actions:
Immediate Actions
Much like a swift action, an immediate action consumes a very small amount of time but represents a larger expenditure of effort and energy than a free action. However, unlike a swift action, an immediate action can be performed at any time—even if it's not your turn. Casting feather fall is an immediate action, since the spell can be cast at any time.
Using an immediate action on your turn is the same as using a swift action and counts as your swift action for that turn. You cannot use another immediate action or a swift action until after your next turn if you have used an immediate action when it is not currently your turn (effectively, using an immediate action before your turn is equivalent to using your swift action for the coming turn). You also cannot use an immediate action if you are flat-footed.
Well here's the thing, Character A declared Windy Escape as a Swift Action for his turn, whereas the actual spell states that it's an Immediate Action.
This doesn't matter, an Immediate Action performed during the character's turn is the same thing as a Swift Action.
I think the real question is can the character start an action, trigger a readied action, then change the original action after learning of the readied action.
I guess I am a little confused at the situation.
The character (do we really need A after it if there is only one character and one enemy in this explanation?) attacked the enemy causing the enemy’s readied action to trigger.
At what point did the character cast Windy Escape?
Why would the character attack and cast Windy Escape at the same time? It makes no sense.
If the character attacked and that triggered the enemy’s readied action to attack, then the character could cast Windy Escape as an immediate action in response to the readied action attack by the enemy. I do not see an issue there, but maybe I am missing something in the description of the incident.
He stated that casting Windy Escape was his "Swift Action" for that turn in case anyone attacked him.
I guess then I would ask the character, even if you could do that according to the rules, why would you do that?
The whole idea of an immediate action is to react and there is no need to state it before hand. To ready an immediate action just seems redundant.
Now for the rules, technically you cannot ready an immediate action as under immediate action it says “you can ready a standard action, a move action, a swift action, or a free action” and an immediate action is “very similar to a swift action” but it is not one.
Also, readying an action is a standard action, so the character could not have attacked and then the enemy could not have his readied action triggered so the whole scenario would be moot.
So again, no readying of an immediate action is needed or allowed. By definition it is supposed to be an action in response to something else and does not need to be declared until it is triggered or used.
When the player says “I attack the enemy and ready to cast Windy Escape as a swift action if I am in turn attacked”, the DM should say “you cannot both attack and ready an action in the same round (baring certain abilities and feats, etc.) and Windy Escape is an immediate action spell so no casting it as a swift action anyway.”
Then the character attacks, the enemy’s readied action is triggered, and the character’s immediate action is declared and goes off as normal. So the enemy has to deal with the effects of the Windy Escape on the character and still gets to attack and when that is resolved the character finally gets their attack.
That is how it should go.
It works fine. You can use an immediate action at any time provided you haven't used your swift action for your current turn (if it's your turn) or for your next turn (if it's not your turn).
