It might be that Blizzard will change the behaviour at some point. I do hope there'll be Patch Notes that warrant these changes, though..
However, I have done a huge amount of work already on an add-on and changing it completely at this point doesn't seem valid.
I did some extensive testing today, and here are the results of the tests. I hope they will help people to develop their add-ons. Also, if someone has a WoW Wiki account, I would be very grateful if they uploaded the data into the database. The events are in upper case, followed immediately by the arguments found in paranthesis. Remember that other events might happen simultaneously with these. Regardless, the events posted are relevant only to the current thing the player is doing.
When casting a spell which has a casting time, following identifiable cases were found:
- Started casting a spell: SPELLCAST_START (arg1 = spell name, arg2 = casting time in msec)
- Spellcast delayed due to damage: SPELLCAST_DELAYED (arg1 = time delayed, in msec)
- Completed casting a spell: SPELLCAST_STOP (no arguments)
- Player moves while casting: SPELLCAST_STOP (no arguments). Followed immediately by CHAT_MSG_SPELL_FAILED_LOCALPLAYER (arg1 = "You fail to cast <spellname>: Interrupted."). Followed by SPELLCAST_INTERRUPTED (no arguments)
When channeling a spell:
- Started channeling: SPELLCAST_CHANNEL_START (arg1 = channeling duration in msec, arg2 = "Channeling"). Followed immediately by SPELLCAST_STOP (no arguments)
- Losing channeling time due to damage: SPELLCAST_CHANNEL_UPDATE (arg1 = remaining duration in msec)
- Completed channeling: SPELLCAST_CHANNEL_UPDATE (arg1 = 0). Followed immediately by SPELLCAST_STOP.
- Player moves while channeling: SPELLCAST_CHANNEL_UPDATE (arg1 = 0). Followed immediately by SPELLCAST_STOP.
When casting a spell without casting time (instacast)
- Started/finished casting: SPELLCAST_STOP (no arguments)
The following are universal cases:
- Target of spell is invalid, such as friendly or you have a more powerful buff active: SPELLCAST_FAILED (no arguments). This is preceded by an appropriate CHAT_MSG_SPELL_ message. For example, CHAT_MSG_SPELL_FAILED_LOCALPLAYER (arg1 = "You fail to cast <spellname>: Invalid target."). Followed by SPELLCAST_FAILED.
- Player moving before casting a spell with casting time: CHAT_MSG_FAILED_LOCALPLAYER (arg1 = "You fail to cast <spellname>: Can't do that while moving.). Followed by SPELLCAST_FAILED (no arguments).
- Finished casting a spell (instant or otherwise) but target is immune: SPELLCAST_START (non-instants), SPELLCAST_STOP, followed by CHAT_MSG_SPELL_SELF_DAMAGE (arg1 = "Your <spellname> failed, <targetname> is immune.")
- Finished casting a spell (instant or otherwise) but target resists. SPELLCAST_START (non-instants), SPELLCAST_STOP, followed by CHAT_MSG_SPELL_SELF_DAMAGE(arg1 = "Your <spellname> was resisted by <targetname>.")
I hope all this data will be helpful to someone. It was helpful to me. Now my add-on can detect 90% of cases it needs with reliable accuracy
And yeah, hooking CastSpell and UseAction will catch the following situations: casting spell from Action Bar (UseAction), creating tradeskill item (CastSpell), casting spell from spell book (CastSpell).
- Gorak