iRules - Matching multiple entries and making decision FIFO basis

Maybe something like this:

when SIP_REQUEST { 
    if {[active_members PoolA ] != 0 and [active_members PoolB ] != 0}{
        log local0. "AMR - Primary Site" 
        if {[SIP::method] eq "INVITE" } { 
            log local0. "AMR SIP Payload [SIP::payload]" 
            if { [SIP::payload] contains "AMR-WB"} {
                log local0. "AMR WB found in Payload" 
                if { [findstr [SIP::payload] "AMR" 0 "AMR-WB"] != "" } {
                    log local0. "AMR before AMR-WB found -> PoolB"
                    pool PoolB
                }
                else {
                    log local0. "Only AMR-WB found -> PoolA"
                    pool PoolA
                }
            } else { 
                pool PoolB 
            } 
        } else { 
           pool PoolB 
        }
    }
}