This macro is straight out of Hend’s Enhancement playbook with only a slight modification: the @player condition at the end.

#showtooltip Lightning Bolt
/cast [@mouseover,help]Healing Surge; [@mouseover,harm]Lightning Bolt; [@target,help]Healing Surge; [@target,harm]Lightning Bolt;[@player]Healing Surge

Macroexplain.com says it does the following:

If the unit your mouse is currently over is a friend then:
Cast Healing Surge on the unit your mouse is currently over

Else, if the unit your mouse is currently over is an enemy then:
Cast Lightning Bolt on the unit your mouse is currently over

Else, if the currently targeted unit is a friend then:
Cast Healing Surge on the currently targeted unit

Else, if the currently targeted unit is an enemy then:
Cast Lightning Bolt on the currently targeted unit

Otherwise:
Cast Healing Surge on you

Enjoy!